[iOS] Alert popup may be displayed on wrong window when modal page navigation is in progress - fix by kubaflo · Pull Request #31016 · dotnet/maui

kubaflo · 2025-08-05T00:07:02Z

Description of Change

By skipping view controllers that are being dismissed (animation is happening, for example ), we ensure DisplayAlert() and other popups are shown only on valid, active UI stacks, preventing the deadlock and improving reliability on iOS/macOS.

Issues Fixed

Fixes #30970

Copilot

Pull Request Overview

This PR fixes an iOS-specific issue where alert popups could be displayed on wrong windows during modal page navigation, potentially causing deadlocks. The fix prevents alerts from being presented on view controllers that are currently being dismissed.

Adds condition to skip view controllers that are being dismissed when finding the top view controller
Includes comprehensive test coverage with both HostApp UI and automated test cases
Targets iOS platform specifically where this navigation timing issue occurs

Reviewed Changes

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

File	Description
`src/Controls/src/Core/Platform/AlertManager/AlertManager.iOS.cs`	Core fix that checks `IsBeingDismissed` property before traversing to presented view controllers
`src/Controls/tests/TestCases.HostApp/Issues/Issue30970.cs`	UI test page that reproduces the modal navigation scenario with alert display
`src/Controls/tests/TestCases.Shared.Tests/Tests/Issues/Issue30970.cs`	Automated test that validates the alert popup appears correctly after modal dismissal

Copilot · 2025-08-05T00:07:24Z

+	protected override async void OnAppearing()
+	{
+		base.OnAppearing();
+		if (_modalPageWasShown)


Accessing Application.Current.Windows[0] could throw an IndexOutOfRangeException if no windows exist. Consider checking if the Windows collection has items before accessing the first element.

Suggested change

if (_modalPageWasShown)

if (_modalPageWasShown && Application.Current.Windows.Count > 0)

Copilot · 2025-08-05T00:07:25Z

+	{
+		base.OnAppearing();
+		if (_modalPageWasShown)
+			await Application.Current.Windows[0].Page!.DisplayAlert("My alert", "Can you see this alert?", "Yes");


The null-forgiving operator ! on Page suggests potential null values. Consider using null-conditional operator or explicit null check for better error handling.

Suggested change

await Application.Current.Windows[0].Page!.DisplayAlert("My alert", "Can you see this alert?", "Yes");

{

var page = Application.Current.Windows[0].Page;

if (page != null)

{

await page.DisplayAlert("My alert", "Can you see this alert?", "Yes");

}

}

dotnet-policy-service · 2025-08-05T00:10:31Z

Hey there @@kubaflo! Thank you so much for your PR! Someone from the team will get assigned to your PR shortly and we'll get it reviewed.

github-actions · 2026-03-16T21:46:45Z

🚀 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://github.com/dotnet/maui/main/eng/scripts/get-maui-pr.sh | bash -s -- 31016

Or

Run remotely in PowerShell:

iex "& { $(irm https://github.com/dotnet/maui/main/eng/scripts/get-maui-pr.ps1) } 31016"

StephaneDelcroix

Multi-Model Consensus Review (5 models: claude-opus-4.6 ×2, claude-sonnet-4.6, gemini-3-pro-preview, gpt-5.3-codex)

CI Status: ✅ All checks passing

Consensus Findings

No consensus bugs found. The fix is narrowly scoped to iOS/macOS only.

The PR adds an IsBeingDismissed guard in AlertManager.iOS.cs to skip view controllers that are in the process of being dismissed when searching for the top VC to present alerts on. This prevents alerts from being shown on a VC that is mid-dismiss, which could cause deadlocks or the alert appearing on the wrong window. Checking IsBeingDismissed before traversing to PresentedViewController is the standard iOS pattern for this scenario.

Test Coverage

✅ Includes both a TestCases.HostApp UI page (Issue30970.cs) and corresponding NUnit test (Issue30970.cs). Coverage is appropriate for the platform-specific scenario.

Verdict: ✅ Approve

Correct, minimal iOS fix using standard UIKit pattern.

MauiBot · 2026-03-26T18:34:53Z

🤖 AI Summary

📊 Expand Full Review — 6d8ae5c · fix 30970

🔍 Pre-Flight — Context & Validation

Issue: #30970 - Alert popup may be displayed on wrong window when modal page navigation is in progress on iOS/MacOS
PR: #31016 - [iOS] Alert popup may be displayed on wrong window when modal page navigation is in progress - fix
Platforms Affected: iOS, macOS (Mac Catalyst)
Files Changed: 1 implementation, 2 test

Key Findings

Bug: DisplayAlert() causes a deadlock on iOS/macOS when called after popping a modal page. The alert is presented on a view controller that is in the process of being dismissed (still in the UIKit hierarchy but IsBeingDismissed == true), resulting in the alert never appearing and the awaited task never completing.
Root cause: GetTopUIViewController() in AlertManager.iOS.cs traverses PresentedViewController without checking if the view controller is being dismissed.
Fix: Add !topUIViewController.PresentedViewController.IsBeingDismissed guard to the while loop condition — stops traversal at a view controller being dismissed so presentation happens on a valid, active view controller.
Test added: UI test Issue30970 opens a modal page, closes it, and verifies that DisplayAlert appears afterward.
Copilot inline review suggested null safety improvements for Application.Current.Windows[0].Page! in the HostApp test page.
The PlatformAffected attribute in the HostApp page only specifies iOS (not macOS), though the issue and PR description mention both iOS and macOS.

Fix Candidates

#	Source	Approach	Test Result	Files Changed	Notes
PR	PR #31016	Skip `PresentedViewController` that has `IsBeingDismissed == true` in `GetTopUIViewController()` loop	⏳ PENDING (Gate)	`AlertManager.iOS.cs`	Simple 1-line guard; stops traversal at dismissing VCs

🚦 Gate — Test Verification

Gate Result: ✅ PASSED

Platform: iOS

#	Type	Test Name	Filter
1	UITest	Issue30970.PopupShouldBeDisplayed	`Issue30970`

Step	Expected	Actual	Result
Without fix	FAIL	FAIL (TimeoutException, WaitForElement("Can you see this alert?") timed out after 16s)	✅
With fix	PASS	PASS (1s, Test Run Successful, Passed: 1)	✅

🔧 Fix — Analysis & Comparison

Fix Candidates

#	Source	Approach	Test Result	Files Changed	Notes
1	try-fix (claude-opus-4.6)	TransitionCoordinator guard: stop traversal if `GetTransitionCoordinator() != null`	✅ PASS	1 file	More general than IsBeingDismissed — catches all mid-transition VCs
2	try-fix (claude-sonnet-4.6)	Break-inside-loop with `IsBeingDismissed \|\| IsBeingPresented` check	✅ PASS	1 file	Two-directional guard; more defensive than PR fix
3	try-fix (gpt-5.3-codex)	Call-site validation: `ViewIfLoaded?.Window != null` check in `PresentPopUp`	❌ FAIL	1 file	Approach too late — presenter not exposed at call site; TimeoutException
4	try-fix (gemini-3-pro-preview)	Backtracking: traverse to leaf VC, then backtrack via `PresentingViewController` if `IsBeingDismissed`	✅ PASS	1 file	Two-pass approach; finds deepest stable VC
5	try-fix (claude-opus-4.6, cross-poll R1)	TransitionCoordinator deferral: present after dismiss animation completes via `AnimateAlongsideTransition`	✅ PASS	1 file	Most complex; preserves original VC traversal unchanged
6	try-fix (gpt-5.3-codex, cross-poll R2)	Per-hop multi-guard: `IsViewLoaded && View.Window != null && !IsBeingDismissed && !IsBeingPresented`	✅ PASS	1 file	Most thorough validity check per traversal hop
PR	PR #31016	Skip `PresentedViewController` with `IsBeingDismissed == true`	✅ PASSED (Gate)	1 file	Simple, targeted

Cross-Pollination

Model	Round	New Ideas?	Details
claude-opus-4.6	1	Yes	TransitionCoordinator deferral via AnimateAlongsideTransition
claude-sonnet-4.6	1	Yes	Same TransitionCoordinator deferral idea
gpt-5.3-codex	1	Yes	TransitionCoordinator deferral/enqueue
gemini-3-pro-preview	1	Yes	TransitionCoordinator deferral
claude-opus-4.6	2	Yes	Dedicated UIWindow at UIWindowLevel.Alert (bypasses VC chain)
claude-sonnet-4.6	2	No	NO NEW IDEAS
gpt-5.3-codex	2	Yes	Per-hop `IsViewLoaded && View.Window != null` (run as Attempt 6)
claude-opus-4.6	3	No	NO NEW IDEAS — all strategy categories covered
gpt-5.3-codex	3	Yes	Check `presented.ViewIfLoaded?.Window == platformWindow` (same window check)
gemini-3-pro-preview	3	Yes	TransitionCoordinator.GetViewController(ToViewControllerKey)

Exhausted: Yes (max 3 rounds reached)
Selected Fix: PR #31016 — Simplest, most targeted fix (single !IsBeingDismissed guard). All 5 passing alternatives are valid but more complex without being meaningfully more robust for this specific bug. The PR's fix directly addresses the root cause with minimal code change.

📋 Report — Final Recommendation

✅ Final Recommendation: APPROVE

Phase Status

Phase	Status	Notes
Pre-Flight	✅ COMPLETE	Issue #30970, iOS/macOS, 1 fix file + 2 test files
Gate	✅ PASSED	iOS — tests FAIL without fix, PASS with fix
Try-Fix	✅ COMPLETE	6 attempts: 5 passing, 1 failing; 3 cross-poll rounds
Report	✅ COMPLETE

Summary

PR #31016 fixes a deadlock in DisplayAlert() on iOS/macOS when called after closing a modal page. The fix is a minimal, targeted 1-line change to GetTopUIViewController() in AlertManager.iOS.cs. A UI test was added to prevent regression. Gate verification confirmed the test correctly catches the bug and passes with the fix. 6 alternative approaches were explored: 5 passed but all were more complex with no clear benefit for this specific bug.

Root Cause

GetTopUIViewController() traverses PresentedViewController chain without checking if any VC in the chain is mid-dismissal (IsBeingDismissed == true). When DisplayAlert() is called during/immediately after PopModalAsync(), the dismissing modal's VC is still in the hierarchy but its view is detached from the window, causing PresentViewControllerAsync to present on an invalid host — the alert never appears and the awaited task deadlocks.

Fix Quality

The fix is excellent: minimal, correct, and well-tested. Adding !topUIViewController.PresentedViewController.IsBeingDismissed to the traversal loop condition stops at the last stable VC before a dismissing one. The test covers the exact reported scenario (open modal → close modal → DisplayAlert). Copilot flagged a minor null-safety concern (Windows[0] indexing without bounds check) in the test's HostApp page that is worth addressing, but it doesn't affect correctness in the test context.

…vigation is in progress - fix (#31016) ### Description of Change By skipping view controllers that are being dismissed (animation is happening, for example ), we ensure DisplayAlert() and other popups are shown only on valid, active UI stacks, preventing the deadlock and improving reliability on iOS/macOS. ### Issues Fixed Fixes #30970

…vigation is in progress - fix (dotnet#31016) ### Description of Change By skipping view controllers that are being dismissed (animation is happening, for example ), we ensure DisplayAlert() and other popups are shown only on valid, active UI stacks, preventing the deadlock and improving reliability on iOS/macOS. ### Issues Fixed Fixes dotnet#30970

…vigation is in progress - fix (#31016) ### Description of Change By skipping view controllers that are being dismissed (animation is happening, for example ), we ensure DisplayAlert() and other popups are shown only on valid, active UI stacks, preventing the deadlock and improving reliability on iOS/macOS. ### Issues Fixed Fixes #30970

…vigation is in progress - fix (dotnet#31016) ### Description of Change By skipping view controllers that are being dismissed (animation is happening, for example ), we ensure DisplayAlert() and other popups are shown only on valid, active UI stacks, preventing the deadlock and improving reliability on iOS/macOS. ### Issues Fixed Fixes dotnet#30970

…vigation is in progress - fix (#31016) ### Description of Change By skipping view controllers that are being dismissed (animation is happening, for example ), we ensure DisplayAlert() and other popups are shown only on valid, active UI stacks, preventing the deadlock and improving reliability on iOS/macOS. ### Issues Fixed Fixes #30970

Copilot AI review requested due to automatic review settings August 5, 2025 00:07

kubaflo requested a review from a team as a code owner August 5, 2025 00:07

kubaflo requested review from mattleibow and rmarinho August 5, 2025 00:07

kubaflo self-assigned this Aug 5, 2025

Copilot AI reviewed Aug 5, 2025

View reviewed changes

kubaflo added area-navigation NavigationPage platform/ios area-controls-modal platform/macos macOS / Mac Catalyst labels Aug 5, 2025

dotnet-policy-service Bot added the community ✨ Community Contribution label Aug 5, 2025

PureWeen added the partner/syncfusion/review label Aug 6, 2025

fix 30970

6d8ae5c

kubaflo force-pushed the fix-30970 branch from 3baa5ff to 6d8ae5c Compare March 16, 2026 21:46

StephaneDelcroix reviewed Mar 18, 2026

View reviewed changes

StephaneDelcroix approved these changes Mar 18, 2026

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MauiBot added s/agent-review-incomplete AI agent could not complete all phases (blocker, timeout, error) s/agent-reviewed PR was reviewed by AI agent workflow (full 4-phase review) labels Mar 25, 2026

dotnet deleted a comment from MauiBot Mar 26, 2026

kubaflo changed the base branch from main to inflight/current March 26, 2026 21:27

kubaflo merged commit 08da508 into dotnet:inflight/current Mar 26, 2026
28 of 31 checks passed

PureWeen mentioned this pull request Apr 14, 2026

April 14th, Candidate #34885

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[iOS] Alert popup may be displayed on wrong window when modal page navigation is in progress - fix#31016

[iOS] Alert popup may be displayed on wrong window when modal page navigation is in progress - fix#31016
kubaflo merged 1 commit intodotnet:inflight/currentfrom
kubaflo:fix-30970

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MauiBot commented Mar 26, 2026

Key Findings

Fix Candidates

Gate Result: ✅ PASSED

Fix Candidates

Cross-Pollination

✅ Final Recommendation: APPROVE

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	if (_modalPageWasShown)
	if (_modalPageWasShown && Application.Current.Windows.Count > 0)

-			await Application.Current.Windows[0].Page!.DisplayAlert("My alert", "Can you see this alert?", "Yes");
+		{
+			var page = Application.Current.Windows[0].Page;
+			if (page != null)
+			{
+				await page.DisplayAlert("My alert", "Can you see this alert?", "Yes");
+			}
+		}

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kubaflo commented Aug 5, 2025

Description of Change

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Multi-Model Consensus Review (5 models: claude-opus-4.6 ×2, claude-sonnet-4.6, gemini-3-pro-preview, gpt-5.3-codex)

CI Status: ✅ All checks passing

Consensus Findings

Test Coverage

Verdict: ✅ Approve

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MauiBot commented Mar 26, 2026

🤖 AI Summary

Key Findings

Fix Candidates

Gate Result: ✅ PASSED

Fix Candidates

Cross-Pollination

✅ Final Recommendation: APPROVE

Phase Status

Summary

Root Cause

Fix Quality

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5 participants