[iOS] Add missing call to ReloadData on NotifyCollectionChangedAction.Reset (#6089) fixes #5793

* Add missing call to ReloadData on INCC Reset; fixes #5793

* Automated test for INCC Reset

Xamarin.Forms.Controls.Issues/Xamarin.Forms.Controls.Issues.Shared/Issue5793.cs

@@ -0,0 +1,50 @@
+using System;
+using System.Collections.Generic;
+using System.Text;
+using Xamarin.Forms.CustomAttributes;
+using Xamarin.Forms.Internals;
+
+#if UITEST
+using Xamarin.Forms.Core.UITests;
+using Xamarin.UITest;
+using NUnit.Framework;
+#endif
+
+
+namespace Xamarin.Forms.Controls.Issues
+{
+#if UITEST
+	[Category(UITestCategories.CollectionView)]
+#endif
+	[Preserve(AllMembers = true)]
+	[Issue(IssueTracker.Github, 5793, "[CollectionView/ListView] Not listening for Reset command",
+		PlatformAffected.iOS | PlatformAffected.Android)]
+	class Issue5793 : TestNavigationPage
+	{
+		protected override void Init()
+		{
+#if APP
+			Device.SetFlags(new List<string>(Device.Flags ?? new List<string>()) { "CollectionView_Experimental" });
+
+			PushAsync(new GalleryPages.CollectionViewGalleries.ObservableCollectionResetGallery());
+#endif
+		}
+
+#if UITEST
+		[Test]
+		public void Reset()
+		{
+			RunningApp.WaitForElement("Reset");
+
+			// Verify the item is there
+			RunningApp.WaitForElement("cover1.jpg, 0");
+
+			// Clear the collection
+			RunningApp.Tap("Reset");	
+
+			// Verify the item is gone
+			RunningApp.WaitForNoElement("cover1.jpg, 0");
+		}
+#endif
+	}
+}

Xamarin.Forms.Controls.Issues/Xamarin.Forms.Controls.Issues.Shared/Xamarin.Forms.Controls.Issues.Shared.projitems

@@ -462,6 +462,7 @@
       <SubType>Code</SubType>
     </Compile>
     <Compile Include="$(MSBuildThisFileDirectory)Issue5535.cs" />
+    <Compile Include="$(MSBuildThisFileDirectory)Issue5793.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)LegacyComponents\NonAppCompatSwitch.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)MapsModalCrash.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)ModalActivityIndicatorTest.cs" />

Xamarin.Forms.Controls/GalleryPages/CollectionViewGalleries/MultiTestObservableCollection.cs

@@ -77,12 +77,7 @@ namespace Xamarin.Forms.Controls.GalleryPages.CollectionViewGalleries
 
 		public void TestReset()
 		{
-			var random = new Random();
-			var randomized = GetRange(0, Count).Select(item => new { Item = item, Index = random.Next(100000) })
-				.OrderBy(x => x.Index).Select(x => x.Item).ToList();
-
 			RemoveRange(0, Count);
-			InsertRange(0, randomized);
 
 			var args = new NotifyCollectionChangedEventArgs(NotifyCollectionChangedAction.Reset);
 			OnNotifyCollectionChanged(this, args);

Xamarin.Forms.Platform.iOS/CollectionView/ObservableItemsSource.cs

@@ -59,6 +59,7 @@ namespace Xamarin.Forms.Platform.iOS
 					Move(args);
 					break;
 				case NotifyCollectionChangedAction.Reset:
+					_collectionView.ReloadData();
 					break;
 				default:
 					throw new ArgumentOutOfRangeException();