fix: Apply x:Bind expressions in control template

src/SourceGenerators/Uno.UI.SourceGenerators.Tests/XamlCodeGeneratorTests/Out/TDBMIDTIRD/XamlCodeGenerator_MyResourceDictionary_92716e07ff456818f6d4125e055d4d57.cs

@@ -95,6 +95,7 @@ public _View Build(object __ResourceOwner_1)
 					__fe.Loading += delegate
 					{
 						_component_0.UpdateResourceBindings();
+						_component_0.ApplyXBind();
 					}
 					;
 				}
@@ -261,6 +262,7 @@ public _View Build(object __ResourceOwner_1)
 				__fe.Loading += delegate
 				{
 					_component_0.UpdateResourceBindings();
+					_component_0.ApplyXBind();
 				}
 				;
 			}
@@ -350,6 +352,7 @@ public _View Build(object __ResourceOwner_1)
 				__fe.Loading += delegate
 				{
 					_component_0.UpdateResourceBindings();
+					_component_0.ApplyXBind();
 				}
 				;
 			}

src/SourceGenerators/Uno.UI.SourceGenerators/XamlGenerator/XamlFileGenerator.cs

@@ -1084,6 +1084,7 @@ private void BuildCompiledBindingsInitializerForTemplate(IIndentedStringBuilder
 					using (writer.BlockInvariant($"__fe.Loading += delegate"))
 					{
 						BuildComponentResouceBindingUpdates(writer);
+						BuildXBindApply(writer);
 						BuildxBindEventHandlerInitializers(writer, CurrentScope.xBindEventsHandlers);
 					}
 					writer.AppendLineIndented(";");
@@ -1117,6 +1118,19 @@ private void BuildComponentResouceBindingUpdates(IIndentedStringBuilder writer)
 			}
 		}
 
+		private void BuildXBindApply(IIndentedStringBuilder writer)
+		{
+			for (var i = 0; i < CurrentScope.Components.Count; i++)
+			{
+				var component = CurrentScope.Components[i];
+
+				if (HasXBindMarkupExtension(component.XamlObject) && IsDependencyObject(component.XamlObject))
+				{
+					writer.AppendLineIndented($"{component.MemberName}.ApplyXBind();");
+				}
+			}
+		}
+
 		private void BuildComponentFields(IIndentedStringBuilder writer)
 		{
 			for (var i = 0; i < CurrentScope.Components.Count; i++)
@@ -4230,8 +4244,10 @@ private string BuildXBindEvalFunction(XamlMemberDefinition member, XamlObjectDef
 			var modeMember = bindNode.Members.FirstOrDefault(m => m.Member.Name == "Mode")?.Value?.ToString() ?? GetDefaultBindMode();
 			var rawBindBack = bindNode.Members.FirstOrDefault(m => m.Member.Name == "BindBack")?.Value?.ToString();
 
+			var sourceInstance = CurrentResourceOwner is not null ? CurrentResourceOwnerName : "__that";
+
 			var applyBindingParameters = _isHotReloadEnabled
-				? "__that, (___b, __that)"
+				? $"{sourceInstance}, (___b, {sourceInstance})"
 				: "___b";
 
 			if (isInsideDataTemplate)
@@ -4396,7 +4412,7 @@ string buildBindBack()
 					? ", new [] {" + string.Join(", ", formattedPaths) + "}"
 					: "";
 
-				return $".BindingApply({applyBindingParameters} =>  /*defaultBindMode{GetDefaultBindMode()} {rawFunction}*/ global::Uno.UI.Xaml.BindingHelper.SetBindingXBindProvider(___b, __that, ___ctx => {bindFunction}, {buildBindBack()} {pathsArray}))";
+				return $".BindingApply({applyBindingParameters} =>  /*defaultBindMode{GetDefaultBindMode()} {rawFunction}*/ global::Uno.UI.Xaml.BindingHelper.SetBindingXBindProvider(___b, {sourceInstance}, ___ctx => {bindFunction}, {buildBindBack()} {pathsArray}))";
 			}
 		}
 

src/Uno.UI.RuntimeTests/Tests/BindingTests/BindingTests.cs

@@ -128,4 +128,24 @@ public async Task When_FallbackValueThemeResource_WithDataContext()
 
 		Assert.AreEqual(Microsoft.UI.Colors.Red, ((SolidColorBrush)myBtn.Foreground).Color);
 	}
+
+	[TestMethod]
+	public async Task When_XBind_To_Const_Page()
+	{
+		var SUT = new XBindConstPage();
+		await UITestHelper.Load(SUT);
+
+		Assert.AreEqual(200, SUT.XBoundBorder.ActualWidth);
+		Assert.AreEqual(200, SUT.XBoundBorder.ActualHeight);
+	}
+
+	[TestMethod]
+	public async Task When_XBind_To_Const_Control_Template()
+	{
+		var SUT = new XBindConstControl();
+		await UITestHelper.Load(SUT);
+
+		Assert.AreEqual(200, SUT.XBoundBorder.ActualWidth);
+		Assert.AreEqual(200, SUT.XBoundBorder.ActualHeight);
+	}
 }

src/Uno.UI.RuntimeTests/Tests/BindingTests/XBindConstControl.xaml

@@ -0,0 +1,48 @@
+<Control
+    x:Class="Uno.UI.RuntimeTests.Tests.XBindConstControl"
+    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
+    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+    xmlns:local="using:Uno.UI.RuntimeTests.Tests"
+    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
+    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
+    mc:Ignorable="d"
+    d:DesignHeight="300"
+    d:DesignWidth="400">
+
+  <Control.Resources>
+    <ResourceDictionary>
+
+      <Style TargetType="local:XBindConstControl">
+        <Setter Property="Template">
+          <Setter.Value>
+            <ControlTemplate TargetType="local:XBindConstControl" >
+              <Grid>
+                <StackPanel
+                  HorizontalAlignment="Center"
+                  VerticalAlignment="Center">
+                  <TextBlock Text="Grid in Control" HorizontalAlignment="Center" />
+                  <Border
+                    Width="100"
+                    Height="100"
+                    BorderBrush="Black"
+                    BorderThickness="1"
+                    Background="LightCoral" />
+                  <TextBlock Text="Grid in Control with x:Bind" HorizontalAlignment="Center" />
+                  <Border
+                    Width="{x:Bind local:XBindConstControl.MyWidth}"
+                    Height="{x:Bind local:XBindConstControl.MyHeight}"
+                    x:Name="BoundBorder"
+                    BorderBrush="Black"
+                    BorderThickness="1"
+                    Background="LawnGreen" />
+                </StackPanel>
+              </Grid>
+            </ControlTemplate>
+          </Setter.Value>
+        </Setter>
+      </Style>
+
+    </ResourceDictionary>
+  </Control.Resources>
+
+</Control>

src/Uno.UI.RuntimeTests/Tests/BindingTests/XBindConstControl.xaml.cs

@@ -0,0 +1,27 @@
+using Microsoft.UI.Xaml.Controls;
+
+namespace Uno.UI.RuntimeTests.Tests;
+
+public sealed partial class XBindConstControl : Control
+{
+	private const double MyWidth = 200;
+	private const double MyHeight = 200;
+
+	public XBindConstControl()
+	{
+		DefaultStyleKey = typeof(XBindConstControl);
+
+		this.InitializeComponent();
+	}
+
+	public Border XBoundBorder { get; set; }
+
+	protected override void OnApplyTemplate()
+	{
+		base.OnApplyTemplate();
+
+		XBoundBorder = GetTemplateChild("BoundBorder") as Border;
+
+
+	}
+}

src/Uno.UI.RuntimeTests/Tests/BindingTests/XBindConstPage.xaml

@@ -0,0 +1,29 @@
+<Page x:Class="Uno.UI.RuntimeTests.Tests.XBindConstPage"
+      xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
+      xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+      xmlns:local="using:Uno.UI.RuntimeTests.Tests"
+      Background="{ThemeResource ApplicationPageBackgroundThemeBrush}">
+  <ScrollViewer>
+    <Grid>
+      <StackPanel
+        HorizontalAlignment="Center"
+        VerticalAlignment="Center">
+        <TextBlock Text="Grid in Page" HorizontalAlignment="Center"/>
+        <Grid
+          Width="100"
+          Height="100"
+          BorderBrush="Black"
+          BorderThickness="1"
+          Background="LightCoral" />
+        <TextBlock Text="Grid in Page, with x:Bind" HorizontalAlignment="Center" />
+        <Border
+          Width="{x:Bind local:XBindConstPage.MyWidth}"
+          Height="{x:Bind local:XBindConstPage.MyHeight}"
+          x:Name="BoundBorder"
+          BorderBrush="Black"
+          BorderThickness="1"
+          Background="LawnGreen" />
+      </StackPanel>
+    </Grid>
+  </ScrollViewer>
+</Page>

src/Uno.UI.RuntimeTests/Tests/BindingTests/XBindConstPage.xaml.cs

@@ -0,0 +1,16 @@
+using Microsoft.UI.Xaml.Controls;
+
+namespace Uno.UI.RuntimeTests.Tests;
+
+public sealed partial class XBindConstPage : Page
+{
+	private const double MyWidth = 200;
+	private const double MyHeight = 200;
+
+	public XBindConstPage()
+	{
+		this.InitializeComponent();
+	}
+
+	public Border XBoundBorder => BoundBorder;
+}