CoderLine
diff --git a/‎playground-template/control.mjs‎
Lines changed: 4 additions & 0 deletions b/‎playground-template/control.mjs‎
Lines changed: 4 additions & 0 deletions
diff --git a/‎playground-template/youtube.html‎
Lines changed: 1 addition & 1 deletion b/‎playground-template/youtube.html‎
Lines changed: 1 addition & 1 deletion
diff --git a/‎src.csharp/AlphaTab.Windows/DelegatedEventEmitter.cs‎
Lines changed: 6 additions & 3 deletions b/‎src.csharp/AlphaTab.Windows/DelegatedEventEmitter.cs‎
Lines changed: 6 additions & 3 deletions
diff --git a/‎src.csharp/AlphaTab/EventEmitter.cs‎
Lines changed: 3 additions & 2 deletions b/‎src.csharp/AlphaTab/EventEmitter.cs‎
Lines changed: 3 additions & 2 deletions
diff --git a/‎src.kotlin/alphaTab/android/src/main/java/alphaTab/platform/android/AndroidUiFacade.kt‎
Lines changed: 2 additions & 1 deletion b/‎src.kotlin/alphaTab/android/src/main/java/alphaTab/platform/android/AndroidUiFacade.kt‎
Lines changed: 2 additions & 1 deletion
@@ -129,6 +129,10 @@ function hideBackingTrack(at) {
 
 
 async function showBackingTrack(at) {
+    if(!at.score.backingTrack) {
+        hideBackingTrack();
+        return;
+    }
 
     const audioElement = at.player.output.audioElement;
     if(audioElement !== backingTrackAudioElement) {
 
@@ -3,7 +3,7 @@
 
 <head>
     <meta charset="utf-8" />
-    <title>AlphaTab Control Demo</title>
+    <title>AlphaTab Youtube Sync</title>
 
     <script src="/node_modules/@popperjs/core/dist/umd/popper.min.js"></script>
     <script src="/node_modules/bootstrap/dist/js/bootstrap.min.js"></script>
 
@@ -13,9 +13,10 @@ public DelegatedEventEmitter(Action<Action> on, Action<Action> off)
             _off = off;
         }
 
-        public void On(Action value)
+        public System.Action On(Action value)
         {
             _on(value);
+            return () => _off(value);
         }
 
         public void Off(Action value)
@@ -35,19 +36,21 @@ public DelegatedEventEmitter(Action<Action<T>> on, Action<Action<T>> off)
             _off = off;
         }
 
-        public void On(Action value)
+        public System.Action On(Action value)
         {
 			// not used internally
+            return () => {};
         }
 
         public void Off(Action value)
         {
             // not used internally
         }
 
-        public void On(Action<T> value)
+        public System.Action On(Action<T> value)
         {
             _on(value);
+            return () => _off(value);
         }
 
         public void Off(Action<T> value)
 
@@ -4,7 +4,7 @@ namespace AlphaTab;
 
 partial interface IEventEmitterOfT<T>
 {
-    void On(System.Action value);
+    System.Action On(System.Action value);
     void Off(System.Action value);
 }
 
@@ -14,14 +14,15 @@ partial class EventEmitterOfT<T>
         new System.Collections.Generic.Dictionary<System.Action, System.Action<T>>();
 
     [Obsolete("Use event registration overload with parameter.", false)]
-    public void On(System.Action value) 
+    public System.Action On(System.Action value) 
     {
         var wrapper = new Action<T>(_=> 
         {
             value();
         });
         _wrappers[value] = wrapper;
         On(wrapper);
+        return () => Off(value);
     }
 
     [Obsolete("Use event unregistration with parameter.", false)]
 
@@ -63,13 +63,14 @@ internal class AndroidUiFacade : IUiFacade<AlphaTabView> {
 
         rootContainerBecameVisible = object : IEventEmitter,
             ViewTreeObserver.OnGlobalLayoutListener, View.OnLayoutChangeListener {
-            override fun on(value: () -> Unit) {
+            override fun on(value: () -> Unit): () -> Unit {
                 if (rootContainer.isVisible) {
                     value()
                 } else {
                     outerScroll.viewTreeObserver.addOnGlobalLayoutListener(this)
                     outerScroll.addOnLayoutChangeListener(this)
                 }
+                return fun() { off(value) }
             }
 
             override fun off(value: () -> Unit) {
Original file line number	Diff line number	Diff line change
`@@ -13,9 +13,10 @@ public DelegatedEventEmitter(Action<Action> on, Action<Action> off)`
`13`	`13`	`_off = off;`
`14`	`14`	`}`
`15`	`15`
`16`		`- public void On(Action value)`
	`16`	`+ public System.Action On(Action value)`
`17`	`17`	`{`
`18`	`18`	`_on(value);`
	`19`	`+ return () => _off(value);`
`19`	`20`	`}`
`20`	`21`
`21`	`22`	`public void Off(Action value)`
`@@ -35,19 +36,21 @@ public DelegatedEventEmitter(Action<Action<T>> on, Action<Action<T>> off)`
`35`	`36`	`_off = off;`
`36`	`37`	`}`
`37`	`38`
`38`		`- public void On(Action value)`
	`39`	`+ public System.Action On(Action value)`
`39`	`40`	`{`
`40`	`41`	`// not used internally`
	`42`	`+ return () => {};`
`41`	`43`	`}`
`42`	`44`
`43`	`45`	`public void Off(Action value)`
`44`	`46`	`{`
`45`	`47`	`// not used internally`
`46`	`48`	`}`
`47`	`49`
`48`		`- public void On(Action<T> value)`
	`50`	`+ public System.Action On(Action<T> value)`
`49`	`51`	`{`
`50`	`52`	`_on(value);`
	`53`	`+ return () => _off(value);`
`51`	`54`	`}`
`52`	`55`
`53`	`56`	`public void Off(Action<T> value)`
Original file line number	Diff line number	Diff line change
`@@ -4,7 +4,7 @@ namespace AlphaTab;`
`4`	`4`
`5`	`5`	`partial interface IEventEmitterOfT<T>`
`6`	`6`	`{`
`7`		`- void On(System.Action value);`
	`7`	`+ System.Action On(System.Action value);`
`8`	`8`	`void Off(System.Action value);`
`9`	`9`	`}`
`10`	`10`
`@@ -14,14 +14,15 @@ partial class EventEmitterOfT<T>`
`14`	`14`	`new System.Collections.Generic.Dictionary<System.Action, System.Action<T>>();`
`15`	`15`
`16`	`16`	`[Obsolete("Use event registration overload with parameter.", false)]`
`17`		`- public void On(System.Action value)`
	`17`	`+ public System.Action On(System.Action value)`
`18`	`18`	`{`
`19`	`19`	`var wrapper = new Action<T>(_=>`
`20`	`20`	`{`
`21`	`21`	`value();`
`22`	`22`	`});`
`23`	`23`	`_wrappers[value] = wrapper;`
`24`	`24`	`On(wrapper);`
	`25`	`+ return () => Off(value);`
`25`	`26`	`}`
`26`	`27`
`27`	`28`	`[Obsolete("Use event unregistration with parameter.", false)]`
Original file line number	Diff line number	Diff line change
`@@ -63,13 +63,14 @@ internal class AndroidUiFacade : IUiFacade<AlphaTabView> {`
`63`	`63`
`64`	`64`	`rootContainerBecameVisible = object : IEventEmitter,`
`65`	`65`	`ViewTreeObserver.OnGlobalLayoutListener, View.OnLayoutChangeListener {`
`66`		`- override fun on(value: () -> Unit) {`
	`66`	`+ override fun on(value: () -> Unit): () -> Unit {`
`67`	`67`	`if (rootContainer.isVisible) {`
`68`	`68`	`value()`
`69`	`69`	`} else {`
`70`	`70`	`outerScroll.viewTreeObserver.addOnGlobalLayoutListener(this)`
`71`	`71`	`outerScroll.addOnLayoutChangeListener(this)`
`72`	`72`	`}`
	`73`	`+ return fun() { off(value) }`
`73`	`74`	`}`
`74`	`75`
`75`	`76`	`override fun off(value: () -> Unit) {`