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

[Tamilarasan-Paranthaman]

Root Cause of the issue

• The items in the ItemsSource collection were being cast to IEnumerable and added to the groups collection, even when they were not actually of an IEnumerable type. As a result, these individual items were incorrectly treated as groups, leading to group-related behaviors such as the display of group headers and footers.

Description of Change

• I have added a type check to ensure that only items that implement IEnumerable are added to the groups collection. If an item is not an IEnumerable, it will no longer be treated as a group, and the groups collection will remain empty in such cases.

Issues Fixed

Fixes #28827

Tested the behaviour in the following platforms

• iOS
• Android
• Windows
• Mac

Screenshot

Before Fix	After Fix
Before-Fix.mov	After-Fix.mov

[jsuarezruiz]

/azp run

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[github-actions]

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[Copilot]

Pull request overview

This PR fixes a bug where CollectionView group headers and footers were incorrectly applied to all items when IsGrouped was set to true with a non-grouped ObservableCollection<T>. The root cause was that individual items were being cast to IEnumerable unconditionally, causing them to be treated as groups even when they weren't enumerable collections.

Key changes:

• Added type check to ensure only items implementing IEnumerable are treated as groups in the Android handler
• Added comprehensive UI test with proper XAML page and NUnit test implementation
• Fix aligns Android behavior with iOS, which already had this check in place

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 3 comments.

File	Description
src/Controls/src/Core/Handlers/Items/Android/ItemsSources/ObservableGroupedSource.cs	Added IEnumerable type check before adding items to groups collection to prevent non-enumerable items from being treated as groups
src/Controls/tests/TestCases.HostApp/Issues/Issue28827.xaml	Created test page UI with CollectionView and radio button controls to toggle grouping and templates
src/Controls/tests/TestCases.HostApp/Issues/Issue28827.xaml.cs	Implemented view model and event handlers for testing grouped collection behavior with templates
src/Controls/tests/TestCases.Shared.Tests/Tests/Issues/Issue28827.cs	Added NUnit UI test that verifies group headers/footers don't appear when grouping is enabled on non-grouped collections (excluded from Windows due to unrelated issue #28824)

[Copilot]

The fix only checks if the item is IEnumerable, but the iOS implementation in ObservableGroupedSource.cs (line 136) has a more restrictive check: if (_groupSource[n] is INotifyCollectionChanged && _groupSource[n] is IEnumerable list).

For consistency across platforms and to ensure proper observable behavior, consider adding the INotifyCollectionChanged check here as well:

if (_groupSource[n] is INotifyCollectionChanged && _groupSource[n] is IEnumerable list)
{
    var source = ItemsSourceFactory.Create(list, _groupableItemsView, this);
    source.HasFooter = _hasGroupFooters;
    source.HasHeader = _hasGroupHeaders;
    _groups.Add(source);
}

This would ensure that only items implementing both interfaces are treated as observable groups, matching the iOS behavior.

[Copilot]

This PR fixes the DEPRECATED Items/ handlers (located at src/Controls/src/Core/Handlers/Items/), not the current Items2/ handlers.

According to the coding guidelines (CodingGuidelineID: 1000002), the Items/ handlers are deprecated and Items2/ is the active implementation. However, since Items2/ only has iOS implementation and Android CollectionView still uses Items/, this fix is appropriate for the current codebase.

Note: When Items2/ Android support is added in the future, this fix will need to be implemented there as well.

[Copilot]

[nitpick] The test is excluded from Windows using #if TEST_FAILS_ON_WINDOWS with a reference to issue #28824, which indicates there's a separate NullReferenceException bug on Windows.

However, according to the PR description, the fix was tested on Windows (MacCatalyst checkbox is checked, which runs on macOS). The compilation directive name suggests the test itself fails on Windows, not that the fix doesn't work there.

Consider clarifying:

1. Does the underlying bug (issue [Android] Group Header/Footer Repeated for All Items When IsGrouped is True for ObservableCollection #28827) affect Windows, or only the test infrastructure?
2. If Windows has the same grouped collection bug, should a Windows-specific version of this test be created once issue [Windows] NullReferenceException thrown When Toggling IsGrouped to True in ObservableCollection Binding #28824 is resolved?
3. Should the comment explain why Windows is excluded more clearly (e.g., "Test excluded on Windows due to unrelated NullReferenceException in test infrastructure - see [Windows] NullReferenceException thrown When Toggling IsGrouped to True in ObservableCollection Binding #28824")?

Suggested change

	#if TEST_FAILS_ON_WINDOWS // NullReferenceException occurs when switching isGrouped to true
	#if TEST_FAILS_ON_WINDOWS // Test excluded on Windows due to unrelated NullReferenceException in test infrastructure - see https://github.com/dotnet/maui/issues/28824. The underlying grouped collection bug (issue #28827) is not Windows-specific; re-enable this test on Windows once issue #28824 is resolved.