Added notification for property changes to implicit animations

Used registered callbacks to avoid the overhead in explicit animations. This way the callbacks and events are only present and used when an implicit animation is actually used, since explicit ones use a new AnimationBuilder instance every time anyway, so notification is not necessary.

Author: Sergio0694

Microsoft.Toolkit.Uwp.UI.Animations/Xaml/Abstract/Animation.cs

@@ -91,14 +91,14 @@ public EasingMode? EasingMode
         /// </summary>
         public RepeatOption Repeat
         {
-            get => (RepeatOption)GetValue(RepeatOptionProperty);
-            set => SetValue(RepeatOptionProperty, value);
+            get => (RepeatOption)GetValue(RepeatProperty);
+            set => SetValue(RepeatProperty, value);
         }
 
         /// <summary>
         /// Identifies the <seealso cref="Repeat"/> dependency property.
         /// </summary>
-        public static readonly DependencyProperty RepeatOptionProperty = DependencyProperty.Register(
+        public static readonly DependencyProperty RepeatProperty = DependencyProperty.Register(
             nameof(Repeat),
             typeof(RepeatOption),
             typeof(Animation),

Microsoft.Toolkit.Uwp.UI.Animations/Xaml/Abstract/ImplicitAnimation{TValue,TKeyFrame}.cs

@@ -4,6 +4,7 @@
 
 #nullable enable
 
+using System;
 using Windows.UI.Composition;
 using Windows.UI.Xaml;
 using static Microsoft.Toolkit.Uwp.UI.Animations.AnimationExtensions;
@@ -14,9 +15,35 @@ namespace Microsoft.Toolkit.Uwp.UI.Animations
     /// A base model representing a typed animation that can be used as an implicit composition animation.
     /// </summary>
     /// <inheritdoc cref="Animation{TValue, TKeyFrame}"/>
-    public abstract class ImplicitAnimation<TValue, TKeyFrame> : Animation<TValue, TKeyFrame>, IImplicitTimeline
+    public abstract class ImplicitAnimation<TValue, TKeyFrame> : Animation<TValue, TKeyFrame>, IImplicitTimeline, IInternalImplicitAnimation
         where TKeyFrame : unmanaged
     {
+        /// <inheritdoc cref="IInternalImplicitAnimation.AnimationPropertyChanged"/>
+        private event EventHandler? AnimationPropertyChanged;
+
+        /// <summary>
+        /// Initializes a new instance of the <see cref="ImplicitAnimation{TValue, TKeyFrame}"/> class.
+        /// </summary>
+        protected ImplicitAnimation()
+        {
+            RegisterPropertyChangedCallback(DelayProperty, RaiseAnimationPropertyChanged);
+            RegisterPropertyChangedCallback(DurationProperty, RaiseAnimationPropertyChanged);
+            RegisterPropertyChangedCallback(EasingTypeProperty, RaiseAnimationPropertyChanged);
+            RegisterPropertyChangedCallback(EasingModeProperty, RaiseAnimationPropertyChanged);
+            RegisterPropertyChangedCallback(RepeatProperty, RaiseAnimationPropertyChanged);
+            RegisterPropertyChangedCallback(DelayBehaviorProperty, RaiseAnimationPropertyChanged);
+            RegisterPropertyChangedCallback(ToProperty, RaiseAnimationPropertyChanged);
+            RegisterPropertyChangedCallback(FromProperty, RaiseAnimationPropertyChanged);
+            RegisterPropertyChangedCallback(KeyFramesProperty, RaiseAnimationPropertyChanged);
+        }
+
+        /// <inheritdoc/>
+        event EventHandler? IInternalImplicitAnimation.AnimationPropertyChanged
+        {
+            add => AnimationPropertyChanged += value;
+            remove => AnimationPropertyChanged -= value;
+        }
+
         /// <summary>
         /// Gets or sets the optional implicit target for the animation. This can act as a trigger property for the animation.
         /// </summary>
@@ -67,5 +94,15 @@ public CompositionAnimation GetAnimation(UIElement element, out string? target)
 
             return builder.GetAnimation(element.GetVisual(), out _);
         }
+
+        /// <summary>
+        /// Raises <see cref="AnimationPropertyChanged"/> event.
+        /// </summary>
+        /// <param name="sender">The instance raising the event.</param>
+        /// <param name="property">The <see cref="DependencyProperty"/> that was changed.</param>
+        private void RaiseAnimationPropertyChanged(DependencyObject sender, DependencyProperty property)
+        {
+            AnimationPropertyChanged?.Invoke(this, EventArgs.Empty);
+        }
     }
 }

Microsoft.Toolkit.Uwp.UI.Animations/Xaml/Interfaces/IInternalImplicitAnimation.cs

@@ -0,0 +1,22 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System;
+
+#nullable enable
+
+namespace Microsoft.Toolkit.Uwp.UI.Animations
+{
+    /// <summary>
+    /// An interface adding notification support to implicit animations. This is needed to
+    /// avoid the type parameters when the event is subscribed to from <see cref="ImplicitAnimationSet"/>.
+    /// </summary>
+    internal interface IInternalImplicitAnimation
+    {
+        /// <summary>
+        /// Raised whenever a property that influences the animation changes.
+        /// </summary>
+        event EventHandler? AnimationPropertyChanged;
+    }
+}