title: Android homescreen project, RuntimeException
body: <p>I developed a android homescreen, the code seems right but when I run the project I get the following error:</p>
  
  <pre><code>java.lang.RuntimeException:
  Unable to instantiate activity ComponentInfo{com.matthieu.launcher/
  com.matthieu.launcher.DragableSpace}:
  java.lang.InstantiationException: com.matthieu.launcher.DragableSpace
  </code></pre>
  
  <p>Here is the complete log: <a href="http://pastebin.com/iYtYW2W6" rel="nofollow">http://pastebin.com/iYtYW2W6</a></p>
  
  <p>The code is straight from the Android Launcher.</p>
  
  <p><strong>DragableSpace</strong>: <a href="http://pastebin.com/jpWDtFPF" rel="nofollow">http://pastebin.com/jpWDtFPF</a></p>
  
  <p><strong>MainActivity</strong>:</p>
  
  <pre><code>public class MainActivity extends Activity {
      public void onCreate(Bundle savedInstanceState) {
          super.onCreate(savedInstanceState);
          DragableSpace space = new DragableSpace(this.getApplicationContext());
          setContentView(space);
      }
  }
  </code></pre>
  
  <p><strong>attr.xml</strong> in values folder:</p>
  
  <pre><code>&lt;?xml version="1.0" encoding="utf-8"?&gt;
  &lt;resources&gt;
      &lt;declare-styleable name="DragableSpace"&gt;
          &lt;attr name="default_screen" format="integer"/&gt;
      &lt;/declare-styleable&gt;
  &lt;/resources&gt;
  </code></pre>
  
  <p>Three xml files <strong>initial_screen</strong>, <strong>left_screen</strong> and <strong>right_screen</strong>, all have same code apart from the id:</p>
  
  <pre><code>&lt;LinearLayout android:id="@+id/center"
      android:layout_width="fill_parent"
      android:layout_height="fill_parent"
      xmlns:android="http://schemas.android.com/apk/res/android"
      android:orientation="vertical"&gt;
  &lt;/LinearLayout&gt;
  </code></pre>
  
  <p>Manifest:</p>
  
  <pre><code>&lt;?xml version="1.0" encoding="utf-8"?&gt;
  &lt;manifest xmlns:android="http://schemas.android.com/apk/res/android"
        package="com.matthieu.launcher"
        android:versionCode="1"
        android:versionName="1.0"&gt;
      &lt;application android:icon="@drawable/icon" android:label="@string/app_name"&gt;
          &lt;activity android:name=".MainActivity"
                    android:label="@string/app_name"&gt;
              &lt;intent-filter&gt;
                  &lt;action android:name="android.intent.action.MAIN" /&gt;
                  &lt;category android:name="android.intent.category.LAUNCHER" /&gt;
              &lt;/intent-filter&gt;
          &lt;/activity&gt;
      &lt;/application&gt;
  &lt;/manifest&gt; 
  </code></pre>
  
  <p>Any ideas how to fix that?</p>