Q: Getting error when creating an activity with coordinator layout Just messing around with different kinds of layouts and wondering why this layout wont work. I downloaded the right dependencies and still getting an error. I want to use this layout because I read that you can position Snackbar with it. All the other layouts work in Android studio except this one. Following tutorials on coordinator layout use them with ease without getting no errors. 
layout
<?xml version="1.0" encoding="utf-8"?>
<android.support.design.widget.CoordinatorLayout 
xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="maginatestudios.com.maginatecrate.test">

</android.support.design.widget.CoordinatorLayout>

build.gradle
dependencies {
implementation fileTree(include: ['*.jar'], dir: 'libs')
implementation 'com.android.support.constraint:constraint-layout:1.1.0'
implementation 'com.google.firebase:firebase-auth:15.0.0'
implementation 'com.google.android.gms:play-services-auth:15.0.0'
implementation 'com.android.support:design:26.1.0'
implementation 'com.android.support:recyclerview-v7:26.1.0'
testImplementation 'junit:junit:4.12'
androidTestImplementation 'com.android.support.test.espresso:espresso-core:3.0.1'
}

Error log
04-25 18:04:43.544 6329-6329/? E/AndroidRuntime: FATAL EXCEPTION: main
                                             Process: maginatestudios.com.maginatecrate, PID: 6329
                                             java.lang.RuntimeException: Unable to start activity ComponentInfo{maginatestudios.com.maginatecrate/maginatestudios.com.maginatecrate.test}: android.view.InflateException: Binary XML file line #0: Binary XML file line #0: Error inflating class android.support.design.widget.CoordinatorLayout
                                                 at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2817)
                                                 at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2892)
                                                 at android.app.ActivityThread.-wrap11(Unknown Source:0)
                                                 at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1593)
                                                 at android.os.Handler.dispatchMessage(Handler.java:105)
                                                 at android.os.Looper.loop(Looper.java:164)
                                                 at android.app.ActivityThread.main(ActivityThread.java:6540)
                                                 at java.lang.reflect.Method.invoke(Native Method)
                                                 at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:240)
                                                 at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:767)
                                              Caused by: android.view.InflateException: Binary XML file line #0: Binary XML file line #0: Error inflating class android.support.design.widget.CoordinatorLayout
                                              Caused by: android.view.InflateException: Binary XML file line #0: Error inflating class android.support.design.widget.CoordinatorLayout
                                              Caused by: java.lang.reflect.InvocationTargetException
                                                 at java.lang.reflect.Constructor.newInstance0(Native Method)
                                                 at java.lang.reflect.Constructor.newInstance(Constructor.java:334)
                                                 at android.view.LayoutInflater.createView(LayoutInflater.java:650)
                                                 at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:793)
                                                 at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:733)
                                                 at android.view.LayoutInflater.inflate(LayoutInflater.java:495)
                                                 at android.view.LayoutInflater.inflate(LayoutInflater.java:426)
                                                 at android.view.LayoutInflater.inflate(LayoutInflater.java:377)
                                                 at com.android.internal.policy.PhoneWindow.setContentView(PhoneWindow.java:418)
                                                 at android.app.Activity.setContentView(Activity.java:2653)
                                                 at maginatestudios.com.maginatecrate.test.onCreate(test.java:11)
                                                 at android.app.Activity.performCreate(Activity.java:6980)
                                                 at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1213)
                                                 at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2770)
                                                 at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2892)
                                                 at android.app.ActivityThread.-wrap11(Unknown Source:0)
                                                 at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1593)
                                                 at android.os.Handler.dispatchMessage(Handler.java:105)
                                                 at android.os.Looper.loop(Looper.java:164)
                                                 at android.app.ActivityThread.main(ActivityThread.java:6540)
                                                 at java.lang.reflect.Method.invoke(Native Method)
                                                 at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:240)
                                                 at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:767)
                                              Caused by: java.lang.IllegalArgumentException: You need to use a Theme.AppCompat theme (or descendant) with the design library.
                                                 at android.support.design.widget.ThemeUtils.checkAppCompatTheme(ThemeUtils.java:33)
                                                 at android.support.design.widget.CoordinatorLayout.<init>(CoordinatorLayout.java:206)
                                                 at android.support.design.widget.CoordinatorLayout.<init>(CoordinatorLayout.java:200)


A: Try to remove:
<?xml version="1.0" encoding="utf-8"?>

Edit, my bad just saw the error down there
try to make your activity extend 
AppCompatActivity

