[WIP] Issue 17744 fix - DataContext Ancestor Inherited Value Change

src/Avalonia.Base/PropertyStore/ValueStore.cs

@@ -656,7 +656,32 @@ public void OnAncestorInheritedValueChanged<T>(
 
             // If the inherited value is set locally, propagation stops here.
             if (_effectiveValues.ContainsKey(property))
-                return;
+            {
+                // BUT, we also need to double-check whether the affected property is the Data-Context AND whether the Data-Context is bound. 
+                // That is, a bound data-context needs re-evaluating even if it's bound locally 
+                // Because a change in the data-context changes what it means for the data-context to be bound 
+                if (property != StyledElement.DataContextProperty)
+                {
+                    return;
+                }
+                var bindingExpression = BindingOperations.GetBindingExpressionBase(Owner, property) as BindingExpression;
+                if (bindingExpression is null)
+                {
+                    return;
+                }
+                // Both of these checks returning false means the affected property is the Data-Context, and it is bound. 
+                // So, continue, because the data-context changing from an inherited context changes the meaning 
+                // of what the property should be after binding. 
+
+                // But now we need to handle cases where the DataContext is intending to change (that is, the path is not `.` )
+                // easiest way is to just get the value of the binding expression and check whether it isn't the same as the newValue
+
+                var bindingValue = bindingExpression.GetValue();
+                if (bindingValue is T tInst && !EqualityComparer<T>.Default.Equals(tInst, newValue))
+                {
+                    return;
+                }
+            }
 
             using var notifying = PropertyNotifying.Start(Owner, property);
 

tests/Avalonia.Markup.Xaml.UnitTests/Avalonia.Markup.Xaml.UnitTests.csproj

@@ -18,6 +18,7 @@
     <ProjectReference Include="..\..\src\Avalonia.Base\Avalonia.Base.csproj" />
     <ProjectReference Include="..\..\src\Avalonia.Controls\Avalonia.Controls.csproj" />
     <ProjectReference Include="..\..\src\Avalonia.Themes.Simple\Avalonia.Themes.Simple.csproj" />
+    <ProjectReference Include="..\..\src\tools\Avalonia.Generators\Avalonia.Generators.csproj" />
     <ProjectReference Include="..\Avalonia.UnitTests\Avalonia.UnitTests.csproj" />
   </ItemGroup>
   <ItemGroup>
@@ -36,6 +37,14 @@
       <Link>PlatformFactAttribute.cs</Link>
     </Compile>
   </ItemGroup>
+  <ItemGroup>
+    <Compile Update="Xaml\CompiledBindingsTests\TestChildControl.axaml.cs">
+      <DependentUpon>TestChildControl.axaml</DependentUpon>
+    </Compile>
+    <Compile Update="Xaml\CompiledBindingsTests\TestWindow.axaml.cs">
+      <DependentUpon>TestWindow.axaml</DependentUpon>
+    </Compile>
+  </ItemGroup>
   <ItemGroup>
     <PackageReference Update="xunit.runner.console" Version="2.9.2">
       <PrivateAssets>all</PrivateAssets>

tests/Avalonia.Markup.Xaml.UnitTests/Xaml/CompiledBindingsTests/BindingTests_InheritedDataContext.cs

@@ -0,0 +1,100 @@
+using System;
+using System.Collections.Generic;
+using System.ComponentModel;
+using System.Globalization;
+using System.Linq;
+using System.Runtime.CompilerServices;
+using System.Text;
+using System.Threading.Tasks;
+using Avalonia.Collections;
+using Avalonia.Controls;
+using Avalonia.UnitTests;
+using Xunit;
+
+namespace Avalonia.Markup.Xaml.UnitTests.Xaml.CompiledBindingsTests
+{
+    // Unit Tests for Github Issue 17755 
+    public class BindingTests_InheritedDataContext : XamlTestBase
+    {
+        [Fact]
+        public void Binding_Inherited_Data_Context_Properly_Notifies_Children()
+        {
+            using (UnitTestApplication.Start(TestServices.StyledWindow))
+            {
+
+                var xaml = @"
+<Window xmlns='https://github.com/avaloniaui'
+        xmlns:x='http://schemas.microsoft.com/winfx/2006/xaml'
+        xmlns:local='clr-namespace:Avalonia.Markup.Xaml.UnitTests.Xaml;assembly=Avalonia.Markup.Xaml.UnitTests'
+        xmlns:datalocal='clr-namespace:Avalonia.Markup.Xaml.UnitTests.Xaml.CompiledBindingsTests'
+        DataContext='{Binding Source={x:Static datalocal:TestingViewModelLocator.ModelLocator}, Path=TestingViewModelInstance}'
+>
+    <Grid DataContext='{Binding .}'>
+        <DockPanel DataContext='{Binding .}'>
+            <Grid DataContext='{Binding .}'>
+                <ListBox x:Name='testingListBox'
+                    DataContext='{Binding .}'
+                    ItemsSource='{Binding ItemsList}'
+                    />
+            </Grid>
+        </DockPanel>
+    </Grid>
+</Window>";
+                var window = (Window)AvaloniaRuntimeXamlLoader.Load(xaml);
+                Assert.NotNull(window);
+                window.Show();
+
+                var listBox = window.Get<ListBox>("testingListBox");
+                Assert.NotNull(listBox);
+                Assert.NotNull(listBox.DataContext);
+                Assert.NotNull(listBox.ItemsSource);
+            }
+        }
+
+        [Fact]
+        public void Compiled_Binding_Inherited_Data_Context_Properly_Notifies_Children()
+        {
+            UnitTestApplication testApp = new(TestServices.StyledWindow);
+            testApp.Resources.Add("ViewModelLocator", new TestingViewModelLocator());
+            using (testApp.StartInstance())
+            {
+                TestWindow testWindow = new();
+                testWindow.Show();
+                Assert.IsType<TestingViewModel>(testWindow.DataContext);
+                var rootControl = testWindow.TestRootControlInstance;
+                Assert.NotNull(rootControl);
+                Assert.IsType<TestingViewModel>(rootControl.DataContext);
+                var childControl = rootControl.TestChildControlInstance;
+                Assert.NotNull(childControl);
+                Assert.IsType<TestingViewModel>(childControl.DataContext);
+                var testListBox = childControl.TestListBox;
+                Assert.NotNull(testListBox);
+                Assert.IsType<TestingViewModel>(testListBox.DataContext);
+                Assert.NotNull(testListBox.ItemsSource);
+            }
+        }
+    }
+
+    // to facilitate Binding Source as a Static Resource 
+    public class TestingViewModelLocator
+    {
+        public TestingViewModel TestingViewModelInstance { get; set; } = new();
+
+        public static TestingViewModelLocator ModelLocator { get; set; } = new();
+    }
+
+    public class TestingViewModel : INotifyPropertyChanged
+    {
+        public event PropertyChangedEventHandler PropertyChanged;
+
+        public AvaloniaList<string> ItemsList { get; private set; } = new();
+
+        public TestingViewModel()
+        {
+            for (var i = 0; i < 20; i++)
+            {
+                ItemsList.Add(i.ToString(CultureInfo.InvariantCulture));
+            }
+        }
+    }
+}

tests/Avalonia.Markup.Xaml.UnitTests/Xaml/CompiledBindingsTests/TestChildControl.axaml

@@ -0,0 +1,22 @@
+<UserControl xmlns="https://github.com/avaloniaui"
+             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+             xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
+             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
+             xmlns:local="clr-namespace:Avalonia.Markup.Xaml.UnitTests.Xaml.CompiledBindingsTests"
+             mc:Ignorable="d" d:DesignWidth="800" d:DesignHeight="450"
+             x:Class="Avalonia.Markup.Xaml.UnitTests.Xaml.CompiledBindingsTests.TestChildControl"
+             x:CompileBindings="True"
+             x:DataType="local:TestingViewModel"
+
+
+             >
+  <Grid>
+    <DockPanel>
+      <ListBox 
+        DataContext="{Binding Path=.}"
+        ItemsSource="{Binding Path=ItemsList}"
+               x:Name="TestListBox"
+               />
+    </DockPanel>
+  </Grid>
+</UserControl>

tests/Avalonia.Markup.Xaml.UnitTests/Xaml/CompiledBindingsTests/TestChildControl.axaml.cs

@@ -0,0 +1,22 @@
+using Avalonia;
+using Avalonia.Controls;
+using Avalonia.Markup.Xaml;
+
+namespace Avalonia.Markup.Xaml.UnitTests.Xaml.CompiledBindingsTests;
+
+public partial class TestChildControl : UserControl
+{
+    public TestChildControl()
+    {
+        InitializeComponent();
+    }
+
+    internal void InitializeComponent()
+    {
+        AvaloniaXamlLoader.Load(this);
+
+        TestListBox = this.Get<ListBox>("TestListBox");
+    }
+
+    public ListBox TestListBox { get; private set; }
+}

tests/Avalonia.Markup.Xaml.UnitTests/Xaml/CompiledBindingsTests/TestRootControl.axaml

@@ -0,0 +1,18 @@
+<UserControl xmlns="https://github.com/avaloniaui"
+             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+             xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
+             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
+             xmlns:local="clr-namespace:Avalonia.Markup.Xaml.UnitTests.Xaml.CompiledBindingsTests"
+             mc:Ignorable="d" d:DesignWidth="800" d:DesignHeight="450"
+             x:Class="Avalonia.Markup.Xaml.UnitTests.Xaml.CompiledBindingsTests.TestRootControl"
+             x:CompileBindings="True"
+             x:DataType="local:TestingViewModel"
+             >
+  <Grid>
+    <DockPanel>
+      <Grid>
+        <local:TestChildControl x:Name="TestChildControlInstance"/>
+      </Grid>
+    </DockPanel>
+  </Grid>
+</UserControl>

tests/Avalonia.Markup.Xaml.UnitTests/Xaml/CompiledBindingsTests/TestRootControl.axaml.cs

@@ -0,0 +1,22 @@
+using Avalonia;
+using Avalonia.Controls;
+using Avalonia.Markup.Xaml;
+
+namespace Avalonia.Markup.Xaml.UnitTests.Xaml.CompiledBindingsTests;
+
+public partial class TestRootControl : UserControl
+{
+    public TestRootControl()
+    {
+        InitializeComponent();
+    }
+
+    internal void InitializeComponent()
+    {
+        AvaloniaXamlLoader.Load(this);
+
+        TestChildControlInstance = this.Get<TestChildControl>("TestChildControlInstance");
+    }
+
+    public TestChildControl TestChildControlInstance { get; private set; }
+}

tests/Avalonia.Markup.Xaml.UnitTests/Xaml/CompiledBindingsTests/TestWindow.axaml

@@ -0,0 +1,18 @@
+<Window xmlns="https://github.com/avaloniaui"
+             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+             xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
+             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
+             xmlns:local="clr-namespace:Avalonia.Markup.Xaml.UnitTests.Xaml.CompiledBindingsTests"
+             mc:Ignorable="d" d:DesignWidth="800" d:DesignHeight="450"
+             x:Class="Avalonia.Markup.Xaml.UnitTests.Xaml.CompiledBindingsTests.TestWindow"
+             x:CompileBindings="True"
+             x:DataType="local:TestingViewModel"
+             DataContext="{Binding (local:TestingViewModelLocator).TestingViewModelInstance, Source={StaticResource ViewModelLocator}}"
+
+             >
+  <Grid>
+    <DockPanel>
+      <local:TestRootControl x:Name="TestRootControlInstance"/>
+    </DockPanel>
+  </Grid>
+</Window>

tests/Avalonia.Markup.Xaml.UnitTests/Xaml/CompiledBindingsTests/TestWindow.axaml.cs

@@ -0,0 +1,22 @@
+using Avalonia;
+using Avalonia.Controls;
+using Avalonia.Markup.Xaml;
+
+namespace Avalonia.Markup.Xaml.UnitTests.Xaml.CompiledBindingsTests;
+
+public partial class TestWindow : Window
+{
+    public TestWindow()
+    {
+        InitializeComponent();
+    }
+
+    internal void InitializeComponent()
+    {
+        AvaloniaXamlLoader.Load(this);
+
+        TestRootControlInstance = this.Get<TestRootControl>("TestRootControlInstance");
+    }
+
+    public TestRootControl TestRootControlInstance { get; private set; }
+}

tests/Avalonia.UnitTests/UnitTestApplication.cs

@@ -58,6 +58,26 @@ public static IDisposable Start(TestServices services = null)
             });
         }
 
+        public IDisposable StartInstance()
+        {
+            var scope = AvaloniaLocator.EnterScope();
+            var oldContext = SynchronizationContext.Current;
+            Dispatcher.ResetForUnitTests();
+            return Disposable.Create(() =>
+            {
+                if (Dispatcher.UIThread.CheckAccess())
+                {
+                    Dispatcher.UIThread.RunJobs();
+                }
+
+                ((ToolTipService)AvaloniaLocator.Current.GetService<IToolTipService>())?.Dispose();
+
+                scope.Dispose();
+                Dispatcher.ResetForUnitTests();
+                SynchronizationContext.SetSynchronizationContext(oldContext);
+            });
+        }
+
         public override void RegisterServices()
         {
             AvaloniaLocator.CurrentMutable