From ebdca5d8083d433c8b594dd16eb8715033bf7eb2 Mon Sep 17 00:00:00 2001
From: Martin Zikmund <martin@zikmund.dev>
Date: Mon, 28 Sep 2020 14:54:06 +0200
Subject: [PATCH] fix(ListViewBase): Item container indices not updated on
 insert/remove

---
 .../Controls/ListViewBase/ListViewBase.cs     | 44 +++++++++++++++++--
 1 file changed, 41 insertions(+), 3 deletions(-)

diff --git a/src/Uno.UI/UI/Xaml/Controls/ListViewBase/ListViewBase.cs b/src/Uno.UI/UI/Xaml/Controls/ListViewBase/ListViewBase.cs
index 873b6b0ebdd1..5a799e3eaa6b 100644
--- a/src/Uno.UI/UI/Xaml/Controls/ListViewBase/ListViewBase.cs
+++ b/src/Uno.UI/UI/Xaml/Controls/ListViewBase/ListViewBase.cs
@@ -49,6 +49,8 @@ public partial class ListViewBase : Selector
 		/// </summary>
 		private bool _isIncrementalLoadingInFlight;
 
+		private readonly Dictionary<DependencyObject, object> _containersForIndexRepair = new Dictionary<DependencyObject, object>();
+
 		protected internal ListViewBase()
 		{
 			Initialize();
@@ -58,7 +60,7 @@ protected internal ListViewBase()
 			SelectedItems = selectedItems;
 		}
 
-		public event TypedEventHandler<ListViewBase, ContainerContentChangingEventArgs> ContainerContentChanging;	
+		public event TypedEventHandler<ListViewBase, ContainerContentChangingEventArgs> ContainerContentChanging;
 
 		protected override Size ArrangeOverride(Size finalSize)
 		{
@@ -173,7 +175,8 @@ internal override void ChangeSelectedItem(object item, bool oldIsSelected, bool
 							{
 								SelectedIndex = -1;
 							}
-						} else
+						}
+						else
 						{
 							SelectedIndex = index;
 						}
@@ -461,7 +464,11 @@ internal override void OnItemsSourceSingleCollectionChanged(object sender, Notif
 					{
 						this.Log().Debug($"Inserting {args.NewItems.Count} items starting at {args.NewStartingIndex}");
 					}
+
+					SaveContainersForIndexRepair(args.NewStartingIndex, args.NewItems.Count);
 					AddItems(args.NewStartingIndex, args.NewItems.Count, section);
+					RepairIndices();
+
 					break;
 				case NotifyCollectionChangedAction.Remove:
 					if (AreEmptyGroupsHidden && (sender as IEnumerable).None())
@@ -475,14 +482,20 @@ internal override void OnItemsSourceSingleCollectionChanged(object sender, Notif
 					{
 						this.Log().Debug($"Deleting {args.OldItems.Count} items starting at {args.OldStartingIndex}");
 					}
+
+					SaveContainersForIndexRepair(args.OldStartingIndex, -args.OldItems.Count);
 					RemoveItems(args.OldStartingIndex, args.OldItems.Count, section);
+					RepairIndices();
+
 					break;
 				case NotifyCollectionChangedAction.Replace:
 					if (this.Log().IsEnabled(Microsoft.Extensions.Logging.LogLevel.Debug))
 					{
 						this.Log().Debug($"Replacing {args.NewItems.Count} items starting at {args.NewStartingIndex}");
 					}
+
 					ReplaceItems(args.NewStartingIndex, args.NewItems.Count, section);
+
 					break;
 				case NotifyCollectionChangedAction.Move:
 					// TODO PBI #19974: Fully implement NotifyCollectionChangedActions and map them to the appropriate calls
@@ -505,6 +518,28 @@ void completeRefresh()
 			}
 		}
 
+		private void SaveContainersForIndexRepair(int startingIndex, int indexChange)
+		{
+			_containersForIndexRepair.Clear();
+			foreach (var container in MaterializedContainers)
+			{
+				var currentIndex = (int)container.GetValue(ItemsControl.IndexForItemContainerProperty);
+				if (currentIndex >= startingIndex)
+				{
+					_containersForIndexRepair.Add(container, currentIndex + indexChange);
+				}
+			}
+		}
+
+		private void RepairIndices()
+		{
+			foreach(var containerPair in _containersForIndexRepair)
+			{
+				containerPair.Key.SetValue(ItemsControl.IndexForItemContainerProperty, containerPair.Value);
+			}
+			_containersForIndexRepair.Clear();
+		}
+
 		internal override void OnItemsSourceGroupsChanged(object sender, NotifyCollectionChangedEventArgs args)
 		{
 			if (RefreshOnCollectionChanged)
@@ -596,6 +631,9 @@ internal override void OnGroupPropertyChanged(ICollectionViewGroup group, int gr
 
 		protected override void PrepareContainerForItemOverride(DependencyObject element, object item)
 		{
+			// Index will be repaired by virtue of ItemsControl.
+			_containersForIndexRepair.Remove(element);
+
 			base.PrepareContainerForItemOverride(element, item);
 
 			if (element is SelectorItem selectorItem)
@@ -607,7 +645,7 @@ protected override void PrepareContainerForItemOverride(DependencyObject element
 		internal override void ContainerPreparedForItem(object item, SelectorItem itemContainer, int itemIndex)
 		{
 			base.ContainerPreparedForItem(item, itemContainer, itemIndex);
-			
+
 			ContainerContentChanging?.Invoke(this, new ContainerContentChangingEventArgs(item, itemContainer, itemIndex));
 		}