[UWP] Fixed sync of ListView items with ListViewProxy (#2512) Fixes #2485

Xamarin.Forms.Controls.Issues/Xamarin.Forms.Controls.Issues.Shared/Bugzilla56771.cs

@@ -52,14 +52,33 @@ namespace Xamarin.Forms.Controls.Issues
 					}
 				})
 			};
+			var buttonI = new Button
+			{
+				Text = "Insert odd",
+				AutomationId = BtnAdd,
+				Command = new Command(() =>
+				{
+					try
+					{
+						for (int j = 1; j < data.Count; j += 2)
+						{
+							data.Insert(j, $"Item {++i} inserted");
+						}
+					}
+					catch (ArgumentException)
+					{
+						label.Text = Success;
+					}
+				})
+			};
 			var button1 = new Button
 			{
 				Text = "Remove 2",
 				Command = new Command(() =>
 				{
-					if (data.Count > 1)
+					if (data.Count > 3)
 					{
-						data.RemoveRangeAt(0, 2);
+						data.RemoveRangeAt(2, 2);
 					}
 				})
 			};
@@ -76,7 +95,7 @@ namespace Xamarin.Forms.Controls.Issues
 
 			Content = new StackLayout
 			{
-				Children = { label, button, button1, button2, listView }
+				Children = { label, button, buttonI, button1, button2, listView }
 			};
 
 			InitializeData();
@@ -112,9 +131,9 @@ namespace Xamarin.Forms.Controls.Issues
 			public void InsertRangeAt(int startIndex, params T[] items)
 			{
 				int idx = this.Count;
-				foreach (var item in items)
+				for (int i = items.Length - 1; i >= 0; i--)
 				{
-					base.Items.Insert(startIndex++, item);
+					base.Items.Insert(startIndex, items[i]);
 				}
 				if (idx < Count)
 				{

Xamarin.Forms.Controls.Issues/Xamarin.Forms.Controls.Issues.Shared/Issue1875.cs

@@ -47,6 +47,8 @@ namespace Xamarin.Forms.Controls
 
 		async void OnItemAppearing(object sender, ItemVisibilityEventArgs e)
 		{
+			if (e.Item == null)
+				return;
 			var item = (int)e.Item;
 			if (!_viewModel.IsLoading && item == _viewModel.Items.Last())
 				await LoadData();

Xamarin.Forms.Platform.UAP/ListViewRenderer.cs

@@ -18,12 +18,15 @@ using WApp = Windows.UI.Xaml.Application;
 using Xamarin.Forms.Internals;
 using Xamarin.Forms.PlatformConfiguration.WindowsSpecific;
 using Specifics = Xamarin.Forms.PlatformConfiguration.WindowsSpecific.ListView;
+using System.Collections.ObjectModel;
 
 namespace Xamarin.Forms.Platform.UWP
 {
 	public class ListViewRenderer : ViewRenderer<ListView, FrameworkElement>
 	{
 		ITemplatedItemsView<Cell> TemplatedItemsView => Element;
+		ObservableCollection<object> SourceItems => context?.Source as ObservableCollection<object>;
+		CollectionViewSource context;
 		bool _itemWasClicked;
 		bool _subscribedToItemClick;
 		bool _subscribedToTapped;
@@ -65,8 +68,7 @@ namespace Xamarin.Forms.Platform.UWP
 					List.SetBinding(ItemsControl.ItemsSourceProperty, "");
 				}
 
-				// WinRT throws an exception if you set ItemsSource directly to a CVS, so bind it.
-				List.DataContext = new CollectionViewSource { Source = Element.ItemsSource, IsSourceGrouped = Element.IsGroupingEnabled };
+				ReloadData();
 
 				if (Element.SelectedItem != null)
 					OnElementItemSelected(null, new SelectedItemChangedEventArgs(Element.SelectedItem));
@@ -79,12 +81,55 @@ namespace Xamarin.Forms.Platform.UWP
 			}
 		}
 
-		void OnCollectionChanged(object sender, System.Collections.Specialized.NotifyCollectionChangedEventArgs e)
+		void ReloadData()
 		{
-			if (e.Action == NotifyCollectionChangedAction.Reset)
+			var allSourceItems = new ObservableCollection<object>();
+			foreach (var item in Element.ItemsSource)
+				allSourceItems.Add(item);
+
+			// WinRT throws an exception if you set ItemsSource directly to a CVS, so bind it.
+			List.DataContext = context = new CollectionViewSource
 			{
-				List.DataContext =
-					new CollectionViewSource { Source = Element.ItemsSource, IsSourceGrouped = Element.IsGroupingEnabled };
+				Source = allSourceItems,
+				IsSourceGrouped = Element.IsGroupingEnabled
+			};
+		}
+
+		void OnCollectionChanged(object sender, NotifyCollectionChangedEventArgs e)
+		{
+			switch (e.Action)
+			{
+				case NotifyCollectionChangedAction.Add:
+					if (e.NewStartingIndex < 0)
+						goto case NotifyCollectionChangedAction.Reset;
+
+					for (int i = e.NewItems.Count - 1; i >= 0; i--)
+						SourceItems.Insert(e.NewStartingIndex, e.NewItems[i]);
+					break;
+				case NotifyCollectionChangedAction.Remove:
+					foreach (var item in e.OldItems)
+						SourceItems.RemoveAt(e.OldStartingIndex);
+					break;
+				case NotifyCollectionChangedAction.Move:
+					for (var i = 0; i < e.OldItems.Count; i++)
+					{
+						var oldi = e.OldStartingIndex;
+						var newi = e.NewStartingIndex;
+
+						if (e.NewStartingIndex < e.OldStartingIndex)
+						{
+							oldi += i;
+							newi += i;
+						}
+
+						SourceItems.Move(oldi, newi);
+					}
+					break;
+				case NotifyCollectionChangedAction.Replace:
+				case NotifyCollectionChangedAction.Reset:
+				default:
+					ReloadData();
+					break;
 			}
 
 			Device.BeginInvokeOnMainThread(() => List.UpdateLayout());