Implement EmptyView on UWP (xamarin#7438)

Xamarin.Forms.Platform.UAP/CollectionView/FormsGridView.cs

@@ -1,14 +1,17 @@
-using Windows.UI.Xaml;
+using System;
+using System.Globalization;
+using Windows.UI.Xaml;
 using Windows.UI.Xaml.Controls;
 using Xamarin.Forms.Platform.UWP;
 
-namespace Xamarin.Forms.Platform.UAP
+namespace Xamarin.Forms.Platform.UWP
 {
-	// TODO hartez 2018/06/06 10:01:48 Consider whether this should be internal; it might be that we just want to make the ItemsPanel resources configurable in CollectionViewRenderer
-	internal class FormsGridView : GridView
+	internal class FormsGridView : GridView, IEmptyView
 	{
 		int _maximumRowsOrColumns;
 		ItemsWrapGrid _wrapGrid;
+		ContentControl _emptyViewContentControl;
+		FrameworkElement _emptyView;
 
 		public FormsGridView()
 		{
@@ -30,14 +33,24 @@ public int MaximumRowsOrColumns
 			}
 		}
 
+		public Visibility EmptyViewVisibility
+		{
+			get { return (Visibility)GetValue(EmptyViewVisibilityProperty); }
+			set { SetValue(EmptyViewVisibilityProperty, value); }
+		}
+
+		public static readonly DependencyProperty EmptyViewVisibilityProperty =
+			DependencyProperty.Register(nameof(EmptyViewVisibility), typeof(Visibility), 
+				typeof(FormsGridView), new PropertyMetadata(Visibility.Collapsed));
+
 		// TODO hartez 2018/06/06 10:01:32 Probably should just create a local enum for this?	
 		public void UseHorizontalItemsPanel()
 		{
 			ItemsPanel =
 				(ItemsPanelTemplate)Windows.UI.Xaml.Application.Current.Resources["HorizontalGridItemsPanel"];
 		}
 
-		public void UseVerticalalItemsPanel()
+		public void UseVerticalItemsPanel()
 		{
 			ItemsPanel =
 				(ItemsPanelTemplate)Windows.UI.Xaml.Application.Current.Resources["VerticalGridItemsPanel"];
@@ -64,5 +77,27 @@ void OnLoaded(object sender, RoutedEventArgs e)
 		{
 			FindItemsWrapGrid();
 		}
+
+		public void SetEmptyView(FrameworkElement emptyView)
+		{
+			_emptyView = emptyView;
+
+			if (_emptyViewContentControl != null)
+			{
+				_emptyViewContentControl.Content = emptyView;
+			}
+		}
+
+		protected override void OnApplyTemplate()
+		{
+			base.OnApplyTemplate();
+
+			_emptyViewContentControl = GetTemplateChild("EmptyViewContentControl") as ContentControl;
+
+			if (_emptyView != null)
+			{
+				_emptyViewContentControl.Content = _emptyView;
+			}
+		}
 	}
 }

Xamarin.Forms.Platform.UAP/CollectionView/FormsListView.cs

@@ -0,0 +1,42 @@
+using Windows.UI.Xaml;
+using Windows.UI.Xaml.Controls;
+
+namespace Xamarin.Forms.Platform.UWP
+{
+	internal class FormsListView : Windows.UI.Xaml.Controls.ListView, IEmptyView
+	{
+		ContentControl _emptyViewContentControl;
+		FrameworkElement _emptyView;
+
+		public Visibility EmptyViewVisibility
+		{
+			get { return (Visibility)GetValue(EmptyViewVisibilityProperty); }
+			set { SetValue(EmptyViewVisibilityProperty, value); }
+		}
+
+		public static readonly DependencyProperty EmptyViewVisibilityProperty =
+			DependencyProperty.Register(nameof(EmptyViewVisibility), typeof(Visibility), typeof(FormsListView), new PropertyMetadata(Visibility.Collapsed));
+
+		public void SetEmptyView(FrameworkElement emptyView)
+		{
+			_emptyView = emptyView;
+
+			if (_emptyViewContentControl != null)
+			{
+				_emptyViewContentControl.Content = emptyView;
+			}
+		}
+
+		protected override void OnApplyTemplate()
+		{
+			base.OnApplyTemplate();
+
+			_emptyViewContentControl = GetTemplateChild("EmptyViewContentControl") as ContentControl;
+
+			if (_emptyView != null)
+			{
+				_emptyViewContentControl.Content = _emptyView;
+			}
+		}
+	}
+}

Xamarin.Forms.Platform.UAP/CollectionView/IEmptyView.cs

@@ -0,0 +1,10 @@
+using Windows.UI.Xaml;
+
+namespace Xamarin.Forms.Platform.UWP
+{
+	internal interface IEmptyView
+	{
+		Visibility EmptyViewVisibility { get; set; }
+		void SetEmptyView(FrameworkElement emptyView);
+	}
+}

Xamarin.Forms.Platform.UAP/CollectionView/ItemsViewRenderer.cs

@@ -14,6 +14,7 @@
 using UwpScrollBarVisibility = Windows.UI.Xaml.Controls.ScrollBarVisibility;
 using UWPApp = Windows.UI.Xaml.Application;
 using UWPDataTemplate = Windows.UI.Xaml.DataTemplate;
+using System.Collections.Specialized;
 
 namespace Xamarin.Forms.Platform.UWP
 {
@@ -28,6 +29,9 @@ public abstract class ItemsViewRenderer : ViewRenderer<ItemsView, ListViewBase>
 		protected UWPDataTemplate ViewTemplate => (UWPDataTemplate)UWPApp.Current.Resources["View"];
 		protected UWPDataTemplate ItemsViewTemplate => (UWPDataTemplate)UWPApp.Current.Resources["ItemsViewDefaultTemplate"];
 
+		FrameworkElement _emptyView;
+		View _formsEmptyView;
+
 		protected ItemsControl ItemsControl { get; private set; }
 
 		protected override void OnElementChanged(ElementChangedEventArgs<ItemsView> args)
@@ -57,6 +61,10 @@ protected override void OnElementPropertyChanged(object sender, PropertyChangedE
 			{
 				UpdateVerticalScrollBarVisibility();
 			}
+			else if (changedProperty.IsOneOf(ItemsView.EmptyViewProperty, ItemsView.EmptyViewTemplateProperty))
+			{
+				UpdateEmptyView();
+			}
 		}
 
 		protected abstract ListViewBase SelectListViewBase();
@@ -76,6 +84,11 @@ protected virtual void UpdateItemsSource()
 
 			if (itemsSource == null)
 			{
+				if (_collectionViewSource?.Source is INotifyCollectionChanged incc)
+				{
+					incc.CollectionChanged -= ItemsChanged;
+				}
+
 				_collectionViewSource = null;
 				return;
 			}
@@ -97,6 +110,11 @@ protected virtual void UpdateItemsSource()
 					Source = TemplatedItemSourceFactory.Create(itemsSource, itemTemplate, Element),
 					IsSourceGrouped = false
 				};
+
+				if (_collectionViewSource?.Source is INotifyCollectionChanged incc)
+				{
+					incc.CollectionChanged += ItemsChanged;
+				}
 			}
 			else
 			{
@@ -108,6 +126,13 @@ protected virtual void UpdateItemsSource()
 			}
 
 			ListViewBase.ItemsSource = _collectionViewSource.View;
+
+			UpdateEmptyViewVisibility();
+		}
+
+		void ItemsChanged(object sender, NotifyCollectionChangedEventArgs e)
+		{
+			UpdateEmptyViewVisibility();
 		}
 
 		protected virtual void UpdateItemTemplate()
@@ -148,6 +173,7 @@ protected virtual void SetUpNewElement(ItemsView newElement)
 			UpdateItemsSource();
 			UpdateVerticalScrollBarVisibility();
 			UpdateHorizontalScrollBarVisibility();
+			UpdateEmptyView();
 
 			// Listen for ScrollTo requests
 			newElement.ScrollToRequested += ScrollToRequested;
@@ -357,5 +383,75 @@ protected virtual async Task ScrollTo(ScrollToRequestEventArgs args)
 				await JumpTo(list, targetItem, args.ScrollToPosition);
 			}
 		}
+
+		protected virtual void UpdateEmptyView()
+		{
+			if (Element == null || ListViewBase == null)
+			{
+				return;
+			}
+
+			var emptyView = Element.EmptyView;
+
+			if (emptyView == null)
+			{
+				return;
+			}
+
+			switch (emptyView)
+			{
+				case string text:
+					_emptyView = new TextBlock { Text = text };
+					break;
+				case View view:
+					_emptyView = RealizeEmptyView(view);
+					break;
+				default:
+					_emptyView = RealizeEmptyViewTemplate(emptyView, Element.EmptyViewTemplate);
+					break;
+			}
+
+			(ListViewBase as IEmptyView)?.SetEmptyView(_emptyView);
+
+			UpdateEmptyViewVisibility();
+		}
+
+		FrameworkElement RealizeEmptyViewTemplate(object bindingContext, DataTemplate emptyViewTemplate)
+		{
+			if (emptyViewTemplate == null)
+			{
+				return new TextBlock { Text = bindingContext.ToString() };
+			}
+
+			var template = emptyViewTemplate.SelectDataTemplate(bindingContext, null);
+			var view = template.CreateContent() as View;
+
+			view.BindingContext = bindingContext;
+			return RealizeEmptyView(view);
+		}
+
+		FrameworkElement RealizeEmptyView(View view)
+		{
+			_formsEmptyView = view;
+			return view.GetOrCreateRenderer().ContainerElement;
+		}
+
+		protected virtual void UpdateEmptyViewVisibility()
+		{
+			if (_emptyView != null && ListViewBase is IEmptyView emptyView)
+			{
+				emptyView.EmptyViewVisibility = (_collectionViewSource?.View?.Count ?? 0) == 0
+					? Visibility.Visible
+					: Visibility.Collapsed;
+
+				if (emptyView.EmptyViewVisibility == Visibility.Visible)
+				{
+					if (ActualWidth >= 0 && ActualHeight >= 0)
+					{
+						_formsEmptyView?.Layout(new Rectangle(0, 0, ActualWidth, ActualHeight));
+					}
+				}
+			}
+		}
 	}
-}
+}