-Fixed background player activity crashes on receiving update when stopped (lifecycle still active).

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

@@ -484,6 +484,12 @@ public final class BackgroundPlayer extends Service {
             triggerProgressUpdate();
         }
 
+        public void removeActivityListener(PlayerEventListener listener) {
+            if (activityListener == listener) {
+                activityListener = null;
+            }
+        }
+
         private void updateMetadata() {
             if (activityListener != null && currentInfo != null) {
                 activityListener.onMetadataUpdate(currentInfo);
@@ -491,7 +497,7 @@ public final class BackgroundPlayer extends Service {
         }
 
         private void updatePlayback() {
-            if (activityListener != null) {
+            if (activityListener != null && simpleExoPlayer != null && playQueue != null) {
                 activityListener.onPlaybackUpdate(currentState, simpleExoPlayer.getRepeatMode(), playQueue.isShuffled(), simpleExoPlayer.getPlaybackParameters());
             }
         }

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

@@ -98,11 +98,6 @@ public class BackgroundPlayerActivity extends AppCompatActivity
         }
 
         serviceConnection = backgroundPlayerConnection();
-    }
-
-    @Override
-    protected void onStart() {
-        super.onStart();
         bind();
     }
 
@@ -121,8 +116,8 @@ public class BackgroundPlayerActivity extends AppCompatActivity
     }
 
     @Override
-    protected void onStop() {
+    protected void onDestroy() {
-        super.onStop();
+        super.onDestroy();
         unbind();
     }
 
@@ -143,6 +138,7 @@ public class BackgroundPlayerActivity extends AppCompatActivity
         if(serviceBound) {
             unbindService(serviceConnection);
             serviceBound = false;
+            stopPlayerListener();
             player = null;
             finish();
         }
@@ -164,6 +160,7 @@ public class BackgroundPlayerActivity extends AppCompatActivity
                     unbind();
                 } else {
                     buildComponents();
+                    startPlayerListener();
                 }
             }
         };
@@ -178,7 +175,6 @@ public class BackgroundPlayerActivity extends AppCompatActivity
         buildMetadata();
         buildSeekBar();
         buildControls();
-        buildListeners();
     }
 
     private void buildQueue() {
@@ -230,10 +226,6 @@ public class BackgroundPlayerActivity extends AppCompatActivity
         buildPlaybackPitchMenu();
     }
 
-    private void buildListeners() {
-        player.setActivityListener(this);
-    }
-
     private void buildPlaybackSpeedMenu() {
         if (playbackSpeedPopupMenu == null) return;
 
@@ -424,6 +416,18 @@ public class BackgroundPlayerActivity extends AppCompatActivity
     // Binding Service Listener
     ////////////////////////////////////////////////////////////////////////////
 
+    private void startPlayerListener() {
+        if (player != null) {
+            player.setActivityListener(this);
+        }
+    }
+
+    private void stopPlayerListener() {
+        if (player != null) {
+            player.removeActivityListener(this);
+        }
+    }
+
     @Override
     public void onPlaybackUpdate(int state, int repeatMode, boolean shuffled, PlaybackParameters parameters) {
         switch (state) {