Instantiate media session and connector in PlayerService

This changes significantly how the MediaSessionCompat and MediaSessionConnector objects are used:
- now they are tied to the service and not to the player, and so they might be reused with multiple players (which should be allowed)
- now they can exist even if there is no player (which is fundamental to be able to answer media browser queries)

Author: Stypox

app/src/main/java/org/schabi/newpipe/player/Player.java

@@ -55,6 +55,7 @@
 import android.graphics.Bitmap;
 import android.graphics.drawable.Drawable;
 import android.media.AudioManager;
+import android.support.v4.media.session.MediaSessionCompat;
 import android.util.Log;
 import android.view.LayoutInflater;
 
@@ -71,6 +72,7 @@
 import com.google.android.exoplayer2.Player.PositionInfo;
 import com.google.android.exoplayer2.Timeline;
 import com.google.android.exoplayer2.Tracks;
+import com.google.android.exoplayer2.ext.mediasession.MediaSessionConnector;
 import com.google.android.exoplayer2.source.MediaSource;
 import com.google.android.exoplayer2.text.CueGroup;
 import com.google.android.exoplayer2.trackselection.DefaultTrackSelector;
@@ -269,7 +271,16 @@ public final class Player implements PlaybackListener, Listener {
     //////////////////////////////////////////////////////////////////////////*/
     //region Constructor
 
-    public Player(@NonNull final PlayerService service) {
+    /**
+     * @param service the service this player resides in
+     * @param mediaSession used to build the {@link MediaSessionPlayerUi}, lives in the service and
+     *                     could possibly be reused with multiple player instances
+     * @param sessionConnector used to build the {@link MediaSessionPlayerUi}, lives in the service
+     *                         and could possibly be reused with multiple player instances
+     */
+    public Player(@NonNull final PlayerService service,
+                  @NonNull final MediaSessionCompat mediaSession,
+                  @NonNull final MediaSessionConnector sessionConnector) {
         this.service = service;
         context = service;
         prefs = PreferenceManager.getDefaultSharedPreferences(context);
@@ -302,7 +313,7 @@ public Player(@NonNull final PlayerService service) {
         // notification ui in the UIs list, since the notification depends on the media session in
         // PlayerUi#initPlayer(), and UIs.call() guarantees UI order is preserved.
         UIs = new PlayerUiList(
-                new MediaSessionPlayerUi(this),
+                new MediaSessionPlayerUi(this, mediaSession, sessionConnector),
                 new NotificationPlayerUi(this)
         );
     }

app/src/main/java/org/schabi/newpipe/player/PlayerService.java

@@ -27,12 +27,15 @@
 import android.os.Bundle;
 import android.os.IBinder;
 import android.support.v4.media.MediaBrowserCompat;
+import android.support.v4.media.session.MediaSessionCompat;
 import android.util.Log;
 
 import androidx.annotation.NonNull;
 import androidx.annotation.Nullable;
 import androidx.media.MediaBrowserServiceCompat;
 
+import com.google.android.exoplayer2.ext.mediasession.MediaSessionConnector;
+
 import org.schabi.newpipe.ktx.BundleKt;
 import org.schabi.newpipe.player.mediasession.MediaSessionPlayerUi;
 import org.schabi.newpipe.player.notification.NotificationPlayerUi;
@@ -52,6 +55,12 @@ public final class PlayerService extends MediaBrowserServiceCompat {
     public static final String SHOULD_START_FOREGROUND_EXTRA = "should_start_foreground_extra";
     public static final String BIND_PLAYER_HOLDER_ACTION = "bind_player_holder_action";
 
+    // these are instantiated in onCreate() as per
+    // https://developer.android.com/training/cars/media#browser_workflow
+    private MediaSessionCompat mediaSession;
+    private MediaSessionConnector sessionConnector;
+
+    @Nullable
     private Player player;
 
     private final IBinder mBinder = new PlayerService.LocalBinder(this);
@@ -71,6 +80,12 @@ public void onCreate() {
         assureCorrectAppLanguage(this);
         ThemeHelper.setTheme(this);
 
+        // see https://developer.android.com/training/cars/media#browser_workflow
+        mediaSession = new MediaSessionCompat(this, "MediaSessionPlayerServ");
+        setSessionToken(mediaSession.getSessionToken());
+        sessionConnector = new MediaSessionConnector(mediaSession);
+        sessionConnector.setMetadataDeduplicationEnabled(true);
+
         // Note: you might be tempted to create the player instance and call startForeground here,
         // but be aware that the Android system might start the service just to perform media
         // queries. In those cases creating a player instance is a waste of resources, and calling
@@ -94,7 +109,7 @@ public int onStartCommand(final Intent intent, final int flags, final int startI
         if (intent.getBooleanExtra(SHOULD_START_FOREGROUND_EXTRA, false)) {
             if (player == null) {
                 // make sure the player exists, in case the service was resumed
-                player = new Player(this);
+                player = new Player(this, mediaSession, sessionConnector);
             }
 
             // Be sure that the player notification is set and the service is started in foreground,
@@ -159,7 +174,11 @@ public void onDestroy() {
             Log.d(TAG, "destroy() called");
         }
         super.onDestroy();
+
         cleanup();
+
+        mediaSession.setActive(false);
+        mediaSession.release();
     }
 
     private void cleanup() {

app/src/main/java/org/schabi/newpipe/player/mediasession/MediaSessionPlayerUi.java

@@ -38,10 +38,10 @@ public class MediaSessionPlayerUi extends PlayerUi
         implements SharedPreferences.OnSharedPreferenceChangeListener {
     private static final String TAG = "MediaSessUi";
 
-    @Nullable
-    private MediaSessionCompat mediaSession;
-    @Nullable
-    private MediaSessionConnector sessionConnector;
+    @NonNull
+    private final MediaSessionCompat mediaSession;
+    @NonNull
+    private final MediaSessionConnector sessionConnector;
 
     private final String ignoreHardwareMediaButtonsKey;
     private boolean shouldIgnoreHardwareMediaButtons = false;
@@ -50,9 +50,13 @@ public class MediaSessionPlayerUi extends PlayerUi
     private List<NotificationActionData> prevNotificationActions = List.of();
 
 
-    public MediaSessionPlayerUi(@NonNull final Player player) {
+    public MediaSessionPlayerUi(@NonNull final Player player,
+                                @NonNull final MediaSessionCompat mediaSession,
+                                @NonNull final MediaSessionConnector sessionConnector) {
         super(player);
-        ignoreHardwareMediaButtonsKey =
+        this.mediaSession = mediaSession;
+        this.sessionConnector = sessionConnector;
+        this.ignoreHardwareMediaButtonsKey =
                 context.getString(R.string.ignore_hardware_media_buttons_key);
     }
 
@@ -61,10 +65,8 @@ public void initPlayer() {
         super.initPlayer();
         destroyPlayer(); // release previously used resources
 
-        mediaSession = new MediaSessionCompat(context, TAG);
         mediaSession.setActive(true);
 
-        sessionConnector = new MediaSessionConnector(mediaSession);
         sessionConnector.setQueueNavigator(new PlayQueueNavigator(mediaSession, player));
         sessionConnector.setPlayer(getForwardingPlayer());
 
@@ -89,27 +91,18 @@ public void initPlayer() {
     public void destroyPlayer() {
         super.destroyPlayer();
         player.getPrefs().unregisterOnSharedPreferenceChangeListener(this);
-        if (sessionConnector != null) {
-            sessionConnector.setMediaButtonEventHandler(null);
-            sessionConnector.setPlayer(null);
-            sessionConnector.setQueueNavigator(null);
-            sessionConnector = null;
-        }
-        if (mediaSession != null) {
-            mediaSession.setActive(false);
-            mediaSession.release();
-            mediaSession = null;
-        }
+        sessionConnector.setMediaButtonEventHandler(null);
+        sessionConnector.setPlayer(null);
+        sessionConnector.setQueueNavigator(null);
+        mediaSession.setActive(false);
         prevNotificationActions = List.of();
     }
 
     @Override
     public void onThumbnailLoaded(@Nullable final Bitmap bitmap) {
         super.onThumbnailLoaded(bitmap);
-        if (sessionConnector != null) {
-            // the thumbnail is now loaded: invalidate the metadata to trigger a metadata update
-            sessionConnector.invalidateMediaSessionMetadata();
-        }
+        // the thumbnail is now loaded: invalidate the metadata to trigger a metadata update
+        sessionConnector.invalidateMediaSessionMetadata();
     }
 
 
@@ -200,8 +193,8 @@ private void updateMediaSessionActions() {
             return;
         }
 
-        if (sessionConnector == null) {
-            // sessionConnector will be null after destroyPlayer is called
+        if (!mediaSession.isActive()) {
+            // mediaSession will be inactive after destroyPlayer is called
             return;
         }