[Windows] Fix CollectionView DisconnectHandler SelectionMode Crash (#…

…23726)

* Reorder events to prevent disconnect issues

* Add test

---------

Co-authored-by: Mike Corsaro <mikecorsaro@microsoft.com>

src/Controls/src/Core/Handlers/Items/SelectableItemsViewHandler.Windows.cs

@@ -49,8 +49,8 @@ protected override void DisconnectHandler(ListViewBase platformView)
 
 			if (oldListViewBase != null)
 			{
-				oldListViewBase.ClearValue(ListViewBase.SelectionModeProperty);
 				oldListViewBase.SelectionChanged -= PlatformSelectionChanged;
+				oldListViewBase.ClearValue(ListViewBase.SelectionModeProperty);
 			}
 
 			if (ItemsView != null)

src/Controls/tests/DeviceTests/Elements/CollectionView/CollectionViewTests.Windows.cs

@@ -1,4 +1,5 @@
-using System.Collections.ObjectModel;
+using System.Collections.Generic;
+using System.Collections.ObjectModel;
 using System.Linq;
 using System.Threading.Tasks;
 using Microsoft.Maui.Controls;
@@ -58,6 +59,51 @@ await CreateHandlerAndAddToWindow<LayoutHandler>(layout, (handler) =>
 			});
 		}
 
+		[Fact(DisplayName = "CollectionView Disconnects Correctly with MultiSelection")]
+		public async Task CollectionViewHandlerDisconnectsWithMultiSelect()
+		{
+			SetupBuilder();
+
+			ObservableCollection<string> data = new ObservableCollection<string>()
+			{
+				"Item 1",
+				"Item 2",
+				"Item 3"
+			};
+
+			var collectionView = new CollectionView()
+			{
+				ItemTemplate = new Controls.DataTemplate(() =>
+				{
+					return new VerticalStackLayout()
+					{
+						new Label()
+					};
+				}),
+				SelectionMode = SelectionMode.Multiple,
+				ItemsSource = data
+			};
+
+			var layout = new VerticalStackLayout()
+			{
+				collectionView
+			};
+
+			await CreateHandlerAndAddToWindow<LayoutHandler>(layout, (handler) =>
+			{
+				collectionView.SelectedItems.Add(data[0]);
+				collectionView.SelectedItems.Add(data[2]);
+
+				// Validate that no exceptions are thrown
+				var collectionViewHandler = (IElementHandler)collectionView.Handler;
+				collectionViewHandler.DisconnectHandler();
+
+				((IElementHandler)handler).DisconnectHandler();
+
+				return Task.CompletedTask;
+			});
+		}
+
 		[Fact]
 		public async Task ValidateItemContainerDefaultHeight()
 		{