.BindCommand(): Search Base Types of Microsoft.Maui.* Classes for CommandProperty and CommandParameterProperty (#83)

* Update `DefaultBindableProperty.Get*` logic

* Update DefaultBindablePropertiesTests.cs

* Update DefaultBindablePropertiesTests.cs

Author: TheCodeTraveler

src/CommunityToolkit.Maui.Markup.UnitTests/DefaultBindablePropertiesTests.cs

@@ -16,213 +16,77 @@ namespace CommunityToolkit.Maui.Markup.UnitTests
 	[TestFixture]
 	class DefaultBindablePropertiesTests : BaseMarkupTestFixture
 	{
-		[Test]
-		public void AllBindableElementsInCoreHaveDefaultBindablePropertyOrAreExcluded()
-		{
-			const string na = "not applicable", tbd = "to be determined";
-			IReadOnlyDictionary<Type, string> excludedTypeReasons = new Dictionary<Type, string>
-			{ // Key: type, Value: reason why it does not have a default bindable property
-				{ typeof(Application), na },
-				{ typeof(AdaptiveTrigger), na },
-				{ typeof(BaseMenuItem), na },
-				{ typeof(BaseShellItem), na },
-				{ typeof(Behavior), na },
-				{ typeof(BindableObject), na },
-				{ typeof(CarouselView), na },
-				{ typeof(Cell), na },
-				{ typeof(ColumnDefinition), na },
-				{ typeof(CompareStateTrigger), na },
-				{ typeof(DataTrigger), na },
-				{ typeof(DeviceStateTrigger), na },
-				{ typeof(DragGestureRecognizer), na },
-				{ typeof(DropGestureRecognizer), na },
-				{ typeof(Element), na },
-				{ typeof(EventTrigger), na },
-				{ typeof(FontImageSource), na },
-				{ typeof(FormattedString), na },
-				{ typeof(GestureElement), na },
-				{ typeof(GestureRecognizer), na },
-				{ typeof(GradientStop), na },
-				{ typeof(GridItemsLayout), na },
-				{ typeof(GroupableItemsView), na },
-				{ typeof(HorizontalStackLayout), na },
-				{ typeof(ImageSource), na },
-				{ typeof(InputView), na },
-				{ typeof(ItemsLayout), na },
-				{ typeof(LinearItemsLayout), na },
-				{ typeof(LinearGradientBrush), na },
-				{ typeof(MenuBar), na },
-				{ typeof(MultiTrigger), na },
-				{ typeof(NavigableElement), na },
-				{ typeof(OpenGLView), na },
-				{ typeof(OrientationStateTrigger), na },
-				{ typeof(PanGestureRecognizer), na },
-				{ typeof(PinchGestureRecognizer), na },
-				{ typeof(RadialGradientBrush), na },
-				{ typeof(RoundRectangleGeometry), na },
-				{ typeof(RowDefinition), na },
-				{ typeof(SelectableItemsView), na },
-				{ typeof(StateTrigger), na },
-				{ typeof(StateTriggerBase), na },
-				{ typeof(StructuredItemsView), na },
-				{ typeof(SwipeItems), na },
-				{ typeof(TableRoot), na },
-				{ typeof(TableSection), na },
-				{ typeof(TableView), na },
-				{ typeof(Trigger), na },
-				{ typeof(TriggerBase), na },
-				{ typeof(VerticalStackLayout), na },
-				{ typeof(View), na },
-				{ typeof(ViewCell), na },
-				{ typeof(VisualElement), na },
-				{ typeof(WebViewSource), na },
-				{ typeof(Microsoft.Maui.Controls.Compatibility.AbsoluteLayout), na },
-				{ typeof(Microsoft.Maui.Controls.Compatibility.FlexLayout), na },
-				{ typeof(Microsoft.Maui.Controls.Compatibility.Grid), na },
-				{ typeof(Microsoft.Maui.Controls.Compatibility.RelativeLayout), na },
-				{ typeof(Microsoft.Maui.Controls.Compatibility.StackLayout), na },
-				{ typeof(AppLinkEntry), tbd },
-				{ typeof(FlyoutItem), tbd },
-				{ typeof(Shell), tbd },
-				{ typeof(ShellContent), tbd },
-				{ typeof(ShellGroupItem), tbd },
-				{ typeof(ShellItem), tbd },
-				{ typeof(ShellSection), tbd },
-				{ typeof(Tab), tbd },
-				{ typeof(TabBar), tbd },
-				{ typeof(ArcSegment), tbd },
-				{ typeof(BezierSegment), tbd },
-				{ typeof(CompositeTransform), tbd },
-				{ typeof(EllipseGeometry), tbd },
-				{ typeof(Geometry), tbd },
-				{ typeof(GeometryGroup), tbd },
-				{ typeof(LineGeometry), tbd },
-				{ typeof(LineSegment), tbd },
-				{ typeof(MatrixTransform), tbd },
-				{ typeof(Path), tbd },
-				{ typeof(PathFigure), tbd },
-				{ typeof(PathGeometry), tbd },
-				{ typeof(PathSegment), tbd },
-				{ typeof(PolyBezierSegment), tbd },
-				{ typeof(PolyLineSegment), tbd },
-				{ typeof(PolyQuadraticBezierSegment), tbd },
-				{ typeof(QuadraticBezierSegment), tbd },
-				{ typeof(RectangleGeometry), tbd },
-				{ typeof(RotateTransform), tbd },
-				{ typeof(ScaleTransform), tbd },
-				{ typeof(SkewTransform), tbd },
-				{ typeof(Shape), tbd },
-				{ typeof(Transform), tbd },
-				{ typeof(TransformGroup), tbd },
-				{ typeof(TranslateTransform), tbd },
-				{ typeof(Ellipse), tbd },
-				{ typeof(Line), tbd },
-				{ typeof(Polygon), tbd },
-				{ typeof(Polyline), tbd },
-				{ typeof(Rectangle), tbd },
-				{ typeof(ScrollView), tbd },
-				{ typeof(RoundRectangle), tbd },
-			};
-
-			var failMessage = new StringBuilder();
-			var bindableObjectTypes = typeof(BindableObject).Assembly.GetExportedTypes()
-				.Where(t => typeof(BindableObject).IsAssignableFrom(t) && !t.IsAbstract && !typeof(Layout).IsAssignableFrom(t) && !t.ContainsGenericParameters);
-
-			// The logical default property for a Layout is for its child view(s), which is not a bindable property.
-			// So we exclude Layouts from this test. Note that it is still perfectly OK to define a default
-			// bindable property for a Layout where that makes sense.
-			// We also do not support specifying default properties for unconstructed generic types.
-
-			foreach (var type in bindableObjectTypes)
-			{
-				if (excludedTypeReasons.TryGetValue(type, out var exclusionReason))
-				{
-					Console.WriteLine($"Info: no default BindableProperty defined for BindableObject type {type.FullName} because {exclusionReason}");
-					continue;
-				}
-
-				if (DefaultBindableProperties.GetFor(type) is null)
-				{
-					failMessage.AppendLine(type.FullName);
-					var propertyNames = type.GetFields(BindingFlags.Public | BindingFlags.Static | BindingFlags.DeclaredOnly)
-										.Where(f => f.FieldType == typeof(BindableProperty)).Select(f => f?.DeclaringType?.Name + "." + f?.Name).ToList();
-
-					if (propertyNames.Count > 0)
-					{
-						failMessage.AppendLine("\tCandidate properties:");
-						foreach (var propertyName in propertyNames)
-						{
-							failMessage.Append('\t').AppendLine(propertyName);
-						}
-					}
-				}
-			}
-
-			if (failMessage.Length > 0)
-			{
-				Assert.Fail(
-					$"Missing default BindableProperty / exclusion for BindableObject types:\n{failMessage}\n" +
-					$"Either register these types in {typeof(DefaultBindableProperties).FullName} or exclude them in this test");
-			}
-		}
-
 		[Test]
 		public void GetDefaultBindablePropertyForBuiltInType()
-			=> Assert.That(DefaultBindableProperties.GetFor(new Label()), Is.Not.Null);
+			=> Assert.That(DefaultBindableProperties.GetDefaultProperty<Label>(), Is.Not.Null);
 
 		[Test]
 		public void GetDefaultBindablePropertyForDerivedType()
-			=> Assert.That(DefaultBindableProperties.GetFor(new DerivedFromBoxView()), Is.Not.Null);
+			=> Assert.That(DefaultBindableProperties.GetDefaultProperty<DerivedFromBoxView>(), Is.Not.Null);
 
 		[Test]
 		public void GetDefaultBindablePropertyForUnsupportedType()
 			=> Assert.Throws<ArgumentException>(
-				() => DefaultBindableProperties.GetFor(new CustomView()),
+				() => DefaultBindableProperties.GetDefaultProperty<CustomView>(),
 				"No default bindable property is registered for BindableObject type XamarinFormsMarkupUnitTestsDefaultBindablePropertiesViews.CustomView" +
 				"\r\nEither specify a property when calling Bind() or register a default bindable property for this BindableObject type");
 
 		[Test]
 		public void RegisterDefaultBindableProperty()
 		{
-			var v = new CustomViewWithText();
-			Assert.Throws<ArgumentException>(() => DefaultBindableProperties.GetFor(v));
+			Assert.Throws<ArgumentException>(() => DefaultBindableProperties.GetDefaultProperty<CustomViewWithText>());
 
 			DefaultBindableProperties.Register(CustomViewWithText.TextProperty);
 		}
 
+		[Test]
+		public void GetDefaultBindablePropertiesForBuiltInType()
+			=> Assert.That(DefaultBindableProperties.GetDefaultProperty<Button>(), Is.Not.Null);
+
+		[Test]
+		public void GetDefaultBindablePropertiesForDerivedType()
+			=> Assert.That(DefaultBindableProperties.GetDefaultProperty<DerivedFromButton>(), Is.Not.Null);
+
+		[Test]
+		public void GetDefaultBindablePropertiesForMauiDerivedType()
+			=> Assert.That(DefaultBindableProperties.GetDefaultProperty<MenuFlyoutItem>(), Is.Not.Null);
+
 		[Test]
 		public void GetDefaultBindableCommandPropertiesForBuiltInType()
-			=> Assert.That(DefaultBindableProperties.GetForCommand(new Button()), Is.Not.Null);
+			=> Assert.That(DefaultBindableProperties.GetCommandAndCommandParameterProperty<Button>(), Is.Not.Null);
 
 		[Test]
 		public void GetDefaultBindableCommandPropertiesForDerivedType()
-			=> Assert.That(DefaultBindableProperties.GetFor(new DerivedFromButton()), Is.Not.Null);
+			=> Assert.That(DefaultBindableProperties.GetCommandAndCommandParameterProperty<DerivedFromButton>(), Is.Not.Null);
+
+		[Test]
+		public void GetDefaultBindableCommandPropertiesForMauiDerivedType()
+			=> Assert.That(DefaultBindableProperties.GetCommandAndCommandParameterProperty<MenuFlyoutItem>(), Is.Not.Null);
 
 		[Test]
 		public void GetDefaultBindableCommandPropertiesForUnsupportedType()
 			=> Assert.Throws<ArgumentException>(
-				() => DefaultBindableProperties.GetFor(new CustomView()),
+				() => DefaultBindableProperties.GetDefaultProperty<CustomView>(),
 				"No command + command parameter properties are registered for BindableObject type XamarinFormsMarkupUnitTestsDefaultBindablePropertiesViews.CustomView" +
 				"\r\nRegister command + command parameter properties for this BindableObject type");
 
 		[Test]
 		public void RegisterDefaultBindableCommandProperties()
 		{
-			var v = new CustomViewWithCommand();
-			Assert.Throws<ArgumentException>(() => DefaultBindableProperties.GetForCommand(v));
+			Assert.Throws<ArgumentException>(() => DefaultBindableProperties.GetCommandAndCommandParameterProperty<CustomViewWithCommand>());
 
 			DefaultBindableProperties.RegisterForCommand((CustomViewWithCommand.CommandProperty, CustomViewWithCommand.CommandParameterProperty));
 		}
 
 		[TearDown]
 		public override void TearDown()
 		{
-			if (DefaultBindableProperties.GetFor(typeof(CustomViewWithText)) != null)
+			if (DefaultBindableProperties.TryGetDefaultProperty<CustomViewWithText>(out _))
 			{
 				DefaultBindableProperties.Unregister(CustomViewWithText.TextProperty);
 			}
 
-			if (DefaultBindableProperties.GetForCommand(typeof(CustomViewWithCommand)) != (null, null))
+			if (DefaultBindableProperties.TryGetCommandAndCommandParameterProperty<CustomViewWithCommand>(out _, out _))
 			{
 				DefaultBindableProperties.UnregisterForCommand(CustomViewWithCommand.CommandProperty);
 			}

src/CommunityToolkit.Maui.Markup/BindableObjectExtensions.cs

@@ -92,7 +92,7 @@ public static TBindable Bind<TBindable>(
 		object? fallbackValue = null) where TBindable : BindableObject
 	{
 		bindable.Bind(
-			DefaultBindableProperties.GetFor(bindable),
+			DefaultBindableProperties.GetDefaultProperty<TBindable>(),
 			path, mode, converter, converterParameter, stringFormat, source, targetNullValue, fallbackValue);
 
 		return bindable;
@@ -112,7 +112,7 @@ public static TBindable Bind<TBindable, TSource, TDest>(
 	{
 		var converter = new FuncConverter<TSource, TDest, object>(convert, convertBack);
 		bindable.Bind(
-			DefaultBindableProperties.GetFor(bindable),
+			DefaultBindableProperties.GetDefaultProperty<TBindable>(),
 			path, mode, converter, null, stringFormat, source, targetNullValue, fallbackValue);
 
 		return bindable;
@@ -133,7 +133,7 @@ public static TBindable Bind<TBindable, TSource, TParam, TDest>(
 	{
 		var converter = new FuncConverter<TSource, TDest, TParam>(convert, convertBack);
 		bindable.Bind(
-			DefaultBindableProperties.GetFor(bindable),
+			DefaultBindableProperties.GetDefaultProperty<TBindable>(),
 			path, mode, converter, converterParameter, stringFormat, source, targetNullValue, fallbackValue);
 
 		return bindable;
@@ -152,7 +152,7 @@ public static TBindable BindCommand<TBindable>(
 		string? parameterPath = bindingContextPath,
 		object? parameterSource = null) where TBindable : BindableObject
 	{
-		(var commandProperty, var parameterProperty) = DefaultBindableProperties.GetForCommand(bindable);
+		(var commandProperty, var parameterProperty) = DefaultBindableProperties.GetCommandAndCommandParameterProperty<TBindable>();
 
 		bindable.SetBinding(commandProperty, new Binding(path: path, source: source));
 

src/CommunityToolkit.Maui.Markup/DefaultBindableProperties.cs

@@ -1,4 +1,5 @@
-using System.Reflection;
+using System.Diagnostics.CodeAnalysis;
+using System.Reflection;
 
 namespace CommunityToolkit.Maui.Markup;
 
@@ -133,43 +134,36 @@ internal static void Unregister(BindableProperty property)
 		bindableObjectTypeDefaultProperty.Remove(property.DeclaringType.FullName);
 	}
 
-	internal static BindableProperty GetFor(BindableObject bindableObject)
+	internal static BindableProperty GetDefaultProperty<T>() where T : BindableObject
 	{
-		var type = bindableObject.GetType();
-		var defaultProperty = GetFor(type);
-
-		if (defaultProperty is null)
+		if (!TryGetDefaultProperty<T>(out var defaultProperty))
 		{
 			throw new ArgumentException(
-				"No default bindable property is registered for BindableObject type " + type.FullName +
+				"No default bindable property is registered for BindableObject type " + typeof(T).FullName +
 				"\r\nEither specify a property when calling Bind() or register a default bindable property for this BindableObject type");
 		}
 
 		return defaultProperty;
 	}
 
-	internal static BindableProperty? GetFor(Type? bindableObjectType)
+	internal static bool TryGetDefaultProperty<T>([NotNullWhen(true)] out BindableProperty? defaultBindableProperty) where T : BindableObject
 	{
-		BindableProperty? defaultProperty = null;
+		defaultBindableProperty = null;
+		var bindableObjectType = typeof(T);
 
 		do
 		{
 			var bindableObjectTypeName = bindableObjectType?.FullName;
-			if (bindableObjectTypeName is not null && bindableObjectTypeDefaultProperty.TryGetValue(bindableObjectTypeName, out defaultProperty))
-			{
-				break;
-			}
-
-			if (bindableObjectTypeName?.StartsWith($"{nameof(Microsoft)}.{nameof(Microsoft.Maui)}.", StringComparison.Ordinal) is true)
+			if (bindableObjectTypeName is not null && bindableObjectTypeDefaultProperty.TryGetValue(bindableObjectTypeName, out defaultBindableProperty))
 			{
-				break;
+				return true;
 			}
 
 			bindableObjectType = bindableObjectType?.GetTypeInfo().BaseType;
 		}
-		while (bindableObjectType != null);
+		while (bindableObjectType is not null && bindableObjectType.GetType() != typeof(BindableObject));
 
-		return defaultProperty;
+		return false;
 	}
 
 	internal static void UnregisterForCommand(BindableProperty commandProperty)
@@ -182,43 +176,38 @@ internal static void UnregisterForCommand(BindableProperty commandProperty)
 		bindableObjectTypeDefaultCommandAndParameterProperties.Remove(commandProperty.DeclaringType.FullName);
 	}
 
-	internal static (BindableProperty, BindableProperty) GetForCommand(BindableObject bindableObject)
+	internal static (BindableProperty CommandProperty, BindableProperty CommandParameterProperty) GetCommandAndCommandParameterProperty<T>() where T : BindableObject
 	{
-		var type = bindableObject.GetType();
-		(var commandProperty, var parameterProperty) = GetForCommand(type);
-		if (commandProperty is null || parameterProperty is null)
+		if (!TryGetCommandAndCommandParameterProperty<T>(out var commandProperty, out var parameterProperty))
 		{
 			throw new ArgumentException(
-				"No command + command parameter properties are registered for BindableObject type " + type.FullName +
+				"No command + command parameter properties are registered for BindableObject type " + typeof(T).FullName +
 				"\r\nRegister command + command parameter properties for this BindableObject type");
 		}
 
 		return (commandProperty, parameterProperty);
 	}
 
-	internal static (BindableProperty?, BindableProperty?) GetForCommand(Type? bindableObjectType)
+	internal static bool TryGetCommandAndCommandParameterProperty<T>([NotNullWhen(true)] out BindableProperty? commandProperty, [NotNullWhen(true)] out BindableProperty? commandParameterProperty) where T : BindableObject
 	{
-		(BindableProperty?, BindableProperty?) commandAndParameterProperties = (null, null);
+		commandProperty = commandParameterProperty = null;
+		var bindableObjectType = typeof(T);
 
 		do
 		{
-			var bindableObjectTypeName = bindableObjectType?.FullName;
+			var bindableObjectTypeName = bindableObjectType.FullName;
 			if (bindableObjectTypeName is not null && bindableObjectTypeDefaultCommandAndParameterProperties.TryGetValue(bindableObjectTypeName, out var dictionaryResult))
 			{
-				commandAndParameterProperties.Item1 = dictionaryResult.Item1;
-				commandAndParameterProperties.Item2 = dictionaryResult.Item2;
-				break;
-			}
+				commandProperty = dictionaryResult.Item1;
+				commandParameterProperty = dictionaryResult.Item2;
 
-			if (bindableObjectTypeName?.StartsWith($"{nameof(Microsoft)}.{nameof(Microsoft.Maui)}.", StringComparison.Ordinal) is true)
-			{
-				break;
+				return true;
 			}
 
 			bindableObjectType = bindableObjectType?.GetTypeInfo().BaseType;
 		}
-		while (bindableObjectType != null);
+		while (bindableObjectType is not null && bindableObjectType.GetType() != typeof(BindableObject));
 
-		return commandAndParameterProperties;
+		return false;
 	}
 }