Change completion to be notified via a callback. Only notify that an animation is complete if all animators used in the animation are complete.

src/Avalonia.Animation/Animation.cs

@@ -43,7 +43,6 @@ namespace Avalonia.Animation
             return null;
         }
 
-        private bool _isChildrenChanged = false;
         private List<IDisposable> _subscription = new List<IDisposable>();
         public AvaloniaList<IAnimator> _animators { get; set; } = new AvaloniaList<IAnimator>();
 
@@ -77,16 +76,6 @@ namespace Avalonia.Animation
         /// </summary>
         public Easing Easing { get; set; } = new LinearEasing();
 
-        /// <summary>
-        /// Triggers when the animation is completed.
-        /// </summary>
-        public event EventHandler Done;
-
-        public Animation()
-        {
-            this.CollectionChanged += delegate { _isChildrenChanged = true; };
-        }
-
         private IList<IAnimator> InterpretKeyframes(Animatable control)
         {
             var handlerList = new List<(Type type, AvaloniaProperty property)>();
@@ -152,11 +141,32 @@ namespace Avalonia.Animation
         }
 
         /// <inheritdocs/>
-        public IDisposable Apply(Animatable control, IObservable<bool> matchObs)
+        public IDisposable Apply(Animatable control, IObservable<bool> match, Action onComplete)
         {
-            foreach (IAnimator animator in InterpretKeyframes(control))
+            var animators = InterpretKeyframes(control);
+            if (animators.Count == 1)
             {
-                _subscription.Add(animator.Apply(this, control, matchObs));
+                _subscription.Add(animators[0].Apply(this, control, match, onComplete));
+            }
+            else
+            {
+                var completionTasks = onComplete != null ? new List<Task>() : null;
+                foreach (IAnimator animator in InterpretKeyframes(control))
+                {
+                    Action animatorOnComplete = null;
+                    if (onComplete != null)
+                    {
+                        var tcs = new TaskCompletionSource<object>();
+                        animatorOnComplete = () => tcs.SetResult(null);
+                        completionTasks.Add(tcs.Task);
+                    }
+                    _subscription.Add(animator.Apply(this, control, match, animatorOnComplete));
+                }
+
+                if (onComplete != null)
+                {
+                    Task.WhenAll(completionTasks).ContinueWith(_ => onComplete());
+                }
             }
             return this;
         }
@@ -169,26 +179,9 @@ namespace Avalonia.Animation
             if (this.RepeatCount == RepeatCount.Loop)
                 run.SetException(new InvalidOperationException("Looping animations must not use the Run method."));
 
-            EventHandler doneCallback = null;
-            doneCallback = (sender, args) =>
-            {
-                if (sender == control)
-                {
-                    run.SetResult(null);
-                    this.Done -= doneCallback;
-                }
-            };
-
-            this.Done += doneCallback;
-
-            this.Apply(control, Observable.Return(true));
+            this.Apply(control, Observable.Return(true), () => run.SetResult(null));
 
             return run.Task;
         }
-
-        internal void SetDone(Animatable control)
-        {
-            Done?.Invoke(control, null);
-        }
     }
 }

src/Avalonia.Animation/AnimatorStateMachine`1.cs

@@ -35,6 +35,7 @@ namespace Avalonia.Animation
         private T _neutralValue;
         internal bool _unsubscribe = false;
         private IObserver<object> _targetObserver;
+        private readonly Action _onComplete;
 
         [Flags]
         private enum KeyFramesStates
@@ -51,7 +52,7 @@ namespace Avalonia.Animation
             Disposed
         }
 
-        public void Initialize(Animation animation, Animatable control, Animator<T> animator)
+        public AnimatorStateMachine(Animation animation, Animatable control, Animator<T> animator, Action onComplete)
         {
             _parent = animator;
             _targetAnimation = animation;
@@ -82,6 +83,7 @@ namespace Avalonia.Animation
                 _currentState = KeyFramesStates.DoDelay;
             else
                 _currentState = KeyFramesStates.DoRun;
+            _onComplete = onComplete;
         }
 
         public void Step(PlayState _playState, Func<double, T, T> Interpolator)
@@ -245,7 +247,7 @@ namespace Avalonia.Animation
                         }
 
                         _targetObserver.OnCompleted();
-                        _targetAnimation.SetDone(_targetControl);
+                        _onComplete?.Invoke();
                         Dispose();
                         handled = true;
                         break;

src/Avalonia.Animation/Animator`1.cs

@@ -35,7 +35,7 @@ namespace Avalonia.Animation
         }
 
         /// <inheritdoc/>
-        public virtual IDisposable Apply(Animation animation, Animatable control, IObservable<bool> obsMatch)
+        public virtual IDisposable Apply(Animation animation, Animatable control, IObservable<bool> obsMatch, Action onComplete)
         {
             if (!_isVerfifiedAndConverted)
                 VerifyConvertKeyFrames();
@@ -45,7 +45,7 @@ namespace Avalonia.Animation
                 .Where(p => p && Timing.GetGlobalPlayState() != PlayState.Pause)
                 .Subscribe(_ =>
                 {
-                    var timerObs = RunKeyFrames(animation, control);
+                    var timerObs = RunKeyFrames(animation, control, onComplete);
                 });
         }
 
@@ -97,10 +97,9 @@ namespace Avalonia.Animation
         /// <summary>
         /// Runs the KeyFrames Animation.
         /// </summary>
-        private IDisposable RunKeyFrames(Animation animation, Animatable control)
+        private IDisposable RunKeyFrames(Animation animation, Animatable control, Action onComplete)
         {
-            var stateMachine = new AnimatorStateMachine<T>();
-            stateMachine.Initialize(animation, control, this);
+            var stateMachine = new AnimatorStateMachine<T>(animation, control, this, onComplete);
 
             Timing.AnimationStateTimer
                         .TakeWhile(_ => !stateMachine._unsubscribe)

src/Avalonia.Animation/IAnimation.cs

@@ -13,11 +13,11 @@ namespace Avalonia.Animation
         /// <summary>
         /// Apply the animation to the specified control
         /// </summary>
-        IDisposable Apply(Animatable control, IObservable<bool> match);
+        IDisposable Apply(Animatable control, IObservable<bool> match, Action onComplete = null);
 
         /// <summary>
         /// Run the animation to the specified control
         /// </summary>
         Task RunAsync(Animatable control);
     }
-}
+}

src/Avalonia.Animation/IAnimator.cs

@@ -17,6 +17,6 @@ namespace Avalonia.Animation
         /// <summary>
         /// Applies the current KeyFrame group to the specified control.
         /// </summary>
-        IDisposable Apply(Animation animation, Animatable control, IObservable<bool> obsMatch);
+        IDisposable Apply(Animation animation, Animatable control, IObservable<bool> obsMatch, Action onComplete);
     }
 }

src/Avalonia.Visuals/Animation/TransformAnimator.cs

@@ -19,7 +19,7 @@ namespace Avalonia.Animation
         DoubleAnimator childKeyFrames;
 
         /// <inheritdoc/>
-        public override IDisposable Apply(Animation animation, Animatable control, IObservable<bool> obsMatch)
+        public override IDisposable Apply(Animation animation, Animatable control, IObservable<bool> obsMatch, Action onComplete)
         {
             var ctrl = (Visual)control;
 
@@ -51,7 +51,7 @@ namespace Avalonia.Animation
                 // It's a transform object so let's target that.
                 if (renderTransformType == Property.OwnerType)
                 {
-                    return childKeyFrames.Apply(animation, ctrl.RenderTransform, obsMatch);
+                    return childKeyFrames.Apply(animation, ctrl.RenderTransform, obsMatch, onComplete);
                 }
                 // It's a TransformGroup and try finding the target there.
                 else if (renderTransformType == typeof(TransformGroup))
@@ -60,7 +60,7 @@ namespace Avalonia.Animation
                     {
                         if (transform.GetType() == Property.OwnerType)
                         {
-                            return childKeyFrames.Apply(animation, transform, obsMatch);
+                            return childKeyFrames.Apply(animation, transform, obsMatch, onComplete);
                         }
                     }
                 }