From 097eeb646fe83c6c9651ddd8110cdcc7a248825f Mon Sep 17 00:00:00 2001
From: Steven Kirk <grokys@gmail.com>
Date: Tue, 25 Feb 2020 16:21:34 +0100
Subject: [PATCH] Don't allow StyledElement.Styles to be set.

It's not settable in Application and I can't see a reason it should be in `StyledElement`. Also add a `Styles` ctor that takes a parent.
---
 src/Avalonia.Controls/Application.cs          |  3 +--
 src/Avalonia.Styling/StyledElement.cs         | 24 ++++---------------
 src/Avalonia.Styling/Styling/Styles.cs        |  6 +++++
 .../StyledElementTests.cs                     | 22 -----------------
 4 files changed, 12 insertions(+), 43 deletions(-)

diff --git a/src/Avalonia.Controls/Application.cs b/src/Avalonia.Controls/Application.cs
index 0ae615fe23..d7b1aec0b7 100644
--- a/src/Avalonia.Controls/Application.cs
+++ b/src/Avalonia.Controls/Application.cs
@@ -167,8 +167,7 @@ namespace Avalonia
             {
                 if (_styles == null)
                 {
-                    _styles = new Styles();
-                    ((ISetResourceParent)_styles).SetParent(this);
+                    _styles = new Styles(this);
                     _styles.ResourcesChanged += ThisResourcesChanged;
                 }
 
diff --git a/src/Avalonia.Styling/StyledElement.cs b/src/Avalonia.Styling/StyledElement.cs
index e9e9ca4d5a..f15f38a5c0 100644
--- a/src/Avalonia.Styling/StyledElement.cs
+++ b/src/Avalonia.Styling/StyledElement.cs
@@ -215,29 +215,15 @@ namespace Avalonia
         /// </remarks>
         public Styles Styles
         {
-            get { return _styles ?? (Styles = new Styles()); }
-            set
+            get
             {
-                Contract.Requires<ArgumentNullException>(value != null);
-
-                if (_styles != value)
+                if (_styles == null)
                 {
-                    if (_styles != null)
-                    {
-                        (_styles as ISetResourceParent)?.SetParent(null);
-                        _styles.ResourcesChanged -= ThisResourcesChanged;
-                    }
-
-                    _styles = value;
-
-                    if (value is ISetResourceParent setParent && setParent.ResourceParent == null)
-                    {
-                        setParent.SetParent(this);
-                    }
-
+                    _styles = new Styles(this);
                     _styles.ResourcesChanged += ThisResourcesChanged;
-                    NotifyResourcesChanged(new ResourcesChangedEventArgs());
                 }
+
+                return _styles;
             }
         }
 
diff --git a/src/Avalonia.Styling/Styling/Styles.cs b/src/Avalonia.Styling/Styling/Styles.cs
index 1929c24017..bef4ef2ee0 100644
--- a/src/Avalonia.Styling/Styling/Styles.cs
+++ b/src/Avalonia.Styling/Styling/Styles.cs
@@ -61,6 +61,12 @@ namespace Avalonia.Styling
                 () => { });
         }
 
+        public Styles(IResourceNode parent)
+            : this()
+        {
+            _parent = parent;
+        }
+
         public event NotifyCollectionChangedEventHandler CollectionChanged
         {
             add => _styles.CollectionChanged += value;
diff --git a/tests/Avalonia.Styling.UnitTests/StyledElementTests.cs b/tests/Avalonia.Styling.UnitTests/StyledElementTests.cs
index d349d9c3e0..c6c48f9aa8 100644
--- a/tests/Avalonia.Styling.UnitTests/StyledElementTests.cs
+++ b/tests/Avalonia.Styling.UnitTests/StyledElementTests.cs
@@ -543,28 +543,6 @@ namespace Avalonia.Styling.UnitTests
             Assert.Same(target, ((IResourceNode)target.Styles).ResourceParent);
         }
 
-        [Fact]
-        public void Assigned_Styles_Parent_Is_Set()
-        {
-            var styles = new Styles();
-            var target = new TestControl { Styles = styles };
-
-            Assert.Same(target, ((IResourceNode)styles).ResourceParent);
-        }
-
-        [Fact]
-        public void Assigning_Styles_Raises_ResourcesChanged()
-        {
-            var styles = new Styles { Resources = { { "foo", "bar" } } };
-            var target = new TestControl();
-            var raised = 0;
-
-            target.ResourcesChanged += (s, e) => ++raised;
-            target.Styles = styles;
-
-            Assert.Equal(1, raised);
-        }
-
         [Fact]
         public void Changing_Parent_Notifies_Styles_ParentResourcesChanged()
         {