[XamlC] Compile x:Reference

[simonrozsival]

The x:Reference markup extension is used to point to another element in the XAML tree which has a corresponding x:Name. To lookup an reference, we use ReferenceExtension which looks up the referenced object in the available namescopes.

When the XAML is compiled, we should be able to reference the local variable corresponding to the XAML element with x:Name directly.

Example

XAML

<?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="MyMauiApp.MainPage">
    <Label Text="Foo" x:Name="foo" />
    <Label Text="{Binding Text, Source={x:Reference foo}}" />
</ContentPage>

Generated code (decompiled)

 [XamlFilePath("MainPage.xaml")]
 public class MainPage : ContentPage
 {
     [GeneratedCode("Microsoft.Maui.Controls.SourceGen", "1.0.0.0")]
     private Label foo;

     public MainPage()
     {
         InitializeComponent();
     }

     [GeneratedCode("Microsoft.Maui.Controls.SourceGen", "1.0.0.0")]
     [MemberNotNull("foo")]
     private void InitializeComponent()
     {
         Label label = new Label();
-        ReferenceExtension referenceExtension = new ReferenceExtension();
         BindingExtension bindingExtension = new BindingExtension();
         Label label2 = new Label();
         MainPage mainPage;
         NameScope nameScope = (NameScope)(NameScope.GetNameScope(mainPage = this) ?? new NameScope());
         NameScope.SetNameScope(mainPage, nameScope);
         ((INameScope)nameScope).RegisterName("foo", (object)label);
         if (label.StyleId == null)
         {
             label.StyleId = "foo";
         }
         foo = label;
         label.SetValue(Label.TextProperty, "Foo");
         mainPage.SetValue(ContentPage.ContentProperty, label);
-        referenceExtension.Name = "foo";
-        XamlServiceProvider xamlServiceProvider = new XamlServiceProvider();
-        Type typeFromHandle = typeof(IProvideValueTarget);
-        object[] array = new object[0 + 3];
-        array[0] = bindingExtension;
-        array[1] = label2;
-        array[2] = mainPage;
-        object obj;
-        xamlServiceProvider.Add(typeFromHandle, obj = new SimpleValueTargetProvider(array, typeof(BindingExtension).GetRuntimeProperty("Source"), new NameScope[4] { nameScope, nameScope, nameScope, nameScope }, false));
-        xamlServiceProvider.Add(typeof(IReferenceProvider), obj);
-        object source = ((IMarkupExtension)referenceExtension).ProvideValue((IServiceProvider)xamlServiceProvider);
-        bindingExtension.Source = source;
+        bindingExtension.Source = foo;
         bindingExtension.Path = "Text";
         BindingBase binding = ((IMarkupExtension<BindingBase>)bindingExtension).ProvideValue((IServiceProvider)null);
         label2.SetBinding(Label.TextProperty, binding);
         mainPage.SetValue(ContentPage.ContentProperty, label2);
     }
 }

Motivation

• Less IL code needed to express each reference
• Faster reference lookup at runtime
• We could compile {Binding Text, Source={x:Reference label}} extensions which have a Source with a type known at build time without a need to specify x:DataType explicitly.

[simonrozsival]

/cc @StephaneDelcroix

[ghost]

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