[Android] Fixed issue where group Header/Footer template was applied to all items when IsGrouped was true for an ObservableCollection

src/Controls/src/Core/Handlers/Items/Android/ItemsSources/ObservableGroupedSource.cs

@@ -226,10 +226,13 @@ void UpdateGroupTracking()
 
 			for (int n = 0; n < _groupSource.Count; n++)
 			{
-				var source = ItemsSourceFactory.Create(_groupSource[n] as IEnumerable, _groupableItemsView, this);
-				source.HasFooter = _hasGroupFooters;
-				source.HasHeader = _hasGroupHeaders;
-				_groups.Add(source);
+				if (_groupSource[n] is IEnumerable list)
+				{
+					var source = ItemsSourceFactory.Create(list, _groupableItemsView, this);
+					source.HasFooter = _hasGroupFooters;
+					source.HasHeader = _hasGroupHeaders;
+					_groups.Add(source);
+				}
 			}
 		}
 

src/Controls/tests/TestCases.HostApp/Issues/Issue28827.xaml

@@ -0,0 +1,81 @@
+<?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.Issue28827"
+             xmlns:ns="clr-namespace:Maui.Controls.Sample.Issues">
+
+  <Grid Padding="10"
+        RowDefinitions="*, *">
+    <CollectionView
+      Grid.Row="0"
+      x:Name="collectionView"
+      x:DataType="ns:Issue28827CollectionViewViewModel"
+      ItemsSource="{Binding ItemsSource}"
+      ItemTemplate="{Binding ItemTemplate}"
+      IsGrouped="{Binding IsGrouped}"
+      GroupHeaderTemplate="{Binding GroupHeaderTemplate}"
+      GroupFooterTemplate="{Binding GroupFooterTemplate}"
+      AutomationId="collectionView">
+    </CollectionView>
+
+    <ScrollView Grid.Row="1">
+      <StackLayout Padding="10"
+                   Spacing="10">
+        <Label Text="GroupHeaderTemplate:"
+               FontAttributes="Bold"
+               FontSize="12"/>
+        <StackLayout Orientation="Horizontal">
+          <RadioButton x:Name="GroupHeaderTemplateNone"
+                       IsChecked="True"
+                       CheckedChanged="OnGroupHeaderTemplateChanged"
+                       Content="None"
+                       FontSize="11"
+                       GroupName="GroupHeaderTemplateGroup"
+                       AutomationId="GroupHeaderTemplateNone"/>
+          <RadioButton x:Name="GroupHeaderTemplateGrid"
+                       CheckedChanged="OnGroupHeaderTemplateChanged"
+                       Content="View"
+                       FontSize="11"
+                       GroupName="GroupHeaderTemplateGroup"
+                       AutomationId="GroupHeaderTemplateGrid"/>
+        </StackLayout>
+
+        <Label Text="GroupFooterTemplate:"
+               FontAttributes="Bold"
+               FontSize="12"/>
+        <StackLayout Orientation="Horizontal">
+          <RadioButton x:Name="GroupFooterTemplateNone"
+                       IsChecked="True"
+                       CheckedChanged="OnGroupFooterTemplateChanged"
+                       Content="None"
+                       FontSize="11"
+                       GroupName="GroupFooterTemplateGroup"
+                       AutomationId="GroupFooterTemplateNone"/>
+          <RadioButton x:Name="GroupFooterTemplateGrid"
+                       CheckedChanged="OnGroupFooterTemplateChanged"
+                       Content="View"
+                       FontSize="11"
+                       GroupName="GroupFooterTemplateGroup"
+                       AutomationId="GroupFooterTemplateGrid"/>
+        </StackLayout>
+
+        <Label Text="IsGrouped:"
+               FontSize="12"
+               FontAttributes="Bold"/>
+        <StackLayout Orientation="Horizontal">
+          <RadioButton x:Name="IsGroupedFalse"
+                       Content="False"
+                       IsChecked="True"
+                       CheckedChanged="OnIsGroupedChanged"
+                       FontSize="11"
+                       AutomationId="IsGroupedFalse"/>
+          <RadioButton x:Name="IsGroupedTrue"
+                       Content="True"
+                       CheckedChanged="OnIsGroupedChanged"
+                       FontSize="11"
+                       AutomationId="IsGroupedTrue"/>
+        </StackLayout>
+      </StackLayout>
+    </ScrollView>
+  </Grid>
+</ContentPage>

src/Controls/tests/TestCases.HostApp/Issues/Issue28827.xaml.cs

@@ -0,0 +1,216 @@
+using System.Collections.ObjectModel;
+using System.ComponentModel;
+using System.Runtime.CompilerServices;
+
+namespace Maui.Controls.Sample.Issues;
+
+[Issue(IssueTracker.Github, 28827, "[Android] Group Header/Footer set for all Items when IsGrouped is True for ObservableCollection", PlatformAffected.Android)]
+public partial class Issue28827 : ContentPage
+{
+	Issue28827CollectionViewViewModel _viewModel;
+	public Issue28827()
+	{
+		InitializeComponent();
+		BindingContext = _viewModel = new Issue28827CollectionViewViewModel();
+	}
+
+	void OnGroupHeaderTemplateChanged(object sender, CheckedChangedEventArgs e)
+	{
+		if (GroupHeaderTemplateNone.IsChecked)
+		{
+			_viewModel.GroupHeaderTemplate = null;
+		}
+		else if (GroupHeaderTemplateGrid.IsChecked)
+		{
+			_viewModel.GroupHeaderTemplate = new DataTemplate(() =>
+			{
+				return new Grid
+				{
+					BackgroundColor = Colors.LightGray,
+					Padding = new Thickness(10),
+					Children =
+					{
+							new Label
+							{
+								Text = "Group Header Template (Grid View)",
+								FontSize = 18,
+								AutomationId = "GroupHeaderTemplate",
+								FontAttributes = FontAttributes.Bold,
+								HorizontalOptions = LayoutOptions.Center,
+								VerticalOptions = LayoutOptions.Center,
+								TextColor = Colors.Green
+							}
+					}
+				};
+			});
+		}
+	}
+
+	void OnGroupFooterTemplateChanged(object sender, CheckedChangedEventArgs e)
+	{
+		if (GroupFooterTemplateNone.IsChecked)
+		{
+			_viewModel.GroupFooterTemplate = null;
+		}
+		else if (GroupFooterTemplateGrid.IsChecked)
+		{
+			_viewModel.GroupFooterTemplate = new DataTemplate(() =>
+			{
+				return new Grid
+				{
+					BackgroundColor = Colors.LightGray,
+					Padding = new Thickness(10),
+					Children =
+					{
+							new Label
+							{
+								Text = "Group Footer Template (Grid View)",
+								FontSize = 18,
+								AutomationId = "GroupFooterTemplate",
+								FontAttributes = FontAttributes.Bold,
+								HorizontalOptions = LayoutOptions.Center,
+								VerticalOptions = LayoutOptions.Center,
+								TextColor = Colors.Red
+							}
+					}
+				};
+			});
+		}
+	}
+
+	void OnIsGroupedChanged(object sender, CheckedChangedEventArgs e)
+	{
+		if (IsGroupedFalse.IsChecked)
+		{
+			_viewModel.IsGrouped = false;
+		}
+		else if (IsGroupedTrue.IsChecked)
+		{
+			_viewModel.IsGrouped = true;
+		}
+	}
+}
+
+public class Issue28827CollectionViewViewModel : INotifyPropertyChanged
+{
+	DataTemplate _groupHeaderTemplate;
+	DataTemplate _groupFooterTemplate;
+	DataTemplate _itemTemplate;
+	bool _isGrouped = false;
+	ObservableCollection<Issue28827ItemModel> _observableCollection;
+
+	public event PropertyChangedEventHandler PropertyChanged;
+
+	public Issue28827CollectionViewViewModel()
+	{
+		LoadItems();
+		ItemTemplate = new DataTemplate(() =>
+		{
+			var stackLayout = new StackLayout
+			{
+				Padding = new Thickness(10),
+				HorizontalOptions = LayoutOptions.Center,
+				VerticalOptions = LayoutOptions.Center
+			};
+
+			var label = new Label
+			{
+				VerticalOptions = LayoutOptions.Center,
+				HorizontalOptions = LayoutOptions.Center
+			};
+			label.SetBinding(Label.TextProperty, "Caption");
+			stackLayout.Children.Add(label);
+			return stackLayout;
+		});
+
+		GroupHeaderTemplate = new DataTemplate(() =>
+		{
+			var stackLayout = new StackLayout
+			{
+				BackgroundColor = Colors.LightGray
+			};
+			var label = new Label
+			{
+				FontAttributes = FontAttributes.Bold,
+				FontSize = 18
+			};
+			label.SetBinding(Label.TextProperty, "Key");
+			stackLayout.Children.Add(label);
+			return stackLayout;
+		});
+	}
+
+	void LoadItems()
+	{
+		_observableCollection = new ObservableCollection<Issue28827ItemModel>
+			{
+				new Issue28827ItemModel { Caption = "Item 1" },
+				new Issue28827ItemModel { Caption = "Item 2" },
+				new Issue28827ItemModel { Caption = "Item 3" }
+			};
+	}
+
+	public DataTemplate GroupHeaderTemplate
+	{
+		get => _groupHeaderTemplate;
+		set { _groupHeaderTemplate = value; OnPropertyChanged(); }
+	}
+
+	public DataTemplate GroupFooterTemplate
+	{
+		get => _groupFooterTemplate;
+		set { _groupFooterTemplate = value; OnPropertyChanged(); }
+	}
+
+	public DataTemplate ItemTemplate
+	{
+		get => _itemTemplate;
+		set { _itemTemplate = value; OnPropertyChanged(); }
+	}
+
+	public bool IsGrouped
+	{
+		get => _isGrouped;
+		set { _isGrouped = value; OnPropertyChanged(); }
+	}
+
+	public object ItemsSource
+	{
+		get => _observableCollection;
+	}
+
+	protected void OnPropertyChanged([CallerMemberName] string propertyName = null)
+	{
+		if (propertyName == nameof(IsGrouped))
+		{
+			OnPropertyChanged(nameof(ItemsSource));
+		}
+
+		PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
+	}
+}
+
+internal class Issue28827Grouping<TKey, TItem> : List<TItem>
+{
+	public TKey Key { get; }
+
+	public Issue28827Grouping(TKey key, List<TItem> items) : base(items)
+	{
+		Key = key;
+	}
+
+	public override string ToString()
+	{
+		return Key?.ToString() ?? base.ToString();
+	}
+}
+
+internal class Issue28827ItemModel
+{
+	public string Caption { get; set; }
+
+	public override string ToString()
+	{
+		return !string.IsNullOrEmpty(Caption) ? Caption : base.ToString();
+	}
+}

src/Controls/tests/TestCases.Shared.Tests/Tests/Issues/Issue28827.cs

@@ -0,0 +1,28 @@
+#if TEST_FAILS_ON_WINDOWS // NullReferenceException occurs when switching isGrouped to true
+// refer to https://github.com/dotnet/maui/issues/28824
+using NUnit.Framework;
+using UITest.Appium;
+using UITest.Core;
+
+namespace Microsoft.Maui.TestCases.Tests.Issues;
+
+public class Issue28827 : _IssuesUITest
+{
+	public override string Issue => "[Android] Group Header/Footer set for all Items when IsGrouped is True for ObservableCollection";
+	public Issue28827(TestDevice device)
+	: base(device)
+	{ }
+
+	[Test]
+	[Category(UITestCategories.CollectionView)]
+	public void CVGroupHFTemplateWithObservableCollection()
+	{
+		App.WaitForElement("collectionView");
+		App.Tap("IsGroupedTrue");
+		App.Tap("GroupHeaderTemplateGrid");
+		App.Tap("GroupFooterTemplateGrid");
+		App.WaitForNoElement("GroupHeaderTemplate");
+		App.WaitForNoElement("GroupFooterTemplate");
+	}
+}
+#endif