Fix VerticalOffset Update When Modifying CollectionView.ItemsSource While Scrolled

[devanathan-vaithiyanathan]

Issue Details

When modifying the CollectionView.ItemsSource while scrolled down in the list on Android, the ItemsViewScrolledEventArgs.VerticalOffset is not updated correctly. The offset "0" should always represent the start of the collection, but instead, it changes inconsistently when items are added or removed. This issue appears when the collection is scrolled beyond the position of the added or deleted items.

Root Cause

The offsets (VerticalOffset and HorizontalOffset) were being calculated incrementally and did not reset properly when the ItemsSource changed, leading to incorrect offset values.

Description of Change

The change resets the VerticalOffset and HorizontalOffset to 0 when the ItemsSource is updated. This ensures correct offset values after adding or removing items, fixing the issue of incorrect offsets while scrolling.

Issues Fixed

Fixes #21708

Validated the behaviour in the following platforms

• Android
• Windows
• iOS
• Mac

Output Screenshot

Before	After
Before.mov	After.mov

[dotnet-policy-service]

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