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Developing Applications for Android
White Paper
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1.0 0.6 04/08/2010
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Date 02/12/2010 02/21/2010 02/22/2010 03/07/2010 03/14/2010 04/08/2010
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White Paper 1.0 Rev 0.6
Developing for Android
AT&T Developer Program .......................................................................................................................... 1 White Paper ................................................................................................................................................. 1 All marks, trademarks, and product names used in this document are the property of their respective owners. .............................................................................................................................. iii Figures ........................................................................................................................................................ vi Tables .......................................................................................................................................................... vi 1. Overview ................................................................................................................................................ 7 1.1 1.2 1.3 1.4 1.5 1.6 Android Overview ......................................................................................................................... 7 Android Architecture ..................................................................................................................... 8 Available Libraries (Available APIs) ............................................................................................ 10 Comparing Android to Other Platforms ...................................................................................... 11 Terms and Acronyms.................................................................................................................. 13 Why Develop for Android ............................................................................................................ 14
2. Developing Applications .................................................................................................................... 15 2.1 2.2 2.3 2.4 How Android Executes Applications ........................................................................................... 15 Application Components ............................................................................................................. 16 The Android Manifest File (AndroidManifest.xml) ...................................................................... 22 Activating Application Components Using Intents ...................................................................... 25
3. Developing App Widgets ................................................................................................................... 29 3.1 3.2 3.3 Creating App Widgets ................................................................................................................. 29 Layouts and Views ...................................................................................................................... 30 Handling Events .......................................................................................................................... 30
4. Communications................................................................................................................................. 33 4.1 4.2 4.3 Basic Networking ........................................................................................................................ 33 Connections and Management ................................................................................................... 35 Telephony ................................................................................................................................... 39
5. Android UI ........................................................................................................................................... 48 5.1 5.2 5.3 5.4 Layouts ....................................................................................................................................... 48 UI Components ........................................................................................................................... 52 Menus ......................................................................................................................................... 55 Events ......................................................................................................................................... 56
White Paper 1.0 Rev 0.6
................................................... 59 Leveraging HTML5 .............................................................................................................. Conclusion ..................................................................... Works Cited ......................... 77 10...3 7.......................................................................................2 Going Native ......................................................................................... 61 7................................................................................................................ 64 Optimizing Code for Android ..........................................1 6.................................... 64 7........................................................................................................ Porting Applications to Android ......... 77 10............. 59 6...............................................................1 7.......................... 78 11............................................. Writing for the Web................................................... 66 Localization ...... Deployment ....................................Developing for Android 6.............................................3 Mobile Web/XHTML Sites.......................................................................................................................................2 6..............1 Signing Your Application................................................................................................................................ 67 Common Issues ............................1 Creating an Android Project ...........0 Rev 0................ 71 9........................................................................................................ 79 12............2 7........................................... 69 8......................................................................4 User Interface ............................................................................................................................................................................................... 75 9...........................................6 v ..................1 J2ME Applications ................................................................ 75 10............................ Android Development Tools and Android SDK ........................................................ 60 Extending the Browser..................................... Best Practices .......................................... 71 8................................................................... 80 White Paper 1...............
......... ....................................................................................................................... ............................. 73 Table 20 — SDK tools needed when using IDEs other than Eclipse + ADT ..........................................................................................................................................................0 Rev 0.............................................. 12 Table 3 — Terms and Acronyms ................................................................................................................... 62 Table 17 — Sample performance times of some common actions ......... 29 Figure 3 —The Android view hierarchy. Source: Adapted from Engadget................................................................................................................................................. Source: Google.......... .......................................... ............................... 51 Tables Table 1 — An overview of the Android libraries..................................... 68 Table 19 — Project files automatically generated by the ADT New Project Wizard.............................................. ............................................................................................... 67 Table 18 — Default resources to define for localization ............................ 40 Table 12 — Parameters for generating SMS messages ...... 14 Table 4 — Default action strings supported by Android...................................................................................................... 35 Table 9 — Public methods for obtaining network information ................................................ 27 Table 5 — Default intent categories supported by Android......................... 38 Table 10 — Public methods for network event notification .................. 55 Table 14 — Event listener interface callback methods ................ ..................................................................................... 48 Figure 4 — A LinearLayout set up in the vertical orientation..................... 46 Table 13 — A partial list of the UI widgets available in Android....... 34 Table 8 — Parameters for setting up a network connection ................................................ 50 Figure 5 — A Table layout ......................... 57 Table 15 — HTML5 features supported in Android .................... ......... 9 Figure 2 — Some examples of App Widgets running on the Android home screen......................... 38 Table 11 — Android telephony methods .......... All three children above are ‗stacked' one atop the other in a single column..... 28 Table 6 — Networking interfaces in Android....... 10 Table 2 — Android SDK compared to other popular mobile SDKs............................................................................................................................................................................................ ..............................Developing for Android Figures Figure 1 — Android Platform Architecture..................................................... Courtesy Google.............6 vi .. 74 White Paper 1........... 60 Table 16 — WebView customization points ...................... 33 Table 7 — Android networking APIs .............. ............................ Source: Google....................................................................................................................................................... 74 Table 21 — Items generated for a new project using the Android tool .......................................................................................................... 50 Figure 6 — A Relative layout .........................
The main topics of this paper are: Developing Applications. 1. Best Practices. Communications.0 Rev 0. Android UI. Overview Times have never been better for mobile software developers. This paper will introduce you to the Android platform and its capabilities. Developing App Widgets. and Porting Application to Android. The Android operating system supports smartphones White Paper 1. Android Development tools and Android SDK. This paper is aimed at experienced software developers who are new to the Android platform. Deployment.Developing for Android 1. With the introduction of Android from Google and the Open Handset Alliance. Writing for the Web. and extend their reach to millions of mobile users. as well as tips and tricks for optimizing your applications and launching them on the AT&T network.1 Android Overview Android is an operating system for mobile devices developed by Google and the Open Handset Alliance. It will give you an overview of developing applications for Android. developers have a robust platform to run their applications.6 7 .
Inc. Chrome. The built-in web browser is built on the WebKit layout engine.0 Rev 0.1 Hardware Designs Android devices are made by a number of manufacturers. RIM BlackBerry. Inc. Open Handset Alliance (OHA) launched the first Android handset in 2008. a small California startup which was later purchased by Google.. and a collection of built-in applications. The Android platform supports a variety of hardware features including accelerometers. in 2005. displays of varying sizes including multi-touch capable screens. cameras. physical keyboards. Android is being used for other devices as well. and a variety of cellular radios. The highly-optimized virtual machine implementation (called the Dalvik virtual machine) adds a level of security to the operating system. the industry assumed Google would launch its own mobile device. 1. By the end of 2009. and in January 2010. White Paper 1. in addition to Google's desktop browser. Inc. However. The initial goal of Android. also used by iPhone. Palm webOS. was to create an open and extensible operating system for mobile devices. When Google bought Android. Android was initially developed by Android. the Google Nexus One. software and telecom companies. and designs vary widely. which is a consortium of 47 hardware.2.2 Android Architecture The Android operating system is comprised of a virtual machine that runs on the Linux kernel. and can do so even on devices with limited memory (RAM). To run multiple applications simultaneously. Google launched its own handset. 1. more than 20 Android handsets were launched. and from each other. Android runs applications within virtual machines (VMs).Developing for Android similar to Apple iPhone. since applications can be kept separate from the main part of the operating system. Windows Mobile. Google continued development on Android and helped form the Open Handset Alliance in 2007. plus APIs. including the Nook e-book reader from Barnes & Noble. Android runs multiple virtual machines. and others. which would give mobile carriers flexibility to create unique devices for their networks. as well as some upcoming tablet computers.6 8 . BREW MP. Palm webOS and some Symbian devices.
calendaring. etc. An Application Framework to write new applications.2. Figure 1 — Android Platform Architecture. Libraries to access device functions from within applications. and memory management.Developing for Android 1.6 9 . Source: Google. The Android Runtime to run built-in and user-installed applications. Android is comprised of: Built-in Applications for messaging. White Paper 1.2 Software Platform Architecture The diagram below gives a high-level view of the architecture of the Android software platform.0 Rev 0. The Linux Kernel for core services such as graphics. security. web browsing. and networking.
Source: Google. White Paper 1. and PNG. Library Description For general application development.6 10 . AMR. Developers can access the functionality of these libraries via the Android Java APIs exposed in the Android SDK. available to all applications System C Library Media Libraries Surface Manager LibWebCore SGL 3D Libraries FreeType SQLite Table 1 — An overview of the Android libraries. Supports many popular formats such as MPEG4. and powers the Android browser and an embeddable web view Provides 2D graphics rendering services Provides hardware-accelerated 3D graphics rendering services. AAC.264. Based on PacketVideo's OpenCORE Manages access to the display subsystem and composites 2D and 3D graphic layers from multiple applications Provides web rendering services.3 Available Libraries (Available APIs) Android includes a set of C/C++ libraries used by various components of the Android system. H.0 Rev 0. An implementation of the standard C system library (libc). based on BSD and tuned for Linux embedded devices Provides media playback and recording services. and still image display services. as well as a highly optimized software rasterizer used when hardware acceleration is not available.Developing for Android 1. JPG. Based on OpenGL ES 1. The table below lists some of the core libraries in the Android 2.x SDK (updated January 2010).0 Provides font rendering for both bitmap and vector-based fonts Provides relational database services. LibWebCore is based on WebKit. MP3.
Windows Phone 7 C++. C++. $99yr for 5 submissions $99 for each additional submission in a year. C#. Java(J2ME) Objective-C Java Python. $99/year. C++. 30% revenue to Apple. C/C++ Yes.. Adobe Flash Yes. 20% revenue to RIM. but Required Digital Certificates for distributi on Required for distribution Required for distriubtion Required for distribution may be required to access certain APIs Varies. $200 for 10 application submissions. C/C++ Java C/C++.NET Category Android BlackBerry BREW MP iPhone J2ME Symbian S60 Java.4 Comparing Android to Other Platforms Table 2 is a high-level comparison of the Android platform to competing mobile/embedded platforms. $25/yr. MIDP. 0.NET. Objective-C No No. 30% revenue to Microsoft Platform Maturity Community Support New Moderate Mature Moderate Mature Mature Excellent Excellent Moderate Excellent Moderate Excellent Excellent Direct via App Installation Method Direct via Android Market RIM Store To Be Announced Direct via iTunes App Store Direct. For Nokia Devices Ovi Store Mature Supported but can be disabled Supported. Retail support via Windows Marketplace for Mobile.6 11 . required for some phones Retail Support Retail support via Android Market. C++ Yes. C++ Yes. No revenue share to 30% revenue to carrier Retail support via Blackberry App World. VB.0 Rev. also via PC tools ActiveSync. VB. free apps ok To Be Announced Full retail support via App Store. C#. Development Language(s) Native Development Java. free apps ok Retail support via Ovi Store. (Microsoft may move to an app store model) White Paper 1.Developing for Android 1. Options include Carrier Deck and third party aggregat ors such as getJar. C++ No Yes.
Source: Adapted from Engadget.6 12 .Developing for Android Category Emulator Available Remote Debugging Android BlackBerry BREW MP iPhone J2ME Symbian S60 Windows Phone 7 Yes Yes Yes Yes Yes Yes Yes Yes Single touch. 0. White Paper 1. (Limited multitouch support) Yes Yes Yes No Yes Yes Touchscreen Support Single-touch Single-touch Multi-touch Singletouch Single-touch (5th Edition only) Single-touch Underlying Architecture Cocoa Linux Blackberry BREW Touch / Mac OS X No Varies Symbian Windows Flash Support No Support coming in 2010 Yes Yes Varies Yes Yes Java Support Yes Yes No Yes Yes Yes Table 2 — Android SDK compared to other popular mobile SDKs.0 Rev.
0 Rev.Developing for Android 1.6 13 . 0.5 Terms and Acronyms Acronym ADT API IDE DHCP GPRS HTTP IP Definition Android Development Tools Application Programming Interface Integrated Development Environment Dynamic Host Configuration Protocol General Packet Radio Service Hypertext Transfer Protocol Internet Protocol J2ME LWUIT MIME MP3 NDK Java 2 Micro Edition Light Weight User Interface Toolkit Multipurpose Internet Mail Extensions Moving Picture Experts Group Layer-3 Audio Native Development Kit OHA RAM SDK SMS URI URL Open Handset Alliance Random-access Memory Software Development Kit Short Messaging Service Universal Resource Identifier Universal Resource Locator White Paper 1.
Additionally. mature and very widely adopted language in the global development community. Android 2. NOTE: While Google releases most of the Android code to the community. Android's Java is not exactly the same as J2ME.Developing for Android Acronym UMTS VM W3C XML Definition Universal Mobile Telecommunication System Virtual Machine World Wide Web Consortium Extensible Markup Language Table 3 — Terms and Acronyms 1. the educational resources available for learning Java far outnumber those for other languages like the iPhone's Objective-C. the vast majority of existing J2ME applications can be ported to Android with minor modifications. White Paper 1.6.6 Why Develop for Android The Android platform differs in some technical and business aspects from its competitors.6 14 . For developers who want to write very specialized applications. Android is built upon an open-source platform. 0. and many find the Java syntax easy to learn. and most of the Android code is released under the free software/open source Apache License. which is a powerful. Google typically only does so once it launches a new Android version (i.0 Rev. this is a major advantage over other systems.0). however. particularly applications which depend on functionality for which there are no libraries. 1.e. which may be of interest to application developers. as opposed to making code available along the way as the code is checked in.1 Technical Advantages Unlike many competitors. Android applications are written in the Java programming language.
The . such as using another app's UI elements like a scrollbar or viewer. Since each application runs its own Linux process in its own VM. The calling application doesn't need to incorporate the code of the host application. 2. its code and data are kept completely isolated from all other applications running on the device. 2. and applications can leverage these elements.6 15 . Applications can share the same user ID. and Applications can be written to make their elements available to other applications.dex files are then zipped into an application bundle — a single file with an .apk extension called an Android Package. Where Apple strives to ensure applications meet its defined standards of quality.dex extension (signifying Dalvik Executable files).2 Business Advantages Google's venue for selling applications — Android Market — is much more of an open marketplace than Apple's iTunes App Store. Applications with the same user ID can also be made to run in the same VM to save system resources. Android applications are packaged into a bundle which contains the compiled application code. Applications are not evaluated on any other grounds. 0.0 Rev. so developers will likely have more freedom to create the type of application or content they like.Developing for Android 1. utility and appropriateness. White Paper 1. Even with this extra layer of security.6. The Dalvik virtual machine relies on the Linux kernel for underlying functionality such as threading and low-level memory management. data files and other resources the application needs. share user data or other resources. Developing Applications Developers will use the tools and APIs in the Android SDK to develop Android applications. which allows them to see each other's files. applications can still interact with each other. Application developers can distribute Android Packages and users can install these packages on their Android devices. Google simply checks that applications meet the terms developers agree to when they sign up for the Android Market.1 How Android Executes Applications Android uses the Dalvik virtual machine to run applications safely. Compiled Android programs have the .
This means that applications do not need to subsume or even link to the application components they want to share — they simply ask Android to run the desired component within the application that contains it. This means an application can ‗publish' its resources. White Paper 1. and vice versa. A text messaging application might have one activity that shows a list of contacts. Android allows the sharing of components with other applications by automatically instantiating the Java objects responsible for the desired component. with Application Components. 2. and instantiate the Java objects for that part. an activity might present a list of menu items users can choose from.6 16 . a second activity to write the message to the chosen contact. Since the system must be able to start an application process when any part of it is needed. Android handles this automatically.0 Rev. or it might display photographs along with their captions. For example. There are four types of components: Activities. and other activities to review old messages or change settings. Android applications don't have a single entry point for everything in the application (no main() function. Rather. Broadcast Receivers.2. they have essential components that the system can instantiate and run as needed. Services. such as user interface elements.1 Activities An activity presents a visual user interface for an action the user can undertake. for example). 2. and Content Providers.Developing for Android or even link to it. so that they can be used by other applications on the device.2 Application Components Android applications are written using application components. 0. which allows for sharing of application resources among all applications installed on an Android device.
2. is actually a series of tasks. a pop-up dialog that calls for a user response in the midst of the activity. What the user perceives as an application — with its various windows. or a window that presents users with vital information when they select a particular item on-screen. each activity is independent of the others.Developing for Android An application user interface is typically comprised of many activities (for various functions and windows) to form a cohesive user experience.1 Tasks Related activities can be grouped into a stack called a Task. revealing the previous task. and given a default window to draw in. To understand what is really happening. The map viewer White Paper 1. and because the user interface is fast and responsive. 0. An activity can also make use of additional windows — for example. The activity at the top of the stack is one that's currently running and currently displaying its user interface.6 17 . Activities are implemented as a subclass of the Activity base class. the new activity becomes the top card on the stack. The current activity is a viewer activity which is rendering the text of the address on the screen. The user launches the Contacts application. the current activity in Contacts creates an Intent object with the required information and passes it to startActivity(). Typically. directly on top of the activity that launched it. including activities from other applications. Tasks give the illusion that a single application is providing all the functionality. Imagine the application can show a map of the address to the user. For example. controls and displays. but it might be smaller than the screen and float on top of other windows.2. which instantiates a series of activities in a stack. Typically this is the activity the user selected in the application launcher. which resumes as the running activity. this activity at the top is ended and is removed from the stack.0 Rev. imagine a stack of cards. When one activity starts another activity. However. Android has built-in activities which can generate maps. At the bottom of the stack is the root activity — the one that began the task in the first place. each one representing an activity.1. so rather than writing the code to do this in the Contacts application. the window fills the screen. imagine the Contacts application — an application which displays the address book on the phone. The user chooses a contact to view its details such as the street address of the contact. because the user does not see an application switch when moving from one activity to another. such as the Contacts application. When the user finishes with the top activity (such as dismissing a window or pressing the Back key).
process data and return the result to an activity that needs it. for example when the user returns to the Home screen to open another application.2. 0. the map rendering functionality was defined in another application and ran in a separate process. the music can play without interruption even if the user is active in other applications such as the web browser or email client. like two separate decks of cards. When the user begins playback of a chosen song. It may consist of activities to generate an album list. the Back button will always move between activity cards in the current stack. White Paper 1. The important distinction is that the activity ―cards‖ within a task are never interleaved with other task stacks — they move as a unit. although both activities appeared in the same task. For example. and provide playback controls. Since the service can run in the background regardless of what's happening in the foreground.6 18 . the map disappears and the address view of the contact reappears on the screen. Some applications might be written to use background services in addition to foreground activities. which runs in the background. a service might play background music as the user runs other applications.Developing for Android will display the map in the top-most activity of the task stack. consider a media player. Each service extends the Service base class. Services can perform tasks for other applications. Services might also be used to fetch data over the network.0 Rev. To the user. not move between activity cards of all tasks chronologically in the way a web browser's back button moves backwards chronologically through a history of pages. for example. Therefore. 2. the entire activity appeared as though it was all done within the same application. When the user hits the BACK key. A task and all the activities it contains move together in a unit when the task is sent to the background and another task is moved to the foreground.2 Services A service is an application with no visual user interface. however. display cover art. the activity will request a service to handle MP3 playback.
an application can let other applications know that some data has been downloaded to the device and is available for them to use. or use NotificationManager to display an alert to the user. An application can have any number of broadcast receivers to respond to any announcements it considers important. and will launch NotificationManager to display a low battery warning when the battery charge is below a certain level. but they can start activities which can generate a user interface. For example. 2.0 Rev. a broadcast receiver may be listening for status messages from the power manager. so if the service will be doing CPU intensive tasks (like MP3 playback). All receivers extend the BroadcastReceiver base class. 0. applications can initiate broadcasts. or Create the receiver dynamically in code and register it with the Context.Developing for Android LEVERAGING SERVICES Each service class must have a corresponding <service> declaration in its package's AndroidManifest.startService() and Context. Developers can make a broadcast receiver known to the system by either: Declaring it in the manifest file with the <receiver> element. Services run in the main thread of the process that spawns them. For example.3 Broadcast Receivers Broadcast receivers are components which are always running. the service should spawn a separate thread for those tasks to avoid blocking the application.2.bindService(). listening for events and carrying out some action in response. Services can be started with Context.xml.registerReceiver() method White Paper 1. Broadcast receivers can't display anything on the device. IMPLEMENTING A BROADCAST RECEIVER The <receiver> call declares a broadcast receiver as one of the application's components. In addition. enabling the application to receive intents from the system or other applications even when other components of the application are not running.6 19 .
</receiver> Coding Example: Making broadcast receiver known to the system. or publically in a content provider. How the rest of the URI is interpreted is up to the content provider. .. and whether they can read and modify this information. which ensures data privacy and security. 2. .6 20 . within their resource bundle. 0.4 Content Providers Content providers are components which store and retrieve data so that it is accessible to other applications. ACCESSING A CONTENT PROVIDER Applications can.0 Rev. Applications can store their data privately. the contacts data is used by multiple applications and is therefore stored in a content provider rather than within the address book application bundle. there is no data storage area common to all applications. In Android. Android ships with a number of content providers for example. The primary methods that need to be implemented for the ContentResolver are: query(Uri.Developing for Android <receiver android:enabled=["true" | "false"] android:exported=["true" | "false"] android:icon="drawable resource" android:label="string resource" android:name="string" android:permission="string" android:process="string" > . Sharing data between applications can only be accomplished using content providers. String) which returns data to the caller. String[]. White Paper 1. String. When requests are made via the ContentResolver's methods call. String[]. query content providers to find out what content they contain. with proper permissions. the system inspects the authority of the given URI and passes the request to the content provider registered with the authority.2.
withAppendedId(Contacts. update(Uri. // WHERE clause. Cursor managedCursor = managedQuery( contactUri. // WHERE clause value substitution // Sort order.Developing for Android insert(Uri.withAppendId(Contacts. and getType(Uri) which returns the MIME type of data in the content provider.People.NAME + " ASC"). Android accesses the contact database on the device from within an Activity and retrieves record #2: // Create URI for contact with an ID of 2 contactUri = ContentUris.CONTENT_URI. ContentUris.6 21 . delete(Uri. projection. String.0 Rev. null. Coding Example: Accessing the contact database on the device from within an activity. which causes the Activity to manage the lifecycle of the Cursor. In the following example. 2). // Which columns to return. ContentValues. null.managedQuery() method. 2). Coding Example: Retrieving a record CREATING A CONTENT PROVIDER An application can make its data public in one of the following ways: White Paper 1.People. ContentValues) which inserts new data into the content which updates provider. // Request a specific record. String. String[]) existing data in the content provider. String[]) which deletes data from the content provider. 0.CONTENT_URI. A query may also be made via the Activity. People.
xml) Whenever there's a request that should be handled by a particular component. A content provider can be created by: Setting up a system for storing the data. either using Android's file storage methods. The SQLiteOpenHelper and SQLiteDatabase classes are available to assist with creating databases and managing them. or By adding data to an existing content provider if one exists which controls the same type of data to be posted. The manifest presents essential information about the application to the Android operating system.0 Rev. Determines which processes will host application components. broadcast receivers. or Declaring the content provider in the manifest file for your application (AndroidManifest. which is the application's unique identifier.3 The Android Manifest File (AndroidManifest. Android will automatically start the component if needed. or will even create the instance of a component if necessary. and content providers) which let Android know what the components are and under what conditions they can be launched. 2. In addition. services.6 22 . Extending the ContentProvider class to provide access to the data. and if the application has permission to write to it. AndroidManifest.xml does the following: Names the Java package for the application. Declares which permissions the application must have and permissions it requires other applications to have to interact with it. 0.Developing for Android By creating a <ContentProvider> subclass. or a custom method you write. the manifest file is created for you automatically. which Android requires before it will run any of the application's code. White Paper 1. Describes the components of the application (activities.xml file in its root directory. If you use the Eclipse development environment with the Android Development Tools plug-in.xml) Every application must have an AndroidManifest. SQLite databases.
White Paper 1.0 Rev.6 23 . The example below shows the general structure of the manifest file and every element that it can contain. 0. is documented in full in a separate file.Developing for Android Lists the Instrumentation classes that provide profiling and other information as the application is running. and Lists the libraries that the application must be linked against. Each element. Declares the minimum level of the Android API that the application requires. along with all of its attributes.
</intent-filter> <meta-data /> </activity-alias> <service> <intent-filter> . .0" encoding="utf-8"?> <manifest> <uses-permission /> <permission /> <permission-tree /> <permission-group /> <instrumentation /> <uses-sdk /> <uses-configuration /> <uses-feature /> <supports-screens /> <application> <activity> <intent-filter> <action /> <category /> <data /> </intent-filter> <meta-data /> </activity> <activity-alias> <intent-filter> . </intent-filter> <meta-data/> </service> <receiver> <intent-filter> . 0.Developing for Android <?xml version="1.6 24 . . </intent-filter> White Paper 1. . .0 Rev. . .
0.0 Rev. the Intent object names the action being announced. An Intent object holds the content of the message. For broadcast receivers.4 Activating Application Components Using Intents The three of the four core application components we have discussed — activities. among other things. services. such as requesting that the phone dial a number passed to it from the web browser. it might announce to listening receivers that the camera button has been pressed. an intent might request an activity to present an image to the user or let the user edit some text. the intent names the action being requested and specifies the URI of the data to act on.startActivityForResult() to launch an activity or get an existing activity to do something new. It can also be passed to Activity. White Paper 1. called intents. There are separate mechanisms for delivering intents to each type of component: An Intent object is passed to Context. and broadcast receivers — are activated through asynchronous messages. An Intent is a message which requests application components to activate to perform a task.startActivity() or Activity.Developing for Android <meta-data /> </receiver> <provider> <grant-uri-permission /> <path-permission /> <meta-data /> </provider> <uses-library /> </application> </manifest> Coding Example: General structure of the manifest file and every element that it can contain 2.setResult() to return information to the activity that called startActivityForResult(). For example. For activities and services. For example.6 25 .
or it can leave it up to Android to determine a suitable target based on the context and content of the intent call. or Context. Android finds the appropriate activity. or setClassName() and read by getComponent() White Paper 1. Many kinds of broadcasts originate in system code.0 Rev.sendOrderedBroadcast(). The component name is set by setComponent().6 26 . Intent myIntent = new Intent(android. Context. or set of broadcast receivers to respond to the intent. or Intent objects passed to any of the broadcast methods (such as Context.798918").bindService() to establish a connection between the calling component and a target service. Uri = Uri.sendStickyBroadcast()) are delivered to all interested broadcast receivers. and so on.Developing for Android An Intent object is passed to Context. COMPONENT NAME The intent object can request a target component by name. and the data to be used as an input for the action. Similarly. locationUri).intent.ACTIONVIEW. among others. It can optionally initiate the service if it's not already running. There is no overlap within these messaging systems: Broadcast intents are delivered only to broadcast receivers. never to a service or broadcast receiver. startActivity(myIntent). Coding Example: Intent response 2. the requested action. instantiating them if necessary.parse("geo: 32.startService() to initiate a service or deliver new instructions to an ongoing service. service.sendBroadcast(). In each case. much in the same way a desktop operating system will launch a suitable application to open a document if no specific application is requested.content. an intent can be passed to Context. 0. An intent passed to startActivity() is delivered only to an activity. setClass(). never to activities or services.4.1 Structure of Intent Objects An Intent object contains information about the target component to carry out the action.779523.-96.
White Paper 1.Developing for Android ACTION is a string naming the action to be performed.6 27 . the data field would be a tel: URI with the number to call. For example. 0. DATA Data contains the URI of the data to be acted on and the MIME type of that data. although developers can create their own action strings for their applications. Similarly. The action string can also be used by broadcast intents to report to listeners an action that just took place. with no data input and no returned output Synchronize data on a server with data on the mobile device A warning that the battery is low Event when headset has been plugged into or removed from the device The screen has been turned on The setting for the time zone has changed ACTION_MAIN activity ACTION_SYNC activity ACTION_BATTERY_LOW broadcast receiver ACTION_HEADSET_PLUG broadcast receiver ACTION_SCREEN_ON ACTION_TIMEZONE_CHANGED broadcast receiver broadcast receiver Table 4 — Default action strings supported by Android. if the action is ACTION_VIEW and the data field is an http: URI. the data field would contain the URI of the document to be displayed for editing. the receiving activity would be called upon to download and display whatever data the URI refers to. if the action field is ACTION_EDIT. Different actions are paired with different kinds of data specifications. If the action is ACTION_CALL.0 Rev. Action Constant ACTION_CALL ACTION_EDIT Target Component activity activity Action Initiate a phone call Display data for the user to edit Start up as the initial activity of a task. Below are constants supported by the action string by default.
Developing for Android When matching an intent to a component that is capable of handling the data. 0. All flags are defined in the Intent class. White Paper 1. EXTRAS Extras allow key-value pairs for additional information that should be delivered to the component handling the intent. which task the activity should belong to) and how to treat the activity after it's launched (for example. and new categories can be created and placed in an Intent object as needed. Extras are useful for handling special information specific to the action. the first screen the user sees when the device is turned on or when the HOME key is pressed The activity can be the initial activity of a task and is listed in the top-level application launcher The target activity is a preference panel CATEGORY_BROWSABLE CATEGORY_GADGET CATEGORY_HOME CATEGORY_LAUNCHER CATEGORY_PREFERENCE Table 5 — Default intent categories supported by Android. a component able to display image data should not be called upon to play an audio file.0 Rev. Some categories are built-in (below). whether it belongs in the list of recent activities). for example a SHOW_COLOR action (which is a custom action) would need a color value set in an extra key-value pair. an image or an e-mail message The activity can be embedded inside of another activity that hosts gadgets The activity displays the home screen. For example. CATEGORY Category is a string containing information about the kind of component that should handle the intent. Constant Description The target activity can be safely invoked by the browser to display data referenced by a link — for example.6 28 . it's important to know the type of data (its MIME type) in addition to its URI. FLAGS Flags instruct Android how to launch an activity (for example.
Developing App Widgets App Widgets are miniature application views that can be embedded in other applications (such as the Home screen) and receive periodic updates.1 Creating App Widgets To create an App Widget. AppWidgetProviderInfo object White Paper 1.0 Rev.Developing for Android 3. These views are referred to as Widgets in the user interface. 0.6 29 . and you can publish one with an App Widget provider. Courtesy Google. An application component that is able to hold other App Widgets is called an App Widget host. Figure 2 — Some examples of App Widgets running on the Android home screen. 3. you need the following: 1.
which do not support every kind of layout or view widget 3. based on broadcast events. Containers are defined using XML and placed in the project's res/layout/ directory.1 below on Layouts for more information about creating containers. 3. When these broadcast events occur. disabled and deleted. which launch a configuration activity for your application when a user adds it to the device Home page. deleted.Developing for Android Describes the metadata for an App Widget.3 Handling Events The AppWidgetProvider class extends BroadcastReceiver as a convenience class to handle App Widget broadcasts. or disabled. update frequency. 2. Note that App Widget layouts are based on RemoteViews. you will receive broadcasts when the App Widget is updated. and the AppWidgetProvider class. See section 5. and 3.2 Layouts and Views App Widgets are placed inside a container defined in the View class. This should be defined in XML. such as the App Widget's layout. This allows an App Widget to be configured by the user when it is created. the AppWidgetProvider receives the following method call: White Paper 1. AppWidgetProvider class implementation Defines the basic methods that allow you to programmatically interface with the App Widget. enabled. enabled. such as when the App Widget is updated. defined in XML. The AppWidgetProvider receives event broadcasts that are relevant to the App Widget. TIP: Additionally. App Widget configuration Activities are available. Through it.6 30 . 0. View layout Defines the initial layout for the App Widget.0 Rev.
int[]) Coding Example: Broadcast event relevant to the app widget This is called to update the App Widget at intervals defined by the updatePeriodMillis attribute in the AppWidgetProviderInfo ADDITIONAL APP WIDGET EVENTS onDeleted(Context. Intent) Called for every broadcast. To do so. you need to update more frequently and/or you do not need to update while the device is asleep. which will only deliver the alarm when the device is awake. AppWidgetManager. onReceive(Context. onDisabled(Context) Called when the last instance of the App Widget is deleted from the App Widget host.e. (i. such as deleting a temporary database. This can be a flag to perform clean-up tasks.0 Rev. this probably won't cause significant problems for the battery life.Developing for Android onUpdate(Context. not called if the user adds a subsequent instance of the App Widget). 0. If you don't update more than once per hour. however. Then set updatePeriodMillis to zero ("0"). TIP: If the device is asleep when it is time for an update (as defined by updatePeriodMillis). using the AlarmManager.6 31 . int[]) Called when an App Widget is deleted from the App Widget host. set an alarm with an Intent that your AppWidgetProvider receives. and before each of the above callback methods. onEnabled(Context) Called when an instance the App Widget is created for the first time. Set the alarm type to either ELAPSED_REALTIME or RTC. then you can instead perform updates based on an alarm that will not wake the device. If. White Paper 1. then the device will wake up in order to perform the update.
then you need to register the event handlers in this callback.0 Rev. White Paper 1. then onUpdated() may be the only callback method you need to define.Developing for Android TIP: The most important AppWidgetProvider callback is onUpdated() because it is called when each App Widget is added to a host (unless you use a configuration Activity). 0. or perform other work that requires clean-up. If your App Widget accepts any user interaction events.6 32 . If your App Widget doesn't create temporary files or databases.
This interface defines a factory for socket implementations. however. Internet addresses and HTTP requests. 4. SocketOptions URLStreamHandlerFactory Table 6 — Networking interfaces in Android White Paper 1.net and Java.Developing for Android 4. Defines an interface for socket implementations to get and set socket options.6 33 . Network IP communications are possible over Wi-Fi and the mobile data network.1 Basic Networking Basic networking in Android is similar to standard Java networking since Android supports the Java. This interface defines a factory for datagram socket implementations. Android supports two APIs to handle network communications: Android. Communications Android supports communications over Wi-Fi.0 Rev. there are a variety of methods for querying about network status and specifying particulars if your application requires fine-grain control. Defines a factory which creates an URLStreamHandler for a specified protocol. Android subsystems handle network acquisition and management so that you can abstract your application from dealing with the details. 0. managing datagram sockets.net interfaces are supported on Android: Interface ContentHandlerFactory DatagramSocketImplFactory FileNameMap SocketImplFactory Description Defines a factory which is responsible for creating a ContentHandler.net APIs to handle tasks such as streaming. The following standard Java.net APIs. Defines a scheme for mapping a filename type to a MIME content type. Bluetooth and of course the mobile data network.
Developing for Android In addition. Sanitize values based on which characters they contain.net API adds these classes: Class ConnectivityManager Credentials DhcpInfo LocalServerSocket LocalSocket LocalSocketAddress MailTo Description Answers queries about the state of network connectivity Handles UNIX credentials on UNIX domain sockets Retrieves the results of a DHCP request Creates inbound UNIX-domain sockets Creates a (non-server) socket in the UNIX-domain namespace A UNIX-domain (AF_LOCAL) socket address Parses mailto scheme URLs. Provides access to the user and default proxy settings Allows SSL certificate chain validation to be skipped when negotiating an SSL session.6 34 . A simple tuple that holds parameter-value pairs.Builder UrlQuerySanitizer UrlQuerySanitizer. Sanitizes the Query portion of a URL.ParameterValu ePair Table 7 — Android networking APIs White Paper 1.0 Rev. NetworkInfo Proxy SSLCertificateSocketFactory Uri Uri. Immutable URI reference. Helper class for building or manipulating URI references. the Android.IllegalCharac terValueSanitizer UrlQuerySanitizer. Can be queried for the parsed parameters Describes the status of a network interface of a given type (either mobile or Wi-Fi). 0.
).Developing for Android 4. UMTS. false on failure. Android will ignore the request. mobile or Wi-Fi) The IP address of the target host Table 8 — Parameters for setting up a network connection White Paper 1.6 35 . and Android abstracts many of the details. Your application will call the public method requestRouteToHost (int networkType. and Provides an API that allows applications to query the coarse-grained or fine-grained state of the available networks 4.2.0 Rev. ConnectivityManager does the following: ConnectivityManager Monitors network connections (Wi-Fi.e. Parameter networkType hostAddress Description The type of the network requested for routing data to specified host (i. If a request is made to set up a connection which already exists. can be queried for the state of network connectivity. Attempts to "fail over" to another network when current network connectivity.2 Connections and Management The Android. Android will return true on success. GPRS. 0. Sends broadcast intents when network connectivity changes. int hostAddress) This instructs Android to ensure a network route exists to deliver traffic to the specified host via the specified network interface. but will treat it as successful. and it can also notify applications when network conditions change. etc.net API offers the ConnectivityManager class to set up and manage connections.1 Setting Up a Network Connection Setting up a network connection or requesting data is a simple procedure.
DETERMINING CURRENT NETWORK TYPE Your application can query to see which network type is currently in use (i. applications should not use the network if the application is not in the foreground. mobile or Wi-Fi) by calling: getType() SPECIFYING A NETWORK TYPE Your application can specify which network type to activate by using: public static final int TYPE_MOBILE.0 Rev. or public static final int TYPE_WIFI When the desired connection type as specified above is active. and check the value of this before performing any background data operations. although your application may request a specific network type for its data requests. 4.Developing for Android TIP: The getBackgroundDataSetting ()call will tell your application whether fetching of data in the background is permitted. for example. White Paper 1.2. if your application downloads large files. set your application to listen to ACTION_BACKGROUND_DATA_SETTING_CHANGED to be notified if the user changes settings allowing this operation. If your application can benefit from accessing the network passively when it is in the background. If the result is <false>. all data traffic from your application will use this connection type by default.e.2 Choosing the Network Bearer Android will automatically use the default network for all requests. Developers should respect this setting. 0. In this case you may wish to only use Wi-Fi connections and not mobile connections.6 36 . This can be useful if.
enum NetworkInfo. GETTING INFORMATION ABOUT NETWORK CONNECTIONS Other calls in the NetworkInfo class are useful for general status. Return a network-type-specific integer describing the subtype of the network. or for troubleshooting: Public Method NetworkInfo. if any was provided by the lower networking layers Report the reason an attempt to establish connectivity failed. ‗Disconnected'.6 37 . or simplified terms (either ‗Connecting'. This class provides functions for learning network state either in detail.0 Rev. 0.State/getStat e() getSubtype() getSubtypeName() getType() getTypeName() isAvailable() isConnected() White Paper 1. Reports the type of network currently in use (i.DetailedState provides fine-grained network state information. if one is available. ‗Disconnecting'. Return a human-readable name describing the subtype of the network.net. Indicates whether network connectivity exists and it is possible to establish connections and pass data.e. Indicates whether network connectivity is possible. Reports the current coarse-grained state of the network. ‗Suspended' or ‗Unknown'). ‗Connected'.DetailedState /getDetailedState() getExtraInfo() Description Reports the current fine-grained state of the network Report the extra information about the network state.NetworkInfo class. for example "WIFI" or "MOBILE".State provides coarse-grained network state information.3 Connection Maintenance Android can provide status about the current state of network connectivity through the android.Developing for Android 4. enum NetworkInfo.2. mobile or Wi-Fi) Return a human-readable name describe the type of the network. getReason() NetworkInfo.
isFailover() isRoaming() toString() Table 9 — Public methods for obtaining network information BEING NOTIFIED OF NETWORK CHANGES The ConnectivityManager class. part of Android.net provides a number of methods for your application to receive notification of changing network conditions. CONNECTIVITY_ACTION EXTRA_IS_FAILOVER EXTRA_NO_CONNECTIVITY EXTRA_OTHER_NETWORK_INFO EXTRA_REASON Table 10 — Public methods for network event notification White Paper 1. Returns a string containing a concise. humanreadable description of this object. Indicates whether there is a complete lack of connectivity Information is supplied when there is another network that may possibly accept connections Indicates why an attempt to connect to a network failed. Indicates whether the current attempt to connect to the network resulted from the ConnectivityManager trying to fail over to this network following a disconnect from another network.Developing for Android Public Method isConnectedOrConnecting() Description Indicates whether network connectivity exists or is in the process of being established.0 Rev.6 38 . 0. Your application can also query to see if the reason for the change is due to a failover condition This indicates whether a connection event is for a given network is an attempt to repair a failover condition. Indicates whether the device is currently roaming on this network. either network has been established or lost. Public Method Description This can notify your application that a change in the network condition has been detected.
and will format them using formatNumber Various utilities for dealing with phone number strings A listener class for monitoring changes in specific telephony states on the device. such as the network type and connection state. including Received Signal Strength and Cell ID location Watches for the user entering phone numbers. signal strength. Android provides a robust set of APIs for monitoring telephone operations. and take action accordingly. etc.6 39 . including service state. this notification can be used to tell your application to wait for another broadcast indicating either that the failover attempt succeeded or failed. 0. Contains phone state and service related information Contains phone signal strength related information Manages SMS operations such as sending data. 4. the NetworkInfo for the new network is also passed as an extra.Developing for Android TIP: If the connectivity manager is attempting to connect (or has already connected) to another network as a result of a failover condition. The classes include: Public Method CellLocation Description Abstract class that represents the location of the device Represents the neighboring cell information. and SMS messages NeighboringCellInfo PhoneNumberFormattingText Watcher PhoneNumberUtils PhoneStateListener ServiceState SignalStrength SmsManager White Paper 1. Instead. This lets any receivers of the broadcast know that Android is attempting to repair network connectivity and that applications should not necessarily tell the user that no data traffic will be possible. message waiting indicator (voicemail).0 Rev. text. plus utilities for manipulating phone number strings.3 Telephony As you would expect.
TIP: The Dialer can normalize some kinds of schemes. Uri .6 40 . Use PhoneNumberUtils or Uri. Coding Example: Dialer App In the above example. 0. to make phone calls. or tel: (212) 555 1212.Developing for Android Public Method TelephonyManager Description Provides access to information about the telephony services on the device Table 11 — Android telephony methods 4. however you should ensure that your formatting scheme will be accepted by the dialer.parse("tel:6365551212")). Android will call the entered phone number.permission.fromParts factory to generate properly formatted numbers A similar function action (ACTION_DIAL) will pre-dial the number. Applications must have permission (as listed in the Android manifest file — <uses-permission id="android. startActivity(dialIntent). and allows users or applications.1 Phone Calls Android provided a built-in application called Dialer which links user input and application intents with the underlying telephony code.3. Intent dialIntent = new Intent(Intent.CALL_PHONE" />) to use this function. respectively.ACTION_CALL. such as: tel:2125551212.0 Rev. provided the number is formatted as a valid (IETF RFC 3966) phone number. so the formats above are not strictly required. White Paper 1. but will not instruct Android to place the call.
4. sendIntent.Developing for Android PHONE NUMBER UTILITIES Android also provides a group of tools under the PhoneNumberUtils class for working with phone numbers."). "Content of the SMS goes here.2 SMS Android supports the creation and sending of plain text messages. Coding Example: Using an Intent object to invoke built-in SMS app.android-dir/mms-sms"). and so on. such as formatting numbers for a variety of global locales.e. comparing phone numbers against the address book for the purposes of matching strings for Caller ID.0 Rev.. converting text (i. Android also provides a function to automatically divide text messages into multi-part messages.3. startActivity(sendIntent). multi-part text messages. White Paper 1.setType("vnd.. 0. To do this.6 41 . use an Intent object to invoke the built-in SMS application: Intent sendIntent = new Intent(Intent.putExtra("sms_body". and data messages. 1-800-FLOWERS) into phone numbers. IMPLEMENTING TEXT MESSAGE FUNCTIONALITY Android provides APIs to integrate with its built-in SMS client.ACTION_VIEW). sendIntent. which is a simple way to handle text messaging tasks by invoking the built-in SMS client from within your application.
xml file located in the res/layout folder to give your application a user interface: White Paper 1.telephony package.6 42 .0 Rev. You will need to add the permissions SEND_SMS and RECEIVE_SMS Create a layout in the in the main. Modify the AndroidManifest.xml file to grant permission for your application to send and receive SMS messages. 0.Developing for Android WRITING YOUR OWN SMS CLIENT You can also write your own SMS client fairly simply using the SMS classes in the android.
0" encoding="utf-8"?> <LinearLayout xmlns:android="http://schemas.0 Rev.android. 0.6 43 .Developing for Android <?xml version="1.com/apk/res/android" android:orientation="vertical" android:layout_width="fill_parent" android:layout_height="fill_parent" > <TextView android:layout_width="fill_parent" android:layout_height="wrap_content" android:text="Enter the phone number of recipient" /> <EditText android:id="@+id/txtPhoneNo" android:layout_width="fill_parent" android:layout_height="wrap_content" /> <TextView android:layout_width="fill_parent" android:layout_height="wrap_content" android:text="Message" /> <EditText android:id="@+id/txtMessage" android:layout_width="fill_parent" android:layout_height="150px" android:gravity="top" /> <Button android:id="@+id/btnSendSMS" android:layout_width="fill_parent" android:layout_height="wrap_content" android:text="Send SMS" /> </LinearLayout> Coding Example: Creating the UI for Figure 3 White Paper 1.
use the SmsManager class. Note: The button view in Figure 3 is "wired up" in code so that the UI elements trigger the appropriate functions. such as the sendSMS()call To send an SMS message. 0. The main function.6 44 . Source: Google.Developing for Android Figure 1 — Android Platform Architecture.0 Rev. the sendSMS() function is defined as follows: White Paper 1.
rather it is called through an SMSManager object.getDefault().. sms.class).. White Paper 1. 0. 0.. String message) { PendingIntent pi = PendingIntent. SmsManager sms = SmsManager. message. such as a function to monitor the sending of the message.6 45 .sendTextMessage(phoneNumber.0 Rev. which will allow you to display another activity.Developing for Android public class SMS extends Activity { //. } //---sends an SMS message to another device--private void sendSMS(String phoneNumber. SMSManager class is not directly instantiated. null). pi..getActivity(this. new Intent(this. } } Coding Example: Sending an SMS Message NOTE: Unlike other classes. */ @Override public void onCreate(Bundle savedInstanceState) { //. The sendTextMessage() method sends the SMS message with a PendingIntent. /** Called when the activity is first created. SMS. null. 0).
ArrayList<PendingIntent> sentIntents. public void sendMultipartTextMessage (String destinationAddress. String scAddress.0 Rev.RESULT_OK for success. 0. ArrayList<PendingIntent> deliveryIntents) White Paper 1.Developing for Android Parameters destinationAddress scAddress text Description The address to send the message to The service center address or null to use the current default SMSC The body of the message to send if not NULL this PendingIntent is broadcast when the message is sucessfully sent. Table 12 — Parameters for generating SMS messages IMPLEMENTING MULTI-PART TEXT MESSAGES Sending a multi-part text message is essentially the same as a standard text message. generally only useful for troubleshooting. ArrayList<String> parts. The result code will be Activity. The per-application based SMS control checks sentIntent. deliveryIntent This PendingIntent is broadcast when the message is delivered to the recipient. which cause smaller number of SMS to be sent in checking period.6 46 . If sentIntent is NULL the caller will be checked against all unknown applications. with the addition of the ArrayList<String> parts parameter. or failed. or one of these errors: RESULT_ERROR_GENERIC_FAILURE RESULT_ERROR_RADIO_OFF RESULT_ERROR_NULL_PDU sentIntent For RESULT_ERROR_GENERIC_FAILURE the sentIntent may include the extra "errorCode" containing a radio technology specific value.
0.Developing for Android Android can also divide the text message into a multi-part message for you by using the following: public ArrayList<String> divideMessage (String text) Coding Example: Sending a multi-part message White Paper 1.0 Rev.6 47 .
There are many types of views and view groups. or Instantiate layout elements at runtime Your application can create View and ViewGroup objects (and manipulate their properties) programmatically. View objects are user interface elements. Figure 3 —The Android view hierarchy. White Paper 1. each of which is a descendant of the View class.1 Layouts Objects are arranged in a spatial container called Layouts. such as linear layouts. Android UI In an Android application. 0. such as those for widgets and layouts.Developing for Android 5. Different types of layouts are available in the ―layouts‖ subclasses. 5. the user interface is built using View objects within the View class and ViewGroup objects.0 Rev. which are contained within a spatial layout. called Children. which hold all of the elements that appear to the user. tabular layouts and relative layouts Layouts can be declared in two ways: Declare UI elements in XML Android provides a straightforward XML vocabulary that corresponds to the View classes and subclasses. The ViewGroup is a special view which can contain other view objects.6 48 . the ViewGroup.
completely or partially obscuring layers below.1.0 Rev. Note that defining layouts in XML has the advantage of keeping the visual presentation layer separate from application code. the height of the tallest child. FrameLayout objects are simple. 0. FrameLayout Additional Child view objects added to the FrameLayout will be drawn over previous ones. runtime or both methods for declaring and managing application user interfaces. and do not allow any control over the position of Child objects placed within them. Child objects are pinned to the upper left corner of the screen. For example.6 49 . such as a picture. A horizontal LinearLayout will line all children along the horizon. A FrameLayout is blank rectangular container on the screen which can be filled with a single object. FRAME LAYOUT is the simplest type of layout object. depending on the size and transparency of the child overlaying the other layers. A vertical LinearLayout stacks all children such that one column is created with one child per row.1 Layout Types Android supports common layout types.Developing for Android TIP: Developers can use either XML. Programmatic changes to the user interface layout can be managed through code which is executed at runtime. which can make it easier to troubleshoot applications. an application"s default layouts could be declared in XML (as the screen appears to the user at application launch). making one row. Layouts are subclasses of ViewGroup. 5. allowing the user interface to change based on activities in the application. and adapt the visual presentation without changing application code or recompiling. LINEAR LAYOUT A LinearLayout aligns all children in a single direction — vertically or horizontally. plus padding. White Paper 1.
All three children above are "stacked" one atop the other in a single column. 0. A table can leave cells empty. TableLayout Figure 5 — A Table layout White Paper 1. as they can in HTML. but cells cannot span columns. or cells).Developing for Android Figure 4 — A LinearLayout set up in the vertical orientation.6 50 . TABLE LAYOUT positions children into rows and columns (without visible border lines for rows.0 Rev. The table will have as many columns as the row with the most cells. columns.
Each layout file must contain exactly one root element. which must be a View or ViewGroup object. or centering items relative to the screen bounds.Developing for Android RELATIVE LAYOUT lets child views specify their position relative to the parent view or to each other. using a series of nested elements — similar to the way HTML web pages are created. the text box is aligned relative to the screen center.2 XML Layout Example Android's XML vocabulary makes it fast and easy to design UI layouts and the screen elements they contain.6 51 . 0. RelativeLayout In the example below. Below is an XML layout that uses a vertical LinearLayout to hold a TextView and a Button: White Paper 1.1. you can add additional layout objects or widgets as child elements to build a View hierarchy that defines the layout. Figure 6 — A Relative layout 5.0 Rev. for example allowing all items to be aligned along their right borders. Once the root element has been defined. and the Cancel button aligned to the left and top of the OK button. the OK button aligned relative to the right of the text box.
Developing for Android
<?xml version="1.0" encoding="utf-8"?> <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="fill_parent" android:layout_height="fill_parent" android:orientation="vertical" > <TextView android:id="@+id/text" android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="Hello, I am a TextView" /> <Button android:id="@+id/button" android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="Hello, I am a Button" /> </LinearLayout>
Coding Example: XML layout utilizing vertical linear layout to hold a text view and button
TIP: You can also draw View and ViewGroups objects in Java code, using the
addView(View) methods to dynamically insert new View and ViewGroup objects.
UI Components
The View class contains subclasses called ―widgets‖ (not to be confused with App Widgets). Widgets are fully implemented UI objects, like text fields and buttons. Widgets can be placed inside ViewGroups as Children.
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The following is a partial list of the UI Widgets available:
AbsSpinner AnalogClock AutoCompleteTextView Button CheckBox CheckedTextView Chronometer CompoundButton DatePicker DialerFilter DigitalClock EditText ExpandableListView ExpandableListView.Ex pandableListContextMe nuInfo Filter Filter.FilterResults FrameLayout Gallery GridView HorizontalScrollView ImageButton Like AnalogClock, but digital. EditText is a thin veneer over TextView that configures itself to be editable. A view that shows items in a vertically scrolling two-level list. Extra menu information specific to an ExpandableListView provided to the onCreateContextMenu(ContextMenu, View, ContextMenuInfo) callback when a context menu is brought up for this AdapterView. A filter constrains data with a filtering pattern. Holds the results of a filtering operation. FrameLayout is designed to block out an area on the screen to display a single item. A view that shows items in a center-locked, horizontally scrolling list. A view that shows items in two-dimensional scrolling grid. Layout container for a view hierarchy that can be scrolled by the user, allowing it to be larger than the physical display. Displays a button with an image (instead of text) that can Description An abstract base class for spinner widgets. This widget display an analogic clock with two hands for hours and minutes. An editable text view that shows completion suggestions automatically while the user is typing. Button represents a push-button widget. A checkbox is a specific type of two-states button that can be either checked or unchecked. An extension to TextView that supports the Checkable interface. Class that implements a simple timer. A button with two states, checked and unchecked. A view for selecting a month / year / day based on a calendar like layout.
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Description be pressed or clicked by the user.
ImageView LinearLayout ListView MediaController PopupWindow ProgressBar QuickContactBadge RadioButton RadioGroup RatingBar RelativeLayout RemoteViews Scroller ScrollView
Displays an arbitrary image, such as an icon. A Layout that arranges its children in a single column or a single row. A view that shows items in a vertically scrolling list. A view containing controls for a MediaPlayer. A popup window that can be used to display an arbitrary view. Visual indicator of progress in some operation. Widget used to show an image with the standard QuickContact badge and on-click behavior. A radio button is a two-states button that can be either checked or unchecked. This class is used to create a multiple-exclusion scope for a set of radio buttons. A RatingBar is an extension of SeekBar and ProgressBar that shows a rating in stars. A Layout where the positions of the children can be described in relation to each other or to the parent. A class that describes a view hierarchy that can be displayed in another process. This class encapsulates scrolling. Layout container for a view hierarchy that can be scrolled by the user, allowing it to be larger than the physical display. A SeekBar is an extension of ProgressBar that adds a draggable thumb. SlidingDrawer hides content out of the screen and allows the user to drag a handle to bring the content on screen. A view that displays one child at a time and lets the user pick among them. Container for a tabbed window view. A tab has a tab indicator, content, and a tag that is used to keep track of it. A layout that arranges its children into rows and columns. Displays a list of tab labels representing each page in the parent's tab collection.
SeekBar SlidingDrawer Spinner TabHost TabHost.TabSpec TableLayout TabWidget
White Paper 1.0 Rev. 0.6
Developing for Android
Description A view for selecting the time of day, in either 24 hour or AM/PM mode. A toast is a view containing a quick little message for the user. The toast class helps you create and show those. Displays checked/unchecked states as a button with a "light" indicator and by default accompanied with the text "ON" or "OFF". Displays a video file. Base class for a FrameLayout container that will perform animations when switching between its views. Simple ViewAnimator that will animate between two or more views that have been added to it. ViewAnimator that switches between two views, and has a factory from which these views are created. The ZoomControls class displays a simple set of controls used for zooming and provides callbacks to register for events.
ToggleButton VideoView ViewAnimator ViewFlipper ViewSwitcher
Table 13 — A partial list of the UI widgets available in Android.
Android offers an easy programming interface for developers to provide standardized application menus for various situations. Three types of application menus are available: OPTIONS MENU This is the primary set of menu items for an Activity. It is revealed by pressing the device MENU key. Within the Options Menu are two groups of menu items: Icon Menu The collection of items initially visible at the bottom of the screen when the MENU key is pressed, and Expanded Menu This is a vertical list of items exposed by the "More" menu item from the Icon Menu.
White Paper 1.0 Rev. 0.6
PhotoPicker. or Define an Intent and allow Android to search the device for matching activities and dynamically show these matches in a list MenuItem menuItem = menu. PHOTO_PICKER_ID.Developing for Android CONTEXT MENU This is a floating list of menu items that may appear when the user presses on a View (such as a list item). EVENT LISTENERS An event listener is an interface in the View class that contains a single callback method. 5. 0. The general approach is to capture events from the specific View object that the user interacts with. SUBMENU This is a floating list of menu items that is revealed by an item in the Options Menu or a Context Menu.4 Events Android provides multiple ways to intercept and act on events created as your application is used. There are two ways to do this: Define an Intent and assign it to a single menu item.3.6 56 . "Select Photo").0 Rev. Coding Example: An Intent for a single item 5.add(0. White Paper 1. by using the View class. as a way to directly launch an activity or application. 0.setIntent(new Intent(this.class)). Android will call these methods when the listener detects that a user has interacted with an item in the user interface. menuItem.1 Menu Item Intents Menu items can also be used to issue Intents.
Called when a Context Menu is being built (as the result of a sustained "long click"). Called when the user is focused on the item and presses or releases a key on the device. or any movement gesture on the screen (within the bounds of the item). Called when the user navigates onto or away from the item. 0.6 57 . using the navigation-keys or trackball. Called when the user either touches and holds the item (when in touch mode). onClick() onLongClick() onFocusChange() onKey() onTouch() onCreateContextMenu() Table 14 — Event listener interface callback methods White Paper 1. or focuses upon the item with the navigation-keys or trackball and presses the suitable "enter" key or presses down on the trackball. or focuses upon the item with the navigation-keys or trackball and presses and holds the suitable "enter" key or presses and holds down on the trackball (for one second). See the discussion on context menus in Creating Menus for more information.0 Rev. Called when the user performs an action qualified as a touch event. including a press.Developing for Android The event listener interface includes the following callback methods: Method Description Called when the user either touches the item (when in touch mode). a release.
0 Rev.6 58 . 0. .. which provides the same functionality without loading extra classes and objects. // Capture our button from layout Button button = (Button)findViewById(R. Coding Example: How to register an "on-click" listener for a button TIP: It is also possible to implement an event listener as part of an Activity using OnClickListener. White Paper 1.setOnClickListener(mCorkyListener).. // Register the onClick listener with the implementation above button.corky)..Developing for Android // Create an anonymous implementation of OnClickListener private OnClickListener mCorkyListener = new OnClickListener() { public void onClick(View v) { // do something when the button is clicked } }.. protected void onCreate(Bundle savedValues) { .id.
While this means you do not necessarily need to develop a simplified version of your website or application for technical reasons as was often needed in the past. with contributors from KDE project. For example. RIM. WebKit is an open source project. mouse_down()may fire. WebKit is a particularly attractive browser engine for developers because it has a modern. Apple.Developing for Android 6. 0. a modern. supports W3C standards. events such as mouse_move(). but White Paper 1. and make controls larger than typical for desktop browser use. and hover styles should not be used. Also. In addition to the usability tips above. Therefore. This is because users may be attempting to interact with your site or application on the go. and display with the same fidelity. and the same development techniques used on iPhone will work on Android as well. links should be larger (or appear as buttons). it's often a good idea to make pages less information-dense. Palm. Because WebKit runs on both desktop systems and mobile systems. powerful and standards-compliant browser engine. which means they may have less time to read the screen and ‗figure out' what to do. spaced farther apart. streamlined code base. requiring users to touch links rather than click on them. many sites or web applications developed for desktop browsers may work perfectly well in a mobile WebKit environment. full-fledged web applications are possible on mobile devices. Google. USABILITY CONSIDERATIONS When designing applications and sites for mobile devices. and others. Writing for the Web Android uses WebKit. you may still want to consider tailoring your code to make it more usable and relevant on mobile devices. Nokia. 6. and is open-source so that developers can enhance the codebase. consider that your site or application may be viewed on a multi-touch device.0 Rev. it will likely work on Android with little modification.1 Mobile Web/XHTML Sites Since WebKit is such a capable rendering engine.6 59 . functions relating to the mouse may not make sense when viewing a web page or application in a multi-touch mobile browser. DEVELOPING MOBILE SITES AND WEB APPLICATIONS FOR ANDROID If your existing site or web application works on iPhone.
without using a plug-in such as Flash or Silverlight Provides services based on geographic (GPS) information Stores data locally to allow applications to work offline or to provide protection against lapses in network connectivity Allows background computation without blocking the user interface Table 15 — HTML5 features supported in Android White Paper 1. which is a special addition for mobile browsers (it is ignored by browsers which do not support it). meaning that pixel dimensions do not need to be specified.: <meta name="viewport" content="width=device-width.2 Leveraging HTML5 Since version 2.Developing for Android they may not be returned in the same order expected. Make use of the viewport metatag. it is always a good idea to know how your web page or application will appear on various target sizes.0 Rev. With viewport. Coding Example: Initial scaling of the webpage While viewport and initial-scale values are screen independent. WebKit on Android now supports several HTML5 features. Also consider that users may view your site in either portrait or landscape orientation.0.0 user-scalable=yes" />. the following HTML5 features are supported: Feature/Element Canvas Video Geolocation App Cache and Database Workers Description Allows for dynamic scriptable rendering of bitmap images Adds support for embedding video in a HTML page.6 60 . developers can specify the initial scaling of the webpage to make it easier to read as it first loads. as many mobile browsers support this feature. 0. For example. initialscale=1. which makes even more capable web applications possible. 6. or may not be returned at all.
loadUrl("http://developer. "android").post(new Runnable() { //invoke a javascript method mWebView. webView. 0.Developing for Android mWebView = new WebView(this).att.someMethod()" public void someMethod() { mHandler.6 63 . White Paper 1.loadUrl("javascript:doSomething()"). //make MyJavaScriptInterface accessible from javascript webView. } } } Coding Example: WebView managing event handling and interacting with JavaScript.0 Rev.addJavascriptInterface(new MyJavaScriptInterface(). setContentView(webView). final class MyJavaScriptInterface { //invoked from javascript "android.com/").
and optimizing the number of items in a menu and placement of those items can make menus very intuitive and easy for the user. White Paper 1. MAKE PROPER USE OF THE BACK BUTTON The BACK button will move backwards chronologically in the stack of activities. putting your application in the background. Best Practices This section introduces some tips. If your application is contained primarily within one screen. pressing the BACK button should bring the previously used application activity into the foreground. such as the Maps application or the web browser. If your application has multiple ‗layers' or windows. it may make more sense for the BACK button to restore a previous state within your application CREATE EASY-TO-USE MENUS Choosing the right type of menu for a given situation. and may make it more likely that a user will chose to download your application over another.1 User Interface Creating a unified look and feel throughout your application's user interface makes your product look professional. Use the correct angles for the specific icon types. 0. Keep icon designs simple. Here are a few tips to achieving a polished. as described in the Android User Interface Guidelines.6 64 . professional look with your application: DESIGN A PROFESSIONAL-LOOKING APPLICATION ICON Use the Android Icon Templates Pack as a starting point for your icon. 7.0 Rev.Developing for Android 7. tricks and best practices for developing Android applications. Restrain the use of color in your icon. as well as things you'll need to know to about optimizing your application for the AT&T network. Note that base of a launcher icon should be grey and feel solid.
"Create Notification" is truncated to something like "Create…ication". but not obvious to all users. Use short. since some device screens can be small and menus may scroll. USE THE NOTIFICATION SYSTEM TO MESSAGE THE USER Use the Android notification system if your background application needs to send an alert to the user. selection-specific commands in the Context menu Global commands for your application should go in the Options menu. distinct names menus Ensure your menu names are not truncated or ambiguous. or only available in some contexts and not others can go within the menus Put global commands in the Options menu. A user should be able to fully use your application without resorting to context menus. White Paper 1.6 65 . such as the ‗Write New' button in an email application. commands related to the current selection should be in the Context menu (i. activated with a touch & hold) List the most frequently used operations first It's always a good idea to put the most frequently used commands first. and are much less likely to get in the way. Other commands used less frequently.Developing for Android Put only the most important commands fixed on the screen The most important and most frequently used commands probably belong fixed to the user interface of your application. the system truncates it in the middle. Context menus are great time-savers. Thus. which means all commands may not be initially visible and obvious. 0. so it is best to keep commands short but descriptive. Truncation should be avoided whenever possible.e. If a text label in the Options icon menu is too long.0 Rev. rather than a modal dialog which could interrupt an important user task. Dim or hide menu items that are not available in the current context Make sure commands not available in a given context are dimmed so that they do not appear as valid options to the user. Don't put commands only in a Context menu Make sure users can ‗discover' your application and figure out how to use it. Standard Android notifications can be viewed at the user's convenience.
0 Rev. An efficient application strives for performance. constrained memory and attempts to preserve battery power as much as possible. Efficient code does more with fewer lines of instructions. Consider performance consequences of API design decisions. 0. optimization and efficiency should be designed into the application from the ground up. Measure performance before and after each attempted optimization. When developing in the simulation environment on a workstation. Avoid creating objects. TIP: There are two basic rules for resource-constrained systems: -Don't do work that you don't need to do -Don't allocate memory if you can avoid it GENERAL OPTIMIZATION TIPS The best way to write efficient code is to truly understand what the code really does. and evaluate whether there may be a simpler. Code optimization should be considered a design task rather than a compilation/packaging task.2 Optimizing Code for Android Android applications should be optimized for efficiency. it's easy to overlook these concerns. but also balances this with the constraints of slower processors. White Paper 1. Don't be concerned about using a memory or CPU intensive operation if you truly need it. Additional ideas include… Strive to write good programs rather than fast ones. faster and less ‗expensive' way to achieve the same effect. compact.Developing for Android 7. That is. It is clever. but ensure these decisions are made with forethought. but getting them right and building an efficient application is crucial. Strive to avoid design decisions that limit performance. smaller screens. and doesn't demand a large memory footprint.6 66 .
Action Add a local variable Add a member variable Call String. which keeps language resources separate from core Java functionality.6 67 . 0.000 7.length() Call empty static native method Call empty static method Call empty virtual method Call empty interface method Call Iterator:next() on a HashMap Call put() on a HashMap Inflate 1 View from XML Inflate 1 LinearLayout containing 1 TextView Inflate 1 LinearLayout containing 6 View objects Inflate 1 LinearLayout containing 6 TextView objects Launch an empty activity Table 17 — Sample performance times of some common actions Time 1 4 5 5 12 12. to provide an illustration of the relative time cost of one operation over another. White Paper 1.0 Rev. To make localization simple.000 3.5 15 165 600 22. SAMPLE PERFORMANCE TIMES The following table gives approximate run times for some common actions.3 Localization Android devices will run on many devices in regions all around the world.000. so it's important that applications can be easily adapted to other locales.000 25. Android applications use the resource framework.Developing for Android Use native methods.000 100. Consider the impact of each action when choosing (or not) to employ it.000 135.
If. which does not belong in resource files. sounds.0 Rev. such as text strings. layouts. use Java to handle the data programmatically rather than storing this data in a locale resource file. Default Resource res/drawable/ res/layout/ res/anim/ res/xml/ res/raw/ Description Required directory holding at least one graphic file. for the application's icon in the Android Market Required directory holding an XML file that defines the default layout Required if any res/anim-<qualifiers> folders exist Required if any res/xml-<qualifiers> folders exist Required if any any res/raw-<qualifiers> folders exist Table 18 — Default resources to define for localization White Paper 1. and any other static data an Android application needs are loaded when an Android application is launched. The default resource set must also include any default drawables and layouts. If the default strings cannot be found. Android automatically selects and loads the resources that best match the device.xml.6 68 . user data needs to be formatted or sorted differently depending on locale. Default text strings for an application must be stored in res/values/strings.Developing for Android TIP: Most or all of the contents of an application's user interface can be put into resource files. for example. RESOURCE SWITCHING Resources. 0. The default strings are loaded if a locale-specific version of strings cannot be found or is not defined. the application will not run. and can include other types of resources such as animations. The behavior of the user interface is driven by Java code. graphics.
version 1. and planned in coming months. Some additional tips include: Design applications to work in any locale.Developing for Android TIP: Ensure each reference to an Android resource in the application code defines the default resource. Test localized apps on the target device. or using the emulator. when designing an application. fail gracefully regardless of the device it runs on and the region it operates in. but the default string file must contain them all. and ensure that the default string file is complete: A localized string file can contain a subset of the strings. ensure it will. This is particularly true where localization is concerned. that is) by the developer beforehand. function normally. DEVICE VERSIONS There is a wide variety of Android devices available.5. the Operating System versions can vary across devices from version 1. While the variety of devices gives great freedom of choice to the consumer. Ensure applications include a full set of default resources. it means that application developers must consider how their applications will run on various devices and plan accordingly. White Paper 1. at worst. 0.4 Common Issues A few tips might help you as you develop applications for Android.0 Rev. Avoid creating more resource files and text strings than you need. Design a flexible layout.6.6 69 . 7. hardware capabilities and screen resolutions. Therefore. Devices vary in form-factor. Additionally. 2. and. at best. since an application may run on devices in other regions which cannot be tested (practically.0 or later. LOCALIZATION STRATEGIES Every situation and operating environment cannot be anticipated when designing an application.
0 Rev. and optimize these sections of code. PERFORMANCE Android handles Garbage Collection automatically. To avoid inadvertently kicking off the Garbage Collection process during performance-critical processes. This means Java applications written for other platforms may need modification to run on Android.Developing for Android JAVA STANDARDS While Android supports many of the standard APIs in Java. However. particularly when executing code which demands high performance. Use the Allocation Tracker tool in the Android SDK to see stack traces which lead to memory allocation requests. such as game rendering. White Paper 1. if needed. Garbage Collection can cause performance issues if it occurs when your application is making heavy use of the CPU. be aware of the memory allocation requests your application is making. it does not offer full compatibility with Java SE and Java ME. 0.6 70 .
Developing for Android 8. Motorola's version of Eclipse can co-exist with any other versions of Eclipse on your development workstation. allowing other versions of Eclipse to be used for non-Motorola device application development. you may wish to use the MOTODEV Studio as your IDE. or even a basic editor (such as Emacs). This is the development environment used internally at Google. and signing functionality all in one place.6 71 . and view thread and process information directly from Eclipse. which can be distributed to users. White Paper 1. MOTODEV Studio is a modified version of Eclipse + ADT plug-in with some additional plug-ins helpful for optimizing applications for unique hardware in some Motorola devices. building. Eclipse + ADT will export projects into a signed APK.1 Creating an Android Project Using the Eclipse IDE with Android Development Tools (ADT) plug-in is the simplest way to set up your development environment. 0. packaging. 8. Eclipse + ADT automates and simplifies the process of building Android applications. Eclipse + ADT provides a New Project Wizard to help quickly create and set up all of the basic files needed for a new Android application. and offers the most integrated functionality. Any IDE can be used (such as IntelliJ). for example to take screenshots. although Eclipse with the ADT (Android Development Tools) plug-in is the recommended method since it provides editing. debugging.0 Rev. Android Development Tools and Android SDK Most application developers will want to use an IDE (Integrated Development Environment) to write code for Android. Eclipse + ADT provides an Android code editor that helps with writing valid XML for Android manifest and resource files. Here are a few of the benefits of using Eclipse with ADT: Eclipse + ADT gives the developer access to other Android development tools from inside the Eclipse IDE. If you are writing for Motorola devices in particular. Eclipse with ADT allows Android applications to be written and debugged faster and more easily. manage port-forwarding. set breakpoints.
select an Android target to be used as the project's Build Target. To create a new project. Under Contents. This is an integer that indicates the minimum API Level required to properly run your application. This will be the name of the folder where your project is created. Select Android > Android Project. 0. you should select a target with the lowest platform version possible. such as Android 1.1. This is the package namespace (following the same rules as for packages in the Java programming language) where all your source code will reside.1 Creating an Android Project in Eclipse with ADT The New Project Wizard dramatically simplifies project setup.6 72 . Under Target. Enter a Min SDK Version. Enter a Package name. simply do the following: Select File > New > Project. fill in all necessary fields. The Build Target specifies which Android platform you'd like your application built against.0 Rev. select Create new project in workspace. Under Properties. TIP: Unless you know that you'll be using new APIs introduced in the latest SDK.Developing for Android 8. Select Create Activity and enter a name for your main Activity class.1. Entering this here automatically sets the minSdkVersion attribute in the <uses-sdk> of your Android White Paper 1. Select the contents for the project: Enter a Project Name. This is the human-readable title for your application — the name that will appear on the Android device. and click Next. Select your project workspace location. Enter an Application name.
The Android Manifest for your project This file contains project settings.0 Rev. This files is integral to the project. It should never be edited manually — to edit project properties. string values.g. layout files. Android 1. All other Java files for your application go in this directory (e.java file and interfaces created from AIDL files Initially empty.Developing for Android Manifest file. such as the build target. Used for storing raw asset files A folder for application resources. You will need to be familiar with the following tools: SDK Tool android Android Emulator Android Debug Description To create/update Android projects and to create/move/delete AVDs To run your Android applications on an emulated Android platform To interface with your emulator or connected device (install White Paper 1.properties Table 19 — Project files automatically generated by the ADT New Project Wizard 8. etc. 0. If you're unsure of the appropriate API Level to use.2 Creating an Android Project in Another IDE When using IDEs other than Eclipse. the following files and directories will be created for your project automatically: Component src/ Description Includes your stub Activity Java file.6 73 . such as your R. rightclick the project folder and select "Properties" <Android Version>/ gen/ assets/ res/ AndroidManifest.1.jar file that your application will build against. This is determined by the build target that you have chosen in the New Project Wizard. such as drawable files. some manual configuration is needed.1/) Includes the android. Click Finish Once you click Finish. it should be maintained in a Source Revision Control system. Contains the Java files generated by ADT. copy the API Level listed for the Build Target you selected in the Target tab.. as such.xml default.
synced to the specified Activity class for the project Build file for Ant Properties for the build system. for testing purposes build. stub files. Do not modify this file. Customizable properties for the build system.apk file (Or similar) To sign your . The Activity class you specified during project creation Output directory for the build script Holds Ant-generated files.j ava bin/ gen/ libs/ res/ src/ tests/ Table 21 — Items generated for a new project using the Android tool Once a project has been created. etc To compile and build your Android project into an installable .0 Rev.Developing for Android SDK Tool Bridge Ant Keytool Jarsigner Description apps. you can begin development.apk file with a private key generated by keytool Table 20 — SDK tools needed when using IDEs other than Eclipse + ADT To create a project.apk file To generate a keystore and private key. such as R. issue commands. used to sign your . default application files.properties Description The application manifest file. run the android tool. It will create the following directories. 0.6 74 . configuration files and a build file: Component AndroidManifest. You will use the Android Debug Bridge (adb) (located in the SDK tools/ directory) to send your application to the emulator. White Paper 1.java Holds private libraries Holds project resources Holds source code Holds a duplicate of all-of-the-above. You can edit this file to override default build settings used by Ant and provide a pointer to your keystore and key alias so that the build tools can sign your application when built in release mode.xml default.xml build.properties src/your/package/nam espace/ActivityName. shell the device.
You can use standard tools — Keytool and Jarsigner — to generate keys and sign your application .0 Rev. use the zipalign tool to optimize the final APK package. This allows applications to be quickly and easily run and tested. Applications are signed either with a debug key or with a private key. Private keys are used for deployment when the application is distributed to end-users. You cannot publish an application that is signed with the debug key generated by the SDK tools The system tests a signer certificate's expiration date only at install time. an exciting step is deploying your application so that the world can discover it. No certificate authority is needed When you are ready to release your application to end-users. White Paper 1. Debug keys are typically used for testing on an emulator. Several important steps must be completed in order to deploy your application. including digitally signing to prove authenticity. If building in the Eclipse environment with the ADT plug-in. 9. 0.apk files automatically with a debug key for the purposes of testing on an emulator or development device.1 Signing Your Application All Android applications must be digitally signed before Android will install them on an emulator or an actual device.6 75 . Deployment Once all the hard work of developing your application is complete. Android will not install an application that is not signed You can use self-signed certificates to sign your applications.apk files. the plug-in will sign . the application will continue to function normally. you must sign it with a suitable private key. IMPORTANT POINTS TO REMEMBER ABOUT SIGNING All applications must be signed. If an application's signer certificate expires after the application is installed. Once you have signed the application.Developing for Android 9.
Sign Your Application With Your Private Key Sign the application with your private key.Developing for Android 9. Here is an overview of the process: 1. 0. A validity period of more than 25 years is recommended (applications signed for Android Market must have a validity period ending after 22 October 2033). The private key may be self-signed. 3. or organizational entity to be identified with the application.1 Signing for Public Release In preparation for releasing your application to the public. 2. Compile the Application In Release Mode Compiling in Release Mode instructs the IDE not to sign the application with the debug key. Ensure the application is signed with a private key before running zipalign. which allows you to sign the application with your private key. Zipalign ensures all uncompressed data starts with a particular byte alignment. use the zipalign tool to process the signed package. White Paper 1. ensuring it has the attributes described in Step 1.1. which reduces the amount of RAM needed to load the application. The private key is private — not the debug key generated by the Android SDK tools. 4. above. The private key has a validity period that exceeds the expected lifespan of the application or application suite. otherwise the zipalign optimizations will be undone if the application is signed afterwards. Align the Final APK Package Once the application has been signed. If you do not have a suitable key. you must generate one using Keytool. it must be signed. Obtain a Suitable Private Key The private key in your possession.0 Rev. Use the Jarsigner utility to do this. corporate.6 76 . which represents the personal.
microemu. It may seem daunting to rewrite your application. plus the vast majority of Java-capable devices.0 Rev. but there are distinct benefits: Applications written for Android run on all Android devices. existing Java ME applications can be run on. 10. making it an attractive target platform for porting existing applications.1 J2ME Applications Since Android runs applications in Java. There are two common approaches to running J2ME applications to Android: Use a J2ME emulator on Android to run the J2ME application. or Rewrite your application to use Android APIs natively. it is rapidly maturing and becoming widely adopted. for example MicroEmulator (http://www. Porting Applications to Android While Android is still relatively new as a platform. but does not support every API defined in the J2ME standard. Opera mini was successfully ported to Android this way.Developing for Android 10. 0. However. meaning your application can virtually be run everywhere. PORTING APPLICATIONS Android runs Java. Applications can have a more polished appearance by taking advantage of Android's User Interface APIs instead of using an add-on library such as LWUIT. and The learning process for J2ME developers is short and easy White Paper 1.6 77 . EMULATORS There are emulators available for Android in the Android Marketplace.org/) includes tools to convert JAD and JAR files into an apk which can be installed on an Android device or emulator. many Java applications can be run on Android with little or no code changes. or ported to Android devices fairly simply.
in addition to the time savings associated with code reuse. For example. it makes sense to run application components in their native languages. Applications which run C or C++ using the NDK are always more complex than pure Android applications. within your application. self-contained routines which do not require much RAM are good candidates. However.0 Rev.6 78 . 0. As an application developer. In some situations. rather than porting them to Android's version of Java. it's possible to embed. in some cases. or at least might not be worth the effort to port and optimize if the gains are small. such as signal processing routines.Developing for Android 10. These components might run better in their native form. and so on. White Paper 1. if at all. you must carefully evaluate when to use Android NDK.2 Going Native With the Android Native Development Kit (NDK). running highly-optimized C or C++ code in the NDK can yield run-time performance benefits over Java code. physics simulations. such as C and C++. components written in other programming languages. highly optimized.
and to get started.com.Developing for Android 11.android.0 Rev. Conclusion Android is a robust platform. giving developers the tools they need to write powerful. For more information. We hope this paper has helped illustrate some of the possibilities for application development on the Android platform. White Paper 1. check out the Android documentation and SDK at http://developer. 0. compelling and useful applications consumers will love.6 79 .
. Wikipedia // Wikipedia. January 19.http://www. 2010. 2010. . 2010. .html. http://www.Wikipedia [Online] / auth.01 20.02 22.wikipedia.http://www. Android Porting Kit [Online] // Viosoft Corporation. 2009. . Android Developers [Online] / auth.wikipedia.168. WebKit .ibm. What is Android? [Online] // Embetek. http://99. .embetek. 2010. // Android SDK and Reference. .com/developing/story/sms-messaging-android.02 19. iPhone SDK Comparison Chart [Online] / auth.February 11. . http://en.2009.http://en. 02 22.http://mobiforge. 2008.org. M Michael // TrueSong Media.html.ibm. Google. 2010. 2010. 2008.com/index.02 12.02 10.5 [Online] // FlashMobileBlog. .com/developerworks/opensource/library/os-androidiphone2/index.com/developerworks/. 2009.org/wiki/Webkit.19/solutions/android-porting-kit/. Part 2: Build a browser-based application for iPhone and Android [Online] / auth. . Frank Ableson. . . Works Cited Android (Operating System) [Online] / auth. Android WebView (WebKit) [Online] / auth.com/2008/03/06/iphone-sdk-comparison-chart/. . .flashmobileblog. White Paper 1.March 6. http://www.engadget.http://developer. 20098.August 11.Developing for Android 12.0 Rev.August 12. 2010. January 20.http://www.com/2009/11/why-develop-for-android/.November 12.android. Patel Nilay // Engadget.July 6. 2010. 2010. . 2010. . Wikipedia // Wikipedia.June 2009. SMS Messaging in Android [Online] / auth.January 19. Lee Wei-Meng // mobiForge. 2010. . .truesongmedia. IBM // http://www. . 0. . . . January 22. 2010.org/wiki/Android_(operating_system).January 21. Android and iPhone browser wars. Flash Development with Android SDK 1. Why Develop for Android? [Online] / auth. 2010. January 05. .01 19.6 80 . . 2010.com/index.com. .February 10.com/tutorials/?p=369. Nazmul // developerlife – Tutorials » Android WebView (WebKit).com.php?option=com_content&view=article&id=49:android.9. 2010.http://developerlife. Inc.
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