[Android] Fix CollectionView LinearItemsLayout first/last items clipped when ItemSpacing changes at runtime

[Shalini-Ashokan]

Note

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Issue Details

CollectionView with LinearItemsLayout, the first and last items become truncated/clipped after changing the ItemSpacing value at runtime. This affects both vertical and horizontal list orientations on Android.

Note: This is inflight/candate branch changes where exsiting PR #27093 causes the regression on this branch. So added this new fix to overcome the regression.

Root Cause

PR #27093 changed SpacingItemDecoration.GetItemOffsets to zero out the outer edge offsets (outRect.Top = 0 for item 0, outRect.Bottom = 0 for last item) for all layout types including LinearItemsLayout. However, MauiRecyclerView.UpdateItemSpacing still applied negative padding (SetPadding(-offset, ...)) on the RecyclerView for linear layouts. This conflict caused the first and last items to be pulled outside the visible area and clipped, since the positive offset that was supposed to cancel the negative padding was removed.

Description of Change

Added a _removeOuterEdgeSpacing boolean flag to SpacingItemDecoration, set to true only for GridItemsLayout. In GetItemOffsets, an early return is added when _removeOuterEdgeSpacing is false, skipping the edge-zeroing logic for LinearItemsLayout. This restores the correct balanced behavior for linear lists: the positive outRect offset (+N) and the negative RecyclerView padding (-N) cancel each other out at the edges, keeping the first and last items correctly positioned at the screen boundary.

Validated the behavior in the following platforms

• Android
• Windows
• iOS
• Mac

Issues Fixed

Fixes #34636

Output ScreenShot

Before	After

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🚦 Gate — Test Verification

📊 Expand Full Gate — d93bff6 · Modified the test case to resolve the ios scrolling issue

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Gate Result: ❌ FAILED

Platform: android

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[MauiBot]

🤖 AI Summary

📊 Expand Full Review — d93bff6 · Modified the test case to resolve the ios scrolling issue

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🔍 Pre-Flight — Context & Validation

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Issue: #34636 - [MAUI] I2_Spacing_ItemSpacing - First and last item on the list is truncated after changing Spacing value.
PR: #34664 - [Android] Fix CollectionView LinearItemsLayout first/last items clipped when ItemSpacing changes at runtime
Platforms Affected: Android (primary), validated on Windows/iOS/Mac
Files Changed: 1 implementation, 2 test files + 2 snapshot PNGs

Key Findings

• Regression introduced by PR [Android] CollectionView: Fix item spacing applied on outer edges causing scroll/rendering issues #27093 on inflight/candate branch — SpacingItemDecoration.GetItemOffsets was changed to zero out outer-edge offsets for ALL layout types (including LinearItemsLayout)
• MauiRecyclerView.UpdateItemSpacing applies negative padding SetPadding(-offset, ...) for LinearItemsLayout to cancel the positive outer-edge offset — when PR [Android] CollectionView: Fix item spacing applied on outer edges causing scroll/rendering issues #27093 removed the positive offset but kept the negative padding, first/last items were pulled outside the visible area
• Fix adds _removeOuterEdgeSpacing boolean flag (set true only for GridItemsLayout); linear layouts return early from GetItemOffsets without zeroing edges, restoring the balanced positive-offset + negative-padding behavior
• Test uses VerifyScreenshot() without retryTimeout, which may cause flakiness after CollectionView layout update
• Gate ❌ FAILED on Android — screenshot test did not pass as expected
• Issue confirmed non-reproducible on main branch; only affects inflight/candate branch

Fix Candidates

#	Source	Approach	Test Result	Files Changed	Notes
PR	PR #34664	Add _removeOuterEdgeSpacing flag; skip edge-zeroing for LinearItemsLayout via early return	❌ Gate FAILED	SpacingItemDecoration.cs	Gate failed on Android screenshot test

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🔧 Fix — Analysis & Comparison

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Fix Candidates

#	Source	Approach	Test Result	Files Changed	Notes
PR	PR #34664	_removeOuterEdgeSpacing flag in SpacingItemDecoration; early return for Linear; keeps negative RecyclerView padding	❌ Gate FAILED	1 fix file	Gate failed — screenshot mismatch or timing
1	Attempt 1 (claude-opus-4.6)	Edge-zeroing applied to ALL layouts (Grid + Linear) + remove negative padding entirely from MauiRecyclerView	✅ PASS	2 files	Simpler — no flag, no branching
2	Attempt 2 (claude-sonnet-4.6)	Direct per-side ternary assignment (top = row==0?0:V) for all layouts, remove negative padding	✅ PASS	2 files	Clean single-pass, no conditionals
3	Attempt 3 (gpt-5.3-codex)	Only remove negative padding from MauiRecyclerView for LinearItemsLayout	❌ BLOCKED	1 file	Unrelated CS0246 build error
4	Attempt 4 (gpt-5.4)	Only remove negative padding from MauiRecyclerView for LinearItemsLayout (minimal)	❌ BLOCKED	1 file	Same CS0246 build error

Cross-Pollination

Model	Round	New Ideas?	Details
claude-opus-4.6	2	No	NO NEW IDEAS
claude-sonnet-4.6	2	Yes	Position-aware edge suppression for Linear only — effectively covered by Attempt 2
gpt-5.3-codex	2	Yes	RecyclerView ClipToPadding=false strategy — significant refactor, too invasive for a regression fix

Exhausted: Yes
Selected Fix: Attempt 1 (claude-opus-4.6) — Apply edge-zeroing to ALL layouts in SpacingItemDecoration + remove negative padding from MauiRecyclerView.

Reason over PR's fix: Attempt 1 is a cleaner, more uniform solution. The PR's fix adds a conditional boolean flag that perpetuates the two-mechanism design (negative padding + selective edge-zeroing). Attempt 1 removes the dual-mechanism entirely, handling outer-edge spacing in one consistent place. Gate failed for PR's fix — attempts 1 and 2 both passed the same screenshot test.

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📋 Report — Final Recommendation

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⚠️ Final Recommendation: REQUEST CHANGES

Phase Status

Phase	Status	Notes
Pre-Flight	✅ COMPLETE	Issue #34636 identified, regression from PR #27093
Gate	❌ FAILED	Android screenshot test failed
Try-Fix	✅ COMPLETE	4 attempts: 2 passing, 2 blocked (env build error)
Report	✅ COMPLETE

Summary

PR #34664 fixes a regression (from PR #27093 on the inflight/candate branch) where CollectionView LinearItemsLayout first/last items become clipped after changing ItemSpacing at runtime. The root cause is a double-compensation conflict: PR #27093 zeroed outer-edge offsets for all layouts in SpacingItemDecoration.GetItemOffsets, while MauiRecyclerView.UpdateItemSpacing still applies negative RecyclerView padding for linear layouts. This combination pulls first/last items outside the clip boundary.

The gate failed on Android, and two independent alternative fixes (Attempts 1 and 2) both passed the same screenshot test, suggesting the PR's specific approach produces a subtly different rendering from what the committed snapshot captures.

Root Cause

MauiRecyclerView.UpdateItemSpacing applies SetPadding(-offset, -offset, -offset, -offset) for LinearItemsLayout, relying on SpacingItemDecoration.GetItemOffsets to add a matching positive offset at the outer edges to cancel the negative padding. PR #27093 removed the positive outer-edge offset (zeroing it) but left the negative padding intact, causing the net outer offset for first/last items to be negative — pulling them outside the visible area.

Fix Quality

PR's Fix Issues:

1. Gate Failed — The screenshot test did not pass with the PR's changes on the gate's Android device, even though a snapshot was committed
2. Perpetuates dual-mechanism design — The fix keeps the negative RecyclerView padding for LinearItemsLayout, which must now be carefully kept in sync with the _removeOuterEdgeSpacing flag in SpacingItemDecoration
3. Test robustness — VerifyScreenshot() called without retryTimeout after a spacing change that triggers CollectionView re-layout; this can cause flaky failures if layout hasn't settled before the screenshot
4. Snapshot quality — No retryTimeout in the test suggests the snapshot may have been captured before the animation/layout completed

Better Alternative Found:
Attempt 1 (claude-opus-4.6) passed the same test with a cleaner, symmetric approach:

• Apply edge-zeroing to ALL layout types (not just Grid) in SpacingItemDecoration.GetItemOffsets
• Remove negative padding from MauiRecyclerView.UpdateItemSpacing entirely (SetPadding(0, 0, 0, 0) always)
• This eliminates the dual-mechanism entirely — outer-edge spacing handled in one place with no conditional branching

Suggested Changes:

1. SpacingItemDecoration.cs: Remove the _removeOuterEdgeSpacing flag; keep GetItemOffsets edge-zeroing for all layout types (the existing logic already works for Linear with span=1)

2. MauiRecyclerView.cs: Remove conditional negative padding; always use SetPadding(0, 0, 0, 0)

3. Issue34636.cs (test): Add retryTimeout to VerifyScreenshot() to prevent flaky failures after layout:

   VerifyScreenshot(retryTimeout: TimeSpan.FromSeconds(2));

4. Snapshot: Regenerate the Android snapshot with the updated test.

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