Core,Controls(Gtk): implement tap/click gestures (lytico#14)

Implement tap/click gestures for Gtk.
Note that due to the way Gtk works only certain widgets can
respond to click events.
I changed ContentView to inherit from EventBox, so many
elements have this capability, including all layouts.
Still many widgets such as label for which adding tap gesture
recognizer will have no effect.
See
https://discourse.gnome.org/t/gtk-widget-mouse-down-event-does-not-seem-to-work/1699.

src/Controls/src/Core/Platform/GestureManager/GestureManager.Gtk.cs

@@ -1,17 +1,268 @@
 #nullable enable
 
 using System;
+using System.Collections.Generic;
+using System.Collections.ObjectModel;
+using System.Collections.Specialized;
+using System.Linq;
+using Gtk;
+using Microsoft.Maui.Controls.Internals;
 
 namespace Microsoft.Maui.Controls.Platform
 {
+	// ported from https://github.com/xamarin/Xamarin.Forms/blob/5.0.0/Xamarin.Forms.Platform.GTK/VisualElementTracker.cs
 	class GestureManager : IDisposable
 	{
+		readonly IPlatformViewHandler _handler;
+		readonly NotifyCollectionChangedEventHandler _collectionChangedHandler;
+		Widget? _container;
+		Widget? _control;
+		VisualElement? _element;
+
+		bool _isDisposed;
+
 		public GestureManager(IViewHandler handler)
 		{
+			_handler = (IPlatformViewHandler)handler;
+			_collectionChangedHandler = ModelGestureRecognizersOnCollectionChanged;
+
+			if (_handler.VirtualView == null)
+				throw new ArgumentNullException(nameof(handler.VirtualView));
+
+			if (_handler.PlatformView == null)
+				throw new ArgumentNullException(nameof(handler.PlatformView));
+
+			Element = (VisualElement)_handler.VirtualView;
+			Control = _handler.PlatformView;
+
+			if (_handler.ContainerView != null)
+				Container = _handler.ContainerView;
+			else
+				Container = _handler.PlatformView;
+		}
+
+		public Widget? Container
+		{
+			get { return _container; }
+			set
+			{
+				if (_container == value)
+					return;
+
+				if (_container != null)
+				{
+					_container.ButtonPressEvent -= OnContainerButtonPressEvent;
+				}
+
+				_container = value;
+
+				UpdatingGestureRecognizers();
+			}
+		}
+
+		public Widget? Control
+		{
+			get { return _control; }
+			set
+			{
+				if (_control == value)
+					return;
+
+				if (_control != null)
+				{
+					_control.ButtonPressEvent -= OnControlButtonPressEvent;
+				}
+
+				_control = value;
+
+				if (PreventGestureBubbling)
+				{
+					UpdatingGestureRecognizers();
+				}
+			}
+		}
+
+		public VisualElement? Element
+		{
+			get { return _element; }
+			set
+			{
+				if (_element == value)
+					return;
+
+				if (_element != null)
+				{
+					var view = _element as View;
+					if (view != null)
+					{
+						var oldRecognizers = (ObservableCollection<IGestureRecognizer>)view.GestureRecognizers;
+						oldRecognizers.CollectionChanged -= _collectionChangedHandler;
+					}
+				}
+
+				_element = value;
+
+				if (_element != null)
+				{
+					var view = _element as View;
+					if (view != null)
+					{
+						var newRecognizers = (ObservableCollection<IGestureRecognizer>)view.GestureRecognizers;
+						newRecognizers.CollectionChanged += _collectionChangedHandler;
+					}
+				}
+			}
+		}
+
+		private bool PreventGestureBubbling
+		{
+			get
+			{
+				return Element switch
+				{
+					Button => true,
+					CheckBox => true,
+					DatePicker => true,
+					Stepper => true,
+					Slider => true,
+					Switch => true,
+					TimePicker => true,
+					ImageButton => true,
+					RadioButton => true,
+					_ => false,
+				};
+			}
 		}
 
 		public void Dispose()
 		{
+			Dispose(true);
+			GC.SuppressFinalize(this);
+		}
+
+		private void Dispose(bool disposing)
+		{
+			if (_isDisposed)
+				return;
+
+			_isDisposed = true;
+
+			if (!disposing)
+				return;
+
+			if (_container != null)
+			{
+				_container.ButtonPressEvent -= OnContainerButtonPressEvent;
+			}
+
+			if (_element != null)
+			{
+				var view = _element as View;
+				if (view != null)
+				{
+					var oldRecognizers = (ObservableCollection<IGestureRecognizer>)view.GestureRecognizers;
+					oldRecognizers.CollectionChanged -= _collectionChangedHandler;
+				}
+			}
+
+			if (_control != null)
+			{
+				_control.ButtonPressEvent -= OnControlButtonPressEvent;
+			}
+
+			Container?.Destroy();
+			Container = null;
+		}
+
+		private void ModelGestureRecognizersOnCollectionChanged(object? sender, NotifyCollectionChangedEventArgs notifyCollectionChangedEventArgs)
+		{
+			UpdatingGestureRecognizers();
+		}
+
+		private void UpdatingGestureRecognizers()
+		{
+			var view = Element as View;
+			var gestures = view?.GestureRecognizers;
+
+			if (_container == null || gestures == null)
+				return;
+
+			_container.ButtonPressEvent -= OnContainerButtonPressEvent;
+
+			if (gestures.GetGesturesFor<TapGestureRecognizer>().Any() || gestures.GetGesturesFor<ClickGestureRecognizer>().Any())
+			{
+				_container.ButtonPressEvent += OnContainerButtonPressEvent;
+			}
+			else
+			{
+				if (_control != null && PreventGestureBubbling)
+				{
+					_control.ButtonPressEvent += OnControlButtonPressEvent;
+				}
+			}
 		}
+
+		private void OnContainerButtonPressEvent(object sender, ButtonPressEventArgs args)
+		{
+			var button = args.Event.Button;
+			if (button != 1 && button != 3)
+			{
+				return;
+			}
+
+			var view = Element as View;
+
+			if (view == null)
+				return;
+
+			int numClicks = 0;
+			switch (args.Event.Type)
+			{
+				case Gdk.EventType.ThreeButtonPress:
+					numClicks = 3;
+					break;
+				case Gdk.EventType.TwoButtonPress:
+					numClicks = 2;
+					break;
+				case Gdk.EventType.ButtonPress:
+					numClicks = 1;
+					break;
+				default:
+					return;
+			}
+
+			// Taps or Clicks
+			if (button == (uint)ButtonsMask.Primary)
+			{
+				IEnumerable<TapGestureRecognizer> tapGestures = view.GestureRecognizers
+					.GetGesturesFor<TapGestureRecognizer>(recognizer => recognizer.NumberOfTapsRequired == numClicks);
+
+				foreach (TapGestureRecognizer recognizer in tapGestures)
+					recognizer.SendTapped(view);
+
+				IEnumerable<ClickGestureRecognizer> clickGestures = view.GestureRecognizers
+					.GetGesturesFor<ClickGestureRecognizer>(recognizer => recognizer.NumberOfClicksRequired == numClicks &&
+															recognizer.Buttons == ButtonsMask.Primary);
+
+				foreach (ClickGestureRecognizer recognizer in clickGestures)
+					recognizer.SendClicked(view, ButtonsMask.Primary);
+			}
+			else
+			{
+				// right click
+				IEnumerable<ClickGestureRecognizer> rightClickGestures = view.GestureRecognizers
+					.GetGesturesFor<ClickGestureRecognizer>(recognizer => recognizer.NumberOfClicksRequired == numClicks &&
+															recognizer.Buttons == ButtonsMask.Secondary);
+
+				foreach (ClickGestureRecognizer recognizer in rightClickGestures)
+					recognizer.SendClicked(view, ButtonsMask.Secondary);
+			}
+		}
+
+		private void OnControlButtonPressEvent(object sender, ButtonPressEventArgs args)
+		{
+			args.RetVal = true;
+		}
+
 	}
 }

src/Core/src/Platform/Gtk/ContentView.cs

@@ -5,10 +5,10 @@
 namespace Microsoft.Maui.Platform
 {
 
-	public class ContentView : Gtk.Box
+	public class ContentView : Gtk.EventBox
 	{
 
-		public ContentView() : base(Orientation.Horizontal, 0) { }
+		public ContentView() : base() { }
 
 		internal Func<double, double, Size>? CrossPlatformMeasure { get; set; }
 
@@ -28,7 +28,7 @@ public Widget? Content
 				}
 				else if (value != null)
 				{
-					PackStart(value, true, true, 0);
+					Add(value);
 				}
 
 				_content = value;