bug fix: add "RELEASED_ALL_BUT_CAST_SESSION" mode

issue this solves:
==================
* in "BrowserActivity":
  * select video URL(s) to watch
* in "VideoActivity":
  * start a cast session
  * playlist of video URLs appears on screen
  * when a video in playlist is clicked:
    * video queue loads in Chromecast
    * position in queue skips to selected playlist item
  * "onPause" runs when Activity screen is closed
    * "PlayerManager" enters "CAST_ONLY" mode and releases all other resources
* in "BrowserActivity":
  * select video URL(s) to watch
* in "VideoActivity":
  * "onResume" runs and detects that "PlayerManager" is running in "CAST_ONLY" mode
    * previously:
      * "PlayerManager" transitioned: "CAST_ONLY" -> "RELEASED" -> "NORMAL"
      * "RELEASED" mode releases all resources, including closing the CastSession
      * "currentPlayer" is an instance of ExoPlayer
    * now:
      * "PlayerManager" transitions: "CAST_ONLY" -> "RELEASED_ALL_BUT_CAST_SESSION" -> "NORMAL"
      * "RELEASED_ALL_BUT_CAST_SESSION" mode is identical to "RELEASED", but CastSession is not closed
      * "currentPlayer" is an instance of CastPlayer
        * the previous video queue that was casting continues uninterupted
        * the new playlist of video URLs appears on screen
        * when a video in playlist is clicked:
          * new video queue loads in Chromecast
          * position in new queue skips to selected playlist item

WebCast/src/main/java/com/github/warren_bank/webcast/exoplayer2/PlayerManager.java

@@ -71,7 +71,7 @@ public interface QueuePositionListener {
   private boolean castMediaQueueCreationPending;
   private Player currentPlayer;
 
-  public static enum PlaybackMode { NORMAL, CAST_ONLY, RELEASED }
+  public static enum PlaybackMode { NORMAL, CAST_ONLY, RELEASED_ALL_BUT_CAST_SESSION, RELEASED }
 
   private PlaybackMode playbackMode;
 
@@ -263,12 +263,18 @@ public void setPlaybackMode(PlaybackMode playbackMode) {
           release_exoPlayer();
         }
         else {
-          release();
+          release(false);
           playbackMode = PlaybackMode.RELEASED;
         }
         break;
+      case RELEASED_ALL_BUT_CAST_SESSION:
+        release(
+          isCasting()
+        );
+        playbackMode = PlaybackMode.RELEASED;
+        break;
       case RELEASED:
-        release();
+        release(false);
         break;
       default:
         return;
@@ -295,11 +301,15 @@ public boolean dispatchKeyEvent(KeyEvent event) {
    * Releases the manager and the players that it holds.
    */
   private void release() {
+    release(false);
+  }
+
+  private void release(boolean retain_CastSession) {
     if (playbackMode == PlaybackMode.RELEASED) return;
 
     try {
       release_exoPlayer();
-      release_castPlayer();
+      release_castPlayer(retain_CastSession);
 
       mediaQueue.clear();
       concatenatingMediaSource.clear();
@@ -332,14 +342,17 @@ private void release_exoPlayer() {
     catch (Exception e){}
   }
 
-  private void release_castPlayer() {
+  private void release_castPlayer(boolean retain_CastSession) {
     if (castPlayer == null) return;
 
     try {
       castControlView.setPlayer(null);
       castPlayer.removeListener(this);
       castPlayer.setSessionAvailabilityListener(null);
-      castPlayer.release();
+
+      if (!retain_CastSession) {
+        castPlayer.release();
+      }
 
       castControlView = null;
       castPlayer = null;

WebCast/src/main/java/com/github/warren_bank/webcast/exoplayer2/VideoActivity.java

@@ -31,10 +31,10 @@
 import java.util.ArrayList;
 
 public class VideoActivity extends AppCompatActivity implements PlayerManager.QueuePositionListener {
+  private static PlayerManager playerManager = null;
 
   private PlayerView localPlayerView;
   private PlayerControlView castControlView;
-  private PlayerManager playerManager;
   private RecyclerView mediaQueueList;
   private MediaQueueListAdapter mediaQueueListAdapter;
   private CastContext castContext;
@@ -111,7 +111,7 @@ public void onResume() {
     }
 
     if ((playerManager != null) && (playerManager.getPlaybackMode() == PlayerManager.PlaybackMode.CAST_ONLY)) {
-        playerManager.setPlaybackMode(PlayerManager.PlaybackMode.RELEASED);
+        playerManager.setPlaybackMode(PlayerManager.PlaybackMode.RELEASED_ALL_BUT_CAST_SESSION);
         playerManager = null;
     }
 

constants.gradle

@@ -1,6 +1,6 @@
 project.ext {
-    releaseVersionCode = 004030416
-    releaseVersion = '004.03.04-16API'
+    releaseVersionCode = 004040016
+    releaseVersion = '004.04.00-16API'
     minSdkVersion = 16
     targetSdkVersion = 28
     compileSdkVersion = 28