IContainer as IList<IView> (#1724)

* IContainer proposal

* Update the test classes to match the updated interfaces

* Make substitution work for new layout interface

* Fix Windows

* Implement methods on stub I missed

* And another thing I forgot to implement

* Remove commented code

* Make IContainer implementation explicit

* Fix child collection access in test

src/Controls/src/Core/HandlerImpl/Layout.Impl.cs

@@ -0,0 +1,76 @@
+using System;
+using System.Collections;
+using System.Collections.Generic;
+using System.Text;
+
+namespace Microsoft.Maui.Controls
+{
+	public abstract partial class Layout<T> 
+	{
+		int ICollection<IView>.Count => _children.Count;
+		bool ICollection<IView>.IsReadOnly => ((ICollection<IView>) _children).IsReadOnly;
+		public IView this[int index] { get => _children[index]; set => _children[index] = (T)value; }
+
+		void ICollection<IView>.Add(IView child)
+		{
+			if (child is T view)
+			{
+				_children.Add(view);
+			}
+		}
+
+		bool ICollection<IView>.Remove(IView child)
+		{
+			if (child is T view)
+			{
+				_children.Remove(view);
+				return true;
+			}
+
+			return false;
+		}
+
+		int IList<IView>.IndexOf(IView child)
+		{
+			return _children.IndexOf(child);
+		}
+
+		void IList<IView>.Insert(int index, IView child)
+		{
+			if (child is T view)
+			{
+				_children.Insert(index, view);
+			}
+		}
+
+		void IList<IView>.RemoveAt(int index)
+		{
+			_children.RemoveAt(index);
+		}
+
+		void ICollection<IView>.Clear()
+		{
+			_children.Clear();
+		}
+
+		bool ICollection<IView>.Contains(IView child)
+		{
+			return _children.Contains(child);
+		}
+
+		void ICollection<IView>.CopyTo(IView[] array, int arrayIndex)
+		{
+			_children.CopyTo(array, arrayIndex);
+		}
+
+		IEnumerator<IView> IEnumerable<IView>.GetEnumerator()
+		{
+			return _children.GetEnumerator();
+		}
+
+		IEnumerator IEnumerable.GetEnumerator()
+		{
+			return _children.GetEnumerator();
+		}
+	}
+}

src/Controls/src/Core/Layout.cs

@@ -1,4 +1,5 @@
 using System;
+using System.Collections;
 using System.Collections.Generic;
 using System.Collections.ObjectModel;
 using System.Collections.Specialized;
@@ -10,11 +11,8 @@
 namespace Microsoft.Maui.Controls
 {
 	[ContentProperty(nameof(Children))]
-	public abstract class Layout<T> : Layout, Microsoft.Maui.ILayout, IViewContainer<T> where T : View
+	public abstract partial class Layout<T> : Layout, Microsoft.Maui.ILayout, IViewContainer<T> where T : View
 	{
-		// TODO ezhart We should look for a way to optimize this a bit
-		IReadOnlyList<Microsoft.Maui.IView> Microsoft.Maui.IContainer.Children => Children.ToList();
-
 		readonly ElementCollection<T> _children;
 
 		protected Layout() => _children = new ElementCollection<T>(InternalChildren);
@@ -46,28 +44,10 @@ protected virtual void OnAdded(T view)
 		protected virtual void OnRemoved(T view)
 		{
 		}
-
-		public void Add(IView child)
-		{
-			if (child is T view)
-			{
-				Children.Add(view);
-			}
-		}
-
-		public void Remove(IView child)
-		{
-			if (child is T view)
-			{
-				Children.Remove(view);
-			}
-		}
 	}
 
-	public abstract class Layout : View, ILayout, ILayoutController, IPaddingElement, IFrameworkElement, Microsoft.Maui.IContainer
+	public abstract class Layout : View, ILayout, ILayoutController, IPaddingElement, IFrameworkElement
 	{
-		IReadOnlyList<Microsoft.Maui.IView> Microsoft.Maui.IContainer.Children => InternalChildren.OfType<IView>().ToList();
-
 		public static readonly BindableProperty IsClippedToBoundsProperty =
 			BindableProperty.Create(nameof(IsClippedToBounds), typeof(bool), typeof(Layout), false);
 

src/Controls/src/Core/Layout/GridLayout.cs

@@ -231,10 +231,10 @@ public override void Add(IView child)
 			}
 		}
 
-		public override void Remove(IView child)
+		public override bool Remove(IView child)
 		{
 			_viewInfo.Remove(child);
-			base.Remove(child);
+			return base.Remove(child);
 		}
 
 		protected override ILayoutManager CreateLayoutManager() => new GridLayoutManager(this);

src/Controls/src/Core/Layout/Layout.cs

@@ -25,11 +25,8 @@ public abstract class Layout : View, Microsoft.Maui.ILayout, IList<IView>, IPadd
 
 		public bool IsReadOnly => ((ICollection<IView>)_children).IsReadOnly;
 
-		IReadOnlyList<IView> IContainer.Children => _children.AsReadOnly();
-
 		public IView this[int index] { get => _children[index]; set => _children[index] = value; }
 
-
 		public Thickness Padding
 		{
 			get => (Thickness)GetValue(PaddingElement.PaddingProperty);
@@ -53,56 +50,44 @@ public override SizeRequest GetSizeRequest(double widthConstraint, double height
 		protected override Size MeasureOverride(double widthConstraint, double heightConstraint)
 		{
 			var margin = (this as IView)?.Margin ?? Thickness.Zero;
-
 			// Adjust the constraints to account for the margins
 			widthConstraint -= margin.HorizontalThickness;
 			heightConstraint -= margin.VerticalThickness;
-
 			var sizeWithoutMargins = LayoutManager.Measure(widthConstraint, heightConstraint);
 			DesiredSize = new Size(sizeWithoutMargins.Width + Margin.HorizontalThickness,
 				sizeWithoutMargins.Height + Margin.VerticalThickness);
-
 			return DesiredSize;
 		}
-
+		
 		protected override Size ArrangeOverride(Rectangle bounds)
 		{
 			base.ArrangeOverride(bounds);
-
 			Frame = bounds;
-
 			LayoutManager.ArrangeChildren(Frame);
-
 			foreach (var child in Children)
 			{
 				child.Handler?.NativeArrange(child.Frame);
 			}
-
 			return Frame.Size;
 		}
 
 		protected override void InvalidateMeasureOverride()
 		{
 			base.InvalidateMeasureOverride();
-
 			foreach (var child in Children)
 			{
 				child.InvalidateMeasure();
 			}
 		}
-
+		
 		public virtual void Add(IView child)
 		{
 			if (child == null)
 				return;
-
 			_children.Add(child);
-
 			if (child is Element element)
 				element.Parent = this;
-
 			InvalidateMeasure();
-
 			LayoutHandler?.Add(child);
 		}
 
@@ -144,19 +129,21 @@ public void Insert(int index, IView child)
 			LayoutHandler?.Add(child);
 		}
 
-		public virtual void Remove(IView child)
+		public virtual bool Remove(IView child)
 		{
 			if (child == null)
-				return;
+				return false;
 
-			_children.Remove(child);
+			var result = _children.Remove(child);
 
 			if (child is Element element)
 				element.Parent = null;
 
 			InvalidateMeasure();
 
 			LayoutHandler?.Remove(child);
+
+			return result;
 		}
 
 		public void RemoveAt(int index)
@@ -178,23 +165,6 @@ public void RemoveAt(int index)
 			LayoutHandler?.Remove(child);
 		}
 
-		bool ICollection<IView>.Remove(IView child)
-		{
-			if (child == null)
-				return false;
-
-			var result = _children.Remove(child);
-
-			if (child is Element element)
-				element.Parent = null;
-
-			InvalidateMeasure();
-
-			LayoutHandler?.Remove(child);
-
-			return result;
-		}
-
 		void IPaddingElement.OnPaddingPropertyChanged(Thickness oldValue, Thickness newValue)
 		{
 			InvalidateMeasure();

src/Controls/tests/Core.UnitTests/Layouts/LayoutCompatTests.cs

@@ -97,7 +97,7 @@ public void GridInsideStackLayout()
 			view.GetDesiredSize(default, default).ReturnsForAnyArgs(expectedSize);
 			label.Handler = view;
 
-			stackLayout.Add(grid);
+			stackLayout.Children.Add(grid);
 			grid.Children.Add(label);
 			contentPage.Content = stackLayout;
 

src/Core/src/Core/IContainer.cs

@@ -5,11 +5,8 @@ namespace Microsoft.Maui
 	/// <summary>
 	/// Provides functionality to act as containers for views. 
 	/// </summary>
-	public interface IContainer
+	public interface IContainer : IList<IView>
 	{
-		/// <summary>
-		/// Gets the collection of children that the Container contains.
-		/// </summary>
-		IReadOnlyList<IView> Children { get; }
+
 	}
 }

src/Core/src/Core/ILayout.cs

@@ -13,18 +13,6 @@ public interface ILayout : IView, IContainer
 		/// </summary>
 		ILayoutHandler LayoutHandler { get; }
 
-		/// <summary>
-		/// Add a child View to the Layout.
-		/// </summary>
-		/// <param name="child">The child View to add to the Layout.</param>
-		void Add(IView child);
-
-		/// <summary>
-		/// Remove a child View from the Layout.
-		/// </summary>
-		/// <param name="child">The child View to remove from the Layout.</param>
-		void Remove(IView child);
-
 		/// <summary>
 		/// The space between the outer edge of the ILayout's content area and its children.
 		/// </summary>

src/Core/src/Handlers/Layout/LayoutHandler.Android.cs

@@ -33,7 +33,7 @@ public override void SetVirtualView(IView view)
 			NativeView.CrossPlatformArrange = VirtualView.Arrange;
 
 			NativeView.RemoveAllViews();
-			foreach (var child in VirtualView.Children)
+			foreach (var child in VirtualView)
 			{
 				NativeView.AddView(child.ToNative(MauiContext));
 			}

src/Core/src/Handlers/Layout/LayoutHandler.Windows.cs

@@ -26,7 +26,7 @@ public override void SetVirtualView(IView view)
 			NativeView.CrossPlatformArrange = VirtualView.Arrange;
 
 			NativeView.Children.Clear();
-			foreach (var child in VirtualView.Children)
+			foreach (var child in VirtualView)
 			{
 				Add(child);
 			}

src/Core/src/Handlers/Layout/LayoutHandler.iOS.cs

@@ -40,7 +40,7 @@ public override void SetVirtualView(IView view)
 				child.RemoveFromSuperview();
 			}
 
-			foreach (var child in VirtualView.Children)
+			foreach (var child in VirtualView)
 			{
 				NativeView.AddSubview(child.ToNative(MauiContext));
 			}

src/Core/src/HotReload/HotReloadExtensions.cs

@@ -29,7 +29,7 @@ public static void CheckHandlers(this IView view)
 
 			if (view is IContainer layout)
 			{
-				foreach (var v in layout.Children)
+				foreach (var v in layout)
 					CheckHandlers(v);
 			}
 		}

src/Core/src/Layouts/FlexLayoutManager.cs

@@ -17,7 +17,7 @@ public void ArrangeChildren(Rectangle childBounds)
 		{
 			FlexLayout.Layout(childBounds.Width, childBounds.Height);
 
-			foreach (var child in FlexLayout.Children)
+			foreach (var child in FlexLayout)
 			{
 				var frame = FlexLayout.GetFlexFrame(child);
 				if (double.IsNaN(frame.X)