PlayerHolder: improve interface docstrings

Author: Profpatsch

app/src/main/java/org/schabi/newpipe/player/event/PlayerHolderLifecycleEventListener.java

@@ -2,9 +2,18 @@
 
 import org.schabi.newpipe.player.PlayerService;
 
-/** Gets signalled if our PlayerHolder (dis)connects from the PlayerService. */
+/** Gets signalled if our PlayerHolder (dis)connects from the PlayerService.
+ * This is currently only implemented by the
+ * {@link org.schabi.newpipe.fragments.detail.VideoDetailFragment}. */
 public interface PlayerHolderLifecycleEventListener {
+
+    /** Our {@link org.schabi.newpipe.player.helper.PlayerHolder} connected to its service.
+     * @param playerService The service the holder connected to
+     * @param playAfterConnect  */
     void onServiceConnected(PlayerService playerService,
                             boolean playAfterConnect);
+    
+    /** Our {@link org.schabi.newpipe.player.helper.PlayerHolder} was unbound and thus
+     * disconnected from the {@link org.schabi.newpipe.player.PlayerService}. */
     void onServiceDisconnected();
 }

app/src/main/java/org/schabi/newpipe/player/helper/PlayerHolder.java

@@ -125,7 +125,8 @@ private Context getCommonContext() {
      * Connect to (and if needed start) the {@link PlayerService}
      * and bind {@link PlayerServiceConnection} to it.
      * If the service is already started, only set the listener.
-     * @param playAfterConnect If the service is started, start playing immediately
+     * @param playAfterConnect If this holder’s service was already started,
+     *                         start playing immediately
      * @param newListener set this listener
      * @param newHolderListener set this listener
      * */