[Android] Fix for CollectionView Scrolled event is triggered on the initial app load.

[BagavathiPerumal]

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!

Root cause

The issue occurs because Android’s RecyclerView natively invokes OnScrolled(0, 0) during the initial layout to notify changes in visible item positions, even when no actual scrolling has occurred. The .NET MAUI CollectionView handler was treating this layout callback as a user scroll event, causing the Scrolled event to fire when the page loaded. This resulted in behavior that was inconsistent with iOS and violated the expectation that the Scrolled event should only be raised in response to actual user interaction.

Description of Issue Fix

The fix introduces a boolean flag (_isInitialLayout) to filter out the first OnScrolled() invocation when both deltas are zero, identifying it as the initial layout callback. This flag is reset when the adapter is updated to correctly handle subsequent layout cycles. As a result, the Scrolled event is now raised only for genuine scroll activity, ensuring consistent behavior across Android and iOS platforms.

Tested the behavior in the following platforms.

• Windows
• Mac
• iOS
• Android

Issues Fixed

Fixes #33333

Output

Before Issue Fix	After Issue Fix
33333-BeforeFix.mov	33333-AfterFix.mov

[sheiksyedm]

/azp run

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Azure Pipelines successfully started running 3 pipeline(s).

[Copilot]

Pull request overview

This PR fixes an Android-specific issue where the CollectionView Scrolled event was incorrectly firing on initial app load. The root cause is that Android's RecyclerView natively calls OnScrolled(0, 0) during initial layout, which MAUI was treating as a user scroll event.

Changes:

• Introduces a _isInitialLayout flag to filter out the first OnScrolled(0, 0) callback during initial layout
• Resets the flag when the adapter is updated to handle subsequent layout cycles correctly
• Adds UI tests to verify the fix

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
src/Controls/src/Core/Handlers/Items/Android/RecyclerViewScrollListener.cs	Implements the fix by adding _isInitialLayout flag and filtering logic in OnScrolled method
src/Controls/tests/TestCases.HostApp/Issues/Issue33333.cs	Creates HostApp test page that demonstrates the issue with a scroll event counter
src/Controls/tests/TestCases.Shared.Tests/Tests/Issues/Issue33333.cs	Adds NUnit test to verify Scrolled event doesn't fire on initial load

[Copilot]

The test only verifies that the Scrolled event doesn't fire on initial load, but doesn't validate that subsequent scrolling events work correctly after the initial load. Consider adding a second test case or extending this test to perform an actual scroll and verify that the event fires properly (e.g., scroll count should be 1 after user scrolls).

[PureWeen]

/rebase

[rmarinho]

✅ PR Review Complete: #33558

Details

### Final Recommendation: **APPROVE** with Minor Suggestion

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📋 Executive Summary

PR #33558 correctly fixes an Android-specific issue where CollectionView's Scrolled event incorrectly fires during initial app load. The root cause was properly identified (RecyclerView natively calls OnScrolled(0, 0) during layout), and the fix is sound. Independent exploration of alternative approaches validates this is the optimal solution.

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✅ What's Good

1. Root Cause Correctly Identified: Android's RecyclerView calls OnScrolled(0, 0) during initial layout as a notification mechanism - not a bug in RecyclerView, but MAUI was incorrectly treating it as a user scroll event.

2. Fix Logic is Sound: The _isInitialLayout flag approach correctly:

   • Filters the first OnScrolled(0, 0) callback (initial layout)
   • Allows all subsequent scrolls (real user interaction)
   • Resets on adapter updates (handles data source changes correctly)

3. Tests Properly Validate:

   • Test directly validates the fixed behavior (scroll count = 0 on initial load)
   • Test will FAIL without fix, PASS with fix ✅

4. Superior Naming: _isInitialLayout clearly communicates intent vs alternatives like _hasScrolled

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⚠️ Minor Code Quality Suggestion (Non-Blocking)

Issue: Line 55 redundantly sets _isInitialLayout = false after line 50 already does it when returning early.

Current code:

if (_isInitialLayout && dx == 0 && dy == 0)
{
    _isInitialLayout = false;  // Line 50
    return;
}

// Clear the flag after first actual scroll to ensure subsequent events work normally
_isInitialLayout = false;  // Line 55 - REDUNDANT (line 50 returns, never reaches here)

Why line 55 exists: It handles the first non-zero scroll (where line 48's condition is false). But the comment is misleading - it suggests it runs "after first actual scroll" but really runs for EVERY scroll after the initial check.

Suggested improvement: Line 55 is functionally correct (sets flag on first real scroll), but the double-setting could be clearer. Consider:

Option A: Keep as-is (works correctly, just slightly verbose)
Option B: Remove comment at line 54, keep line 55 for clarity

---

🔍 Independent Fix Exploration Results

Explored 3 independent alternatives to validate the PR's approach:

Attempt	Approach	Result
#1	Skip ALL OnScrolled(0, 0) callbacks	❌ Too broad - blocks legitimate layout updates
#2	Track _hasScrolled, skip first only	❌ Incomplete - missing adapter update reset
#3	Track _hasScrolled + reset on adapter update	✅ Equivalent to PR

Conclusion: PR's approach is optimal. Alternative #3 works but PR's naming (_isInitialLayout) is more descriptive.

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📊 Test Coverage Assessment

Current coverage: ✅ Adequate for the fix

• Validates event doesn't fire on initial load
• Android-focused (matching issue scope)

Reviewer feedback noted tests don't validate subsequent scrolling works - this is acceptable because:

• Subsequent scroll functionality is pre-existing behavior (already working)
• Fix only touches initial layout filter - doesn't modify scroll event logic
• Test focuses on the specific bug being fixed

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🎯 Final Verdict

APPROVE - The fix is correct, well-tested, and the optimal solution. The minor redundancy at line 55 is non-blocking and could be addressed in a follow-up if desired.

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�[37mAPI time spent: �[39m8m 20.944s
�[37mTotal session time: �[39m11m 44.641s
�[37mTotal code changes: �[32m+0�[39m �[31m-0�[39m
�[37mBreakdown by AI model:�[39m
claude-sonnet-4.5 4.5m in, 18.7k out, 4.4m cached (Est. 1 Premium request)

[PureWeen]

/rebase

[PureWeen]

🤖 AI Summary

📊 Expand Full Review

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🔍 Pre-Flight — Context & Validation

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📝 Review Session — fix-33333-Changes committed. · b009ee4

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Issue: #33333 - [Android] CollectionView Scrolled event is triggered on the initial app load.
Platforms Affected: Android only
Files Changed: 1 implementation file, 2 test files

Issue Summary

On Android, the CollectionView Scrolled event fires immediately on initial app load without any user interaction. Root cause: Android's RecyclerView natively calls OnScrolled(0, 0) during initial layout to notify changes in visible item positions. MAUI was treating this layout callback as a user scroll event, inconsistent with iOS/Windows/MacCatalyst behavior.

PR Details

• Author: BagavathiPerumal (Syncfusion partner)
• Title: [Android] Fix for CollectionView Scrolled event is triggered on the initial app load
• Labels: platform/android, area-controls-collectionview, community ✨, partner/syncfusion

Prior Agent Review

A prior agent review (rmarinho) gave APPROVE with Minor Suggestion on an older version using _isInitialLayout flag. The PR has since been updated to the current implementation using _hasCompletedFirstLayout + recyclerView.IsLaidOut check.

Files Changed

• Fix files: src/Controls/src/Core/Handlers/Items/Android/RecyclerViewScrollListener.cs (+14)
• Test files: src/Controls/tests/TestCases.HostApp/Issues/Issue33333.cs (+65), src/Controls/tests/TestCases.Shared.Tests/Tests/Issues/Issue33333.cs (+23)

Current Fix Implementation (Key Logic)

bool _hasCompletedFirstLayout = false;

// In UpdateAdapter: _hasCompletedFirstLayout = false; (reset on adapter change)

// In OnScrolled:
if (!_hasCompletedFirstLayout && !recyclerView.IsLaidOut && dx == 0 && dy == 0)
{
    return;  // Skip initial layout callback
}

_hasCompletedFirstLayout = true;  // Mark as complete for subsequent calls

Reviewer Feedback

File:Line	Reviewer Says	Status
RecyclerViewScrollListener.cs	Copilot: Redundant flag clearing (applies to old code)	Outdated - doesn't apply to current implementation
Issue33333.cs:22	Copilot: Test doesn't validate subsequent scroll works	⚠️ Note - test covers initial load only

Fix Candidates

#	Source	Approach	Test Result	Files Changed	Notes
PR	PR #33558	_hasCompletedFirstLayout flag + !recyclerView.IsLaidOut check to filter initial layout callback	⏳ PENDING (Gate)	RecyclerViewScrollListener.cs (+14)	Current PR

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🚦 Gate — Test Verification

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📝 Review Session — fix-33333-Changes committed. · b009ee4

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Result: ✅ PASSED
Platform: android
Mode: Full Verification (verify-tests-fail-without-fix skill)

Check	Expected	Actual	Result
Tests WITHOUT fix	FAIL	FAIL	✅
Tests WITH fix	PASS	PASS	✅

• Tests FAIL without fix ✅ (bug is present and detectable)
• Tests PASS with fix ✅ (fix correctly resolves the issue)

Test: CollectionViewScrolledEventShouldNotFireOnInitialLoad in Issue33333

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🔧 Fix — Analysis & Comparison

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📝 Review Session — fix-33333-Changes committed. · b009ee4

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Fix Candidates

#	Source	Approach	Test Result	Files Changed	Notes
1	try-fix (claude-sonnet-4.5)	OnScrollStateChanged override + _userHasScrolled flag (set on non-IDLE state)	✅ PASS	RecyclerViewScrollListener.cs, PublicAPI.Unshipped.txt	Requires new public API override; semantically clean
2	try-fix (claude-opus-4.6)	Stateless: dx==0 && dy==0 && _horizontalOffset==0 && _verticalOffset==0	✅ PASS	RecyclerViewScrollListener.cs	No new state; but edge case if offsets accumulate back to 0
3	try-fix (gpt-5.2)	recyclerView.ScrollState == ScrollStateIdle && dx==0 && dy==0	✅ PASS	RecyclerViewScrollListener.cs	One-liner; could suppress idle-state programmatic scrolls
4	try-fix (gpt-5.2-codex)	recyclerView.IsComputingLayout && dx==0 && dy==0	❌ FAIL	RecyclerViewScrollListener.cs	Initial callback fires AFTER layout computation, not during
5	try-fix (gemini-3-pro-preview)	Strict dx==0 && dy==0 guard (always)	✅ PASS	RecyclerViewScrollListener.cs	Too broad; PR author explicitly rejected this approach
6	try-fix (gemini-3-pro-preview)	Latch: _hasFiredNonZeroScroll flag, suppress zero-delta until first non-zero	✅ PASS	RecyclerViewScrollListener.cs	Similar to PR but without IsLaidOut check
PR	PR #33558	_hasCompletedFirstLayout boolean + !recyclerView.IsLaidOut + dx==0 && dy==0	✅ PASS (Gate)	RecyclerViewScrollListener.cs (+14)	Most targeted: specifically filters pre-layout zero-delta callbacks

Exhausted: Yes — Round 3 cross-pollination: claude-opus-4.6 confirmed NO NEW IDEAS; remaining models suggested variations already covered.

Selected Fix: PR's fix — The !recyclerView.IsLaidOut condition is the most precise, targeting specifically the pre-layout state. After the first layout completes, IsLaidOut = true and the guard never triggers again. This is more precise than alternatives 3 (suppresses all idle-state zero-delta) or 5 (suppresses all zero-delta permanently). Alternatives 1 and 2 also work, but Attempt 1 requires a new public API surface, and Attempt 2 has a theoretical edge case. The PR's fix is the best balance of precision and simplicity.

Cross-Pollination Summary

Round	claude-sonnet-4.5	claude-opus-4.6	gpt-5.2	gpt-5.2-codex	gemini-3-pro-preview
2	NEW IDEAS (5)	NO NEW IDEAS	NEW IDEA (ViewTreeObserver)	NEW IDEA (touch listener)	NEW IDEA → ran as Attempt 6
3	NEW IDEAS	NO NEW IDEAS	(rate limited)	NEW IDEA (Post()-based)	NEW IDEA (ChildCount)

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📋 Report — Final Recommendation

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📝 Review Session — fix-33333-Changes committed. · b009ee4

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✅ Final Recommendation: APPROVE

Summary

PR #33558 correctly fixes issue #33333 where Android's CollectionView Scrolled event incorrectly fires on initial app load without user interaction. The fix is sound, well-targeted, and independently validated by multi-model try-fix exploration (5 of 6 alternative approaches also passed tests). Gate verified tests properly catch the bug.

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Root Cause

Android's RecyclerView natively calls OnScrolled(0, 0) during initial layout as a notification that visible item positions may have changed. This is Android's internal layout mechanism, NOT a user scroll event. MAUI's RecyclerViewScrollListener.OnScrolled was treating this layout callback identically to a real user scroll event, causing CollectionView.Scrolled to fire on page load — inconsistent with iOS behavior.

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Fix Quality Assessment

Approach: Boolean flag _hasCompletedFirstLayout combined with !recyclerView.IsLaidOut + zero-delta check.

Why this approach is correct:

• recyclerView.IsLaidOut is false only before the first layout completes — precisely the window when the spurious callback occurs
• After first layout, IsLaidOut = true permanently, so the guard never triggers again for real scrolls
• Most targeted of all alternatives: specifically filters pre-layout state rather than broader conditions like scroll state

Comparison with alternatives found via try-fix:

Approach	Correctness	Simplicity	Risk
PR's fix: !IsLaidOut + dx==0&&dy==0	✅ Most precise	Medium	Low
Attempt 1: OnScrollStateChanged	✅ Semantic	Medium	Adds public API
Attempt 2: Stateless offsets==0	✅ Works	High	Theoretical edge case
Attempt 3: ScrollState==Idle	✅ Works	High	Could suppress programmatic
Attempt 5: dx==0&&dy==0 only	✅ Works	High	Too broad (rejected by PR author)

The PR's fix is the best balance of precision and robustness.

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Minor Issues (Non-Blocking)

1. ⚠️ Description mentions old variable name: PR body says "introduces a boolean flag (_isInitialLayout)" but the code uses _hasCompletedFirstLayout. The description is from an older iteration.

2. ⚠️ Comment accuracy in UpdateAdapter: Comment says "Reset flag when adapter changes to handle ItemsSource updates" but after initial layout, recyclerView.IsLaidOut = true, so resetting _hasCompletedFirstLayout to false doesn't re-trigger the guard. The reset is harmless but the comment overstates its effect.

3. ⚠️ Test coverage gap: Test only verifies event count = 0 on initial load. Does not verify that actual scrolling DOES fire the event. This was noted by copilot review but is not blocking.

4. ⚠️ Missing newline at end of file: Issue33333.cs (tests) is missing final newline.

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Title Recommendation

Current: [Android] Fix for CollectionView Scrolled event is triggered on the initial app load.
Recommended: [Android] CollectionView: Fix Scrolled event firing on initial load

Reasons: "Fix for CollectionView Scrolled event is triggered" is grammatically awkward; trailing period is not standard.

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Code Review Findings

✅ Looks Good

• Fix is appropriately scoped to Android only
• _hasCompletedFirstLayout naming clearly communicates intent
• Test page has proper AutomationId values and [Issue] attribute
• Test class uses [Category(UITestCategories.CollectionView)] correctly
• _horizontalOffset and _verticalOffset still accumulate correctly (update happens before guard)

🟡 Minor Suggestions (Non-Blocking)

• Initialize: bool _hasCompletedFirstLayout; (remove = false, it's the default)
• Update PR description to reflect current variable name _hasCompletedFirstLayout
• Add newline at end of TestCases.Shared.Tests/Tests/Issues/Issue33333.cs
• Consider adding a second test case verifying scrolling DOES fire the event after initial load

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📋 Expand PR Finalization Review

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Title: ✅ Good

Current: [Android] Fix for CollectionView Scrolled event is triggered on the initial app load.

Description: ✅ Good

• "Fix for ... is triggered" is awkward passive phrasing
• Trailing period (not standard for PR titles)
• "on the initial app load" is slightly verbose

✨ Suggested PR Description

[!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!

Root Cause

Android's RecyclerView natively invokes OnScrolled(0, 0) during the initial layout pass to notify the listener of the initial visible item positions, even when no actual scrolling has occurred. The .NET MAUI CollectionView handler's RecyclerViewScrollListener was treating this layout callback as a user scroll event, causing the Scrolled event to fire when the page first loaded. This was inconsistent with iOS behavior and violated the expectation that Scrolled should only fire in response to genuine user interaction.

Description of Change

Introduces a boolean flag _hasCompletedFirstLayout in RecyclerViewScrollListener<TItemsView, TItemsViewSource> to suppress the spurious initial OnScrolled callback.

Guard condition in OnScrolled:

if (!_hasCompletedFirstLayout && !recyclerView.IsLaidOut && dx == 0 && dy == 0)
{
    return;
}
_hasCompletedFirstLayout = true;

This ensures only the very first layout callback (where the view is not yet laid out and no delta exists) is suppressed. All subsequent OnScrolled invocations proceed normally.

Flag reset in UpdateAdapter:
_hasCompletedFirstLayout is reset to false when the adapter is updated, so that a fresh ItemsSource swap correctly suppresses the next initial layout callback too.

Files changed:

• src/Controls/src/Core/Handlers/Items/Android/RecyclerViewScrollListener.cs — fix
• src/Controls/tests/TestCases.HostApp/Issues/Issue33333.cs — UI test host page
• src/Controls/tests/TestCases.Shared.Tests/Tests/Issues/Issue33333.cs — UI test

Issues Fixed

Fixes #33333

Platforms Tested

• Android
• iOS (Android-only fix)
• Windows (Android-only fix)
• Mac (Android-only fix)

Code Review: ⚠️ Issues Found

Code Review — PR #33558

🔴 Critical Issues

None.

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🟡 Suggestions

1. Description references stale flag name

File: PR description (not code)
Problem: The description says "introduces a boolean flag (_isInitialLayout)" but the actual field in the code is _hasCompletedFirstLayout. This is a leftover from a prior iteration of the implementation and will confuse future readers of the git history.
Recommendation: Update the description to reference _hasCompletedFirstLayout and clarify that the condition also checks !recyclerView.IsLaidOut.

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2. UI test does not verify scroll events fire after initial load

File: src/Controls/tests/TestCases.Shared.Tests/Tests/Issues/Issue33333.cs
Problem: The test only verifies the scroll count is 0 on initial load. It does not verify that the Scrolled event fires correctly after a real user scroll. This means the test would pass even if the flag accidentally suppressed all scroll events, not just the initial one.
Recommendation: Add a second assertion that performs a scroll and verifies the count increments. Example:

// Verify event fires on real scroll
App.ScrollDown("TestCollectionView", ScrollStrategy.Gesture, 0.5);
App.WaitForElement("ScrollCountLabel");
var afterScrollText = App.FindElement("ScrollCountLabel").GetText();
Assert.That(afterScrollText, Is.Not.EqualTo("Scrolled Event Count: 0"),
    "Scrolled event should fire when user scrolls");

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3. StackLayout used instead of VerticalStackLayout

File: src/Controls/tests/TestCases.HostApp/Issues/Issue33333.cs, line ~61
Problem: StackLayout is the legacy layout control. VerticalStackLayout is preferred in new code.
Recommendation: Replace StackLayout with VerticalStackLayout.

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4. Missing newline at end of test file

File: src/Controls/tests/TestCases.Shared.Tests/Tests/Issues/Issue33333.cs
Problem: File ends without a trailing newline (\ No newline at end of file).
Recommendation: Add a trailing newline.

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5. Platforms Tested checklist inaccuracy

File: PR description
Problem: The description checks off Windows and Mac as tested, but the fix is Android-only (changes only Android code in Handlers/Items/Android/). This is misleading.
Recommendation: Only check Android, and add a note that the fix is Android-only.

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✅ Looks Good

• Core fix logic is correct: The condition !_hasCompletedFirstLayout && !recyclerView.IsLaidOut && dx == 0 && dy == 0 precisely identifies the initial layout callback. Using !recyclerView.IsLaidOut as an additional guard (beyond just zero deltas) makes the filter robust — a legitimate scroll of (0, 0) is less likely to be mistakenly suppressed.
• Flag reset in UpdateAdapter is correct: Resetting _hasCompletedFirstLayout = false when the adapter changes ensures that ItemsSource swaps also benefit from suppression of the initial layout callback.
• Offset accumulation before the guard is harmless: dx and dy are both 0 at that point so _horizontalOffset and _verticalOffset are not incorrectly modified.
• No impact on other platforms: The change is in an Android-specific file (Handlers/Items/Android/).
• [Issue] attribute is correct: Platform is correctly set to PlatformAffected.Android.
• Test category is correct: [Category(UITestCategories.CollectionView)].

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[PureWeen]

let me know if you agree with the agents summary #33558 (comment)

[BagavathiPerumal]

let me know if you agree with the agents summary #33558 (comment)

@PureWeen, The Zero-Delta Filter suggestion is not working properly. Using a simple condition such as if (dx == 0 && dy == 0) return; would permanently suppress all (0, 0) scroll events and could break valid scenarios like ItemsSource updates.

Instead, I used alternative approach 5 with the !IsLaidOut check, which suppresses the initial layout event while allowing subsequent events. This resolves the issue with a single file change and no cross-class impact.

[sheiksyedm]

/azp run maui-pr-uitests

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