fix: Handle nullable value types correctly in BindableTypeProvidersSo…

…urceGenerator

src/SourceGenerators/Uno.UI.SourceGenerators/BindableTypeProviders/BindableTypeProvidersGenerationTask.cs

@@ -376,12 +376,11 @@ where field.IsStatic
 								&& property.SetMethod.IsLocallyPublic(_currentModule!)
 								)
 							{
-								if (property.Type.IsValueType)
-								{
-									writer.AppendLineIndented($@"bindableType.AddProperty(""{propertyName}"", typeof({propertyTypeName}), Get{propertyName}, Set{propertyName});");
-
-									postWriter.AppendLineIndented($@"private static object Get{propertyName}(object instance, Microsoft.UI.Xaml.DependencyPropertyValuePrecedences? precedence) => (({ownerTypeName})instance).{propertyName};");
+								writer.AppendLineIndented($@"bindableType.AddProperty(""{propertyName}"", typeof({propertyTypeName}), Get{propertyName}, Set{propertyName});");
+								postWriter.AppendLineIndented($@"private static object Get{propertyName}(object instance, Microsoft.UI.Xaml.DependencyPropertyValuePrecedences? precedence) => (({ownerTypeName})instance).{propertyName};");
 
+								if (property.Type.IsValueType && property.Type.OriginalDefinition.SpecialType != SpecialType.System_Nullable_T)
+								{
 									using (postWriter.BlockInvariant($@"private static void Set{propertyName}(object instance, object value, Microsoft.UI.Xaml.DependencyPropertyValuePrecedences? precedence)"))
 									{
 										using (postWriter.BlockInvariant($"if(value != null)"))
@@ -392,9 +391,6 @@ where field.IsStatic
 								}
 								else
 								{
-									writer.AppendLineIndented($@"bindableType.AddProperty(""{propertyName}"", typeof({propertyTypeName}), Get{propertyName}, Set{propertyName});");
-
-									postWriter.AppendLineIndented($@"private static object Get{propertyName}(object instance,  Microsoft.UI.Xaml.DependencyPropertyValuePrecedences? precedence) => (({ownerTypeName})instance).{propertyName};");
 									postWriter.AppendLineIndented($@"private static void Set{propertyName}(object instance, object value, Microsoft.UI.Xaml.DependencyPropertyValuePrecedences? precedence) => (({ownerTypeName})instance).{propertyName} = ({propertyTypeName})value;");
 								}
 

src/Uno.UI.RuntimeTests/Tests/Windows_UI_Xaml_Data/BindableNullableValueTypeTestPage.xaml

@@ -0,0 +1,14 @@
+<Page
+    x:Class="Uno.UI.RuntimeTests.Tests.Windows_UI_Xaml_Data.BindableNullableValueTypeTestPage"
+    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.Windows_UI_Xaml_Data"
+    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
+    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
+    mc:Ignorable="d"
+    Background="{ThemeResource ApplicationPageBackgroundThemeBrush}">
+
+    <Grid>
+		<TextBlock Tag="{Binding MyProperty, Mode=TwoWay}" x:FieldModifier="public" x:Name="textBlock" />
+	</Grid>
+</Page>

src/Uno.UI.RuntimeTests/Tests/Windows_UI_Xaml_Data/BindableNullableValueTypeTestPage.xaml.cs

@@ -0,0 +1,33 @@
+#nullable enable
+
+using System.ComponentModel;
+using Microsoft.UI.Xaml.Controls;
+
+namespace Uno.UI.RuntimeTests.Tests.Windows_UI_Xaml_Data;
+
+[Bindable(true)]
+public sealed partial class BindableNullableValueTypeTestPage : Page, INotifyPropertyChanged
+{
+	private int? _myProperty;
+
+	public BindableNullableValueTypeTestPage()
+	{
+		this.InitializeComponent();
+		this.DataContext = this;
+	}
+
+	public event PropertyChangedEventHandler? PropertyChanged;
+
+	public int? MyProperty
+	{
+		get => _myProperty;
+		set
+		{
+			if (_myProperty != value)
+			{
+				_myProperty = value;
+				PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(nameof(MyProperty)));
+			}
+		}
+	}
+}

src/Uno.UI.RuntimeTests/Tests/Windows_UI_Xaml_Data/Given_BindableNullableValueType.cs

@@ -0,0 +1,23 @@
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+using System;
+using System.Collections.Generic;
+using System.ComponentModel;
+using System.Text;
+
+namespace Uno.UI.RuntimeTests.Tests.Windows_UI_Xaml_Data;
+
+[TestClass]
+public class Given_BindableNullableValueType
+{
+	[TestMethod]
+	[RunsOnUIThread]
+	public void When_BindableNullableValueTypeTestPage()
+	{
+		var x = new BindableNullableValueTypeTestPage();
+		var tb = x.textBlock;
+		tb.Tag = "10";
+		Assert.AreEqual(10, x.MyProperty);
+		tb.Tag = null;
+		Assert.AreEqual(null, x.MyProperty);
+	}
+}