diff --git a/app/src/main/java/com/example/android/classicalmusicquiz/QuizActivity.java b/app/src/main/java/com/example/android/classicalmusicquiz/QuizActivity.java
index e0cd02a8..26aa6174 100644
--- a/app/src/main/java/com/example/android/classicalmusicquiz/QuizActivity.java
+++ b/app/src/main/java/com/example/android/classicalmusicquiz/QuizActivity.java
@@ -24,6 +24,8 @@
 import android.os.Bundle;
 import android.os.Handler;
 import android.support.v4.content.ContextCompat;
+import android.support.v4.media.session.MediaSessionCompat;
+import android.support.v4.media.session.PlaybackStateCompat;
 import android.support.v7.app.AppCompatActivity;
 import android.util.Log;
 import android.view.View;
@@ -65,6 +67,9 @@ public class QuizActivity extends AppCompatActivity implements View.OnClickListe
     private SimpleExoPlayer mExoPlayer;
     private SimpleExoPlayerView mPlayerView;
 
+    private MediaSessionCompat mMediaSession;
+    private PlaybackStateCompat.Builder mStateBuilder;
+
 
     @Override
     protected void onCreate(Bundle savedInstanceState) {
@@ -108,9 +113,10 @@ protected void onCreate(Bundle savedInstanceState) {
         // Initialize the buttons with the composers names.
         mButtons = initializeButtons(mQuestionSampleIDs);
 
-        // TODO (1): Create a method to initialize the MediaSession. It should create the MediaSessionCompat object, set the flags for external clients, set the available actions you want to support, and start the session.
-        // TODO (2): Create an inner class that extends MediaSessionCompat.Callbacks, and override the onPlay(), onPause(), and onSkipToPrevious() callbacks. Pass an instance of this class into the MediaSession.setCallback() method in the method you created in TODO 1.
-        
+        //  (1): Create a method to initialize the MediaSession. It should create the MediaSessionCompat object, set the flags for external clients, set the available actions you want to support, and start the session.
+        //  (2): Create an inner class that extends MediaSessionCompat.Callbacks, and override the onPlay(), onPause(), and onSkipToPrevious() callbacks. Pass an instance of this class into the MediaSession.setCallback() method in the method you created in TODO 1.
+
+        initializeMediaSession();
         Sample answerSample = Sample.getSampleByID(this, mAnswerSampleID);
 
         if (answerSample == null) {
@@ -123,6 +129,31 @@ protected void onCreate(Bundle savedInstanceState) {
         initializePlayer(Uri.parse(answerSample.getUri()));
     }
 
+    private void initializeMediaSession() {
+        //create a mediaSessionCompat
+        mMediaSession = new MediaSessionCompat(this, TAG);
+        //Enable callbacks from MediaButtons and TransportControls
+        mMediaSession.setFlags(
+                MediaSessionCompat.FLAG_HANDLES_MEDIA_BUTTONS |
+                        MediaSessionCompat.FLAG_HANDLES_TRANSPORT_CONTROLS);
+        //不让MediaButtons重启当app不可见的时候
+        mMediaSession.setMediaButtonReceiver(null);
+        mStateBuilder = new PlaybackStateCompat.Builder()
+                .setActions(
+                        PlaybackStateCompat.ACTION_PLAY |
+                                PlaybackStateCompat.ACTION_PAUSE |
+                                PlaybackStateCompat.ACTION_SKIP_TO_PREVIOUS |
+                                PlaybackStateCompat.ACTION_PLAY_PAUSE
+                );
+        mMediaSession.setPlaybackState(mStateBuilder.build());
+
+        mMediaSession.setCallback(new MySessionCallBack());
+        ;
+        //打开Media Session
+        mMediaSession.setActive(true);
+
+    }
+
 
     /**
      * Initializes the button to the correct views, and sets the text to the composers names,
@@ -148,6 +179,7 @@ private Button[] initializeButtons(ArrayList<Integer> answerSampleIDs) {
 
     /**
      * Initialize ExoPlayer.
+     *
      * @param mediaUri The URI of the sample to play.
      */
     private void initializePlayer(Uri mediaUri) {
@@ -160,7 +192,7 @@ private void initializePlayer(Uri mediaUri) {
 
             // Set the ExoPlayer.EventListener to this activity.
             mExoPlayer.addListener(this);
-            
+
             // Prepare the MediaSource.
             String userAgent = Util.getUserAgent(this, "ClassicalMusicQuiz");
             MediaSource mediaSource = new ExtractorMediaSource(mediaUri, new DefaultDataSourceFactory(
@@ -266,12 +298,13 @@ private void showCorrectAnswer() {
      */
     @Override
     protected void onDestroy() {
-        // TODO (4): When the activity is destroyed, set the MediaSession to inactive.
+        //  (4): When the activity is destroyed, set the MediaSession to inactive.
         super.onDestroy();
         releasePlayer();
+        mMediaSession.setActive(false);
     }
 
-    
+
     // ExoPlayer Event Listeners
 
     @Override
@@ -288,13 +321,18 @@ public void onLoadingChanged(boolean isLoading) {
 
     @Override
     public void onPlayerStateChanged(boolean playWhenReady, int playbackState) {
-        if((playbackState == ExoPlayer.STATE_READY) && playWhenReady){
-            // TODO (3): When ExoPlayer is playing, update the PlayBackState.
+        if ((playbackState == ExoPlayer.STATE_READY) && playWhenReady) {
+            //  (3): When ExoPlayer is playing, update the PlayBackState.
             Log.d(TAG, "onPlayerStateChanged: PLAYING");
-        } else if((playbackState == ExoPlayer.STATE_READY)){
-            // TODO (3): When ExoPlayer is paused, update the PlayBackState.
+            mStateBuilder.setState(PlaybackStateCompat.STATE_PLAYING,
+                    mExoPlayer.getCurrentPosition(), 1f);
+        } else if ((playbackState == ExoPlayer.STATE_READY)) {
+            //  (3): When ExoPlayer is paused, update the PlayBackState.
             Log.d(TAG, "onPlayerStateChanged: PAUSED");
+            mStateBuilder.setState(PlaybackStateCompat.STATE_PAUSED,
+                    mExoPlayer.getCurrentPosition(), 1f);
         }
+        mMediaSession.setPlaybackState(mStateBuilder.build());
     }
 
     @Override
@@ -304,4 +342,22 @@ public void onPlayerError(ExoPlaybackException error) {
     @Override
     public void onPositionDiscontinuity() {
     }
+
+
+    private class MySessionCallBack extends MediaSessionCompat.Callback {
+        @Override
+        public void onPlay() {
+            mExoPlayer.setPlayWhenReady(true);
+        }
+
+        @Override
+        public void onPause() {
+            mExoPlayer.setPlayWhenReady(false);
+        }
+
+        @Override
+        public void onSkipToPrevious() {
+            mExoPlayer.seekTo(0);
+        }
+    }
 }