[iOS / Mac] Fix CollectionView.ScrollTo(index) silently failing whenIsGrouped="True"

[Dhivya-SF4094]

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:

When a CollectionView has IsGrouped="True", calling ScrollTo(index) should scroll to the item at that position. This works correctly on Android, but on iOS, MacCatalyst, and Windows scrolled not at all.

Root Cause:

• When ScrollTo(index) is called with no explicit group (GroupIndex == -1), both iOS paths fell through to:
  return NSIndexPath.Create(0, args.Index); // always section 0
• For a grouped CollectionView with multiple sections, any flat index that exceeded the count of section 0 produced an invalid NSIndexPath — UICollectionView.ScrollToItem silently did nothing.
• Additionally, IsIndexPathValid in the Items1 handler (ItemsViewHandler.iOS.cs) lacked a null guard. Since ConvertFlatIndexToGroupedIndexPath returns null for out-of-range indices, this could cause a NullReferenceException.

Description of change:

• Added ConvertFlatIndexToGroupedIndexPath to both ItemsViewHandler.iOS.cs and ItemsViewHandler2.iOS.cs :
• Activated only when groupable.IsGrouped == true.
• Bounds-checks flat index against itemsSource.ItemCount before walking groups
• Iterates IItemsViewSource.ItemCountInGroup(section) to resolve the NSIndexPath(section, item). Returns null for out-of-range indices (safely handled by
• Also added indexPath is null || guard to IsIndexPathValid (Items1) to NullReferenceException on out-of-range scroll requests.

Validated the behaviour in the following platforms

• Android
• Windows
• iOS
• Mac

Fixes

Fixes #35326

Screenshots

Before	After
35326_BeforeFix.mov	35326_AfterFix.mov

[github-actions]

🚀 Dogfood this PR with:

⚠️ WARNING: Do not do this without first carefully reviewing the code of this PR to satisfy yourself it is safe.

curl -fsSL https://raw.githubusercontent.com/dotnet/maui/main/eng/scripts/get-maui-pr.sh | bash -s -- 35609

Or

• Run remotely in PowerShell:

iex "& { $(irm https://raw.githubusercontent.com/dotnet/maui/main/eng/scripts/get-maui-pr.ps1) } 35609"

[kubaflo]

/review -b feature/refactor-copilot-yml

[MauiBot]

Expert Review — 1 findings

See inline comments for details.

[Dhivya-SF4094]

Analyzed the AI summary, confirmed the legitimate concern, and applied the appropriate resolution.

[kubaflo]

/review -b feature/enhanced-reviewer

[MauiBot]

Expert Review — 1 findings

See inline comments for details.

[MauiBot]

[major] Regression prevention - This UI test is discovered when the CollectionView category runs on every compiled test platform, but the PR fix only changes the iOS/MacCatalyst handlers and the issue page metadata scopes the scenario to iOS/MacCatalyst. _IssuesUITest does not use PlatformAffected to skip NUnit test discovery, so please explicitly scope this test to iOS/MacCatalyst (or fix/validate the behavior on Windows too) to avoid adding a latent non-iOS UI test failure.

[MauiBot]

AI Review Summary

@Dhivya-SF4094 — new AI review results are available based on this last commit: dc5a553.
Updated Test To request a fresh review after new comments or commits, comment /review rerun.

Review Sessions — click to expand

Gate — Test Before & After Fix

Gate Result: ✅ PASSED

Platform: IOS · Base: main · Merge base: b0ea772f

Test	Without Fix (expect FAIL)	With Fix (expect PASS)
🖥️ Issue35326 Issue35326	✅ FAIL — 355s	✅ PASS — 125s

🔴 Without fix — 🖥️ Issue35326: FAIL ✅ · 355s

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  Optimizing assemblies for size may change the behavior of the app. Be sure to test after publishing. See: https://aka.ms/dotnet-illink
  Optimizing assemblies for size. This process might take a while.

Build succeeded.

/Users/cloudtest/vss/_work/1/s/.dotnet/packs/Microsoft.iOS.Sdk.net10.0_26.0/26.0.11017/targets/Xamarin.Shared.Sdk.targets(309,3): warning : RuntimeIdentifier was set on the command line, and will override the value for RuntimeIdentifiers set in the project file. [/Users/cloudtest/vss/_work/1/s/src/Controls/tests/TestCases.HostApp/Controls.TestCases.HostApp.csproj::TargetFramework=net10.0-ios]
    1 Warning(s)
    0 Error(s)

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Test run for /Users/cloudtest/vss/_work/1/s/artifacts/bin/Controls.TestCases.iOS.Tests/Debug/net10.0/Controls.TestCases.iOS.Tests.dll (.NETCoreApp,Version=v10.0)
VSTest version 18.0.1 (arm64)

Starting test execution, please wait...
A total of 1 test files matched the specified pattern.
[xUnit.net 00:00:00.00] xUnit.net VSTest Adapter v2.8.2+699d445a1a (64-bit .NET 10.0.0)
[xUnit.net 00:00:00.07]   Discovering: Controls.TestCases.iOS.Tests
[xUnit.net 00:00:00.21]   Discovered:  Controls.TestCases.iOS.Tests
NUnit Adapter 4.5.0.0: Test execution started
Running selected tests in /Users/cloudtest/vss/_work/1/s/artifacts/bin/Controls.TestCases.iOS.Tests/Debug/net10.0/Controls.TestCases.iOS.Tests.dll
   NUnit3TestExecutor discovered 1 of 1 NUnit test cases using Current Discovery mode, Non-Explicit run
>>>>> 6/1/2026 7:08:28 AM FixtureSetup for Issue35326(iOS)
>>>>> 6/1/2026 7:08:33 AM GroupedCollectionViewScrollToIndexScrollsToCorrectItem Start
>>>>> 6/1/2026 7:08:49 AM GroupedCollectionViewScrollToIndexScrollsToCorrectItem Stop
>>>>> 6/1/2026 7:08:49 AM Log types: syslog, crashlog, performance, safariConsole, safariNetwork, server
  Failed GroupedCollectionViewScrollToIndexScrollsToCorrectItem [17 s]
  Error Message:
   System.TimeoutException : Timed out waiting for element...
  Stack Trace:
     at UITest.Appium.HelperExtensions.Wait(Func`1 query, Func`2 satisfactory, String timeoutMessage, Nullable`1 timeout, Nullable`1 retryFrequency) in /_/src/TestUtils/src/UITest.Appium/HelperExtensions.cs:line 2757
   at UITest.Appium.HelperExtensions.WaitForAtLeastOne(Func`1 query, String timeoutMessage, Nullable`1 timeout, Nullable`1 retryFrequency) in /_/src/TestUtils/src/UITest.Appium/HelperExtensions.cs:line 2784
   at UITest.Appium.HelperExtensions.WaitForElement(IApp app, String marked, String timeoutMessage, Nullable`1 timeout, Nullable`1 retryFrequency, Nullable`1 postTimeout) in /_/src/TestUtils/src/UITest.Appium/HelperExtensions.cs:line 793
   at Microsoft.Maui.TestCases.Tests.Issues.Issue35326.GroupedCollectionViewScrollToIndexScrollsToCorrectItem() in /_/src/Controls/tests/TestCases.Shared.Tests/Tests/Issues/Issue35326.cs:line 23
   at System.Reflection.MethodBaseInvoker.InterpretedInvoke_Method(Object obj, IntPtr* args)
   at System.Reflection.MethodBaseInvoker.InvokeWithNoArgs(Object obj, BindingFlags invokeAttr)

NUnit Adapter 4.5.0.0: Test execution complete
Results File: /Users/cloudtest/vss/_work/1/s/CustomAgentLogsTmp/UITests/TestResults/Issue35326.trx

Test Run Failed.
Total tests: 1
     Failed: 1
 Total time: 1.7540 Minutes
>>> TRX_RESULT_FILE: /Users/cloudtest/vss/_work/1/s/CustomAgentLogsTmp/UITests/TestResults/Issue35326.trx

🟢 With fix — 🖥️ Issue35326: PASS ✅ · 125s

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/Users/cloudtest/vss/_work/1/s/.dotnet/packs/Microsoft.iOS.Sdk.net10.0_26.0/26.0.11017/targets/Xamarin.Shared.Sdk.targets(309,3): warning : RuntimeIdentifier was set on the command line, and will override the value for RuntimeIdentifiers set in the project file. [/Users/cloudtest/vss/_work/1/s/src/Controls/tests/TestCases.HostApp/Controls.TestCases.HostApp.csproj::TargetFramework=net10.0-ios]
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  Optimizing assemblies for size may change the behavior of the app. Be sure to test after publishing. See: https://aka.ms/dotnet-illink
  Optimizing assemblies for size. This process might take a while.

Build succeeded.

/Users/cloudtest/vss/_work/1/s/.dotnet/packs/Microsoft.iOS.Sdk.net10.0_26.0/26.0.11017/targets/Xamarin.Shared.Sdk.targets(309,3): warning : RuntimeIdentifier was set on the command line, and will override the value for RuntimeIdentifiers set in the project file. [/Users/cloudtest/vss/_work/1/s/src/Controls/tests/TestCases.HostApp/Controls.TestCases.HostApp.csproj::TargetFramework=net10.0-ios]
    1 Warning(s)
    0 Error(s)

Time Elapsed 00:01:03.94
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VSTest version 18.0.1 (arm64)

Starting test execution, please wait...
A total of 1 test files matched the specified pattern.
[xUnit.net 00:00:00.00] xUnit.net VSTest Adapter v2.8.2+699d445a1a (64-bit .NET 10.0.0)
[xUnit.net 00:00:00.06]   Discovering: Controls.TestCases.iOS.Tests
[xUnit.net 00:00:00.20]   Discovered:  Controls.TestCases.iOS.Tests
NUnit Adapter 4.5.0.0: Test execution started
Running selected tests in /Users/cloudtest/vss/_work/1/s/artifacts/bin/Controls.TestCases.iOS.Tests/Debug/net10.0/Controls.TestCases.iOS.Tests.dll
   NUnit3TestExecutor discovered 1 of 1 NUnit test cases using Current Discovery mode, Non-Explicit run
>>>>> 6/1/2026 7:10:51 AM FixtureSetup for Issue35326(iOS)
>>>>> 6/1/2026 7:10:56 AM GroupedCollectionViewScrollToIndexScrollsToCorrectItem Start
>>>>> 6/1/2026 7:10:58 AM GroupedCollectionViewScrollToIndexScrollsToCorrectItem Stop
  Passed GroupedCollectionViewScrollToIndexScrollsToCorrectItem [2 s]
NUnit Adapter 4.5.0.0: Test execution complete
Results File: /Users/cloudtest/vss/_work/1/s/CustomAgentLogsTmp/UITests/TestResults/Issue35326.trx

Test Run Successful.
Total tests: 1
     Passed: 1
 Total time: 26.7576 Seconds
>>> TRX_RESULT_FILE: /Users/cloudtest/vss/_work/1/s/CustomAgentLogsTmp/UITests/TestResults/Issue35326.trx

📁 Fix files reverted (3 files)

• eng/pipelines/ci-copilot.yml
• src/Controls/src/Core/Handlers/Items/ItemsViewHandler.iOS.cs
• src/Controls/src/Core/Handlers/Items2/ItemsViewHandler2.iOS.cs

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UI Tests — CollectionView

Detected UI test categories: CollectionView

✅ Deep UI tests — 416 passed, 0 failed across 1 category on platform-pool agent (replaces in-process counts above).

🧪 UI Test Execution Results (deep, platform pool)

Category	Tests	Snapshot diffs
CollectionView	416/418 ✓	—
📎 Download drop-deep-uitests artifact (TRX + snapshot diffs)

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Pre-Flight — Context & Validation

Issue: #35326 - CollectionView.ScrollTo(index) doesn't work correctly when IsGrouped="True" on iOS and MacCatalyst
PR: #35609 - Fix grouped CollectionView ScrollTo(index) on iOS/MacCatalyst
Platforms Affected: iOS, MacCatalyst
Files Changed: 2 implementation, 2 test

Key Findings

• The bug is an iOS UICollectionView index-path semantics mismatch: grouped CollectionView.ScrollTo(index) supplies a flat item index, but native scrolling requires section/item coordinates.
• The PR fix correctly converts a flat grouped index to NSIndexPath(section,item), but duplicates the same conversion loop in both Items and Items2 handlers.
• Test coverage is UI/Appium-based through Issue35326 and targets the CollectionView category.
• GitHub CLI API access was unavailable in this environment, so pre-flight used the checked-out PR branch, local diff, commit metadata, and repository files.

Code Review Summary

Verdict: LGTM
Confidence: high
Errors: 0 | Warnings: 1 | Suggestions: 1

Key code review findings:
Duplicate grouped flat-index conversion exists in both ItemsViewHandler.iOS.cs and ItemsViewHandler2.iOS.cs; centralizing would reduce Items/Items2 divergence risk.-

Fix Candidates

#	Source	Approach	Test Result	Files Changed	Notes
PR	PR #35609	Convert grouped flat index to inside both iOS handlers	PASSED (Gate, prior step)	4 files	Original PR fix; functionally sound but duplicates conversion logic

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Code Review — Deep Analysis

Code PR #35609Review

Independent Assessment

What this changes: The iOS and Items2 iOS CollectionView handlers translate ScrollTo(index) calls on grouped CollectionView instances from a flat item index into the native NSIndexPath(section,item) required by UICollectionView.ScrollToItem. The PR also adds a UI regression page and Appium test for issue 35326.

Inferred motivation: On iOS/MacCatalyst, ScrollTo(index) with IsGrouped=true previously treated the flat index as an item in section 0, so indexes beyond the first group did not scroll to the expected grouped item.

Reconciliation with PR Narrative

Author claims: Issue 35326 reports that grouped CollectionView.ScrollTo(index) does not work correctly on iOS/MacCatalyst. The PR fixes grouped flat-index scrolling and adds an end-to-end UI test.
Agreement/disagreement: The local diff matches the claimed issue and addresses the iOS section/item mapping problem. The added test exercises the reported endpoint scenario, ScrollTo(49) on 5 groups of 10 items.

Findings

Conversion logic is duplicated between Items and Items2 handlersWarning ####
The same flat-index-to-grouped-index-path loop is implemented in both src/Controls/src/Core/Handlers/Items/ItemsViewHandler.iOS.cs and src/Controls/src/Core/Handlers/Items2/ItemsViewHandler2.iOS.cs. The logic is correct for the added test, but duplication between legacy Items and Items2 handlers increases the chance of future divergence.

The UI test covers index 0 and index 49 for uniform groups. Additional lower-level or UI coverage for group-boundary indexes (for example 10), uneven group sizes, and empty groups would further protect the index math.####

Failure Modes

• Negative or out-of-range flat indexes must not crash; the PR returns null and the existing validity check prevents scrolling.
• Boundary flat indexes must map to the first item of the next group rather than the last item of the previous group.
• Explicit grouped calls with groupIndex >= 0 must retain existing behavior and not be remapped.

Blast Radius

Low-to-medium. The implementation is scoped to iOS/MacCatalyst CollectionView/CarouselView handler ScrollToRequested handling for grouped views with GroupIndex == -1; ungrouped scrolling and item-based scrolling remain unchanged.

Verdict: LGTM

Confidence: high
Summary: The PR fix is functionally sound for the reported bug. The main improvement opportunity is maintainability: centralize the shared index conversion rather than duplicating it in both iOS handler implementations.

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Fix — Analysis & Comparison

Fix Candidates

#	Source	Approach	Test Result	Files Changed	Notes
1	try-fix	Centralize grouped flat-index conversion in internal IndexPathHelpers.GetIndexPathForFlatIndex, then call it from both iOS handlers	PASS	3 files	Better than PR fix: same behavior, less duplication, no public API change
PR	PR #35609	Duplicate grouped flat-index conversion locally in both iOS handlers	PASSED (Gate)	4 files	Original PR; functionally sound but less maintainable

Cross-Pollination

Model	Round	New Ideas?	Details
maui-expert-reviewer	1	Yes	Proposed centralizing conversion in IndexPathHelpers or moving resolution into controllers/source abstractions; recommended helper/controller approaches as lowest risk.
maui-expert-reviewer	refinement	Yes	After RS0016 failure, confirmed helper should remain internal to avoid public API surface changes.

Exhausted: No - stopped because candidate #1 passed targeted iOS validation and is demonstrably better than the PR's duplicated implementation.
Selected Fix: Candidate #1 - preserves PR behavior and passing Issue35326 coverage while reducing Items/Items2 divergence risk.

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Report — Final Recommendation

Comparative Report - PR #35609

Candidates Compared

Rank	Candidate	Regression Result	Assessment
1	pr-plus-reviewer	PASS inherited from PR gate on iOS; no iOS runtime behavior change	Best available candidate. It keeps the functionally correct PR fix and applies the expert reviewer's actionable feedback by scoping the new UI test to iOS/MacCatalyst, avoiding latent non-iOS test exposure.
2	try-fix-1	PASS (dotnet build ... net10.0-ios26.0; BuildAndRunHostApp.ps1 -Platform ios -TestFilter ...Issue35326)	Strong implementation candidate. It centralizes the grouped flat-index conversion in IndexPathHelpers, reducing duplication between Items and Items2, but it does not address the expert reviewer's test-platform scoping finding.
3	pr	PASS (gate: tests fail without fix and pass with fix)	Functionally correct for the reported iOS/MacCatalyst bug, but it duplicates conversion logic in both handler implementations and leaves the shared UI test discoverable outside the fixed platform scope.

Analysis

The raw PR fix correctly handles the root cause: for grouped iOS/MacCatalyst CollectionView scrolling, a flat MAUI index must be mapped to the native NSIndexPath(section, item). The gate already proved the regression test fails without the PR fix and passes with it.

try-fix-1 is the cleanest handler implementation because it factors the conversion into an internal IndexPathHelpers.GetIndexPathForFlatIndex helper and uses it from both Items and Items2. It also passed targeted iOS validation. However, the expert review of the PR surfaced a separate release-readiness problem in the added shared UI test: the test is not platform-scoped even though the fix is iOS/MacCatalyst-specific. Since try-fix-1 did not include that correction, it remains behind pr-plus-reviewer.

pr-plus-reviewer is the only candidate that incorporates the expert reviewer's actionable feedback while preserving the already-passing iOS behavior. Its remaining weakness is the duplicate conversion logic in the handlers, but that is a maintainability concern rather than a correctness or CI-scope risk. A future ideal patch would combine try-fix-1's shared helper with pr-plus-reviewer's platform-scoped test, but that combined patch is not one of the available STEP 5a candidates.

Winner

pr-plus-reviewer wins because it preserves the verified PR fix and addresses the highest-severity expert reviewer finding. No candidate with a failed regression result was ranked above a passing candidate.

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Future Action — review latest findings

No alternative fix was selected for this run. Review the session findings and CI results before merging.