Fix for VisualStateManager Setter.TargetName failing when ControlTemplate is applied

src/Controls/src/Core/Setter.cs

@@ -67,7 +67,7 @@ internal void Apply(BindableObject target, SetterSpecificity specificity)
 			var targetObject = target;
 
 			if (!string.IsNullOrEmpty(TargetName) && target is Element element)
-				targetObject = element.FindByName(TargetName) as BindableObject ?? throw new XamlParseException($"Cannot resolve '{TargetName}' as Setter Target for '{target}'.");
+				targetObject = FindTargetByName(element, TargetName) ?? throw new XamlParseException($"Cannot resolve '{TargetName}' as Setter Target for '{target}'.");
 
 			if (Property == null)
 				return;
@@ -90,7 +90,7 @@ internal void UnApply(BindableObject target, SetterSpecificity specificity)
 			var targetObject = target;
 
 			if (!string.IsNullOrEmpty(TargetName) && target is Element element)
-				targetObject = element.FindByName(TargetName) as BindableObject ?? throw new ArgumentNullException(nameof(targetObject));
+				targetObject = FindTargetByName(element, TargetName) ?? throw new ArgumentNullException(nameof(targetObject));
 
 			if (Property == null)
 				return;
@@ -100,5 +100,25 @@ internal void UnApply(BindableObject target, SetterSpecificity specificity)
 				targetObject.RemoveDynamicResource(Property, specificity);
 			targetObject.ClearValue(Property, specificity);
 		}
+
+		static BindableObject FindTargetByName(Element element, string name)
+		{
+			// Try standard lookup first (works for same or child namescopes)
+			if (element.FindByName(name) is BindableObject target)
+				return target;
+
+			// Walk up parent tree to handle ControlTemplate namescope boundaries
+			var current = element.Parent;
+			while (current != null)
+			{
+				var namescope = current.GetNameScope();
+				if (namescope?.FindByName(name) is BindableObject parentTarget)
+					return parentTarget;
+
+				current = current.Parent;
+			}
+
+			return null;
+		}
 	}
 }

src/Controls/tests/TestCases.HostApp/Issues/Issue26977.xaml

@@ -0,0 +1,51 @@
+<?xml version="1.0" encoding="utf-8" ?>
+<ContentPage xmlns="http://schemas.microsoft.com/dotnet/2021/maui"
+             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
+             x:Class="Maui.Controls.Sample.Issues.Issue26977">
+    <ContentPage.ControlTemplate>
+        <ControlTemplate>
+            <ContentPresenter/>
+        </ControlTemplate>
+    </ContentPage.ControlTemplate>
+
+    <VerticalStackLayout x:Name="RootStackLayout"
+                         Padding="30,0"
+                         Spacing="25"
+                         VerticalOptions="Center">
+        <HorizontalStackLayout Spacing="10">
+            <Label Text="Active State"
+                   VerticalOptions="Center"/>
+            <Switch x:Name="StateSwitch"
+                    AutomationId="StateSwitch"
+                    Toggled="OnStateSwitchToggled"/>
+        </HorizontalStackLayout>
+
+        <Label x:Name="TargetLabel"
+               AutomationId="TargetLabel"/>
+
+        <VisualStateManager.VisualStateGroups>
+            <VisualStateGroup Name="Group1">
+                <VisualState Name="State1">
+                    <VisualState.Setters>
+                        <Setter TargetName="TargetLabel"
+                                Property="Label.Text"
+                                Value="Value from Setter in State1"/>
+                        <Setter TargetName="TargetLabel"
+                                Property="Label.BackgroundColor"
+                                Value="Orange"/>
+                    </VisualState.Setters>
+                </VisualState>
+                <VisualState Name="State2">
+                    <VisualState.Setters>
+                        <Setter TargetName="TargetLabel"
+                                Property="Label.Text"
+                                Value="Value from Setter in State2"/>
+                        <Setter TargetName="TargetLabel"
+                                Property="Label.BackgroundColor"
+                                Value="Aqua"/>
+                    </VisualState.Setters>
+                </VisualState>
+            </VisualStateGroup>
+        </VisualStateManager.VisualStateGroups>
+    </VerticalStackLayout>
+</ContentPage>

src/Controls/tests/TestCases.HostApp/Issues/Issue26977.xaml.cs

@@ -0,0 +1,20 @@
+namespace Maui.Controls.Sample.Issues;
+
+[Issue(IssueTracker.Github, 26977, "Setter.TargetName + ControlTemplate crash", PlatformAffected.Android)]
+public partial class Issue26977 : ContentPage
+{
+	public Issue26977()
+	{
+		InitializeComponent();
+	}
+
+	void OnStateSwitchToggled(object sender, ToggledEventArgs e)
+	{
+		if (sender is not Switch stateSwitch)
+		{
+			return;
+		}
+
+		VisualStateManager.GoToState(RootStackLayout, stateSwitch.IsToggled ? "State1" : "State2");
+	}
+}

src/Controls/tests/TestCases.Shared.Tests/Tests/Issues/Issue26977.cs

@@ -0,0 +1,24 @@
+using NUnit.Framework;
+using UITest.Appium;
+using UITest.Core;
+
+namespace Microsoft.Maui.TestCases.Tests.Issues;
+
+public class Issue26977 : _IssuesUITest
+{
+	public Issue26977(TestDevice device) : base(device) { }
+
+	public override string Issue => "Setter.TargetName + ControlTemplate crash";
+
+	[Test]
+	[Category(UITestCategories.Page)]
+	public void SetterTargetNameWithControlTemplateShouldNotCrash()
+	{
+		App.WaitForElement("StateSwitch");
+		App.Tap("StateSwitch");
+
+		var normalText = App.FindElement("TargetLabel").GetText();
+		Assert.That(normalText, Is.EqualTo("Value from Setter in State1"),
+			"Label text should change to 'Value from Setter in State1' after the switch is toggled");
+	}
+}