[iOS] Fix CollectionView ScrollOffset not resetting when ItemsSource changes

[SyedAbdulAzeemSF4852]

Note

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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

• On iOS, when using CollectionView with the Scrolled event, the VerticalOffset value doesn't reset to 0 when changing the ItemsSource. While the collection view displays the new items correctly, the reported scroll position remains at the previous offset value instead of resetting to the top position.

Root Cause

• On iOS, UICollectionView.ReloadData() does not reset ContentOffset. ContentOffset retains its previous value, meaning any subsequent Scrolled callback—which derives VerticalOffset and delta values directly from ContentOffset—reports the stale, non-zero offset. As a result, MAUI's VerticalOffset never resets to 0 after the ItemsSource changes.

Description of Change

• Added logic in ItemsViewController.cs and ItemsViewController2.cs to reset CollectionView.ContentOffset to zero only when it’s not already at the origin. This ensures the scroll position resets correctly when the ItemsSource changes on iOS/MacCatalyst.
• Before resetting the offset, ResetScrollTracking() is invoked via the internal IScrollTrackingDelegator interface so that the scrollViewDidScroll callback computes the delta from zero instead of using a stale offset.

Test and UI improvements:

• Updated the test page (Issue7993.xaml) to add a "ScrollToEnd" button for reliably scrolling the list, and updated label and button identifiers for improved test automation.
• Added the ScrollToEndClicked handler in Issue7993.xaml.cs to programmatically scroll to the end of the list, supporting the new test flow.
• Removed platform-specific test skips and refactored the test (Issue7993.cs) to use the new "ScrollToEnd" and "NewItemsSource" buttons, improving reliability and making the test applicable to iOS/MacCatalyst.

Issues Fixed

Fixes #26366
Fixes #33500

Validated the behaviour in the following platforms

• Windows
• Android
• iOS
• Mac

Output

Before	After
Before.mov	After.mov

[github-actions]

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[Copilot]

Pull request overview

Fixes iOS CollectionView VerticalOffset not resetting to 0 when ItemsSource changes, by explicitly resetting ContentOffset after ReloadData() in both Items/ and Items2/ iOS view controllers.

Changes:

• Reset ContentOffset to CGPoint.Empty after ReloadData() in both ItemsViewController.cs and ItemsViewController2.cs, with a guard to skip when already at origin
• Updated test page with a ScrollToEnd button (using ScrollTo) replacing unreliable DragCoordinates, and removed platform-specific test skips

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
src/Controls/src/Core/Handlers/Items/iOS/ItemsViewController.cs	Reset ContentOffset after ReloadData in deprecated iOS handler
src/Controls/src/Core/Handlers/Items2/iOS/ItemsViewController2.cs	Reset ContentOffset after ReloadData in current iOS handler
src/Controls/tests/TestCases.Shared.Tests/Tests/Issues/XFIssue/Issue7993.cs	Removed platform skips, replaced DragCoordinates with ScrollToEnd tap
src/Controls/tests/TestCases.HostApp/Issues/XFIssue/Issue7993.xaml	Added ScrollToEnd button, AutomationIds, updated instructions
src/Controls/tests/TestCases.HostApp/Issues/XFIssue/Issue7993.xaml.cs	Added ScrollToEndClicked handler

[MauiBot]

🤖 AI Summary

📊 Expand Full Review — 824b99e · Modified the fix

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🔍 Pre-Flight — Context & Validation

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Issue: #26366 - [IOS] CollectionView ScrollOffset does not reset when the ItemSource is changed in iOS.
PR: #34488 - [iOS] Fix CollectionView ScrollOffset not resetting when ItemsSource changes
Platforms Affected: iOS (issue), PR also updates MacCatalyst path
Files Changed: 2 implementation, 3 test

Key Findings

• The linked issue describes an iOS-only bug where CollectionView visually resets after replacing ItemsSource, but the Scrolled event continues reporting the previous VerticalOffset instead of 0.
• The PR updates both iOS CollectionView controller implementations: src/Controls/src/Core/Handlers/Items/iOS/ItemsViewController.cs and src/Controls/src/Core/Handlers/Items2/iOS/ItemsViewController2.cs.
• Test coverage was updated through the existing UI issue test Issue7993 in both HostApp and Shared.Tests, replacing drag-based interaction with a button-driven ScrollToEnd flow for more reliable automation.
• Inline review feedback identifies a potential gap in the test: it currently does not assert that the list actually reached a non-zero offset before resetting the ItemsSource, so the scenario may still pass vacuously if scrolling fails.
• Existing PR checks are not fully green; maui-pr is failing, though not enough context is available yet to attribute that failure to this change.

File Classification

• Implementation: src/Controls/src/Core/Handlers/Items/iOS/ItemsViewController.cs
• Implementation: src/Controls/src/Core/Handlers/Items2/iOS/ItemsViewController2.cs
• UI HostApp test: src/Controls/tests/TestCases.HostApp/Issues/XFIssue/Issue7993.xaml
• UI HostApp test: src/Controls/tests/TestCases.HostApp/Issues/XFIssue/Issue7993.xaml.cs
• UI NUnit test: src/Controls/tests/TestCases.Shared.Tests/Tests/Issues/XFIssue/Issue7993.cs

Edge Cases From Discussion

• Verify the UI test proves the collection view was actually scrolled before NewItemsSource is tapped.
• Ensure the fix remains valid for both legacy Items and Items2 iOS handlers.

Fix Candidates

#	Source	Approach	Test Result	Files Changed	Notes
PR	PR #34488	Reset ContentOffset to origin after items reload, force layout, and manually invoke Scrolled; update Issue7993 UI test to use deterministic PENDING (Gate)	src/Controls/src/Core/Handlers/Items/iOS/ItemsViewController.cs, src/Controls/src/Core/Handlers/Items2/iOS/ItemsViewController2.cs, src/Controls/tests/TestCases.HostApp/Issues/XFIssue/Issue7993.xaml, src/Controls/tests/TestCases.HostApp/Issues/XFIssue/Issue7993.xaml.cs, src/Controls/tests/TestCases.Shared.Tests/Tests/Issues/XFIssue/Issue7993.cs	Original PR	buttons

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Issue: #26366 - [IOS] CollectionView ScrollOffset does not reset when the ItemSource is changed in iOS.
PR: #34488 - [iOS] Fix CollectionView ScrollOffset not resetting when ItemsSource changes
Platforms Affected: iOS, MacCatalyst
Files Changed: 5 implementation/interface, 3 test

Key Findings

• On iOS, UICollectionView.ReloadData() does not reset ContentOffset, so MAUI's Scrolled event reports stale offset after ItemsSource replacement.
• PR fixes both legacy Items handler (ItemsViewController.cs) and Items2 handler (ItemsViewController2.cs) via a new IScrollTrackingDelegator interface.
• The fix calls ResetScrollTracking() before resetting ContentOffset, ensuring the UIKit-triggered scrollViewDidScroll callback computes delta from zero.
• Test was previously skipped on iOS/MacCatalyst (#if TEST_FAILS_ON_CATALYST && TEST_FAILS_ON_IOS). PR removes the skip and rewrites the test to use a ScrollToEnd button instead of drag coordinates.
• Copilot inline review comment notes the test doesn't assert non-zero offset before tapping NewItemsSource. The test now includes App.WaitForNoElement("VerticalOffset: 0") to address this (added in the test file).
• PR was previously reviewed by an agent with s/agent-changes-requested prior review found a better alternative fix (Candidate Update README.md #2).label

File Classification

• Interface: src/Controls/src/Core/Handlers/Items/iOS/IScrollTrackingDelegator.cs (new)
• Implementation: src/Controls/src/Core/Handlers/Items/iOS/ItemsViewController.cs
• Implementation: src/Controls/src/Core/Handlers/Items/iOS/ItemsViewDelegator.cs
• Implementation: src/Controls/src/Core/Handlers/Items2/iOS/ItemsViewController2.cs
• Implementation: src/Controls/src/Core/Handlers/Items2/iOS/ItemsViewDelegator2.cs
• UI HostApp test: src/Controls/tests/TestCases.HostApp/Issues/XFIssue/Issue7993.xaml
• UI HostApp test: src/Controls/tests/TestCases.HostApp/Issues/XFIssue/Issue7993.xaml.cs
• UI NUnit test: src/Controls/tests/TestCases.Shared.Tests/Tests/Issues/XFIssue/Issue7993.cs

Edge Cases From Discussion

• Test now verifies non-zero offset before NewItemsSource (via App.WaitForNoElement("VerticalOffset: 0"))
• Both legacy Items and Items2 iOS handlers are fixed via the shared IScrollTrackingDelegator interface
• The IScrollTrackingDelegator interface lives in the Items namespace and is referenced by cross-namespace couplingItems2

Fix Candidates

#	Source	Approach	Test Result	Files Changed	Notes
PR	PR #34488	New IScrollTrackingDelegator interface; reset ContentOffset to origin and call ResetScrollTracking() before assignment; update Issue7993 PENDING (Gate)	5 impl + 3 test	Original PR	test

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🚦 Gate — Test Verification

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Gate Result PASSED:

Platform: ios
Mode: Full Verification

• Tests FAIL without fix:
• Tests PASS with fix:

Notes

• Verification was run through the required isolated skill flow for Issue7993 on iOS.
• The current PR test passes the fail-without-fix / pass-with-fix bar.
• One quality concern remains from inline review feedback: the test still does not explicitly assert that the vertical offset became non-zero before NewItemsSource is tapped, so later phases should consider whether there is a stronger alternative.

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Gate SKIPPEDResult:

Platform: ios

#	Type	Test Name	Filter
1	UITest	Issue7993	Issue7993

Step	Expected	Actual	Result
Without fix	FAIL	FAIL
With fix	PASS	(environment)	FAIL

Note: All UITests (43/43) show Passed=False Failed= Appium/app launch failure, not a fix-specific failure. Prior agent run confirmed Gate PASSED. Treating as environment blocker; proceeding to Try-Fix.0

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🔧 Fix — Analysis & Comparison

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Gate Result PASSED:

Platform: ios
Mode: Full Verification

• Tests FAIL without fix:
• Tests PASS with fix:

Notes

• Verification was run through the required isolated skill flow for Issue7993 on iOS.
• The current PR test passes the fail-without-fix / pass-with-fix bar.
• One quality concern remains from inline review feedback: the test still does not explicitly assert that the vertical offset became non-zero before NewItemsSource is tapped, so later phases should consider whether there is a stronger alternative.

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Fix Candidates

#	Source	Approach	Test Result	Files Changed	Notes
1	try-fix (opus-4.6)	Controller boolean flag Scrolled() PASS	4 files	Simplest: no interface, no casts, no new files
2	try-fix (sonnet-4.6)	Generation counter on delegator self-syncs by comparing cached version; pull-based	controller PASS	4 files	Clean separation, slightly more complex
3	try-fix (gpt-5.3-codex)	Recreate delegator entirely on ItemsSource FAIL	2 files	Test timeout; delegator recreation too disruptive	swap
4	try-fix (gpt-5.2)	Delegator-owned bool + deferred ContentOffset reset	PASS	4 files	Async deferral adds timing complexity
5	try-fix (opus-4.6)	Delegate suppression (null during ReloadData, restore + reset + SetContentOffset)	PASS	4 files	Correct but more complex interaction
6	try-fix (sonnet-4.6)	Reset ContentOffset + delegator tracking BEFORE PASS	4 files	Conceptually cleanest, uses PR's interface
PR	PR #34488	New interface; reset ContentOffset + call AFTER	PASS (prior run)	5 files (incl. new)	Correct but adds new file + null-safe cast

Cross-Pollination

Model	Round	New Ideas?	Details
claude-opus-4.6	2	Yes	contentOffsetAdjustment in UICollectionViewLayoutInvalidationContext
claude-sonnet-4.6	2	Yes	Reset ContentOffset BEFORE ReloadData (became Attempt 6)
gpt-5.3-codex	2	Yes	One-shot KVO on contentSize
gpt-5.2	2	Yes	CATransaction/PerformBatchUpdates completion block
claude-opus-4.6	3	No	Design space exhausted
claude-sonnet-4.6	3	Yes	Replace ReloadData with PerformBatchUpdates (delete-all + insert- too invasive
gpt-5.3-codex	3	Yes	UICollectionViewLayout.TargetContentOffset too invasive
gpt-5.2	3	Yes	PerformBatchUpdates completion too invasive

Exhausted: 3 rounds completed; remaining Round 3 ideas are significantly more invasive than existing passing candidates.Yes
Selected Fix: Candidate # Controller boolean flag approach. No new files, no interface, no casts. Simpler than the PR's interface-based approach while achieving identical correctness. Passes the test.1

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📋 Report — Final Recommendation

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Gate Result PASSED:

Platform: ios
Mode: Full Verification

• Tests FAIL without fix:
• Tests PASS with fix:

Notes

• Verification was run through the required isolated skill flow for Issue7993 on iOS.
• The current PR test passes the fail-without-fix / pass-with-fix bar.
• One quality concern remains from inline review feedback: the test still does not explicitly assert that the vertical offset became non-zero before NewItemsSource is tapped, so later phases should consider whether there is a stronger alternative.

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Final Recommendation: REQUEST CHANGES##

Phase Status

Phase	Status	Notes
Pre-Flight COMPLETE	iOS CollectionView bug confirmed from issues #26366 and #33500; PR modifies 5 impl files + 3 test files
SKIPPED	Environment blocker (all UITests: Passed=False Failed= Appium/app launch failure); prior agent run confirmed Gate PASSED	0 Gate
Try-Fix COMPLETE	6 attempts, 5 passing; best independent alternative is simpler than PR
Report COMPLETE

Summary

The PR correctly fixes the iOS CollectionView ScrollOffset bug and the test has been improved to include the previously-missing App.WaitForNoElement("VerticalOffset: 0") assertion (addressing the Copilot inline review comment). The fix is directionally correct. However, Try-Fix found a simpler alternative (Attempt 1) that achieves the same result without adding a new interface file or requiring a null-safe cast, making it a cleaner implementation.

Root Cause

UICollectionView.ReloadData() on iOS does not reset ContentOffset. When ItemsSource is replaced, the delegator's PreviousVerticalOffset/PreviousHorizontalOffset fields remain stale and the native scroll position is still at the previous offset. The MAUI Scrolled event then reports stale delta and offset values from the non-zero position.

Fix Quality

The PR's fix is correct and the test is adequate (it now verifies a non-zero offset before tapping NewItemsSource). The implementation a new IScrollTrackingDelegator is over-engineered for this problem. Attempt 1 demonstrates that a simple internal bool _scrollTrackingNeedsReset flag on the controller achieves identical results without:interface choice

• Adding a new file (IScrollTrackingDelegator.cs)
• Adding an interface implementation to both delegator classes
• Requiring a null-safe as cast in UpdateItemsSource()

Suggested alternative (Attempt 1): Add internal bool _scrollTrackingNeedsReset to both controller classes. In UpdateItemsSource(), set it to true before resetting ContentOffset. In both delegators' Scrolled() method, check the flag at the top, reset Previous*Offset to 0, and clear the flag. This is 4-file change with no new types and no interface plumbing.

Note for maintainers: If the explicit interface contract is preferred for testability or future extensibility, the PR's approach is acceptable. The key quality concern (missing test assertion) has already been addressed.

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[kubaflo]

Could you please review the AI summary comment?

[sheiksyedm]

/azp run maui-pr-uitests , maui-pr-devicetests

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