[Android] Fix CollectionView KeepScrollOffset regressed after PR #29255

[HarishwaranVijayakumar]

Note

Are you waiting for the changes in this PR to be merged?
It would be very helpful if you could test the resulting artifacts from this PR and let us know in a comment if this change resolves your issue. Thank you!

Issue Details

• Android CollectionView.ItemsUpdatingScrollMode = KeepScrollOffset stops working after ItemsSource is replaced.
• After the reassignment, inserting a new item at index 0 leaves the previous top item anchored on screen and hides the new item above the viewport — effectively KeepItemsInView semantics instead of KeepScrollOffset.
• Only Android is affected. iOS behaves correctly.

Root Cause of the issue

• MauiRecyclerView.RemoveScrollListener() calls ClearOnScrollListeners(), which removes all scroll listeners registered on the RecyclerView — including the one ScrollHelper self-registered.
• ScrollHelper._maintainingScrollOffsets flag is never reset, so it goes stale (true while the listener is actually detached).
• Subsequent ScrollHelper.AddScrollListener() calls short-circuit on the stale flag, so ScrollHelper is never re-attached.
• With no scroll callbacks reaching ScrollHelper, TrackOffsets() never runs and the ScrollBy(-delta) correction that drives KeepScrollOffset is silently skipped.

Before PR #29255

• ScrollHelper attached its listener lazily, inside UndoNextScrollAdjustment(), only when an insert actually needed it.
• The stale-flag desync caused by ClearOnScrollListeners() was a latent bug, but the lazy re-register path inside UndoNextScrollAdjustment() masked it for the typical user — the listener got attached the next time it was needed, so most KeepScrollOffset scenarios still worked.

After PR #29255

• Listener registration was moved out of UndoNextScrollAdjustment() and into an explicit ScrollHelper.AddScrollListener() method, called eagerly from MauiRecyclerView.UpdateItemsUpdatingScrollMode().
• Both AddScrollListener() and the old lazy block use the same _maintainingScrollOffsets guard, but the lazy self-heal block in UndoNextScrollAdjustment() was deleted.
• Now, when ClearOnScrollListeners() detaches ScrollHelper's listener, the flag stays true, the eager AddScrollListener() no-ops, the lazy safety net is gone, and KeepScrollOffset is permanently broken after the first ItemsSource reassignment.

Description of Change

Bug fix:

• Fixed the scroll listener removal logic in RemoveScrollListener() by removing only the specific listener instead of clearing all listeners, which resolves the KeepScrollOffset issue when replacing the ItemsSource in CollectionView on Android. (src/Controls/src/Core/Handlers/Items/Android/MauiRecyclerView.cs)

Test coverage:

• Added a new test case page that reproduces the issue and provides buttons to replace the ItemsSource, scroll to the top, and insert items at the top, making it easier to manually verify the fix. (src/Controls/tests/TestCases.HostApp/Issues/Issue35806.cs)
• Introduced an automated UI test (Android only) that verifies the KeepScrollOffset behavior after replacing the ItemsSource, ensuring the regression is caught in the future. (src/Controls/tests/TestCases.Shared.Tests/Tests/Issues/Issue35806.cs)

Issues Fixed

Fixes #35806

Tested the behavior in the following platforms

• Windows
• Android
• iOS
• Mac

Output

Before	After
Before-35806.mov	After-35806.mov

[dotnet-policy-service]

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

[kubaflo]

/azp run

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Azure Pipelines successfully started running 3 pipeline(s).

[kubaflo]

/azp run

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Azure Pipelines successfully started running 3 pipeline(s).

[HarishwaranVijayakumar]

@kubaflo, This appears to be an existing failure on the Windows InFlight/Current branch, not a failure introduced by this PR.