[iOS][CV2] Fix CollectionView2 on iOS iPad jumps/scrolls randomly when item size changes

[devanathan-vaithiyanathan]

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

In CollectionView2, when an item’s size changes, the CollectionView jumps or scrolls unexpectedly instead of keeping its current position.

Description of Change

Replaced the cell update logic from invalidateLayout to reconfigureItems for the affected cell.
reconfigureItems (iOS 15+) is lighter and works correctly on iPad iOS 26.

Issues Fixed

Fixes #32796
Fixes #33833

Regarding test case

Since the issue reproduces only on iPadOS 26, I haven’t added a test case.

Tested the behavior in the following platforms.

• Android
• Windows
• iOS
• Mac

Before	After
iOS Before.mov	iOS After.mov

[Copilot]

Pull request overview

This PR fixes a CollectionView2 issue on iPad where the view jumps or scrolls unexpectedly when item sizes change. The fix replaces the cell invalidation approach from using InvalidateLayout to using ReconfigureItems (iOS 15+), which is designed to handle size changes more efficiently without full cell recreation.

Changes:

• Adds a new code path that uses ReconfigureItems for iOS 15+ when cells need layout invalidation
• Wraps the reconfiguration in UIView.PerformWithoutAnimation to prevent visual artifacts
• Falls back to the existing InvalidateLayout approach for older iOS versions

[devanathan-vaithiyanathan]

🤖 AI Summary

📊 Expand Full Review
🔍 Pre-Flight — Context & Validation
📝 Review Session — fix modified for #33833 · a88fe75
Issue: #32796 - CollectionView2 on iOS iPad jumps/scrolls randomly when item size changes (iOS 26.0) Issue (2): #33833 - [iOS] Grouped CollectionView scroll jump/skip during normal scrolling (iOS 18.7.3) PR: #32874 - [iOS][CV2] Fix CollectionView2 on iOS iPad jumps/scrolls randomly when item size changes Platforms Affected: iOS / iPadOS (iPad-specific reproduction, also affects MacCatalyst due to .ios.cs file scope) Files Changed: 1 implementation file (no test files)

Issue Summary

In CollectionView2, when an item's size changes at runtime (e.g., expand/collapse), the CollectionView unexpectedly jumps or scrolls to a different position instead of maintaining the current scroll offset. Reproducible on iPad/iPadOS 18+ / iOS 26, NOT reproducible on iPhone. Two separate issues with the same root cause.

Fix Approach (PR)

In ItemsViewController2.InvalidateLayoutIfItemsMeasureChanged(), instead of calling InvalidateLayout on the layout context for cells with changed sizes, the PR introduces:

• A new ShouldApplyCellReConfiguration() static method that returns true for iOS 15+
• When true: calls collectionView.ReconfigureItems(...) wrapped in UIView.PerformWithoutAnimation
• This uses the iOS 15+ API specifically designed for cell content updates without recreation, avoiding scroll position disruption

Reviewer Comments (from copilot-pull-request-reviewer)

File:Line Reviewer Says Author Says Status
ItemsViewController2.cs:248 ShouldApplyCellReConfiguration() should also check OperatingSystem.IsMacCatalystVersionAtLeast(15) since .ios.cs compiles for both platforms N/A ⚠️ NEEDS FIX
ItemsViewController2.cs:227 Comment says "Apple bug in iPadOS 18+" but no bug reference (radar/forum) N/A ⚠️ NEEDS UPDATE
ItemsViewController2.cs:226 Comment says "iPadOS 18+" but linked issue #32796 says "iOS 26.0" (same version, different naming) N/A ⚠️ NEEDS CLARIFICATION

Code Issues Identified

1. Missing MacCatalyst version check: ShouldApplyCellReConfiguration() returns OperatingSystem.IsIOSVersionAtLeast(15) only. Since ItemsViewController2.cs has a .ios.cs extension (compiles for both iOS and MacCatalyst), it must also check OperatingSystem.IsMacCatalystVersionAtLeast(15). The existing pattern at line 165-171 of the same file demonstrates the correct approach: OperatingSystem.IsIOSVersionAtLeast(11) || OperatingSystem.IsMacCatalystVersionAtLeast(11).
2. Version comment inconsistency: "iPadOS 18+" and "iOS 26.0" refer to the same OS (Apple rebranded iOS 18 as iOS 26). Should be clarified.

Fix Candidates

Source Approach Test Result Files Changed Notes

PR PR #32874 Use ReconfigureItems (iOS 15+) instead of InvalidateLayout for cells with changed sizes, wrapped in PerformWithoutAnimation ⏳ PENDING (Gate) ItemsViewController2.cs (+19) Missing MacCatalyst check in ShouldApplyCellReConfiguration()
🚦 Gate — Test Verification
📝 Review Session — fix modified for #33833 · a88fe75
Result: ❌ FAILED - No tests exist Platform: ios Mode: N/A - Tests not present

Findings

• No test files found for issue CollectionView2 on iOS iPad jumps/scrolls randomly when item size changes #32796 or [iOS] Grouped CollectionView scroll jump/skip during normal scrolling #33833 in TestCases.HostApp or TestCases.Shared.Tests
• PR author explicitly stated: "Since the issue reproduces only on iPadOS 26, I haven't added a test case."
• The issue involves visual scroll position behavior during dynamic item size changes, which is difficult to automate but not impossible

Impact

Gate FAILED. Cannot verify that automated tests catch the regression. The PR has no automated test coverage.

🔧 Fix — Analysis & Comparison
📝 Review Session — fix modified for #33833 · a88fe75
Skipped: Gate FAILED (no tests found), Phase 3 was not executed per workflow rules.

Exhausted: N/A (skipped) Selected Fix: PR's fix (Gate did not pass; no alternative exploration performed. The PR's fix was evaluated via code review only.)

📋 Report — Final Recommendation
📝 Review Session — fix modified for #33833 · a88fe75

⚠️ Final Recommendation: REQUEST CHANGES

Summary

PR #32874 addresses a real and verified bug in CollectionView2 where item size changes cause unexpected scroll position jumps on iPad/iOS. The fix approach (using ReconfigureItems instead of InvalidateLayout) is conceptually sound and aligns with Apple's recommended API for this use case. However, the PR has two blocking issues that must be addressed before it can be merged.

Root Cause

In ItemsViewController2.InvalidateLayoutIfItemsMeasureChanged(), when visible cells have changed sizes, the code calls InvalidateLayout on a UICollectionViewLayoutInvalidationContext. On iPadOS/iOS 18+ (a.k.a. iOS 26) with UICollectionViewCompositionalLayout, this causes UIKit to recalculate layout and disrupt the current scroll offset. The ReconfigureItems API (iOS 15+) is the correct replacement: it triggers a reconfigure callback on the cell without full layout invalidation, preserving scroll position.

Fix Quality

The core fix is reasonable — ReconfigureItems wrapped in PerformWithoutAnimation is the right mechanism to update cell content/size while avoiding scroll jumps. However:

Issue 1 (Blocking): Missing MacCatalyst version check

ShouldApplyCellReConfiguration() currently reads:

static bool ShouldApplyCellReConfiguration()
{
    return OperatingSystem.IsIOSVersionAtLeast(15);
}

Since ItemsViewController2.cs uses the .ios.cs extension, it compiles for both iOS and MacCatalyst. The ReconfigureItems API requires macOS Catalyst 15.0+. Without the MacCatalyst check, on MacCatalyst < 15 the code will either fail or fall through to the old path unexpectedly. The existing pattern at line 165-171 of the same file demonstrates the correct approach:

static bool ShouldApplyCellReConfiguration()
{
    return OperatingSystem.IsIOSVersionAtLeast(15)
        || OperatingSystem.IsMacCatalystVersionAtLeast(15);
}

Issue 2 (Blocking): No automated tests

The PR author states the issue only reproduces on iPadOS 26. While visual scroll jump behavior is hard to test automatically, the underlying code path (InvalidateLayoutIfItemsMeasureChanged) can be unit tested or device-tested by simulating a cell size change event. Lack of tests means regressions could go undetected.

Non-blocking observations:

• The comment "Apple bug in iPadOS 18+" vs the issue saying "iOS 26.0" is potentially confusing (these are the same OS under different names). Suggest updating to "UICollectionViewCompositionalLayout layout invalidation issue on iPadOS 18+ (also known as iOS 26)" or similar.
• No Apple bug report reference is provided. If one exists, it should be included for future maintainers.
• The version gating is very broad: IsIOSVersionAtLeast(15) means ALL iOS 15+ users get the new code path. This might be intentional (the new path is strictly better), but it would be worth confirming the author tested on both newer and older iOS versions.

Required Changes

1. Fix ShouldApplyCellReConfiguration() to include the MacCatalyst check:

   static bool ShouldApplyCellReConfiguration()
   {
       return OperatingSystem.IsIOSVersionAtLeast(15)
           || OperatingSystem.IsMacCatalystVersionAtLeast(15);
   }

2. Add automated tests - even a basic UI test that changes an item's bound height and verifies the CollectionView scroll position remains stable would provide regression coverage. The write-tests-agent can help.
3. Update comments to resolve the "iPadOS 18+" vs "iOS 26" naming confusion and remove the "Apple bug" framing if no bug report number is available.

📋 Expand PR Finalization Review

The issue reproduces only on iPad and not on the Mac version. Therefore, the agent’s suggestion is not applicable.

[PaoloPorcellatoTC]

Hi, @devanathan-vaithiyanathan are there any available artifacts or binary to test? I'm not able to find them into pipeline artifacts

[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 -- 32874

Or

• Run remotely in PowerShell:

iex "& { $(irm https://raw.githubusercontent.com/dotnet/maui/main/eng/scripts/get-maui-pr.ps1) } 32874"