Merge pull request #6844 from 0x416c6578/shuffle-mode-ui-fix

Fixed shuffle button opacity UI bug

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

@@ -774,6 +774,8 @@ public final class Player implements
         destroyPlayer();
         initPlayer(playOnReady);
         setRepeatMode(repeatMode);
+        // #6825 - Ensure that the shuffle-button is in the correct state on the UI
+        setShuffleButton(binding.shuffleButton, simpleExoPlayer.getShuffleModeEnabled());
         setPlaybackParameters(playbackSpeed, playbackPitch, playbackSkipSilence);
 
         playQueue = queue;

app/src/main/java/org/schabi/newpipe/player/playqueue/PlayQueue.java

@@ -436,14 +436,16 @@ public abstract class PlayQueue implements Serializable {
      * top, so shuffling a size-2 list does nothing)
      */
     public synchronized void shuffle() {
-        // Can't shuffle an list that's empty or only has one element
-        if (size() <= 2) {
-            return;
-        }
         // Create a backup if it doesn't already exist
+        // Note: The backup-list has to be created at all cost (even when size <= 2).
+        // Otherwise it's not possible to enter shuffle-mode!
         if (backup == null) {
             backup = new ArrayList<>(streams);
         }
+        // Can't shuffle a list that's empty or only has one element
+        if (size() <= 2) {
+            return;
+        }
 
         final int originalIndex = getIndex();
         final PlayQueueItem currentItem = getItem();