[Android] CV RemainingItemsThresholdReachedCommand fires on initial data load - fix

[kubaflo]

Issues Fixed

Fixes #28279

Before	After	iOS
Screen.Recording.2025-03-11.at.18.24.14.mov	Screen.Recording.2025-03-11.at.18.23.26.mov	Screen.Recording.2025-03-11.at.18.25.29.mov

<Grid RowDefinitions="Auto,*">
        <Label>
            <Label.FormattedText>
                <FormattedString>
                    <Span Text="Loaded items: "/>
                    <Span Text="{Binding Items.Count}"/>
                </FormattedString>
            </Label.FormattedText>
        </Label>
        <CollectionView
            Grid.Row="1"
            RemainingItemsThresholdReachedCommand="{Binding LoadMoreItemsCommand}"
            RemainingItemsThreshold="0"
            ItemsSource="{Binding Items}">
            <CollectionView.ItemTemplate>
                <DataTemplate>
                    <Label Text="{Binding .}"
                           HeightRequest="100"
                           BackgroundColor="Green"/>
                </DataTemplate>
            </CollectionView.ItemTemplate>
        </CollectionView>
    </Grid>

public class MainPageViewModel : INotifyPropertyChanged
{
	public event PropertyChangedEventHandler PropertyChanged;

	protected void OnPropertyChanged([CallerMemberName] string propertyName = null)
	{
		PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
	}

	public ObservableCollection<string> Items { get; set; }
	public Command LoadMoreItemsCommand { get; }
	public MainPageViewModel()
	{
		LoadMoreItemsCommand = new Command(() =>
		{
			int size = Items.Count;
			for (int i = size; i < size + 10; i++)
				Items.Add($"Item{i}");
		});
		_ = LoadItems();
	}

	async Task LoadItems()
	{
		await Task.Delay(1000);
		Items = new ObservableCollection<string>(Enumerable.Range(0, 4).Select(x => $"Item{x}").ToList());
		OnPropertyChanged(nameof(Items));
	}
}

[jsuarezruiz]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 3 pipeline(s).

[jsuarezruiz]

Could you include a test based on https://github.com/DharunAR/MAUICollectionView?

[kubaflo]

Could you include a test based on https://github.com/DharunAR/MAUICollectionView?

Done

[kubaflo]

🤖 AI Summary

🚦 Test Verification

Result: ✅ PASSED
Mode: Failure Only
Platform: ANDROID

Expand Details

Test Verification Report

Date: 2026-01-28 15:19:07 | Platform: ANDROID | Status: ✅ PASSED

Summary

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

✅ Final Verdict

VERIFICATION PASSED ✅

The tests correctly detect the issue:

• ✅ Tests FAIL without the fix (as expected - bug is present)
• ✅ Tests PASS with the fix (as expected - bug is fixed)

Conclusion: The tests properly validate the fix and catch the bug when it's present.

---

Configuration

Platform: android
Test Filter: Issue28321
Mode: FullVerification

Fix Files

• src/Controls/src/Core/Handlers/Items/Android/RecyclerViewScrollListener.cs

Test Results Details

Test Run 1: WITHOUT Fix

Expected: Tests should FAIL (bug is present)
Actual: Tests FAILED ✅

Test Run 2: WITH Fix

Expected: Tests should PASS (bug is fixed)
Actual: Tests PASSED ✅

Test: RemainingItemsThresholdReachedCommandShouldNotFireOnInitialDataLoad - Passed in 2s

[Copilot]

Pull request overview

Fixes an Android CollectionView regression where RemainingItemsThresholdReachedCommand can fire during initial layout/data load instead of only after user-initiated scrolling.

Changes:

• Gate RemainingItemsThresholdReached dispatch on Android behind an actual scroll-state transition (non-idle).
• Add a new HostApp issue page reproducing the scenario with delayed initial item load.
• Add an Appium UI test asserting the command does not fire on initial data load.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 4 comments.

File	Description
src/Controls/src/Core/Handlers/Items/Android/RecyclerViewScrollListener.cs	Tracks scroll state and prevents threshold events firing before scrolling begins.
src/Controls/tests/TestCases.HostApp/Issues/Issue28321.xaml	Adds a repro UI for the delayed-load + threshold command scenario.
src/Controls/tests/TestCases.HostApp/Issues/Issue28321.xaml.cs	Adds the repro page code-behind and view model to load items and append on threshold command.
src/Controls/tests/TestCases.Shared.Tests/Tests/Issues/Issue28321.cs	Adds a UI test validating the initial item count remains unchanged (command not invoked).

[Copilot]

Data record struct is declared but never used. Please remove it to avoid dead code/noise in this new test page.

Suggested change

public readonly record struct Data(string Text, string AutomationId);

[Copilot]

The XAML page is named/title’d Issue28321, but this PR is intended to fix issue #28279 per the PR title/description. Please rename the page/class to match the actual issue number so the UI test infrastructure navigates to the correct page.

[Copilot]

This new UI test class/file is named Issue28321, but the PR/linked report is #28279. Please align the test name/issue number with the actual issue being fixed so the test clearly covers the reported regression (rename test class/file and corresponding HostApp page).

[Copilot]

PR metadata says this change fixes GitHub issue #28279, but this new HostApp issue page is numbered 28321 (file/class name and [Issue] attribute). Please align the issue number with the actual fixed issue so the test page is discoverable and traceable (rename file/class and update the [Issue] attribute accordingly).

[marcojak]

When should we expect to see this fixed? This is a very serious bug!

[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 -- 28321

Or

• Run remotely in PowerShell:

iex "& { $(irm https://raw.githubusercontent.com/dotnet/maui/main/eng/scripts/get-maui-pr.ps1) } 28321"

[MauiBot]

🤖 AI Summary

📊 Expand Full Review — 67ac195 · Merge branch 'inflight/current' into fix-28279

---

🔍 Pre-Flight — Context & Validation

---

Issue: #28279 - CollectionView RemainingItemsThresholdReachedCommand fires on initial data load
PR: #28321 - [Android] CV RemainingItemsThresholdReachedCommand fires on initial data load - fix
Platforms Affected: Android
Files Changed: 2 implementation/support, 3 test

Key Findings

• The linked issue describes an Android regression where RemainingItemsThresholdReachedCommand fires during initial async data load before any user scroll.
• Changed files split into one Android implementation file (RecyclerViewScrollListener.cs), one Android public API metadata file, and three UI-test files (HostApp XAML/code-behind plus Shared NUnit/Appium test).
• Reviewer-requested test coverage was added based on the public repro, and a later AI verification comment claims FAIL-without-fix / PASS-with-fix on Android.
• Unresolved inline review comments flag test hygiene issues: the new test page/class/file are numbered 28321 instead of the linked issue 28279, and the HostApp page includes an unused Data record.
• Issue discussion raises an edge-case expectation question for non-zero thresholds when the initial item count already satisfies the threshold; the reported bug is specifically threshold 0 firing on initial load without scrolling.

Fix Candidates

#	Source	Approach	Test Result	Files Changed	Notes
PR	PR #28321	Track Android RecyclerView scroll state and suppress threshold dispatch until scrolling has actually started; add Android UI repro/test coverage.	⏳ PENDING (Gate)	src/Controls/src/Core/Handlers/Items/Android/RecyclerViewScrollListener.cs, src/Controls/src/Core/PublicAPI/net-android/PublicAPI.Unshipped.txt, src/Controls/tests/TestCases.HostApp/Issues/Issue28321.xaml, src/Controls/tests/TestCases.HostApp/Issues/Issue28321.xaml.cs, src/Controls/tests/TestCases.Shared.Tests/Tests/Issues/Issue28321.cs	Original PR; review comments still question test naming/cleanup.

---

🚦 Gate — Test Verification

---

Result: ⚠️ SKIPPED

Gate Result: ⚠️ SKIPPED

Platform: android
Mode: Full Verification

• Tests FAIL without fix: not verified locally
• Tests PASS with fix: not verified locally

Notes:

• Required gate execution was attempted twice via task agent.
• Attempt 1 failed because the verification skill auto-detected thousands of unrelated changed files from the review branch diff and never reached test execution.
• Attempt 2 retried with explicit fix file context, but the skill invocation environment did not pass the explicit FixFiles parameter through to the script, so it fell back to the same invalid auto-detection path.
• Prior PR discussion includes an AI summary claiming Android full verification passed, but this review run could not independently reproduce that result due to the environment blocker above.

---

🔧 Fix — Analysis & Comparison

---

Fix Candidates

#	Source	Approach	Test Result	Files Changed	Notes
1	try-fix (claude-opus-4.6)	Query RecyclerView.ScrollState directly in OnScrolled and only evaluate threshold while non-idle, keeping existing deferred idle dispatch.	✅ PASS	src/Controls/src/Core/Handlers/Items/Android/RecyclerViewScrollListener.cs, src/Controls/src/Core/PublicAPI/net-android/PublicAPI.Unshipped.txt	Simpler than PR boolean tracking; uses native scroll state as source of truth.
2	try-fix (claude-sonnet-4.6)	Skip threshold evaluation on zero-displacement OnScrolled callbacks (dx == 0 && dy == 0) while leaving idle dispatch behavior intact.	✅ PASS	src/Controls/src/Core/Handlers/Items/Android/RecyclerViewScrollListener.cs	Smallest passing change so far; fully stateless.
3	try-fix (gpt-5.3-codex)	Skip threshold evaluation on the first OnScrolled callback after item count transitions from zero to non-zero.	❌ FAIL	src/Controls/src/Core/Handlers/Items/Android/RecyclerViewScrollListener.cs	Not empirically validated; test command failed before execution due to missing/up-to-date MSBuild task prerequisite.
4	try-fix (gemini-3-pro-preview)	Track adapter item count and suppress threshold evaluation on the initial 0→N load transition, while retaining deferred idle dispatch.	✅ PASS	src/Controls/src/Core/Handlers/Items/Android/RecyclerViewScrollListener.cs, src/Controls/src/Core/PublicAPI/net-android/PublicAPI.Unshipped.txt	Passing alternative; also surfaced that current PR diff duplicates OnScrollStateChanged and duplicates its PublicAPI entry.
5	try-fix round 2 (claude-opus-4.6)	Arm threshold logic only after the visible range moves beyond its initial layout snapshot.	✅ PASS	src/Controls/src/Core/Handlers/Items/Android/RecyclerViewScrollListener.cs, src/Controls/src/Core/PublicAPI/net-android/PublicAPI.Unshipped.txt	Distinct passing alternative based on visible-range movement rather than scroll state or displacement.
6	try-fix round 2 (claude-sonnet-4.6)	Skip threshold evaluation while recyclerView.IsInLayout is true.	✅ PASS	src/Controls/src/Core/Handlers/Items/Android/RecyclerViewScrollListener.cs, src/Controls/src/Core/PublicAPI/net-android/PublicAPI.Unshipped.txt	Directly targets layout-driven callbacks from initial population.
7	try-fix round 2 (gpt-5.3-codex)	Require explicit touch intent from MauiRecyclerView before threshold evaluation can run.	❌ FAIL	src/Controls/src/Core/Handlers/Items/Android/RecyclerViewScrollListener.cs, src/Controls/src/Core/Handlers/Items/Android/MauiRecyclerView.cs	Could not be empirically validated because Android build failed in unrelated EntryHandler2.Android.cs before test execution.
PR	PR #28321	Track Android RecyclerView scroll state with a _scrollStarted field and suppress threshold dispatch until scrolling has started; add Android UI repro/test coverage.	⚠️ GATE BLOCKED LOCALLY	src/Controls/src/Core/Handlers/Items/Android/RecyclerViewScrollListener.cs, src/Controls/src/Core/PublicAPI/net-android/PublicAPI.Unshipped.txt, src/Controls/tests/TestCases.HostApp/Issues/Issue28321.xaml, src/Controls/tests/TestCases.HostApp/Issues/Issue28321.xaml.cs, src/Controls/tests/TestCases.Shared.Tests/Tests/Issues/Issue28321.cs	Local gate blocked by verification script environment; PR also has unresolved review comments on test numbering/cleanup, and the current diff shape duplicates OnScrollStateChanged plus its PublicAPI entry.

Cross-Pollination

Model	Round	New Ideas?	Details
claude-opus-4.6	1	N/A	Independent attempt completed.
claude-sonnet-4.6	1	N/A	Independent attempt completed.
gpt-5.3-codex	1	N/A	Independent attempt hit build prerequisite blocker before test execution.
gemini-3-pro-preview	1	N/A	Independent attempt completed.
claude-opus-4.6	2	Yes	Arm threshold only after visible range changes from the initial snapshot.
claude-sonnet-4.6	2	Yes	Gate threshold evaluation on !recyclerView.IsInLayout.
gpt-5.3-codex	2	Yes	Gate threshold evaluation on explicit touch input.
gemini-3-pro-preview	2	No	NO NEW IDEAS
claude-opus-4.6	3	Yes	Arm threshold only after cumulative post-load scroll distance exceeds touch slop.
claude-sonnet-4.6	3	Yes	Suppress threshold evaluation while ItemAnimator is running.
gpt-5.3-codex	3	Yes	Delay attaching the scroll listener until after initial global layout.
gemini-3-pro-preview	3	Yes	Skip threshold evaluation when scroll range changed due to content-size change.

Exhausted: Yes (max 3 rounds reached)
Selected Fix: Candidate #2 — it is the simplest passing fix, requires only a tiny localized change in RecyclerViewScrollListener, introduces no additional state or listener wiring, and still directly blocks layout/data-load callbacks from triggering threshold logic.

---

📋 Report — Final Recommendation

---

Result: ⚠️ REQUEST CHANGES

⚠️ Final Recommendation: REQUEST CHANGES

Phase Status

Phase	Status	Notes
Pre-Flight	✅ COMPLETE	Issue/PR discussion reviewed; implementation/test files classified.
Gate	⚠️ SKIPPED	Android verification skill was attempted twice but blocked by diff/parameter-passing issues in this environment.
Try-Fix	✅ COMPLETE	7 attempts total, 5 passing alternatives, 3 cross-pollination rounds completed (max reached).
Report	✅ COMPLETE

Summary

This PR addresses a real Android regression, and the added repro coverage is directionally correct, but I do not recommend approval in its current state.

The strongest issue is correctness of the current diff itself: src/Controls/src/Core/Handlers/Items/Android/RecyclerViewScrollListener.cs contains two OnScrollStateChanged(RecyclerView, int) overrides, and src/Controls/src/Core/PublicAPI/net-android/PublicAPI.Unshipped.txt contains the same OnScrollStateChanged API entry twice. That is a concrete defect in the submitted change, independent of the local gate blocker.

Beyond that, try-fix exploration found multiple simpler passing alternatives. The best validated option was candidate #2: ignore threshold evaluation for zero-displacement OnScrolled callbacks (dx == 0 && dy == 0), which solves the repro with a much smaller, stateless change than the PR’s _scrollStarted tracking.

The PR also still carries unresolved review feedback on the test assets: the added issue page/test are numbered after PR 28321 rather than linked issue 28279, and the HostApp code-behind includes an unused Data record.

Root Cause

Android RecyclerView emits OnScrolled callbacks during initial layout/data population even when no user scroll has occurred. The threshold logic currently treats those callbacks as eligible for RemainingItemsThresholdReached, so the command can fire on first load.

Fix Quality

The PR fix is plausible in intent, but the current implementation is not ready:

• it introduces duplicate override/API declarations in the current diff,
• it uses extra state where several smaller passing alternatives exist,
• and the test additions still need cleanup/alignment with the linked issue.

Given the duplicate method/API entries plus the existence of simpler validated alternatives, this should be revised before approval.

---

[kubaflo]

Code Review — PR #28321

Independent Assessment

What this changes: Adds a _scrollStarted boolean to RecyclerViewScrollListener (Android) that gates RemainingItemsThresholdReached dispatch. The flag is set in a new OnScrollStateChanged override and checked in OnScrolled before evaluating the threshold. Also adds a UI test page and NUnit/Appium test to verify the command does not fire on initial data load.

Inferred motivation: Android's RecyclerView emits OnScrolled(0, 0) callbacks during initial layout/data population. The existing threshold logic treated these as eligible scroll events, causing RemainingItemsThresholdReachedCommand to fire before the user ever scrolled.

Reconciliation with PR Narrative

Author claims: Fixes #28279 — RemainingItemsThresholdReachedCommand fires on initial data load on Android.
Agreement/disagreement: The root cause analysis is correct and the approach of gating on scroll state is reasonable. However, the current diff has a critical merge conflict that must be resolved before this can merge.

Findings

❌ Critical — Duplicate OnScrollStateChanged override (compile error)

The file src/Controls/src/Core/Handlers/Items/Android/RecyclerViewScrollListener.cs on the PR head contains two OnScrollStateChanged(RecyclerView, int) overrides:

1. Lines ~41-45 (added by this PR): Sets _scrollStarted based on scroll state
2. Lines ~107-117 (from inflight/current base): Handles deferred _pendingRemainingItemsThresholdReached dispatch when idle

C# does not allow two overrides of the same method — this will not compile, and CI confirms all builds are failing. These two methods must be merged into one:

public override void OnScrollStateChanged(RecyclerView recyclerView, int newState)
{
    base.OnScrollStateChanged(recyclerView, newState);
    _scrollStarted = newState != RecyclerView.ScrollStateIdle;
    
    if (_pendingRemainingItemsThresholdReached && newState == RecyclerView.ScrollStateIdle)
    {
        _pendingRemainingItemsThresholdReached = false;
        if (!_disposed && _itemsView is not null)
        {
            _itemsView.SendRemainingItemsThresholdReached();
        }
    }
}

❌ Duplicate PublicAPI entry

src/Controls/src/Core/PublicAPI/net-android/PublicAPI.Unshipped.txt contains the OnScrollStateChanged entry twice (lines 9 and 11). One must be removed.

⚠️ Missing trailing newlines

All three new test files lack a newline at end-of-file:

• src/Controls/tests/TestCases.HostApp/Issues/Issue28321.xaml
• src/Controls/tests/TestCases.HostApp/Issues/Issue28321.xaml.cs
• src/Controls/tests/TestCases.Shared.Tests/Tests/Issues/Issue28321.cs

⚠️ Unused Data record struct

Issue28321.xaml.cs line 8 declares public readonly record struct Data(string Text, string AutomationId) which is never referenced. Should be removed.

Devil's Advocate

• The _scrollStarted approach tracks extra state whereas simpler alternatives exist (e.g., checking dx == 0 && dy == 0 in OnScrolled, or querying recyclerView.ScrollState directly). However, the explicit state tracking is arguably more intentional/readable and correctly handles edge cases where a zero-displacement scroll might occur mid-fling. The approach is defensible once the merge conflict is resolved.
• One could argue the threshold should fire on initial load if items already satisfy the threshold — but the linked issue and Android documentation both indicate it should only fire in response to user scrolling, so the current gating is correct.

Verdict: NEEDS_CHANGES

Confidence: high
Summary: The fix correctly identifies and addresses the root cause, and the test is well-structured. However, the PR branch has diverged badly from inflight/current (205 commits, 2292 files), resulting in a duplicate OnScrollStateChanged override that won't compile and a duplicate PublicAPI entry. A rebase and merge of the two OnScrollStateChanged bodies is required before this can proceed.

[kubaflo]

🟡 .NET MAUI Review - Changes Suggested

Expand Full Review - 67ac195 - [Android] CV RemainingItemsThresholdReachedCommand fires on initial data load - fix

---

Independent Assessment

What this changes: Adds a _scrollStarted boolean to RecyclerViewScrollListener (Android) that gates RemainingItemsThresholdReached dispatch. The flag is set in a new OnScrollStateChanged override and checked in OnScrolled before evaluating the threshold. Also adds a UI test page and NUnit/Appium test to verify the command does not fire on initial data load.

Inferred motivation: Android's RecyclerView emits OnScrolled(0, 0) callbacks during initial layout/data population. The existing threshold logic treated these as eligible scroll events, causing RemainingItemsThresholdReachedCommand to fire before the user ever scrolled.

Reconciliation with PR Narrative

Author claims: Fixes #28279 — RemainingItemsThresholdReachedCommand fires on initial data load on Android.
Agreement/disagreement: The root cause analysis is correct and the approach of gating on scroll state is reasonable. However, the current diff has a critical merge conflict that must be resolved before this can merge.

Findings

❌ Critical — Duplicate OnScrollStateChanged override (compile error)

The file src/Controls/src/Core/Handlers/Items/Android/RecyclerViewScrollListener.cs on the PR head contains two OnScrollStateChanged(RecyclerView, int) overrides:

1. Lines ~41-45 (added by this PR): Sets _scrollStarted based on scroll state
2. Lines ~107-117 (from inflight/current base): Handles deferred _pendingRemainingItemsThresholdReached dispatch when idle

C# does not allow two overrides of the same method — this will not compile, and CI confirms all builds are failing. These two methods must be merged into one:

public override void OnScrollStateChanged(RecyclerView recyclerView, int newState)
{
    base.OnScrollStateChanged(recyclerView, newState);
    _scrollStarted = newState != RecyclerView.ScrollStateIdle;
    
    if (_pendingRemainingItemsThresholdReached && newState == RecyclerView.ScrollStateIdle)
    {
        _pendingRemainingItemsThresholdReached = false;
        if (!_disposed && _itemsView is not null)
        {
            _itemsView.SendRemainingItemsThresholdReached();
        }
    }
}

❌ Duplicate PublicAPI entry

src/Controls/src/Core/PublicAPI/net-android/PublicAPI.Unshipped.txt contains the OnScrollStateChanged entry twice (lines 9 and 11). One must be removed.

⚠️ Missing trailing newlines

All three new test files lack a newline at end-of-file:

• src/Controls/tests/TestCases.HostApp/Issues/Issue28321.xaml
• src/Controls/tests/TestCases.HostApp/Issues/Issue28321.xaml.cs
• src/Controls/tests/TestCases.Shared.Tests/Tests/Issues/Issue28321.cs

⚠️ Unused Data record struct

Issue28321.xaml.cs line 8 declares public readonly record struct Data(string Text, string AutomationId) which is never referenced. Should be removed.

Devil's Advocate

• The _scrollStarted approach tracks extra state whereas simpler alternatives exist (e.g., checking dx == 0 && dy == 0 in OnScrolled, or querying recyclerView.ScrollState directly). However, the explicit state tracking is arguably more intentional/readable and correctly handles edge cases where a zero-displacement scroll might occur mid-fling. The approach is defensible once the merge conflict is resolved.
• One could argue the threshold should fire on initial load if items already satisfy the threshold — but the linked issue and Android documentation both indicate it should only fire in response to user scrolling, so the current gating is correct.

Verdict: NEEDS_CHANGES

Confidence: high
Summary: The fix correctly identifies and addresses the root cause, and the test is well-structured. However, the PR branch has diverged badly from inflight/current (205 commits, 2292 files), resulting in a duplicate OnScrollStateChanged override that won't compile and a duplicate PublicAPI entry. A rebase and merge of the two OnScrollStateChanged bodies is required before this can proceed.

[kubaflo]

Not needed anymore