Make KeyFrame an AvaloniaObject and move the setters to a dedicated property.

src/Avalonia.Animation/Animation.cs

@@ -113,7 +113,7 @@ namespace Avalonia.Animation
 
             foreach (var keyframe in Children)
             {
-                foreach (var setter in keyframe)
+                foreach (var setter in keyframe.Setters)
                 {
                     var handler = GetAnimatorType(setter.Property);
 

src/Avalonia.Animation/KeyFrame.cs

@@ -4,6 +4,7 @@
 using System;
 using System.Collections.Generic;
 using Avalonia.Collections;
+using Avalonia.Metadata;
 
 namespace Avalonia.Animation
 {
@@ -17,7 +18,7 @@ namespace Avalonia.Animation
     /// Stores data regarding a specific key
     /// point and value in an animation.
     /// </summary>
-    public class KeyFrame : AvaloniaList<IAnimationSetter>
+    public class KeyFrame : AvaloniaObject
     {
         private TimeSpan _ktimeSpan;
         private Cue _kCue;
@@ -26,13 +27,11 @@ namespace Avalonia.Animation
         {
         }
 
-        public KeyFrame(IEnumerable<IAnimationSetter> items) : base(items)
-        {
-        }
-
-        public KeyFrame(params IAnimationSetter[] items) : base(items)
-        {
-        }
+        /// <summary>
+        /// Gets the setters of <see cref="KeyFrame"/>.
+        /// </summary>
+        [Content]
+        public AvaloniaList<IAnimationSetter> Setters { get; } = new AvaloniaList<IAnimationSetter>();
 
         internal KeyFrameTimingMode TimingMode { get; private set; }
 

src/Avalonia.Visuals/Animation/CrossFade.cs

@@ -33,36 +33,40 @@ namespace Avalonia.Animation
         {
             _fadeOutAnimation = new Animation
             {
-                Children  = 
+                Children =
                 {
-                    new KeyFrame
-                    (
-                        new Setter
-                        {
-                            Property = Visual.OpacityProperty,
-                            Value = 0d
-                        }
-                    )
+                    new KeyFrame()
                     {
+                        Setters =
+                        {
+                            new Setter
+                            {
+                                Property = Visual.OpacityProperty,
+                                Value = 0d
+                            }
+                        },
                         Cue = new Cue(1d)
                     }
+
                 }
             };
             _fadeInAnimation = new Animation
             {
-                Children = 
+                Children =
                 {
-                    new KeyFrame
-                    (
-                        new Setter
-                        {
-                            Property = Visual.OpacityProperty,
-                            Value = 0d
-                        }
-                    )
+                    new KeyFrame()
                     {
+                        Setters =
+                        {
+                            new Setter
+                            {
+                                Property = Visual.OpacityProperty,
+                                Value = 0d
+                            }
+                        },
                         Cue = new Cue(0d)
                     }
+
                 }
             };
             _fadeOutAnimation.Duration = _fadeInAnimation.Duration = duration;

src/Avalonia.Visuals/Animation/PageSlide.cs

@@ -81,27 +81,29 @@ namespace Avalonia.Animation
                     Children = 
                     {
                         new KeyFrame
-                        (
-                            new Setter
+                        {
+                            Setters =
                             {
-                                Property = translateProperty,
+                                new Setter
+                                {
+                                    Property = translateProperty,
                                 Value = 0d
-                            }
-                        )
-                        {
+                                }
+                            },
                             Cue = new Cue(0d)
                         },
                         new KeyFrame
-                        (
-                            new Setter
-                            {
-                                Property = translateProperty,
-                                Value = forward ? -distance : distance
-                            }
-                        )
                         {
+                            Setters =
+                            {
+                                new Setter
+                                {
+                                    Property = translateProperty,
+                                    Value = forward ? -distance : distance
+                                }
+                            },
                             Cue = new Cue(1d)
-                        }
+                        }                       
                     }
                 };
                 animation.Duration = Duration;
@@ -115,28 +117,31 @@ namespace Avalonia.Animation
                 {
                     Children =
                     {
+
                         new KeyFrame
-                        (
-                            new Setter
-                            {
-                                Property = translateProperty,
-                                Value = forward ? distance : -distance
-                            }
-                        )
                         {
+                            Setters =
+                            {
+                                new Setter
+                                {
+                                    Property = translateProperty,
+                                    Value = forward ? distance : -distance
+                                }
+                            },
                             Cue = new Cue(0d)
                         },
                         new KeyFrame
-                        (
-                            new Setter
-                            {
-                                Property = translateProperty,
-                                Value = 0d
-                            }
-                        )
                         {
+                            Setters =
+                            {
+                                new Setter
+                                {
+                                    Property = translateProperty,
+                                    Value = 0d
+                                }
+                            },
                             Cue = new Cue(1d)
-                        },
+                        }
                     }
                 };
                 animation.Duration = Duration;

tests/Avalonia.Animation.UnitTests/AnimationIterationTests.cs

@@ -18,17 +18,20 @@ namespace Avalonia.Animation.UnitTests
         {
             var keyframe1 = new KeyFrame()
             {
-                new Setter(Border.WidthProperty, 200d),
+                Setters = {
+                    new Setter(Border.WidthProperty, 200d),
+                },
+                Cue = new Cue(1d)
             };
-
+  
             var keyframe2 = new KeyFrame()
             {
-                new Setter(Border.WidthProperty, 100d),
+                Setters = {
+                    new Setter(Border.WidthProperty, 100d),
+                },
+                Cue = new Cue(0d)
             };
 
-            keyframe1.Cue = new Cue(1d);
-            keyframe2.Cue = new Cue(0d);
-
             var animation = new Animation()
             {
                 Duration = TimeSpan.FromSeconds(3),