From c438f9301e8d8a53269d485cdb05f551457afef7 Mon Sep 17 00:00:00 2001
From: Steven Kirk <grokys@users.noreply.github.com>
Date: Fri, 15 Feb 2019 00:13:57 +0100
Subject: [PATCH] Make DesignWindowLoader expect PreviewWith on Styles.

---
 samples/ControlCatalog/SideBar.xaml                | 8 ++++++++
 src/Avalonia.Controls/Design.cs                    | 6 +++---
 src/Avalonia.DesignerSupport/DesignWindowLoader.cs | 8 ++++----
 3 files changed, 15 insertions(+), 7 deletions(-)

diff --git a/samples/ControlCatalog/SideBar.xaml b/samples/ControlCatalog/SideBar.xaml
index 625b344b8c..fea55bcb07 100644
--- a/samples/ControlCatalog/SideBar.xaml
+++ b/samples/ControlCatalog/SideBar.xaml
@@ -1,6 +1,14 @@
 <Styles xmlns="https://github.com/avaloniaui"
         xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
         x:Class="ControlCatalog.SideBar">
+    <Design.PreviewWith>
+        <Border Padding="20">
+            <TabControl Classes="sidebar">
+                <TabItem Header="Item1"/>
+                <TabItem Header="Item2"/>
+            </TabControl> 
+        </Border>
+    </Design.PreviewWith>
     <Style Selector="TabControl.sidebar">
         <Setter Property="TabStripPlacement" Value="Left"/>
         <Setter Property="Padding" Value="8 0 0 0"/>
diff --git a/src/Avalonia.Controls/Design.cs b/src/Avalonia.Controls/Design.cs
index 894240a09f..0d05e19e53 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<Style, Control>("PreviewWith", typeof (Design));
+            .RegisterAttached<AvaloniaObject, Control>("PreviewWith", typeof (Design));
 
-        public static void SetPreviewWith(Style target, Control control)
+        public static void SetPreviewWith(AvaloniaObject target, Control control)
         {
             target.SetValue(PreviewWithProperty, control);
         }
 
-        public static Control GetPreviewWith(Style target)
+        public static Control GetPreviewWith(AvaloniaObject target)
         {
             return target.GetValue(PreviewWithProperty);
         }
diff --git a/src/Avalonia.DesignerSupport/DesignWindowLoader.cs b/src/Avalonia.DesignerSupport/DesignWindowLoader.cs
index 68feb2edb5..5d49ddf6a1 100644
--- a/src/Avalonia.DesignerSupport/DesignWindowLoader.cs
+++ b/src/Avalonia.DesignerSupport/DesignWindowLoader.cs
@@ -40,13 +40,13 @@ namespace Avalonia.DesignerSupport
 
                 var localAsm = assemblyPath != null ? Assembly.LoadFile(Path.GetFullPath(assemblyPath)) : null;
                 var loaded = loader.Load(stream, localAsm, null, baseUri);
-                var styles = loaded as Styles;
-                if (styles != null)
+                var style = loaded as IStyle;
+                if (style != null)
                 {
-                    var substitute = styles.OfType<Style>().Select(Design.GetPreviewWith).FirstOrDefault(s => s != null);
+                    var substitute = Design.GetPreviewWith((AvaloniaObject)style);
                     if (substitute != null)
                     {
-                        substitute.Styles.AddRange(styles);
+                        substitute.Styles.Add(style);
                         control = substitute;
                     }
                     else