Fix: Enable VisualStateManager to set Style property dynamically

src/Controls/src/Core/Setter.cs

@@ -78,6 +78,12 @@ internal void Apply(BindableObject target, SetterSpecificity specificity)
 				targetObject.SetDynamicResource(Property, dynamicResource.Key, specificity);
 			else if (Value is IList<VisualStateGroup> visualStateGroupCollection)
 				targetObject.SetValue(Property, visualStateGroupCollection.Clone(), specificity);
+			else if (Value is Style style && (Property == StyleableElement.StyleProperty || Property == Span.StyleProperty))
+			{
+				// When setting a Style through a Setter (e.g., in VisualStateManager),
+				// we need to call the Style's Apply method to ensure all its setters are applied
+				((IStyle)style).Apply(targetObject, specificity);
+			}
 			else
 				targetObject.SetValue(Property, Value, specificity: specificity);
 		}
@@ -98,6 +104,13 @@ internal void UnApply(BindableObject target, SetterSpecificity specificity)
 				targetObject.RemoveBinding(Property, specificity);
 			else if (Value is DynamicResource dynamicResource)
 				targetObject.RemoveDynamicResource(Property, specificity);
+			else if (Value is Style style && (Property == StyleableElement.StyleProperty || Property == Span.StyleProperty))
+			{
+				// When un-applying a Style that was set through a Setter,
+				// we need to call the Style's UnApply method to properly clean up
+				((IStyle)style).UnApply(targetObject);
+				return;
+			}
 			targetObject.ClearValue(Property, specificity);
 		}
 	}

src/Controls/tests/TestCases.HostApp/Issues/Issue17175.xaml

@@ -0,0 +1,91 @@
+<?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.Issue17175"
+             Title="Issue 17175 - VSM Can Set Style Property">
+
+    <ContentPage.Resources>
+        <ResourceDictionary>
+            <!-- Base style without VSM -->
+            <Style x:Key="BaseButtonStyle"
+                   TargetType="Button">
+                <Setter Property="BackgroundColor"
+                        Value="LightBlue"/>
+                <Setter Property="TextColor"
+                        Value="Black"/>
+                <Setter Property="Padding"
+                        Value="20"/>
+            </Style>
+
+            <!-- Highlighted style for Selected state -->
+            <Style x:Key="HighlightButtonStyle"
+                   TargetType="Button">
+                <Setter Property="BackgroundColor"
+                        Value="Orange"/>
+                <Setter Property="TextColor"
+                        Value="White"/>
+                <Setter Property="Padding"
+                        Value="20"/>
+                <Setter Property="FontAttributes"
+                        Value="Bold"/>
+            </Style>
+
+            <!-- Disabled style -->
+            <Style x:Key="DisabledButtonStyle"
+                   TargetType="Button">
+                <Setter Property="BackgroundColor"
+                        Value="Gray"/>
+                <Setter Property="TextColor"
+                        Value="DarkGray"/>
+                <Setter Property="Padding"
+                        Value="20"/>
+                <Setter Property="Text"
+                        Value="State: Disabled"/>
+            </Style>
+        </ResourceDictionary>
+    </ContentPage.Resources>
+
+    <VerticalStackLayout Padding="20"
+                         Spacing="10">
+        <Button x:Name="TestButton"
+                Text="State: Normal"
+                Style="{StaticResource BaseButtonStyle}"
+                HorizontalOptions="Center">
+            <VisualStateManager.VisualStateGroups>
+                <VisualStateGroup Name="CommonStates">
+                    <VisualState Name="Normal">
+                        <VisualState.Setters>
+                            <Setter Property="Style"
+                                    Value="{StaticResource BaseButtonStyle}"/>
+                            <Setter Property="Text"
+                                    Value="State: Normal"/>
+                        </VisualState.Setters>
+                    </VisualState>
+                    <VisualState Name="Selected">
+                        <VisualState.Setters>
+                            <Setter Property="Style"
+                                    Value="{StaticResource HighlightButtonStyle}"/>
+                        </VisualState.Setters>
+                    </VisualState>
+                    <VisualState Name="Disabled">
+                        <VisualState.Setters>
+                            <Setter Property="Style"
+                                    Value="{StaticResource DisabledButtonStyle}"/>
+                        </VisualState.Setters>
+                    </VisualState>
+                </VisualStateGroup>
+            </VisualStateManager.VisualStateGroups>
+        </Button>
+
+        <Label x:Name="StateLabel"
+               AutomationId="StateLabel"
+               Text="State: Normal"
+               HorizontalOptions="Center"
+               Margin="0,10,0,0"/>
+
+        <Button Text="Go to Disabled"
+                AutomationId="GoToDisabledButton"
+                Clicked="OnGoToDisabledClicked"
+                HorizontalOptions="Center"/>
+    </VerticalStackLayout>
+</ContentPage>

src/Controls/tests/TestCases.HostApp/Issues/Issue17175.xaml.cs

@@ -0,0 +1,16 @@
+namespace Maui.Controls.Sample.Issues;
+
+[Issue(IssueTracker.Github, 17175, "VisualStateManager should be able to set Style property dynamically", PlatformAffected.All)]
+public partial class Issue17175 : ContentPage
+{
+    public Issue17175()
+    {
+        InitializeComponent();
+    }
+
+    private void OnGoToDisabledClicked(object sender, System.EventArgs e)
+    {
+        TestButton.IsEnabled = !TestButton.IsEnabled;
+        StateLabel.Text = TestButton.Text;
+    }
+}

src/Controls/tests/TestCases.Shared.Tests/Tests/Issues/Issue17175.cs

@@ -0,0 +1,34 @@
+using NUnit.Framework;
+using UITest.Appium;
+using UITest.Core;
+
+namespace Microsoft.Maui.TestCases.Tests.Issues;
+
+public class Issue17175 : _IssuesUITest
+{
+    public override string Issue => "VisualStateManager should be able to set Style property dynamically";
+
+    public Issue17175(TestDevice device) : base(device) { }
+
+    [Test]
+    [Category(UITestCategories.Button)]
+    public void VisualStateManagerCanSetStyleProperty()
+    {
+        App.WaitForElement("GoToDisabledButton");
+
+        // Normal → Disabled
+        App.Tap("GoToDisabledButton");
+        var stateLabel = App.FindElement("StateLabel").GetText();
+        Assert.That(stateLabel, Is.EqualTo("State: Disabled"));
+
+        // Disabled → Normal (verifies UnApply restores correctly)
+        App.Tap("GoToDisabledButton");
+        stateLabel = App.FindElement("StateLabel").GetText();
+        Assert.That(stateLabel, Is.EqualTo("State: Normal"));
+
+        // Normal → Disabled again (verifies second cycle works)
+        App.Tap("GoToDisabledButton");
+        stateLabel = App.FindElement("StateLabel").GetText();
+        Assert.That(stateLabel, Is.EqualTo("State: Disabled"));
+    }
+}