From 2b4d4aa1d44e5256d0f00e74308d085d33b9521a Mon Sep 17 00:00:00 2001
From: Martin Zikmund <martin@zikmund.dev>
Date: Tue, 17 Nov 2020 15:34:50 +0100
Subject: [PATCH] feat: ItemsSource-bound ItemCollection

---
 src/Uno.UI/UI/Xaml/Controls/ItemCollection.cs | 91 ++++++++++++++++---
 1 file changed, 80 insertions(+), 11 deletions(-)

diff --git a/src/Uno.UI/UI/Xaml/Controls/ItemCollection.cs b/src/Uno.UI/UI/Xaml/Controls/ItemCollection.cs
index e31c410b6879..9b87503f5090 100644
--- a/src/Uno.UI/UI/Xaml/Controls/ItemCollection.cs
+++ b/src/Uno.UI/UI/Xaml/Controls/ItemCollection.cs
@@ -7,6 +7,8 @@
 using Uno.Extensions;
 using Uno.Extensions.Specialized;
 using System.Linq;
+using Uno.Disposables;
+using System.Collections.Specialized;
 
 namespace Windows.UI.Xaml.Controls
 {
@@ -14,7 +16,8 @@ public sealed partial class ItemCollection : IList<object>, IEnumerable<object>,
 	{
 		private readonly IList<object> _inner = new List<object>();
 
-		private IEnumerable _itemsSource = null;
+		private IList _itemsSource = null;
+		private readonly SerialDisposable _itemsSourceCollectionChangeDisposable = new SerialDisposable();
 
 		public event VectorChangedEventHandler<object> VectorChanged;
 
@@ -58,7 +61,7 @@ public void Clear()
 
 		public bool Contains(object item)
 		{
-			if (_itemsSource != null)
+			if (_itemsSource == null)
 			{
 				return _inner.Contains(item);
 			}
@@ -70,13 +73,18 @@ public bool Contains(object item)
 
 		public void CopyTo(object[] array, int arrayIndex)
 		{
-			if (_itemsSource != null)
+			if (_itemsSource == null)
 			{
 				_inner.CopyTo(array, arrayIndex);
 			}
 			else
 			{
-				throw new NotImplementedException();
+				int targetIndex = arrayIndex;
+				foreach (var item in _itemsSource)
+				{
+					array[targetIndex] = item;
+					targetIndex++;
+				}
 			}
 		}
 
@@ -138,22 +146,83 @@ public object this[int index]
 
 		internal void SetItemsSource(object itemsSource)
 		{
-			var unwrappedSource = UnwrapItemsSource(itemsSource);
+			if (_itemsSource == itemsSource)
+			{
+				// Items source did not actually change.
+				return;
+			}
 
-			if (unwrappedSource is IList itemsSourceList)
+			if (itemsSource == null)
 			{
-				_itemsSource = itemsSourceList;
+				_itemsSource = null;
 			}
-			else if (unwrappedSource is IEnumerable itemsSourceEnumerable)
+			else
 			{
-				_itemsSource = itemsSourceEnumerable.ToObjectArray();
+				var unwrappedSource = UnwrapItemsSource(itemsSource);
+
+				if (unwrappedSource is IList itemsSourceList)
+				{
+					_itemsSource = itemsSourceList;
+				}
+				else if (unwrappedSource is IEnumerable itemsSourceEnumerable)
+				{
+					_itemsSource = itemsSourceEnumerable.ToObjectArray();
+				}
+				else
+				{
+					throw new InvalidOperationException("Only IList- or IEnumerable-based ItemsSource is supported.");
+				}
+
+				ObserveCollectionChanged();
+			}
+
+			VectorChanged?.Invoke(this, new VectorChangedEventArgs(CollectionChange.Reset, 0));
+		}
+
+		private void ObserveCollectionChanged()
+		{
+			if (_itemsSource is INotifyCollectionChanged existingObservable)
+			{
+				// This is a workaround for a bug with EventRegistrationTokenTable on Xamarin, where subscribing/unsubscribing to a class method directly won't 
+				// remove the handler.
+				NotifyCollectionChangedEventHandler handler = OnItemsSourceCollectionChanged;
+				_itemsSourceCollectionChangeDisposable.Disposable = Disposable.Create(() =>
+					existingObservable.CollectionChanged -= handler
+				);
+				existingObservable.CollectionChanged += handler;
+			}
+			else if (_itemsSource is IObservableVector<object> observableVector)
+			{
+				// This is a workaround for a bug with EventRegistrationTokenTable on Xamarin, where subscribing/unsubscribing to a class method directly won't 
+				// remove the handler.
+				VectorChangedEventHandler<object> handler = OnItemsSourceVectorChanged;
+				_itemsSourceCollectionChangeDisposable.Disposable = Disposable.Create(() =>
+					observableVector.VectorChanged -= handler
+				);
+				observableVector.VectorChanged += handler;
+			}
+			else if (_itemsSource is IObservableVector genericObservableVector)
+			{
+				VectorChangedEventHandler handler = OnItemsSourceVectorChanged;
+				_itemsSourceCollectionChangeDisposable.Disposable = Disposable.Create(() =>
+					genericObservableVector.UntypedVectorChanged -= handler
+				);
+				genericObservableVector.UntypedVectorChanged += handler;
 			}
 			else
 			{
-				throw new InvalidOperationException("Only IList- or IEnumerable-based ItemsSource is supported.");
+				_itemsSourceCollectionChangeDisposable.Disposable = null;
 			}
+		}
 
-			//TODO: Observe items source changes to raise VectorChanged
+		private void OnItemsSourceVectorChanged(object sender, IVectorChangedEventArgs args)
+		{
+			VectorChanged?.Invoke(this, args);
+		}
+
+		private void OnItemsSourceCollectionChanged(object sender, NotifyCollectionChangedEventArgs args)
+		{
+			VectorChanged?.Invoke(this, args.ToVectorChangedEventArgs());
 		}
 
 		private void ThrowIfItemsSourceSet()