Fix for CollectionView with RefreshView when ObservableCollection<T>.Clear() throws System.ArgumentOutOfRangeException

[SuthiYuvaraj]

Root Cause:

The issue arises because the UICollectionView's internal _itemSource becomes empty during pull-to-refresh, even though the ItemsSource in the controller still holds a valid count. This discrepancy causes an invalid state, where the GetSizeForItem method tries to access an index that no longer exists, resulting in a System.ArgumentOutOfRangeException. The issue was further compounded by the fact that GetSizeForItem was being called before the CollectionChanged event was triggered. This occurs because the ContentOffset is set during the pull-to-refresh operation, which prematurely triggers layout recalculations, leading to an invalid state.

Description of Change:

The change ensures the ElementAt method safely accesses elements by validating the index with (index >= 0 && index < list.Count). Using a ternary operator, it immediately returns the item or -1 for invalid indices, preventing System.ArgumentOutOfRangeException and simplifying the logic for better reliability.

Issues Fixed

Fixes #23868

Tested the behaviour in the following platforms

• Android
• Windows
• iOS
• Mac

###Output Video

Before Issue Fix	After Issue Fix
withoutfix.mov	withfix.mov

[dotnet-policy-service]

Hey there @SuthiYuvaraj! Thank you so much for your PR! Someone from the team will get assigned to your PR shortly and we'll get it reviewed.

[PureWeen]

Can you add the following test to this PR?

maui/src/Compatibility/ControlGallery/src/Issues.Shared/Issue7678.cs

Line 22 in 0a96700

public class Issue7678Ios : TestContentPage

When you copy the test over can you make sure to put it inside the XFIssue folder?

It looks like the ObservableItemSource changes were made in the following PR xamarin/Xamarin.Forms#7711 and I worry that the fixes here are reverting those fixes a bit.

[praveenkumarkarunanithi]

Can you add the following test to this PR?

maui/src/Compatibility/ControlGallery/src/Issues.Shared/Issue7678.cs

Line 22 in 0a96700

public class Issue7678Ios : TestContentPage

When you copy the test over can you make sure to put it inside the XFIssue folder?

It looks like the ObservableItemSource changes were made in the following PR xamarin/Xamarin.Forms#7711 and I worry that the fixes here are reverting those fixes a bit.

@PureWeen Regarding the changes to ObservableItemSource, we’d like to clarify that our fix now ensures functionality without modifying the Count property directly. Instead, we’ve implemented proper index validation to prevent exceptions when the list is empty or the index is out of range. This approach preserves the integrity of the existing logic and aligns with the previous changes introduced in PR xamarin/Xamarin.Forms#7711.
Additionally, we ensured the Issue7678 test case works as expected with the fix.