Fixed the CollectionView grouped item highlighting issue on selection

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

@@ -378,6 +378,8 @@ int IndexInGroup(object item, object group)
 						{
 							return index;
 						}
+
+						index++;
 					}
 					return -1;
 			}

src/Controls/tests/TestCases.HostApp/Issues/Issue22320.cs

@@ -0,0 +1,87 @@
+using System.Collections;
+using System.Collections.ObjectModel;
+
+namespace Maui.Controls.Sample.Issues;
+[Issue(IssueTracker.Github, 22320, "CollectionView does not highlight selected grouped items correctly", PlatformAffected.iOS | PlatformAffected.macOS)]
+public class Issue22320 : ContentPage
+{
+	public Issue22320()
+	{
+		var layout = new StackLayout();
+		var bindingContext = new Issue22320ViewModel();
+		var collectionView = new CollectionView();
+		collectionView.BindingContext = bindingContext;
+		collectionView.IsGrouped = true;
+		collectionView.AutomationId = "CollectionView";
+		collectionView.SelectionMode = SelectionMode.Single;
+
+		collectionView.ItemTemplate = new DataTemplate(() =>
+		{
+			var border = new Border
+			{
+				HeightRequest = 20
+			};
+
+			var label = new Label();
+			label.SetBinding(Label.TextProperty, ".");
+
+			border.Content = label;
+
+			return border;
+		});
+
+		collectionView.GroupHeaderTemplate = new DataTemplate(() =>
+		{
+			var border = new Border
+			{
+				Background = Colors.LightGrey,
+				HeightRequest = 20
+			};
+
+			var label = new Label();
+			label.SetBinding(Label.TextProperty, "Key");
+
+			border.Content = label;
+
+			return border;
+		});
+
+		// Set the ItemsSource binding
+		collectionView.SetBinding(CollectionView.ItemsSourceProperty, "Items");
+		layout.Children.Add(collectionView);
+
+		Content = layout;
+	}
+}
+
+public class Issue22320ItemGroup : IEnumerable<string>
+{
+	private readonly string _key;
+	private readonly IEnumerable<string> _items;
+
+	public Issue22320ItemGroup(string key, IEnumerable<string> items)
+	{
+		_key = key;
+		_items = items;
+	}
+
+	public string Key => _key;
+
+	public IEnumerator<string> GetEnumerator() => _items.GetEnumerator();
+
+	IEnumerator IEnumerable.GetEnumerator() => GetEnumerator();
+}
+
+public class Issue22320ViewModel
+{
+	public Issue22320ViewModel()
+	{
+
+		Items.Add(new Issue22320ItemGroup("Vegetables", new[] { "Carrot", "Broccoli", "Spinach", "Potato", "Tomato" }));
+		Items.Add(new Issue22320ItemGroup("Fruits", new[] { "Apple", "Banana", "Orange", "Grapes", "Mango" }));
+	}
+
+	public ObservableCollection<Issue22320ItemGroup> Items { get; } = new();
+}
+
+

src/Controls/tests/TestCases.Shared.Tests/Tests/Issues/Issue22320.cs

@@ -0,0 +1,24 @@
+using NUnit.Framework;
+using UITest.Appium;
+using UITest.Core;
+
+namespace Microsoft.Maui.TestCases.Tests.Issues;
+
+public class Issue22320 : _IssuesUITest
+{
+	public Issue22320(TestDevice device) : base(device)
+	{
+	}
+
+	public override string Issue => "CollectionView does not highlight selected grouped items correctly";
+
+	[Test]
+	[Category(UITestCategories.CollectionView)]
+	public void SelectionShouldNotMovedToTopWithGroupedCollection()
+	{
+		App.WaitForElement("CollectionView");
+		App.Tap("Grapes");
+		App.Tap("Potato");
+		VerifyScreenshot();
+	}
+}