From 4eec8b42715233343e13bb403f204b56a78c304e Mon Sep 17 00:00:00 2001
From: Jeremy Koritzinsky <jkoritzinsky@gmail.com>
Date: Tue, 29 May 2018 15:14:52 -0500
Subject: [PATCH 1/2] Fix #1531 by making IStyle an IAvaloniaObject.

---
 src/Avalonia.Controls/Design.cs        | 18 +++++++-----------
 src/Avalonia.Styling/Styling/IStyle.cs |  2 +-
 src/Avalonia.Styling/Styling/Style.cs  |  2 +-
 3 files changed, 9 insertions(+), 13 deletions(-)

diff --git a/src/Avalonia.Controls/Design.cs b/src/Avalonia.Controls/Design.cs
index ce52891749..3a67e554ac 100644
--- a/src/Avalonia.Controls/Design.cs
+++ b/src/Avalonia.Controls/Design.cs
@@ -1,5 +1,6 @@
 
 using System.Runtime.CompilerServices;
+using Avalonia.Styling;
 
 namespace Avalonia.Controls
 {
@@ -45,23 +46,18 @@ namespace Avalonia.Controls
         {
             return control.GetValue(DataContextProperty);
         }
-
-        static readonly ConditionalWeakTable<object, Control> Substitutes = new ConditionalWeakTable<object, Control>();
-
+        
         public static readonly AttachedProperty<Control> PreviewWithProperty = AvaloniaProperty
-            .RegisterAttached<AvaloniaObject, Control>("PreviewWith", typeof (Design));
+            .RegisterAttached<IStyle, Control>("PreviewWith", typeof (Design));
 
-        public static void SetPreviewWith(object target, Control control)
+        public static void SetPreviewWith(IStyle target, Control control)
         {
-            Substitutes.Remove(target);
-            Substitutes.Add(target, control);
+            target.SetValue(PreviewWithProperty, control);
         }
 
-        public static Control GetPreviewWith(object target)
+        public static Control GetPreviewWith(IStyle target)
         {
-            Control rv;
-            Substitutes.TryGetValue(target, out rv);
-            return rv;
+            return target.GetValue(PreviewWithProperty);
         }
 
         public static void ApplyDesignModeProperties(Control target, Control source)
diff --git a/src/Avalonia.Styling/Styling/IStyle.cs b/src/Avalonia.Styling/Styling/IStyle.cs
index 5f12763825..2ce06cc36c 100644
--- a/src/Avalonia.Styling/Styling/IStyle.cs
+++ b/src/Avalonia.Styling/Styling/IStyle.cs
@@ -8,7 +8,7 @@ namespace Avalonia.Styling
     /// <summary>
     /// Defines the interface for styles.
     /// </summary>
-    public interface IStyle : IResourceNode
+    public interface IStyle : IAvaloniaObject, IResourceNode
     {
         /// <summary>
         /// Attaches the style to a control if the style's selector matches.
diff --git a/src/Avalonia.Styling/Styling/Style.cs b/src/Avalonia.Styling/Styling/Style.cs
index 88ff695ba2..203f679683 100644
--- a/src/Avalonia.Styling/Styling/Style.cs
+++ b/src/Avalonia.Styling/Styling/Style.cs
@@ -15,7 +15,7 @@ namespace Avalonia.Styling
     /// <summary>
     /// Defines a style.
     /// </summary>
-    public class Style : IStyle, ISetStyleParent
+    public class Style : AvaloniaObject, IStyle, ISetStyleParent
     {
         private static Dictionary<IStyleable, List<IDisposable>> _applied =
             new Dictionary<IStyleable, List<IDisposable>>();

From 1bbc155303dbcdaffec3d8f36356e2467ba9fd99 Mon Sep 17 00:00:00 2001
From: Jeremy Koritzinsky <jkoritzinsky@gmail.com>
Date: Tue, 29 May 2018 15:35:08 -0500
Subject: [PATCH 2/2] Use a concrete type for the host type to avoid #959.

---
 src/Avalonia.Controls/Design.cs                    | 6 +++---
 src/Avalonia.DesignerSupport/DesignWindowLoader.cs | 3 +--
 src/Avalonia.Styling/Styling/IStyle.cs             | 2 +-
 3 files changed, 5 insertions(+), 6 deletions(-)

diff --git a/src/Avalonia.Controls/Design.cs b/src/Avalonia.Controls/Design.cs
index 3a67e554ac..894240a09f 100644
--- a/src/Avalonia.Controls/Design.cs
+++ b/src/Avalonia.Controls/Design.cs
@@ -48,14 +48,14 @@ namespace Avalonia.Controls
         }
         
         public static readonly AttachedProperty<Control> PreviewWithProperty = AvaloniaProperty
-            .RegisterAttached<IStyle, Control>("PreviewWith", typeof (Design));
+            .RegisterAttached<Style, Control>("PreviewWith", typeof (Design));
 
-        public static void SetPreviewWith(IStyle target, Control control)
+        public static void SetPreviewWith(Style target, Control control)
         {
             target.SetValue(PreviewWithProperty, control);
         }
 
-        public static Control GetPreviewWith(IStyle target)
+        public static Control GetPreviewWith(Style target)
         {
             return target.GetValue(PreviewWithProperty);
         }
diff --git a/src/Avalonia.DesignerSupport/DesignWindowLoader.cs b/src/Avalonia.DesignerSupport/DesignWindowLoader.cs
index d1958ac9bf..6dca479d38 100644
--- a/src/Avalonia.DesignerSupport/DesignWindowLoader.cs
+++ b/src/Avalonia.DesignerSupport/DesignWindowLoader.cs
@@ -36,8 +36,7 @@ namespace Avalonia.DesignerSupport
                 var styles = loaded as Styles;
                 if (styles != null)
                 {
-                    var substitute = Design.GetPreviewWith(styles) ??
-                                     styles.Select(Design.GetPreviewWith).FirstOrDefault(s => s != null);
+                    var substitute = styles.OfType<Style>().Select(Design.GetPreviewWith).FirstOrDefault(s => s != null);
                     if (substitute != null)
                     {
                         substitute.Styles.AddRange(styles);
diff --git a/src/Avalonia.Styling/Styling/IStyle.cs b/src/Avalonia.Styling/Styling/IStyle.cs
index 2ce06cc36c..5f12763825 100644
--- a/src/Avalonia.Styling/Styling/IStyle.cs
+++ b/src/Avalonia.Styling/Styling/IStyle.cs
@@ -8,7 +8,7 @@ namespace Avalonia.Styling
     /// <summary>
     /// Defines the interface for styles.
     /// </summary>
-    public interface IStyle : IAvaloniaObject, IResourceNode
+    public interface IStyle : IResourceNode
     {
         /// <summary>
         /// Attaches the style to a control if the style's selector matches.