Fix Crash when ItemsSource is set to null in the SelectionChanged handler

src/Controls/src/Core/Handlers/Items/iOS/SelectableItemsViewController.cs

@@ -25,18 +25,31 @@ protected override UICollectionViewDelegateFlowLayout CreateDelegator()
 		// _Only_ called if the user initiates the selection change; will not be called for programmatic selection
 		public override void ItemSelected(UICollectionView collectionView, NSIndexPath indexPath)
 		{
+			if (ItemsView?.ItemsSource is null)
+			{
+				return;
+			}
 			FormsSelectItem(indexPath);
 		}
 
 		// _Only_ called if the user initiates the selection change; will not be called for programmatic selection
 		public override void ItemDeselected(UICollectionView collectionView, NSIndexPath indexPath)
 		{
+			if (ItemsView?.ItemsSource is null)
+			{
+				return;
+			}
 			FormsDeselectItem(indexPath);
 		}
 
 		// Called by Forms to mark an item selected 
 		internal void SelectItem(object selectedItem)
 		{
+			if (ItemsView?.ItemsSource is null)
+			{
+				return;
+			}
+
 			var index = GetIndexForItem(selectedItem);
 
 			if (index.Section > -1 && index.Item > -1)
@@ -52,6 +65,11 @@ internal void SelectItem(object selectedItem)
 		// Called by Forms to clear the native selection
 		internal void ClearSelection()
 		{
+			if (ItemsView?.ItemsSource is null)
+			{
+				return;
+			}
+
 			var selectedItemIndexes = CollectionView.GetIndexPathsForSelectedItems();
 
 			foreach (var index in selectedItemIndexes)
@@ -95,7 +113,7 @@ void FormsDeselectItem(NSIndexPath indexPath)
 
 		internal void UpdatePlatformSelection()
 		{
-			if (ItemsView == null)
+			if (ItemsView?.ItemsSource is null)
 			{
 				return;
 			}

src/Controls/src/Core/Handlers/Items2/iOS/SelectableItemsViewController2.cs

@@ -25,18 +25,31 @@ protected override UICollectionViewDelegateFlowLayout CreateDelegator()
 		// _Only_ called if the user initiates the selection change; will not be called for programmatic selection
 		public override void ItemSelected(UICollectionView collectionView, NSIndexPath indexPath)
 		{
+			if (ItemsView?.ItemsSource is null)
+			{
+				return;
+			}
 			FormsSelectItem(indexPath);
 		}
 
 		// _Only_ called if the user initiates the selection change; will not be called for programmatic selection
 		public override void ItemDeselected(UICollectionView collectionView, NSIndexPath indexPath)
 		{
+			if (ItemsView?.ItemsSource is null)
+			{
+				return;
+			}
 			FormsDeselectItem(indexPath);
 		}
 
 		// Called by Forms to mark an item selected 
 		internal void SelectItem(object selectedItem)
 		{
+			if (ItemsView?.ItemsSource is null)
+			{
+				return;
+			}
+
 			var index = GetIndexForItem(selectedItem);
 
 			if (index.Section > -1 && index.Item > -1)
@@ -52,6 +65,11 @@ internal void SelectItem(object selectedItem)
 		// Called by Forms to clear the native selection
 		internal void ClearSelection()
 		{
+			if (ItemsView?.ItemsSource is null)
+			{
+				return;
+			}
+
 			var selectedItemIndexes = CollectionView.GetIndexPathsForSelectedItems();
 
 			foreach (var index in selectedItemIndexes)
@@ -95,7 +113,7 @@ void FormsDeselectItem(NSIndexPath indexPath)
 
 		internal void UpdatePlatformSelection()
 		{
-			if (ItemsView == null)
+			if (ItemsView?.ItemsSource is null)
 			{
 				return;
 			}

src/Controls/tests/TestCases.HostApp/Issues/Issue29882.xaml

@@ -0,0 +1,27 @@
+<?xml version="1.0" encoding="utf-8" ?>
+<ContentPage xmlns="http://schemas.microsoft.com/dotnet/2021/maui"
+             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
+             x:Class="Maui.Controls.Sample.Issues.Issue29882"
+             Title="Issue29882">
+    <VerticalStackLayout>
+        <Label Text="Issue 29882" AutomationId="MauiLabel" />
+       <CollectionView
+                    SelectionMode="Single"  ItemsSource="{Binding Items}" 
+                    x:Name="MyCollectionView"  SelectionChanged="MyCollectionView_SelectionChanged"
+                    Margin="10">
+        <CollectionView.ItemTemplate>
+            <DataTemplate>
+                <Border Stroke="LightGray"  Padding="10" Margin="5">
+                  <VerticalStackLayout>
+                      <Label Text="{Binding .}" 
+                           FontSize="18" AutomationId="{Binding .}"
+                           VerticalOptions="Center"
+                           HorizontalOptions="Center"/>
+                  </VerticalStackLayout>
+                </Border>
+            </DataTemplate>
+        </CollectionView.ItemTemplate>
+
+    </CollectionView>
+    </VerticalStackLayout>
+</ContentPage>

src/Controls/tests/TestCases.HostApp/Issues/Issue29882.xaml.cs

@@ -0,0 +1,33 @@
+using System.Collections.ObjectModel;
+
+namespace Maui.Controls.Sample.Issues;
+
+[Issue(IssueTracker.Github, 29882, "[iOS] Crash occurs when ItemsSource is set to null in the SelectionChanged handler",PlatformAffected.iOS)]
+public partial class Issue29882 : ContentPage
+{
+	private ObservableCollection<string> items;
+	public ObservableCollection<string> Items
+	{
+		get => items;
+		set
+		{
+			items = value;
+			OnPropertyChanged();
+		}
+	}
+	public Issue29882()
+	{
+		InitializeComponent();
+		Items = new ObservableCollection<string>();
+		for (int i = 1; i <= 10; i++)
+		{
+			Items.Add($"Item{i}");
+		}
+		BindingContext = this;
+	}
+
+	private void MyCollectionView_SelectionChanged(object sender, SelectionChangedEventArgs e)
+	{
+		Items = null;
+	}
+}

src/Controls/tests/TestCases.Shared.Tests/Tests/Issues/Issue29882.cs

@@ -0,0 +1,24 @@
+using System;
+using NUnit.Framework;
+using UITest.Appium;
+using UITest.Core;
+
+namespace Microsoft.Maui.TestCases.Tests.Issues;
+
+public class Issue29882 : _IssuesUITest
+{
+    public Issue29882(TestDevice device) : base(device)
+    {
+    }
+
+    public override string Issue => "[iOS] Crash occurs when ItemsSource is set to null in the SelectionChanged handler";
+
+    [Test]
+    [Category(UITestCategories.CollectionView)]
+    public void SettingItemSourceToNullShouldNotCrash()
+    {
+        App.WaitForElement("Item1");
+        App.Tap("Item1");
+        App.WaitForElement("MauiLabel"); // If app doesn't crash, test passes.
+	}
+}