Added minimal Avalonia sample

src/Avalonia.Markup.Declarative.sln

@@ -9,6 +9,8 @@ Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "Avalonia.Markup.Declarative
 EndProject
 Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "AvaloniaExtensionGenerator", "AvaloniaExtensionGenerator\AvaloniaExtensionGenerator.csproj", "{5183B326-2752-4CA5-A233-D9F5B83324DF}"
 EndProject
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "AvaloniaMarkupSample", "Samples\AvaloniaMarkupSample\AvaloniaMarkupSample.csproj", "{612D87E7-CF30-4E08-A7C3-AF4482924EBC}"
+EndProject
 Global
 	GlobalSection(SolutionConfigurationPlatforms) = preSolution
 		Debug|Any CPU = Debug|Any CPU
@@ -27,6 +29,10 @@ Global
 		{5183B326-2752-4CA5-A233-D9F5B83324DF}.Debug|Any CPU.Build.0 = Debug|Any CPU
 		{5183B326-2752-4CA5-A233-D9F5B83324DF}.Release|Any CPU.ActiveCfg = Release|Any CPU
 		{5183B326-2752-4CA5-A233-D9F5B83324DF}.Release|Any CPU.Build.0 = Release|Any CPU
+		{612D87E7-CF30-4E08-A7C3-AF4482924EBC}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{612D87E7-CF30-4E08-A7C3-AF4482924EBC}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{612D87E7-CF30-4E08-A7C3-AF4482924EBC}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{612D87E7-CF30-4E08-A7C3-AF4482924EBC}.Release|Any CPU.Build.0 = Release|Any CPU
 	EndGlobalSection
 	GlobalSection(SolutionProperties) = preSolution
 		HideSolutionNode = FALSE

src/Avalonia.Markup.Declarative/ControlExtensions.cs

@@ -69,7 +69,7 @@ public static partial class ControlExtensions
         BindingMode? bindingMode = null,
         IValueConverter converter = null,
         [CallerArgumentExpression("value")] string ps = null)
-        where TElement : StyledElement
+        where TElement : StyledElement where TDataContext : class
     {
         dataContext = value;
         return control._setEx(StyledElement.DataContextProperty, ps, () => control.DataContext = value, bindingMode, converter, null);

src/Samples/AvaloniaMarkupSample/App.cs

@@ -0,0 +1,26 @@
+AppBuilder.Configure<Application>()
+    .UsePlatformDetect()
+    .UseFluentTheme()
+    .StartWithClassicDesktopLifetime(desktop =>
+    {
+        var count = 0;
+
+        desktop.MainWindow = 
+            new Window().Ref(out var wnd).Content(
+
+                new StackPanel().Children(
+                    new Button().Ref(out var button)
+                        .Content("Welcome to Avalonia, please click me!"),
+
+                    new TextBox().Ref(out var tb1)
+                        .Text("Minimal Declarative Avalonia"),
+
+                    new TextBox()
+                        .Text(@wnd.Title, BindingMode.TwoWay, bindingSource: wnd),
+
+                    new Label().Content(
+                        button.OnClick().Select(_ => count++).Select(x => $"You clicked {x} times.").ToBinding())
+                ))
+            .Title(tb1.GetObservable(TextBox.TextProperty).Select(x => x.ToUpper()).ToBinding());
+    }, args);
+

src/Samples/AvaloniaMarkupSample/AppBuilderMinimalExtensions.cs

@@ -0,0 +1,24 @@
+public static class AppBuilderMinimalExtensions
+{
+    public static TAppBuilder UseFluentTheme<TAppBuilder>(this TAppBuilder builder, FluentThemeMode mode = FluentThemeMode.Light)
+        where TAppBuilder : AppBuilderBase<TAppBuilder>, new()
+    {
+        return builder.AfterSetup(_ =>
+            builder.Instance.Styles.Add(new FluentTheme(new Uri($"avares://{System.Reflection.Assembly.GetExecutingAssembly().GetName()}")) { Mode = mode }));
+    }
+
+    public static int StartWithClassicDesktopLifetime<T>(this T builder, Action<IClassicDesktopStyleApplicationLifetime> callback, string[]? args, ShutdownMode shutdownMode = ShutdownMode.OnLastWindowClose) where T : AppBuilderBase<T>, new()
+    {
+        var classicDesktopStyleApplicationLifetime = new ClassicDesktopStyleApplicationLifetime
+        {
+            Args = args,
+            ShutdownMode = shutdownMode
+        };
+
+        builder.SetupWithLifetime(classicDesktopStyleApplicationLifetime);
+
+        callback?.Invoke(classicDesktopStyleApplicationLifetime);
+
+        return classicDesktopStyleApplicationLifetime.Start(args);
+    }
+}

src/Samples/AvaloniaMarkupSample/AvaloniaMarkupSample.csproj

@@ -0,0 +1,30 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <OutputType>WinExe</OutputType>
+    <TargetFramework>net6.0</TargetFramework>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="Avalonia.Desktop" Version="0.10.11" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="..\..\Avalonia.Markup.Declarative\Avalonia.Markup.Declarative.csproj" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <Using Include="System" />
+    <Using Include="System.Reactive.Linq" />
+    <Using Include="Avalonia" />
+    <Using Include="Avalonia.Controls" />
+    <Using Include="Avalonia.Controls.ApplicationLifetimes" />
+    <Using Include="Avalonia.Data" />
+    <Using Include="Avalonia.Interactivity" />
+    <Using Include="Avalonia.Themes.Fluent" />
+    <Using Include="Avalonia.Markup.Declarative" />
+  </ItemGroup>
+
+</Project>

src/Samples/AvaloniaMarkupSample/EventsExtensions.cs

@@ -0,0 +1,7 @@
+public static class EventsExtensions
+{
+    public static IObservable<RoutedEventArgs> OnClick(this Button button)
+    {
+        return Observable.FromEventPattern<EventHandler<RoutedEventArgs>, RoutedEventArgs>(h => button.Click += h, h => button.Click -= h).Select(x => x.EventArgs);
+    }
+}