Use attached property

samples/RenderDemo/Pages/CustomAnimatorPage.xaml

@@ -11,10 +11,10 @@
           <Style.Animations>
             <Animation Duration="0:0:1" IterationCount="Infinite">
               <KeyFrame Cue="0%">
-                <Setter Property="Text" Value="" Animator="{x:Type pages:CustomStringAnimator}"/>
+                <Setter Property="Text" Value="" Animation.Animator="{x:Type pages:CustomStringAnimator}"/>
               </KeyFrame>
               <KeyFrame Cue="100%">
-                <Setter Property="Text" Value="0123456789" Animator="{x:Type pages:CustomStringAnimator}"/>
+                <Setter Property="Text" Value="0123456789" Animation.Animator="{x:Type pages:CustomStringAnimator}"/>
               </KeyFrame>
             </Animation>
           </Style.Animations>

src/Avalonia.Animation/Animation.cs

@@ -194,6 +194,22 @@ namespace Avalonia.Animation
         [Content]
         public KeyFrames Children { get; } = new KeyFrames();
 
+        private static readonly Dictionary<object, Type> s_animators = new Dictionary<object, Type>();
+
+        public static Type GetAnimator(object obj)
+        {
+            if (s_animators.TryGetValue(obj, out var type))
+            {
+                return type;
+            }
+            return null;
+        }
+
+        public static void SetAnimator(object obj, Type value)
+        {
+            s_animators[obj] = value;
+        }
+
         private readonly static List<(Func<AvaloniaProperty, bool> Condition, Type Animator)> Animators = new List<(Func<AvaloniaProperty, bool>, Type)>
         {
             ( prop => typeof(bool).IsAssignableFrom(prop.PropertyType), typeof(BoolAnimator) ),
@@ -248,7 +264,7 @@ namespace Avalonia.Animation
             {
                 foreach (var setter in keyframe.Setters)
                 {
-                    var handler = setter.Animator ?? GetAnimatorType(setter.Property);
+                    var handler = Animation.GetAnimator(setter) ?? GetAnimatorType(setter.Property);
 
                     if (handler == null)
                     {

src/Avalonia.Animation/IAnimationSetter.cs

@@ -6,6 +6,5 @@ namespace Avalonia.Animation
     {
         AvaloniaProperty Property { get; set; }
         object Value { get; set; }
-        Type Animator { get; set; }
     }
 }

src/Avalonia.Styling/Styling/Setter.cs

@@ -59,11 +59,6 @@ namespace Avalonia.Styling
             }
         }
 
-        /// <summary>
-        /// Gets or sets the property animator.
-        /// </summary>
-        public Type? Animator { get; set; }
-
         public ISetterInstance Instance(IStyleable target)
         {
             target = target ?? throw new ArgumentNullException(nameof(target));