From 05a742bc5ecab4e0e6af51a189748de99c150d5a Mon Sep 17 00:00:00 2001
From: Max Katz <maxkatz6@outlook.com>
Date: Wed, 17 Apr 2024 20:47:46 -0700
Subject: [PATCH] Fix ReactiveUI regression, when DataContext type is different
 (#15423)

---
 src/Avalonia.ReactiveUI/ReactiveUserControl.cs   |  5 +++--
 src/Avalonia.ReactiveUI/ReactiveWindow.cs        |  5 +++--
 .../ReactiveUserControlTest.cs                   | 16 ++++++++++++++++
 3 files changed, 22 insertions(+), 4 deletions(-)

diff --git a/src/Avalonia.ReactiveUI/ReactiveUserControl.cs b/src/Avalonia.ReactiveUI/ReactiveUserControl.cs
index 94090f2614..76a4f29b16 100644
--- a/src/Avalonia.ReactiveUI/ReactiveUserControl.cs
+++ b/src/Avalonia.ReactiveUI/ReactiveUserControl.cs
@@ -48,14 +48,15 @@ namespace Avalonia.ReactiveUI
 
             if (change.Property == DataContextProperty)
             {
-                if (Object.ReferenceEquals(change.OldValue, ViewModel))
+                if (ReferenceEquals(change.OldValue, ViewModel)
+                    && change.NewValue is null or TViewModel)
                 {
                     SetCurrentValue(ViewModelProperty, change.NewValue);
                 }
             }
             else if (change.Property == ViewModelProperty)
             {
-                if (Object.ReferenceEquals(change.OldValue, DataContext))
+                if (ReferenceEquals(change.OldValue, DataContext))
                 {
                     SetCurrentValue(DataContextProperty, change.NewValue);
                 }
diff --git a/src/Avalonia.ReactiveUI/ReactiveWindow.cs b/src/Avalonia.ReactiveUI/ReactiveWindow.cs
index 727c22f016..4048ef1e25 100644
--- a/src/Avalonia.ReactiveUI/ReactiveWindow.cs
+++ b/src/Avalonia.ReactiveUI/ReactiveWindow.cs
@@ -48,14 +48,15 @@ namespace Avalonia.ReactiveUI
 
             if (change.Property == DataContextProperty)
             {
-                if (Object.ReferenceEquals(change.OldValue, ViewModel))
+                if (ReferenceEquals(change.OldValue, ViewModel)
+                    && change.NewValue is null or TViewModel)
                 {
                     SetCurrentValue(ViewModelProperty, change.NewValue);
                 }
             }
             else if (change.Property == ViewModelProperty)
             {
-                if (Object.ReferenceEquals(change.OldValue, DataContext))
+                if (ReferenceEquals(change.OldValue, DataContext))
                 {
                     SetCurrentValue(DataContextProperty, change.NewValue);
                 }
diff --git a/tests/Avalonia.ReactiveUI.UnitTests/ReactiveUserControlTest.cs b/tests/Avalonia.ReactiveUI.UnitTests/ReactiveUserControlTest.cs
index 4bf999bed0..67790789e3 100644
--- a/tests/Avalonia.ReactiveUI.UnitTests/ReactiveUserControlTest.cs
+++ b/tests/Avalonia.ReactiveUI.UnitTests/ReactiveUserControlTest.cs
@@ -134,6 +134,22 @@ namespace Avalonia.ReactiveUI.UnitTests
             Assert.Same(vm2, view.ViewModel);
         }
 
+        // https://github.com/AvaloniaUI/Avalonia/issues/15060
+        [Fact]
+        public void Should_Not_Inherit_DataContext_Of_Wrong_Type()
+        {
+            var view = new ExampleView();
+            var root = new TestRoot(view);
+            
+            Assert.Null(view.DataContext);
+            Assert.Null(view.ViewModel);
+
+            root.DataContext = this;
+
+            Assert.Same(this, view.DataContext);
+            Assert.Null(view.ViewModel);
+        }
+
         [Fact]
         public void Should_Not_Overlap_Change_Notifications()
         {