feat(xamlreader): Update Setter.Value when theme changes

src/Uno.UI.Tests/Windows_UI_Xaml_Markup/XamlReaderTests/Given_XamlReader.cs

@@ -832,6 +832,52 @@ public void When_StaticResource_And_NonDependencyProperty()
 
 		}
 
+		[TestMethod]
+		public void When_ThemeResource_And_Setter_And_Theme_Changed()
+		{
+			var app = UnitTestsApp.App.EnsureApplication();
+			var themeDict = new ResourceDictionary
+			{
+				ThemeDictionaries =
+				{
+					{"Light", new ResourceDictionary
+						{
+							{"MyIntResourceThemed", 244 }
+						}
+					},
+					{"Dark", new ResourceDictionary
+						{
+							{"MyIntResourceThemed", 9 }
+						}
+					},
+				}
+			};
+			app.Resources.MergedDictionaries.Add(themeDict);
+			try
+			{
+				var s = GetContent(nameof(When_ThemeResource_And_Setter_And_Theme_Changed));
+				var r = Windows.UI.Xaml.Markup.XamlReader.Load(s) as Page;
+
+				var root = r.FindName("root") as Grid;
+				var inner = root.Children.First() as Button;
+
+				app.HostView.Children.Add(r);
+
+				Assert.AreEqual(ApplicationTheme.Light, app.RequestedTheme);
+				Assert.AreEqual(244, inner.Tag);
+
+				app.SetExplicitRequestedTheme(ApplicationTheme.Dark);
+				Assert.AreEqual(ApplicationTheme.Dark, app.RequestedTheme);
+				Assert.AreEqual(9, inner.Tag);
+			}
+			finally
+			{
+				app.SetExplicitRequestedTheme(null);
+				app.Resources.MergedDictionaries.Remove(themeDict);
+			}
+
+		}
+
 		private string GetContent(string testName)
 		{
 			var assembly = this.GetType().Assembly;

src/Uno.UI.Tests/Windows_UI_Xaml_Markup/XamlReaderTests/When_ThemeResource_And_Setter_And_Theme_Changed.xamltest

@@ -0,0 +1,17 @@
+<Page xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
+      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:controls="Uno.UI.Tests.Windows_UI_Xaml_Markup.XamlReaderTests"
+      mc:Ignorable="d">
+  <Page.Resources>
+    <Style TargetType="Button">
+      <Setter Property="Tag"
+              Value="{ThemeResource MyIntResourceThemed}" />
+    </Style>
+  </Page.Resources>
+
+  <Grid x:Name="root">
+    <Button Content="Dummy"/>
+  </Grid>
+</Page>

src/Uno.UI/UI/Xaml/Markup/Reader/XamlObjectBuilder.cs

@@ -7,6 +7,7 @@
 using System.Text.RegularExpressions;
 using Uno.Extensions;
 using Uno.UI;
+using Uno.UI.Helpers.Xaml;
 using Uno.UI.Xaml;
 using Uno.Xaml;
 using Windows.UI.Xaml.Controls;
@@ -494,9 +495,20 @@ private void ProcessStaticResourceMarkupNode(object instance, XamlMemberDefiniti
 				else if (propertyInfo != null)
 				{
 					GetPropertySetter(propertyInfo).Invoke(
-						instance,
-						new[] { ResourceResolver.ResolveResourceStatic(keyName, propertyInfo.PropertyType) }
-					);
+								instance,
+								new[] { ResourceResolver.ResolveResourceStatic(keyName, propertyInfo.PropertyType) }
+							);
+
+					if (instance is Setter setter && propertyInfo.Name == "Value")
+					{
+						// Register StaticResource/ThemeResource assignations to Value for resource updates
+						setter.ApplyThemeResourceUpdateValues(
+							keyName,
+							null,
+							IsThemeResourceMarkupNode(member),
+							true
+						);
+					}
 				}
 			}
 		}