Scrollview handler (#1669)

* A mostly-functioning WASDK ScrollView handler

* Forgot to check these in

* Add request method to IScrollView

* Working implementation of CommandMapper and working WinUI ScrollView scroll requests

* Remove Actions from PropertyMapper and into CommandMapper

* Ported Android ScrollViewRenderer to handler

* De-linqify

* iOS ScrollViewHandler

* ScrollViewHandler iOS (with ContentSize)

* Add device tests for ScrollViewHandlers

* Remove defunct tests

* Fix NRE

* Reinstate IntrinsicContentSize check - the bug this was removed to prevent
is fixed by PR #1700.

* Fix nullability

* Fix whitespace

* Whitespace

* Whitespace

* Yes, I'm being picky about whitespace

Co-authored-by: Jonathan Dick <jondick@gmail.com>
Co-authored-by: Matthew Leibowitz <mattleibow@live.com>

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

@@ -28,6 +28,12 @@ double IScrollView.VerticalOffset
 			}
 		}
 
+		void IScrollView.RequestScrollTo(double horizontalOffset, double verticalOffset, bool instant)
+		{
+			var request = new ScrollToRequest(horizontalOffset, verticalOffset, instant);
+			Handler?.Invoke(nameof(IScrollView.RequestScrollTo), request);
+		}
+
 		void IScrollView.ScrollFinished() => SendScrollFinished();
 	}
-}
+}

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

@@ -79,7 +79,7 @@ void IFrameworkElement.InvalidateMeasure()
 
 		// InvalidateMeasureOverride provides a way to allow subclasses (e.g., Layout) to override InvalidateMeasure even though
 		// the interface has to be explicitly implemented to avoid conflict with the VisualElement.InvalidateMeasure method
-		protected virtual void InvalidateMeasureOverride() => Handler?.UpdateValue(nameof(IFrameworkElement.InvalidateMeasure));
+		protected virtual void InvalidateMeasureOverride() => Handler?.Invoke(nameof(IFrameworkElement.InvalidateMeasure));
 
 		void IFrameworkElement.InvalidateArrange()
 		{

src/Controls/src/Core/Hosting/AppHostBuilderExtensions.cs

@@ -27,9 +27,7 @@ public static partial class AppHostBuilderExtensions
 			{ typeof(Layout2.Layout), typeof(LayoutHandler) },
 			{ typeof(Picker), typeof(PickerHandler) },
 			{ typeof(ProgressBar), typeof(ProgressBarHandler) },
-#if WINDOWS
 			{ typeof(ScrollView), typeof(ScrollViewHandler) },
-#endif			
 			{ typeof(SearchBar), typeof(SearchBarHandler) },
 			{ typeof(Slider), typeof(SliderHandler) },
 			{ typeof(Stepper), typeof(StepperHandler) },

src/Controls/src/Core/Picker.cs

@@ -212,8 +212,8 @@ void OnItemsCollectionChanged(object sender, NotifyCollectionChangedEventArgs e)
 			// If the index has not changed, still need to change the selected item
 			if (newIndex == oldIndex)
 				UpdateSelectedItem(newIndex);
-			//This sends the notification to the Maui Handler to reload
-			OnPropertyChanged("Reload");
+
+			Handler?.Invoke("Reload");
 		}
 
 		static void OnItemsSourceChanged(BindableObject bindable, object oldValue, object newValue)

src/Controls/src/Core/ScrollToRequestedEventArgs.cs

@@ -67,5 +67,9 @@ object ITemplatedItemsListScrollToRequestedEventArgs.Item
 			}
 		}
 
+		public ScrollToRequest ToRequest()
+		{
+			return new ScrollToRequest(ScrollX, ScrollY, !ShouldAnimate);
+		}
 	}
 }

src/Controls/src/Core/ScrollView.cs

@@ -128,6 +128,8 @@ public View Content
 				if (_content != null)
 					InternalChildren.Add(_content);
 				OnPropertyChanged();
+
+				Handler?.UpdateValue(nameof(Content));
 			}
 		}
 
@@ -276,9 +278,9 @@ protected override SizeRequest OnSizeRequest(double widthConstraint, double heig
 
 			SizeRequest contentRequest;
 
-			if (Content is IFrameworkElement fe)
+			if (Content is IFrameworkElement fe && fe.Handler != null)
 			{
-				contentRequest = fe.Measure(widthConstraint, heightConstraint);
+				contentRequest = fe.Handler.GetDesiredSize(widthConstraint, heightConstraint);
 			}
 			else
 			{
@@ -361,6 +363,8 @@ void OnScrollToRequested(ScrollToRequestedEventArgs e)
 		{
 			CheckTaskCompletionSource();
 			ScrollToRequested?.Invoke(this, e);
+
+			Handler?.Invoke(nameof(IScrollView.RequestScrollTo), e.ToRequest());
 		}
 
 		protected override Size MeasureOverride(double widthConstraint, double heightConstraint)

src/Core/src/CommandMapper.cs

@@ -0,0 +1,104 @@
+using System;
+using System.Collections.Generic;
+using Command = System.Action<Microsoft.Maui.IElementHandler, Microsoft.Maui.IElement, object?>;
+
+namespace Microsoft.Maui
+{
+	public abstract class CommandMapper
+	{
+		readonly Dictionary<string, Command> _mapper = new();
+
+		CommandMapper? _chained;
+
+		public CommandMapper()
+		{
+		}
+
+		public CommandMapper(CommandMapper chained)
+		{
+			Chained = chained;
+		}
+
+		private protected virtual void SetPropertyCore(string key, Command action)
+		{
+			_mapper[key] = action;
+		}
+
+		private protected virtual void InvokeCore(string key, IElementHandler viewHandler, IElement virtualView, object? args)
+		{
+			var action = GetCommandCore(key);
+			action?.Invoke(viewHandler, virtualView, args);
+		}
+
+		private protected virtual Command? GetCommandCore(string key)
+		{
+			if (_mapper.TryGetValue(key, out var action))
+				return action;
+			else if (Chained is not null)
+				return Chained.GetCommandCore(key);
+			else
+				return null;
+		}
+
+		internal void Invoke(IElementHandler viewHandler, IElement? virtualView, string property, object? args)
+		{
+			if (virtualView == null)
+				return;
+
+			InvokeCore(property, viewHandler, virtualView, args);
+		}
+
+		public CommandMapper? Chained
+		{
+			get => _chained;
+			set
+			{
+				_chained = value;
+			}
+		}
+	}
+
+	public class CommandMapper<TVirtualView, TViewHandler> : CommandMapper
+		where TVirtualView : IElement
+		where TViewHandler : IElementHandler
+	{
+		public CommandMapper()
+		{
+		}
+
+		public CommandMapper(CommandMapper chained)
+			: base(chained)
+		{
+		}
+
+		public Action<TViewHandler, TVirtualView, object?> this[string key]
+		{
+			get
+			{
+				var action = GetCommandCore(key) ?? throw new IndexOutOfRangeException($"Unable to find mapping for '{nameof(key)}'.");
+				return new Action<TViewHandler, TVirtualView, object?>((h, v, o) => action.Invoke(h, v, o));
+			}
+			set => Add(key, value);
+		}
+
+
+		public void Add(string key, Action<TViewHandler, TVirtualView> action) =>
+			Add(key, action);
+
+		public void Add(string key, Action<TViewHandler, TVirtualView, object?> action) =>
+			SetPropertyCore(key, (h, v, o) => action?.Invoke((TViewHandler)h, (TVirtualView)v, o));
+	}
+
+	public class CommandMapper<TVirtualView> : PropertyMapper<TVirtualView, IElementHandler>
+		where TVirtualView : IElement
+	{
+		public CommandMapper()
+		{
+		}
+
+		public CommandMapper(PropertyMapper chained)
+			: base(chained)
+		{
+		}
+	}
+}

src/Core/src/Core/IScrollView.cs

@@ -3,7 +3,7 @@
 
 namespace Microsoft.Maui
 {
-	public interface IScrollView : IView
+	public interface IScrollView : IView 
 	{
 		// TODO ezhart 2021-07-08 It might make sense for IPage and IScrollView to derive from (the not yet created) IContentView 
 
@@ -46,5 +46,7 @@ public interface IScrollView : IView
 		/// Allows the native ScrollView to inform that cross-platform code that a scroll operation has completed.
 		/// </summary>
 		void ScrollFinished();
+
+		void RequestScrollTo(double horizontalOffset, double verticalOffset, bool instant);
 	}
 }

src/Core/src/Handlers/Element/ElementHandler.cs

@@ -9,13 +9,15 @@ public abstract partial class ElementHandler : IElementHandler
 		};
 
 		protected PropertyMapper _mapper;
+		protected CommandMapper? CommandMapper;
 		protected readonly PropertyMapper _defaultMapper;
 
-		protected ElementHandler(PropertyMapper mapper)
+		protected ElementHandler(PropertyMapper mapper, CommandMapper? commandMapper = null)
 		{
 			_ = mapper ?? throw new ArgumentNullException(nameof(mapper));
 			_defaultMapper = mapper;
 			_mapper = _defaultMapper;
+			CommandMapper = commandMapper;
 		}
 
 		public IMauiContext? MauiContext { get; private set; }
@@ -75,6 +77,14 @@ public virtual void UpdateValue(string property)
 			_mapper?.UpdateProperty(this, VirtualView, property);
 		}
 
+		public virtual void Invoke(string command, object? args) 
+		{
+			if (VirtualView == null)
+				return;
+
+			CommandMapper?.Invoke(this, VirtualView, command, args);
+		}
+
 		private protected abstract object OnCreateNativeElement();
 
 		object CreateNativeElement() =>

src/Core/src/Handlers/IElementHandler.cs

@@ -8,6 +8,8 @@ public interface IElementHandler
 
 		void UpdateValue(string property);
 
+		void Invoke(string command, object? args = null);
+
 		void DisconnectHandler();
 
 		object? NativeView { get; }

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

@@ -1,5 +1,4 @@
 using System;
-using System.Linq;
 using NativeView = UIKit.UIView;
 
 namespace Microsoft.Maui.Handlers
@@ -34,9 +33,12 @@ public override void SetVirtualView(IView view)
 			NativeView.CrossPlatformMeasure = VirtualView.Measure;
 			NativeView.CrossPlatformArrange = VirtualView.Arrange;
 
-			//Cleanup the old view when reused
-			var oldChildren = NativeView.Subviews.ToList();
-			oldChildren.ForEach(x => x.RemoveFromSuperview());
+			// Remove any previous children 
+			var oldChildren = NativeView.Subviews;
+			foreach (var child in oldChildren)
+			{
+				child.RemoveFromSuperview();
+			}
 
 			foreach (var child in VirtualView.Children)
 			{

src/Core/src/Handlers/Page/PageHandler.cs

@@ -7,15 +7,19 @@ public partial class PageHandler : IViewHandler
 		{
 			[nameof(IPage.Title)] = MapTitle,
 			[nameof(IPage.Content)] = MapContent,
+		};
+
 #if __IOS__
-			Actions =
-			{
-				[nameof(IFrameworkElement.Frame)] = MapFrame,
-			}
-#endif
+		public static CommandMapper<IPicker, PickerHandler> PageCommandMapper = new(ViewCommandMapper)
+		{
+			[nameof(IFrameworkElement.Frame)] = MapFrame,
 		};
 
+		public PageHandler() : base(PageMapper, PageCommandMapper)
+#else
 		public PageHandler() : base(PageMapper)
+#endif
+
 		{
 
 		}

src/Core/src/Handlers/Page/PageHandler.iOS.cs

@@ -59,7 +59,7 @@ public static void MapContent(PageHandler handler, IPage page)
 
 		public static void MapFrame(PageHandler handler, IView view)
 		{
-			ViewHandler.MapFrame(handler, view);
+			ViewHandler.MapFrame(handler, view, null);
 
 			// TODO MAUI: Currently the background layer frame is tied to the layout system
 			// which needs to be investigated more

src/Core/src/Handlers/Picker/PickerHandler.Android.cs

@@ -59,7 +59,7 @@ void Reload()
 
 			NativeView.UpdatePicker(VirtualView);
 		}
-		public static void MapReload(PickerHandler handler, IPicker picker) => handler.Reload();
+		public static void MapReload(PickerHandler handler, IPicker picker, object? args) => handler.Reload();
 
 		public static void MapTitle(PickerHandler handler, IPicker picker)
 		{

src/Core/src/Handlers/Picker/PickerHandler.Standard.cs

@@ -6,7 +6,7 @@ public partial class PickerHandler : ViewHandler<IPicker, object>
 	{
 		protected override object CreateNativeView() => throw new NotImplementedException();
 
-		public static void MapReload(PickerHandler handler, IPicker picker) { }
+		public static void MapReload(PickerHandler handler, IPicker picker, object? args) { }
 		public static void MapTitle(PickerHandler handler, IPicker view) { }
 		public static void MapTitleColor(PickerHandler handler, IPicker view) { }
 		public static void MapSelectedIndex(PickerHandler handler, IPicker view) { }

src/Core/src/Handlers/Picker/PickerHandler.Windows.cs

@@ -31,9 +31,8 @@ protected override void DisconnectHandler(MauiComboBox nativeView)
 		void SetupDefaults(MauiComboBox nativeView)
 		{
 			_defaultForeground = nativeView.Foreground;
-
-
 		}
+
 		void Reload()
 		{
 
@@ -42,7 +41,7 @@ void Reload()
 			NativeView.ItemsSource = new ItemDelegateList<string>(VirtualView);
 		}
 
-		public static void MapReload(PickerHandler handler, IPicker picker) => handler.Reload();
+		public static void MapReload(PickerHandler handler, IPicker picker, object? args) => handler.Reload();
 
 		public static void MapTitle(PickerHandler handler, IPicker picker) 
 		{

src/Core/src/Handlers/Picker/PickerHandler.cs

@@ -2,7 +2,7 @@
 {
 	public partial class PickerHandler
 	{
-		public static PropertyMapper<IPicker, PickerHandler> PickerMapper = new PropertyMapper<IPicker, PickerHandler>(ViewHandler.ViewMapper)
+		public static PropertyMapper<IPicker, PickerHandler> PickerMapper = new(ViewMapper)
 		{
 #if __ANDROID__
 			[nameof(IPicker.Background)] = MapBackground,
@@ -14,13 +14,14 @@ public partial class PickerHandler
 			[nameof(IPicker.Title)] = MapTitle,
 			[nameof(IPicker.TitleColor)] = MapTitleColor,
 			[nameof(IPicker.HorizontalTextAlignment)] = MapHorizontalTextAlignment,
-			Actions =
-			{
-				["Reload"] = MapReload,
-			}
 		};
 
-		public PickerHandler() : base(PickerMapper)
+		public static CommandMapper<IPicker, PickerHandler> PickerCommandMapper = new(ViewCommandMapper)
+		{
+			["Reload"] = MapReload
+		};
+
+		public PickerHandler() : base(PickerMapper, PickerCommandMapper)
 		{
 
 		}