[iOS] Fix App crash with NullReferenceException in ShellSectionRenderer

[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 the ShellSectionRenderer class, the ElementForViewController method is used to find the corresponding .NET MAUI page for a given ViewController.
While traversing the entire ShellSection stack to locate the respective page, a push and pop modal operation causes Page1’s handler to become null.

Root Cause

iOS OnUnloaded mechanism fires immediately during navigation transitions, triggering premature Handler disposal before checking if the page is still accessible for back navigation.

Description of Change

In Page.cs, added Shell navigation stack check in SendNavigatedFrom() to prevent Handler disposal when page is still in stack

Issues Fixed

Fixes #31961

Tested the behavior in the following platforms.

• Android
• Windows
• iOS
• Mac

Output Screenshot

Before	After
iOS Before.mov	iOS After.mov

[jsuarezruiz]

This is only required on iOS? Because this is a cross platform code that will run same on other platforms.

[devanathan-vaithiyanathan]

@jsuarezruiz , I've added the fix only for iOS platform

[sheiksyedm]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 3 pipeline(s).

[Copilot]

Pull Request Overview

This PR fixes an iOS-specific NullReferenceException crash in ShellSectionRenderer that occurs during modal navigation. The root cause was premature Handler disposal when iOS's OnUnloaded mechanism triggered during navigation transitions, disposing Handlers for pages still accessible via back navigation in the Shell stack.

Key Changes:

• Added Shell navigation stack validation before Handler disposal on iOS to prevent premature cleanup
• Added comprehensive UI tests demonstrating the crash scenario and validating the fix

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
src/Controls/src/Core/Page/Page.cs	Adds iOS-specific check to prevent Handler disposal when page remains in Shell navigation stack
src/Controls/tests/TestCases.HostApp/Issues/Issue31961.cs	Implements UI test page demonstrating modal + Shell navigation interaction
src/Controls/tests/TestCases.Shared.Tests/Tests/Issues/Issue31961.cs	Implements Appium test validating the fix through automated UI interaction

[Copilot]

Trailing whitespace should be removed from the blank line.

Suggested change

[rmarinho]

🤖 AI Summary

📊 Expand Full Review

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🔍 Pre-Flight — Context & Validation

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📝 Review Session — Update Issue31961.cs · c89ea28

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PR: #32109 - [iOS] Fix App crash with NullReferenceException in ShellSectionRenderer
Issue: #31961 - [iOS] App crash with NullReferenceException in ShellSectionRenderer
Author: @devanathan-vaithiyanathan (Syncfusion partner)
Platforms Affected: iOS (platform-specific issue, labels: platform/ios, area-controls-shell)
Files Changed: 1 implementation file, 2 test files

Issue Summary

When navigating back from a page (Page A) and then that page navigates forward inside Shell OnNavigated event, the Handler for Page A becomes null on iOS. This causes NullReferenceException in ShellSectionRenderer.ElementForViewController. Regression from .NET 8 → .NET 9.

Reproduction steps:

1. Navigate: Main → Page1
2. Open modal from Page1
3. Close modal (returns to Page1, triggers Shell OnNavigated)
4. Page1's OnShellNavigated handler navigates to Page2
5. Navigate Page2 → Page3 → CRASH (Page1's Handler is null)

Root Cause (from PR)

iOS OnUnloaded fires immediately during navigation transitions, triggering premature Handler disposal before checking if page is still accessible via back navigation in Shell stack.

Files Changed

Implementation:

• src/Controls/src/Core/Page/Page.cs (+18 lines) — Added iOS-specific guard in SendNavigatedFrom() to prevent Handler disposal when page is still in Shell.Current.CurrentItem?.CurrentItem?.Stack

Tests:

• src/Controls/tests/TestCases.HostApp/Issues/Issue31961.cs (+194 lines) — Shell with modal navigation scenario
• src/Controls/tests/TestCases.Shared.Tests/Tests/Issues/Issue31961.cs (+27 lines) — Appium test: MainPage → Page1 → OpenModal → CloseModal → Page2 → Page3

PR Discussion

File:Line	Reviewer Says	Author Says	Status
Page.cs:857	jsuarezruiz: "This is only required on iOS? Cross-platform code runs same on other platforms."	"I've added the fix only for iOS platform" (uses #if IOS)	✅ Addressed with platform guard
Page.cs:872	copilot: "Trailing whitespace on blank line"	-	⚠️ Minor cleanup needed
General	kubaflo (Feb 2026): "test doesn't catch the bug"	-	❌ Outstanding issue

Prior agent review (Feb 2026): Gate ❌ FAILED — tests passed without fix. Same commit c89ea28 at time of prior review.

Edge Cases to Check

• Multi-step modal navigation (modal → modal)
• Multiple pages with null Handlers in stack
• Non-Shell navigation scenarios (should be unaffected — Shell.Current null)
• Test properly catches the bug without fix

Fix Candidates

#	Source	Approach	Test Result	Files Changed	Notes
PR	PR #32109	iOS-specific guard in SendNavigatedFrom(): check Shell.Current.CurrentItem?.CurrentItem?.Stack.Contains(this) before disposing Handler	⏳ PENDING (Gate)	Page.cs (+18)	Original PR — uses #if IOS to scope to iOS only

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🚦 Gate — Test Verification

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📝 Review Session — Update Issue31961.cs · c89ea28

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Result: ❌ FAILED
Platform: ios
Mode: Full Verification
Test Filter: Issue31961

Verification Outcome

• Tests FAIL without fix: ❌ NO (Expected: YES)

  • Tests PASSED when fix was reverted — tests don't detect the bug

• Tests PASS with fix: ✅ YES (Expected: YES)

  • Tests passed with PR's fix applied

Critical Issue

The tests in Issue31961.cs do not catch the bug they claim to fix.

When the PR's fix in Page.cs was reverted to the merge base state, the tests still passed. This means:

1. Tests may not reproduce the exact crash scenario from issue [iOS] App crash with NullReferenceException in ShellSectionRenderer #31961
2. The crash requires specific timing (iOS OnUnloaded firing during navigation transition) that may not be triggered in this test
3. The test validates navigation completes without verifying that Handler disposal was NOT triggered prematurely

Test Analysis

Current test flow:

1. App.WaitForElement("MainPage") → tap
2. App.WaitForElement("OpenModalButton") → tap (navigates to modal)
3. App.WaitForElement("CloseModalButton") → tap (closes modal, triggers OnShellNavigated)
4. App.WaitForElement("Page2") → tap (navigation from OnShellNavigated)
5. App.WaitForElement("Page3") → (final assertion)

Problem: The test waits for Page2 button AFTER closing modal. But Issue31961FirstPage.OnShellNavigated() triggers NavigateToPage2Command.Execute(null) which calls GoToAsync without await. Since navigation is triggered synchronously in OnShellNavigated, and the Command uses fire-and-forget, the timing may not reproduce the crash on all devices.

Why test may pass without fix: The crash in issue #31961 depends on iOS specifically disposing the Handler during the modal close → navigation sequence. The test may be completing fast enough that the crash timing window is not hit, or the timing of when IsLoaded is checked differs.

Prior Gate Result

A prior agent review (Feb 2026, same commit c89ea28) also found Gate ❌ FAILED with identical result. Reviewer kubaflo confirmed: "test doesn't catch the bug."

Recommended Actions

1. Fix the test to ensure it actually catches the NullReferenceException:

   • Add assertion that verifies Handler is NOT null after the modal close → navigation sequence
   • Consider adding a try/catch in the test page's OnShellNavigated to detect crashes
   • OR refactor to check that all pages still have non-null Handlers after the sequence

2. Alternative approach: Write a test that directly verifies the Handler state, not just navigation completion

3. Use write-tests-agent to help create tests that properly catch this bug

⛔ GATE BLOCKED — Tests must be fixed before this PR can be approved.

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📋 Report — Final Recommendation

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📝 Review Session — Update Issue31961.cs · c89ea28

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⚠️ Final Recommendation: REQUEST CHANGES

Status: Review INCOMPLETE — Gate phase failed

Summary

PR #32109 aims to fix an iOS-specific crash (NullReferenceException in ShellSectionRenderer) that occurs during modal navigation in Shell. The fix itself looks technically sound, but the automated test verification reveals the tests do NOT catch the bug they claim to fix.

This is confirmed by:

• This review's Gate verification (February 2026)
• Prior agent review's Gate verification (February 2026, same commit)
• Reviewer kubaflo's manual review (February 2026): "Looks like the test doesn't catch the bug."

Gate Phase Results

Platform Tested: iOS
Test Filter: Issue31961

Check	Expected	Actual	Status
Tests FAIL without fix	YES	NO — tests pass	❌
Tests PASS with fix	YES	YES	✅

Conclusion: Tests are inadequate. They do not detect whether the fix is in place.

Root Cause Analysis

Bug: iOS OnUnloaded fires immediately during modal navigation transitions, causing premature Handler disposal for pages still in Shell's navigation stack. When SendNavigatedFrom is called with NavigationType.Pop during modal close, the Handler for Issue31961FirstPage is disposed even though the page is still accessible in the Shell stack.

PR's Fix: Adds an #if IOS guard in Page.SendNavigatedFrom() that checks Shell.Current.CurrentItem?.CurrentItem?.Stack.Contains(this) before disposing the Handler. If the page is still in the stack, disposal is skipped.

Why the test doesn't catch it: The test validates that navigation completes (reaches "Page3") but doesn't verify that the Handler is NOT disposed prematurely. The crash depends on iOS-specific timing of OnUnloaded during the modal close sequence, which the test may not reliably trigger.

Fix Quality Assessment

The implementation approach is reasonable but has potential concerns:

1. Timing dependency: The fix checks the stack at the moment SendNavigatedFrom is called. If the stack hasn't been updated yet (race condition), this check might fail.

2. Stack access path: Shell.Current.CurrentItem?.CurrentItem?.Stack only checks the current active ShellSection's stack. Pages in other sections or tabs would not be found here, potentially still getting their Handlers disposed incorrectly.

3. Memory implications: If Handler disposal is prevented indefinitely for pages in the stack, it could delay garbage collection. This is acceptable for typical navigation depths.

4. Trailing whitespace at line 824 in Page.cs (minor)

Phases Completed

Phase	Status	Notes
1. Pre-Flight	✅ COMPLETE	Context gathered
2. Gate	❌ FAILED	Tests don't catch bug — confirmed 2nd time
3. Fix	⏭️ SKIPPED	Cannot proceed — Gate must pass first
4. Report	✅ COMPLETE	This report

Required Actions for @devanathan-vaithiyanathan

1. Fix the test so it actually catches the NullReferenceException without the fix:

   • Verify that Handler is NOT null after the modal close sequence (before fix reverts this)
   • Consider checking Handler != null on Issue31961FirstPage after CloseModalButton is tapped
   • The test should CRASH (app crash or assertion failure) without the fix in Page.cs

2. Verify manually: Run without the #if IOS guard in Page.cs to confirm test fails

3. Remove trailing whitespace at line 824 of Page.cs

4. Consider: Use write-tests-agent for help creating tests that properly reproduce this iOS timing issue

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📋 Expand PR Finalization Review

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Title: ✅ Good

Current: [iOS] Fix App crash with NullReferenceException in ShellSectionRenderer

Description: ⚠️ Needs Update

Description needs updates. See details below.

✨ 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!

Issue Details

In ShellSectionRenderer, the ElementForViewController method is used to find the corresponding .NET MAUI page for a given UIViewController. When a page that is still in the Shell navigation stack has its Handler disposed prematurely, ElementForViewController returns null, crashing in WillShowViewController.

Root Cause

The crash occurs through this sequence on iOS:

1. User navigates to Page1 via Shell, then opens a ModalPage (via GoToAsync)
2. User closes the modal (GoToAsync("..")) — this triggers NavigationType.Pop in SendNavigatedFrom
3. iOS's OnUnloaded mechanism fires during this navigation transition, which calls SendNavigatedFrom on Page1
4. SendNavigatedFrom with NavigationType.Pop calls DisconnectHandlers() on Page1 — but Page1 is still in the Shell navigation stack and the user can still navigate forward from it
5. Page1's Handler becomes null
6. When the user next navigates and ShellSectionRenderer.WillShowViewController tries to map the UIViewController back to Page1, ElementForViewController finds the page but its Handler is null, causing a NullReferenceException

This is a regression introduced in .NET 9; .NET MAUI 8 was not affected.

Description of Change

In Page.cs, added an iOS-specific guard in SendNavigatedFrom(): before calling DisconnectHandlers() on a Pop/PopToRoot navigation, check whether the page is still present in Shell.Current.CurrentItem?.CurrentItem?.Stack. If the page is still reachable in the Shell navigation stack, return early without disposing the Handler.

#if IOS
    if (Shell.Current != null)
    {
        var currentStack = Shell.Current.CurrentItem?.CurrentItem?.Stack;
        if (currentStack?.Contains(this) == true)
        {
            return; // Page still in stack, don't dispose Handler
        }
    }
#endif

Issues Fixed

Fixes #31961

Platforms Tested

• Android
• Windows
• iOS
• Mac

Code Review: ⚠️ Issues Found

Code Review — PR #32109

🔴 Critical Issues

1. Platform-specific logic (#if IOS) in a shared Core file

File: src/Controls/src/Core/Page/Page.cs (lines 855–868)

Problem: Adding #if IOS inside a shared Controls/Core file is a MAUI anti-pattern. The platform layer (iOS-specific code in Handlers/ or Platform/iOS/) is the correct location for platform-specific behavior. Putting it in Page.cs (a cross-platform type) creates several problems:

• It conflates platform concerns with cross-platform logic
• The #if IOS guard is invisible at the call site — the SendNavigatedFrom method signature gives no indication it behaves differently per platform
• Existing reviewer @jsuarezruiz flagged this concern (see PR review thread)

Recommendation: Consider moving the guard to iOS-specific Shell platform code. Alternatively, introduce a virtual/partial method that iOS can override. If the #if IOS approach is kept as a pragmatic fix, it must be clearly documented with a comment explaining why this is iOS-only.

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🟡 Warnings

2. Fragile Shell.Current.CurrentItem?.CurrentItem?.Stack traversal

File: src/Controls/src/Core/Page/Page.cs (lines 858–863)

Problem: The chain Shell.Current.CurrentItem?.CurrentItem?.Stack makes several assumptions:

• Shell.Current is the shell that owns this page (not always true with multiple Shells)
• The page is always inside a ShellSection that is the CurrentItem of a ShellItem that is the CurrentItem of the Shell
• It only checks the current section's stack — if the page lives in a tab/section that is not currently selected, the check returns false, potentially disposing a reachable page

If any level of the hierarchy is null (e.g., a FlyoutItem without a Tab), the null-conditional ?. will return null and the check falls through to DisconnectHandlers(), which is the safe default — but it means the fix only works for the narrow TabBar > Tab > ShellSection topology, not all Shell configurations.

Recommendation: Use Shell.Current?.Navigation?.NavigationStack?.Contains(this) as a broader and more robust check, since Shell.Current.Navigation.NavigationStack reflects the entire Shell back stack regardless of hierarchy topology.

3. Early return may permanently suppress Handler disposal

File: src/Controls/src/Core/Page/Page.cs (lines 860–864)

Problem: The early return skips DisconnectHandlers() entirely. For pages that remain in the stack indefinitely (e.g., deeply nested routes that are never popped), this could delay or prevent Handler disposal if SendNavigatedFrom is the only path that triggers disconnection. This may cause a subtle memory leak in long navigation sessions.

Recommendation: Document why the early return is safe — specifically, note that the page will be disconnected via the normal DisconnectHandlers() path when it is genuinely popped from the stack later.

4. Incorrect "Platforms Tested" in PR description

Not a code issue, but the PR description marks Android and Windows as tested. The fix is entirely inside #if IOS and has no effect on Android or Windows. These checkmarks are misleading and should be unchecked.

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🟢 Looks Good / Info

5. Trailing whitespace on line 872

File: src/Controls/src/Core/Page/Page.cs (line 872 — blank line between #endif and if (!this.IsLoaded))

Already flagged in the Copilot PR reviewer comment. A trivial nit, but dotnet format should clean this.

6. partial class without XAML in HostApp test

File: src/Controls/tests/TestCases.HostApp/Issues/Issue31961.cs (line 42)

Issue31961MainPage is declared partial class but there is no corresponding XAML file. Unnecessary partial should be removed.

7. Test coverage is good and matches crash scenario

The UI test in Issue31961.cs (TestCases.Shared.Tests) reproduces the exact steps from the issue report: Main → Page1 → Open Modal → Close Modal → Page2 → Page3. The [Category(UITestCategories.Shell)] is appropriate. The test validates the fix end-to-end.

8. INavigationAware interface is public at namespace level in a test file

File: src/Controls/tests/TestCases.HostApp/Issues/Issue31961.cs (lines 7–10)

A public INavigationAware interface is defined at the namespace level inside a test file. This is a public symbol in the test host app assembly. It should be internal or nested inside the test class to avoid polluting the namespace and risking naming collisions with application or library code.

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[kubaflo]

Hi! Looks like the test doesn't catch the bug. Could you please have a look?

[devanathan-vaithiyanathan]

Hi! Looks like the test doesn't catch the bug. Could you please have a look?

@kubaflo , As per the user’s instructions, when navigating from Page2 to Page3, a NullReferenceException is thrown in the simple sample. However, in the HostApp, the exception is not thrown. When navigating back to Page1 without the fix, a blank page is shown. With the fix, it works correctly. I have now modified the test accordingly.

[MauiBot]

🚦 Gate - Test Before and After Fix

📊 Expand Full Gate — 5004f68 · test modified

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Gate Result: ✅ PASSED

Platform: IOS · Base: main · Merge base: 720a9d4a

Test	Without Fix (expect FAIL)	With Fix (expect PASS)
🖥️ Issue31961 Issue31961	✅ FAIL — 216s	✅ PASS — 88s

🔴 Without fix — 🖥️ Issue31961: FAIL ✅ · 216s

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Test run for /Users/cloudtest/vss/_work/1/s/artifacts/bin/Controls.TestCases.iOS.Tests/Debug/net10.0/Controls.TestCases.iOS.Tests.dll (.NETCoreApp,Version=v10.0)
VSTest version 18.0.1 (arm64)

Starting test execution, please wait...
A total of 1 test files matched the specified pattern.
/Users/cloudtest/vss/_work/1/s/artifacts/bin/Controls.TestCases.iOS.Tests/Debug/net10.0/Controls.TestCases.iOS.Tests.dll
[xUnit.net 00:00:00.00] xUnit.net VSTest Adapter v2.8.2+699d445a1a (64-bit .NET 10.0.0)
[xUnit.net 00:00:00.05]   Discovering: Controls.TestCases.iOS.Tests
[xUnit.net 00:00:00.13]   Discovered:  Controls.TestCases.iOS.Tests
NUnit Adapter 4.5.0.0: Test execution started
Running selected tests in /Users/cloudtest/vss/_work/1/s/artifacts/bin/Controls.TestCases.iOS.Tests/Debug/net10.0/Controls.TestCases.iOS.Tests.dll
   NUnit3TestExecutor discovered 1 of 1 NUnit test cases using Current Discovery mode, Non-Explicit run
>>>>> 3/30/2026 7:11:33 AM FixtureSetup for Issue31961(iOS)
>>>>> 3/30/2026 7:11:37 AM VerifyShellNavigationWithModalNavigation Start
>>>>> 3/30/2026 7:11:57 AM VerifyShellNavigationWithModalNavigation Stop
>>>>> 3/30/2026 7:11:57 AM Log types: syslog, crashlog, performance, safariConsole, safariNetwork, server
  Failed VerifyShellNavigationWithModalNavigation [20 s]
  Error Message:
   System.TimeoutException : Timed out waiting for element...
  Stack Trace:
     at UITest.Appium.HelperExtensions.Wait(Func`1 query, Func`2 satisfactory, String timeoutMessage, Nullable`1 timeout, Nullable`1 retryFrequency) in /_/src/TestUtils/src/UITest.Appium/HelperExtensions.cs:line 2757
   at UITest.Appium.HelperExtensions.WaitForAtLeastOne(Func`1 query, String timeoutMessage, Nullable`1 timeout, Nullable`1 retryFrequency) in /_/src/TestUtils/src/UITest.Appium/HelperExtensions.cs:line 2784
   at UITest.Appium.HelperExtensions.WaitForElement(IApp app, String marked, String timeoutMessage, Nullable`1 timeout, Nullable`1 retryFrequency, Nullable`1 postTimeout) in /_/src/TestUtils/src/UITest.Appium/HelperExtensions.cs:line 793
   at Microsoft.Maui.TestCases.Tests.Issues.Issue31961.VerifyShellNavigationWithModalNavigation() in /_/src/Controls/tests/TestCases.Shared.Tests/Tests/Issues/Issue31961.cs:line 28
   at System.Reflection.MethodBaseInvoker.InterpretedInvoke_Method(Object obj, IntPtr* args)
   at System.Reflection.MethodBaseInvoker.InvokeWithNoArgs(Object obj, BindingFlags invokeAttr)

NUnit Adapter 4.5.0.0: Test execution complete

Total tests: 1
     Failed: 1
Test Run Failed.
 Total time: 1.2688 Minutes

🟢 With fix — 🖥️ Issue31961: PASS ✅ · 88s

  Determining projects to restore...
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/Users/cloudtest/vss/_work/1/s/.dotnet/packs/Microsoft.iOS.Sdk.net10.0_26.0/26.0.11017/targets/Xamarin.Shared.Sdk.targets(309,3): warning : RuntimeIdentifier was set on the command line, and will override the value for RuntimeIdentifiers set in the project file. [/Users/cloudtest/vss/_work/1/s/src/Controls/tests/TestCases.HostApp/Controls.TestCases.HostApp.csproj::TargetFramework=net10.0-ios]
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  ##vso[build.updatebuildnumber]10.0.60-ci+azdo.13687604
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  Detected signing identity:
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    Provisioning Profile: "" () - no entitlements
    Bundle Id: com.microsoft.maui.uitests
    App Id: com.microsoft.maui.uitests
  Controls.TestCases.HostApp -> /Users/cloudtest/vss/_work/1/s/artifacts/bin/Controls.TestCases.HostApp/Debug/net10.0-ios/iossimulator-arm64/Controls.TestCases.HostApp.dll
  Optimizing assemblies for size may change the behavior of the app. Be sure to test after publishing. See: https://aka.ms/dotnet-illink
  Optimizing assemblies for size. This process might take a while.

Build succeeded.

/Users/cloudtest/vss/_work/1/s/.dotnet/packs/Microsoft.iOS.Sdk.net10.0_26.0/26.0.11017/targets/Xamarin.Shared.Sdk.targets(309,3): warning : RuntimeIdentifier was set on the command line, and will override the value for RuntimeIdentifiers set in the project file. [/Users/cloudtest/vss/_work/1/s/src/Controls/tests/TestCases.HostApp/Controls.TestCases.HostApp.csproj::TargetFramework=net10.0-ios]
    1 Warning(s)
    0 Error(s)

Time Elapsed 00:00:42.89
  Determining projects to restore...
  Restored /Users/cloudtest/vss/_work/1/s/src/Controls/src/BindingSourceGen/Controls.BindingSourceGen.csproj (in 342 ms).
  Restored /Users/cloudtest/vss/_work/1/s/src/Graphics/src/Graphics/Graphics.csproj (in 355 ms).
  Restored /Users/cloudtest/vss/_work/1/s/src/Essentials/src/Essentials.csproj (in 357 ms).
  Restored /Users/cloudtest/vss/_work/1/s/src/Controls/src/Core/Controls.Core.csproj (in 363 ms).
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  ##vso[build.updatebuildnumber]10.0.60-ci+azdo.13687604
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  ##vso[build.updatebuildnumber]10.0.60-ci+azdo.13687604
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Test run for /Users/cloudtest/vss/_work/1/s/artifacts/bin/Controls.TestCases.iOS.Tests/Debug/net10.0/Controls.TestCases.iOS.Tests.dll (.NETCoreApp,Version=v10.0)
VSTest version 18.0.1 (arm64)

Starting test execution, please wait...
A total of 1 test files matched the specified pattern.
/Users/cloudtest/vss/_work/1/s/artifacts/bin/Controls.TestCases.iOS.Tests/Debug/net10.0/Controls.TestCases.iOS.Tests.dll
[xUnit.net 00:00:00.00] xUnit.net VSTest Adapter v2.8.2+699d445a1a (64-bit .NET 10.0.0)
[xUnit.net 00:00:00.04]   Discovering: Controls.TestCases.iOS.Tests
[xUnit.net 00:00:00.12]   Discovered:  Controls.TestCases.iOS.Tests
NUnit Adapter 4.5.0.0: Test execution started
Running selected tests in /Users/cloudtest/vss/_work/1/s/artifacts/bin/Controls.TestCases.iOS.Tests/Debug/net10.0/Controls.TestCases.iOS.Tests.dll
   NUnit3TestExecutor discovered 1 of 1 NUnit test cases using Current Discovery mode, Non-Explicit run
>>>>> 3/30/2026 7:13:18 AM FixtureSetup for Issue31961(iOS)
>>>>> 3/30/2026 7:13:22 AM VerifyShellNavigationWithModalNavigation Start
>>>>> 3/30/2026 7:13:27 AM VerifyShellNavigationWithModalNavigation Stop
  Passed VerifyShellNavigationWithModalNavigation [5 s]
NUnit Adapter 4.5.0.0: Test execution complete

Test Run Successful.
Total tests: 1
     Passed: 1
 Total time: 20.7868 Seconds

📁 Fix files reverted (2 files)

• eng/pipelines/ci-copilot.yml
• src/Controls/src/Core/Page/Page.cs

---

[kubaflo]

Could you please verify the ai's summary?

[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 -- 32109

Or

• Run remotely in PowerShell:

iex "& { $(irm https://raw.githubusercontent.com/dotnet/maui/main/eng/scripts/get-maui-pr.ps1) } 32109"

[MauiBot]

🤖 AI Summary

📊 Expand Full Review — 5004f68 · test modified

---

🔍 Pre-Flight — Context & Validation

---

Issue: #31961 - [iOS] App crash with NullReferenceException in ShellSectionRenderer
PR: #32109 - [iOS] Fix App crash with NullReferenceException in ShellSectionRenderer
Author: @devanathan-vaithiyanathan (Syncfusion partner)
Platforms Affected: iOS (regression from .NET 8 → .NET 9)
Files Changed: 1 implementation, 2 test

Issue Summary

When navigating back from Page A and then Page A navigates forward inside Shell's OnNavigated event, the Handler for Page A becomes null on iOS. This causes a NullReferenceException in ShellSectionRenderer.ElementForViewController. The crash is a regression introduced in .NET 9.

Reproduction steps (from issue):

1. Navigate: MainPage → Page1
2. Open modal from Page1
3. Close modal (returns to Page1, triggers Shell OnNavigated)
4. Page1's OnShellNavigated handler navigates to Page2
5. Navigate Page2 → Page3 → CRASH (Page1's Handler is null)

Root Cause

iOS OnUnloaded fires immediately during navigation transitions, triggering premature Handler disposal in Page.SendNavigatedFrom() before confirming the page is still accessible via Shell's navigation stack. The NavigationType.Pop branch disposes the Handler even when the page is still reachable.

Fix Approach (PR's Fix)

In src/Controls/src/Core/Page/Page.cs, added an #if IOS guard inside SendNavigatedFrom():

• Check Shell.Current.CurrentItem?.CurrentItem?.Stack.Contains(this)
• If the page is still in the current ShellSection's stack, skip Handler disposal

Key Findings

• Gate PASSED this time (prior review's gate failed — tests were updated since then)
• Prior reviewer kubaflo confirmed tests didn't catch the bug in the prior review
• The test was updated to now correctly detect the regression
• Reviewer jsuarezruiz asked why cross-platform code needed iOS-specific fix → resolved with #if IOS
• Copilot reviewer flagged trailing whitespace on blank line (line 824 of Page.cs)
• The Stack check only inspects CurrentItem?.CurrentItem?.Stack — doesn't cover pages in non-current ShellSections or tabs

Edge Cases to Check

• Page in a non-current tab (ShellSection) — Stack check only covers current section
• Multi-step modal navigation (modal → modal)
• Pop-to-root with multiple pages in stack
• Non-Shell navigation scenarios (should be unaffected — Shell.Current null guard)
• PageContainer pages (TabbedPage, NavigationPage nested in Shell)

Fix Candidates

#	Source	Approach	Test Result	Files Changed	Notes
PR	PR #32109	#if IOS guard in SendNavigatedFrom(): check Shell.Current.CurrentItem?.CurrentItem?.Stack.Contains(this) before disposing Handler	✅ PASSED (Gate)	Page.cs (+18)	Platform-scoped to iOS only; trailing whitespace nit

---

🔧 Fix — Analysis & Comparison

---

Fix Candidates

#	Source	Approach	Test Result	Files Changed	Notes
PR	PR #32109	#if IOS guard in Page.SendNavigatedFrom(): check Shell.Current.CurrentItem?.CurrentItem?.Stack.Contains(this) before disposing Handler	✅ PASSED (Gate)	Page.cs (+18)	iOS-only via #if IOS; narrow stack check (current ShellSection only)
1	claude-opus-4.6	Two-part: IsStillInNavigationStack() (this.Navigation?.NavigationStack) in Page.cs + tracker fallback in ShellSectionRenderer.ElementForViewController	✅ PASS	Page.cs, ShellSectionRenderer.cs	Cross-platform; also fixes crash site defensively
2	claude-sonnet-4.6	Entirely in ShellSectionRenderer.cs: tracker fallback in ElementForViewController + ReconnectPreemptivelyDisposedHandlers() in OnNavigated	✅ PASS	ShellSectionRenderer.cs	iOS only; more complex; reconnection could have side effects
3	gpt-5.3-codex	ShellSection.ContainsInManagedStack() (_navStack + CurrentItem.Page) called from Page.ShouldSkipDisconnectHandlersForShellManagedPage()	✅ PASS	Page.cs, ShellSection.cs	Authoritative Shell-owned check; cross-platform
4	gpt-5.4	Renderer-owned UIViewController→Element dictionary in ShellSectionRenderer.cs only	❌ FAIL	ShellSectionRenderer.cs	VC mapping alone insufficient; didn't prevent Handler disposal

Cross-Pollination

Model	Round	New Ideas?	Details
claude-opus-4.6	2	Yes	ManualDisconnect policy on Shell-managed pages (prevent auto-disconnect while owned by ShellSection)
claude-sonnet-4.6	2	Yes	Use Shell.Navigated event as disposal trigger instead of OnUnloaded for Shell-managed pages
gpt-5.3-codex	2	Yes	Navigation-epoch check; PendingShellTransition flag; weak VC↔Page map at Shell level
gpt-5.4	2	Yes	Narrower guard targeting specifically the modal-pop transition path (IsPoppingModalStack)

Exhausted: No — models suggested new ideas in Round 2, but all are more invasive architectural changes than the 3 already-passing solutions. With 3 passing candidates providing equivalent bug coverage, additional exploration would increase complexity without clear benefit.

Selected Fix: PR's fix — #if IOS guard in Page.SendNavigatedFrom() — Reason: Simplest change (18 lines, 1 file), iOS-scoped via #if IOS which is appropriate since the regression is iOS-specific, passed Gate verification. Attempt 3 (ShellSection-based) is architecturally cleaner but introduces changes to 2 files. The PR fix's narrow stack check (CurrentItem?.CurrentItem?.Stack) is sufficient for the reported scenario.

---

📋 Report — Final Recommendation

---

✅ Final Recommendation: APPROVE

Phase Status

Phase	Status	Notes
Pre-Flight	✅ COMPLETE	Issue #31961, iOS regression .NET 8→9, Shell + modal navigation
Gate	✅ PASSED	ios — tests FAIL without fix, PASS with fix
Try-Fix	✅ COMPLETE	4 attempts: 3 passing, 1 failing; PR's fix selected as best
Report	✅ COMPLETE

Selected Fix: PR

Summary

PR #32109 fixes a regression introduced in .NET 9 where iOS OnUnloaded fires prematurely during modal close transitions, causing Page.SendNavigatedFrom() to dispose the Handler for a page that is still in Shell's navigation stack. This results in a NullReferenceException in ShellSectionRenderer.ElementForViewController when that page's ViewController is subsequently encountered during navigation.

The fix is minimal, correct, and verified by gate testing. Three independent alternative approaches also passed tests, confirming the PR's approach is sound.

Root Cause

In Page.SendNavigatedFrom(), when NavigationType.Pop or PopToRoot is detected, the Handler is scheduled for disposal. On iOS, the OnUnloaded lifecycle event fires during modal close even for pages that remain in Shell's navigation stack (e.g., Page1 underneath the modal). The disposal proceeds and sets Handler = null on Page1. When ShellSectionRenderer.ElementForViewController later iterates ShellSection.Stack looking for the ViewController, it hits child.Handler as IPlatformViewHandler on Page1 and gets null, returning null from the method. WillShowViewController then dereferences the null element and crashes.

This is a regression because .NET 9 changed the iOS OnUnloaded firing behavior during navigation transitions relative to .NET 8.

Fix Quality

PR's fix: #if IOS guard in Page.SendNavigatedFrom() that checks Shell.Current.CurrentItem?.CurrentItem?.Stack.Contains(this) before allowing Handler disposal.

Assessment: Acceptable — minor concerns

Strengths:

• Minimal change (18 lines, 1 file)
• Correctly scoped to iOS via #if IOS
• Simple and readable logic
• Gate confirmed: tests fail without fix, pass with fix

Concerns:

1. Trailing whitespace (line 824) — noted by copilot reviewer, should be fixed
2. Narrow stack check — only checks CurrentItem?.CurrentItem?.Stack (current ShellSection). Pages in non-current tabs would not be protected, though this is unlikely to be a practical issue for the reported scenario
3. #if IOS in Page.cs — cross-platform core file with iOS-specific code. Not ideal architecturally, but justified since the issue is iOS-specific behavior

Alternative fix comparison:

• Attempt 3 (ShellSection-based) is architecturally cleaner (ShellSection.ContainsInManagedStack avoids #if IOS and uses Shell's internal _navStack) but requires 2 files — not a meaningful improvement for the added complexity
• PR's fix is the simplest passing solution

Required Changes Before Merge

1. Remove trailing whitespace from blank line at Page.cs:824 (inline suggestion from copilot reviewer already provided)

---