Fixed the NRE in CarouselViewController on iOS 15.5 & 16.4 by Ahamed-Ali · Pull Request #30838 · dotnet/maui

Ahamed-Ali · 2025-07-25T12:01:21Z

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 of the issue

Upon analysis, in iOS versions 18.4 and 18.0, GetCell is called when PopAsync is invoked—navigating back to the MainPage (which contains the CarouselView). At this point, _carouselViewLoopManager is properly set through the Setup method, and a valid IndexPath is passed into GetCell, resulting in correct updates.
However, in iOS versions 15.5 and 16.0, GetCell is triggered immediately when _viewModel.Source[0] is updated. At that time, the CarouselViewLoopManager is still null, and since a valid index cannot be retrieved, the else part of GetCell is executed with an invalid IndexPath, leading to an ArgumentNullException.

Description of Change

To prevent ArgumentNullException caused by invalid IndexPath values during the loop initialization phase, ensure that the CarouselViewLoopManager is fully initialized before it is used. Once initialized, it correctly returns a valid IndexPath using FromRowSection, allowing the templated cell to be updated as expected in all iOS versions.

Issues Fixed

Fixes #28557

Tested the behaviour in the following platforms

Android
Windows
iOS
Mac

Tested Version

iOS Version	App Crashed
15.5	Yes
16.0	Yes
17.4	No
18.4	No

Screenshot

iOS 15.5

Before Issue Fix	After Issue Fix
CrashiniOS15.5.mov	FixedinIOS15.5.mov

iOS 16.0

Before Issue Fix	After Issue Fix
CrashiniOS16.0.mov	FixediniOS16.0.mov

iOS 17.4 && iOS 18.4

iOS 17.4	iOS 18.4
NoCrashiniOS17.4.mov	NoCrashiniOS18.4.mov

dotnet-policy-service · 2025-07-25T12:01:40Z

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

Copilot

Pull Request Overview

This PR fixes a null reference exception in CarouselViewController that occurs on iOS 15.5 and 16.4 when updating CarouselView's ItemsSource from another page. The issue stems from iOS version differences in when GetCell is called during navigation scenarios.

Adds a null check and initialization for _carouselViewLoopManager before use
Provides fallback handling when the loop manager cannot be initialized
Includes comprehensive UI tests to verify the fix across different iOS versions

Reviewed Changes

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

File	Description
src/Controls/src/Core/Handlers/Items/iOS/CarouselViewController.cs	Adds null check and initialization logic for _carouselViewLoopManager to prevent NRE
src/Controls/tests/TestCases.HostApp/Issues/Issue28557.cs	Creates UI test page with CarouselView and navigation scenario to reproduce the issue
src/Controls/tests/TestCases.Shared.Tests/Tests/Issues/Issue28557.cs	Implements automated test case to verify the fix works correctly

Copilot · 2025-07-28T12:11:57Z

src/Controls/src/Core/Handlers/Items/iOS/CarouselViewController.cs

+				if (_carouselViewLoopManager is null)
 				{
-					UpdateDefaultCell(defaultCell, correctedIndexPath);
+					InitializeCarouselViewLoopManager();


The InitializeCarouselViewLoopManager() method is called but not defined in this class. This will cause a compilation error unless the method exists elsewhere in the class hierarchy.

The InitializeCarouselViewLoopManager() method is properly implemented in the CarouselViewController class, so calling it will not cause any compilation errors.

jsuarezruiz · 2025-07-29T07:13:36Z

/azp run MAUI-UITests-public

azure-pipelines · 2025-07-29T07:13:48Z

Azure Pipelines successfully started running 1 pipeline(s).

jsuarezruiz · 2025-07-29T07:16:52Z

src/Controls/src/Core/Handlers/Items/iOS/CarouselViewController.cs

+				if (_carouselViewLoopManager is null)
 				{
-					UpdateDefaultCell(defaultCell, correctedIndexPath);
+					InitializeCarouselViewLoopManager();


Called on every GetCell when Loop == true and manager is null, have an impact in the performance?

This initialization typically occurs in either ViewDidLoad() or the Setup() method, which is called during AttachingToWindow().

The edge case that this fix addresses is specific to iOS 15/16, where navigation between pages involving CarouselView updates can cause the initialization to happen only once—just when it's needed.

After the initial setup, subsequent calls to GetCell() will bypass the null check, resulting in virtually no performance impact. @jsuarezruiz

jsuarezruiz · 2025-07-29T07:17:28Z

src/Controls/src/Core/Handlers/Items/iOS/CarouselViewController.cs

 				{
-					UpdateTemplatedCell(templatedCell, correctedIndexPath);
+					// Fallback to base implementation if manager couldn't be initialized
+					cell = base.GetCell(collectionView, indexPath);


The fallback completely bypasses loop behavior, could we include a comment indicating it here?

I have added the comment

jsuarezruiz · 2025-07-29T07:18:00Z

src/Controls/src/Core/Handlers/Items/iOS/CarouselViewController.cs

-				if (cell is DefaultCell defaultCell)
+			if (ItemsView?.Loop == true)
+			{
+				// In iOS 15 and 16, when the ItemsSource of the CarouselView is updated from another page


Nice comment!

jsuarezruiz · 2025-10-21T07:57:04Z

/rebase

… CarouselView1

jsuarezruiz · 2025-10-21T10:29:04Z

/azp run

azure-pipelines · 2025-10-21T10:29:24Z

Azure Pipelines successfully started running 3 pipeline(s).

> [!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](https://github.com/dotnet/maui/wiki/Testing-PR-Builds) from this PR and let us know in a comment if this change resolves your issue. Thank you! ### Root Cause of the issue - Upon analysis, in iOS versions 18.4 and 18.0, GetCell is called when PopAsync is invoked—navigating back to the MainPage (which contains the CarouselView). At this point, _carouselViewLoopManager is properly set through the Setup method, and a valid IndexPath is passed into GetCell, resulting in correct updates. - However, in iOS versions 15.5 and 16.0, GetCell is triggered immediately when _viewModel.Source[0] is updated. At that time, the CarouselViewLoopManager is still null, and since a valid index cannot be retrieved, the else part of GetCell is executed with an invalid IndexPath, leading to an ArgumentNullException. ### Description of Change - To prevent ArgumentNullException caused by invalid IndexPath values during the loop initialization phase, ensure that the CarouselViewLoopManager is fully initialized before it is used. Once initialized, it correctly returns a valid IndexPath using FromRowSection, allowing the templated cell to be updated as expected in all iOS versions. ### Issues Fixed Fixes #28557 ### Tested the behaviour in the following platforms - [x] Android - [x] Windows - [x] iOS - [x] Mac ### Tested Version | iOS Version | App Crashed | |----------|----------| | 15.5 | Yes | | 16.0 | Yes | | 17.4 | No | | 18.4 | No | ### Screenshot ### iOS 15.5 | Before Issue Fix | After Issue Fix | |----------|----------| | <video src="https://github.com/user-attachments/assets/4df6973e-c658-4c89-a085-cc2035a593bf"> | <video src="https://github.com/user-attachments/assets/25840d66-fa41-4a00-8e53-a262b405eca3"> | ### iOS 16.0 | Before Issue Fix | After Issue Fix | |----------|----------| | <video src="https://github.com/user-attachments/assets/882829ed-fef4-40e9-a450-2972b4134c8e"> | <video src="https://github.com/user-attachments/assets/4a5d0c48-e340-4b51-939e-6a6bf7518db7"> | ### iOS 17.4 && iOS 18.4 | iOS 17.4 | iOS 18.4 | |----------|----------| | <video src="https://github.com/user-attachments/assets/5c167003-f5af-4989-87c7-d09b8d3b7b81"> | <video src="https://github.com/user-attachments/assets/9c44bc1d-0956-4795-994b-2c4c314d40a7"> |

@Ahamed-Ali

## CollectionView - Fixed the NRE in CarouselViewController on iOS 15.5 & 16.4 by @Ahamed-Ali in #30838 <details> <summary>🔧 Fixes</summary> - [NRE in CarouselViewController on iOS 15.5 & 16.4](#28557) </details> - [iOS, macOS] Fixed CollectionView group header size changes with ItemSizingStrategy by @NanthiniMahalingam in #33161 <details> <summary>🔧 Fixes</summary> - [[NET 10] I6_Grouping - Grouping_with_variable_sized_items changing the 'ItemSizingStrategy' also changes the header size.](#33130) </details> ## Flyout - Add unit tests for TabBar and FlyoutItem navigation ApplyQueryAttributes (#25663) by @StephaneDelcroix in #33006 ## Flyoutpage - Fixed the FlyoutPage.Flyout Disappearing When Maximizing the Window on Mac Platform by @NanthiniMahalingam in #26701 <details> <summary>🔧 Fixes</summary> - [FlyoutPage.Flyout - navigation corrupted when running om mac , on window ok](#22719) </details> ## Mediapicker - [Windows] Fix for PickPhotosAsync throws exception if image is modified by @HarishwaranVijayakumar in #32952 <details> <summary>🔧 Fixes</summary> - [PickPhotosAsync throws exception if image is modified.](#32408) </details> ## Navigation - Fix for TabBar Navigation does not invoke its IQueryAttributable.ApplyQueryAttributes(query) by @SuthiYuvaraj in #25663 <details> <summary>🔧 Fixes</summary> - [Tabs defined in AppShell.xaml does not invoke its view model's IQueryAttributable.ApplyQueryAttributes(query) implementaion](#13537) - [`ShellContent` routes do not call `ApplyQueryAttributes`](#28453) </details> ## ScrollView - Fix ScrollToPosition.Center behavior in ScrollView on iOS and MacCatalyst by @devanathan-vaithiyanathan in #26825 <details> <summary>🔧 Fixes</summary> - [ScrollToPosition.Center Centers the First Item too in iOS and Catalyst](#26760) - [On iOS - ScrollView.ScrollToAsync Element, ScrollToPosition.MakeVisible shifts view to the right, instead of just scrolling vertically](#28965) </details> ## Searchbar - [iOS, Mac, Windows] Fixed CharacterSpacing for SearchBar text and placeholder text by @Dhivya-SF4094 in #30407 <details> <summary>🔧 Fixes</summary> - [[iOS, Mac, Windows] SearchBar CharacterSpacing property is not working as expected](#30366) </details> ## Shell - Update logic for large title display mode on iOS - shell by @kubaflo in #33039 ## TitleView - [iOS] Fixed memory leak with PopToRootAsync when using TitleView by @Vignesh-SF3580 in #28547 <details> <summary>🔧 Fixes</summary> - [NavigationPage.TitleView causes memory leak with PopToRootAsync](#28201) </details> ## Xaml - [C] Fix binding to interface-inherited properties like IReadOnlyList<T>.Count by @StephaneDelcroix in #32912 <details> <summary>🔧 Fixes</summary> - [Compiled Binding to Array.Count provides no result](#13872) </details> - Fix #31939: CommandParameter TemplateBinding lost during reparenting by @StephaneDelcroix in #32961 <details> <summary>🔧 Fixes</summary> - [CommandParameter TemplateBinding Lost During ControlTemplate Reparenting](#31939) </details> <details> <summary>🧪 Testing (4)</summary> - [Testing] Fixed Test case failure in PR 33185 - [12/22/2025] Candidate by @TamilarasanSF4853 in #33257 - [Testing] Re-saved ShouldFlyoutBeVisibleAfterMaximizingWindow test case images in PR 33185 - [12/22/2025] Candidate by @TamilarasanSF4853 in #33271 - [Testing] Fixed Test case failure in PR 33185 - [12/22/2025] Candidate - 2 by @TamilarasanSF4853 in #33299 - [Testing] Fixed Test case failure in PR 33185 - [12/22/2025] Candidate - 3 by @TamilarasanSF4853 in #33311 </details> <details> <summary>📦 Other (2)</summary> - [XSG][BindingSourceGen] Add support for RelayCommand to compiled bindings by @simonrozsival via @Copilot in #32954 <details> <summary>🔧 Fixes</summary> - [Issue #25818](#25818) </details> - Revert "Update logic for large title display mode on iOS - shell (#33039)" in cff7f35 </details> **Full Changelog**: main...inflight/candidate

dotnet-policy-service bot added community ✨ Community Contribution partner/syncfusion Issues / PR's with Syncfusion collaboration labels Jul 25, 2025

Ahamed-Ali marked this pull request as ready for review July 28, 2025 12:11

Copilot AI review requested due to automatic review settings July 28, 2025 12:11

Ahamed-Ali requested a review from a team as a code owner July 28, 2025 12:11

Ahamed-Ali requested review from jfversluis and rmarinho July 28, 2025 12:11

Copilot AI reviewed Jul 28, 2025

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jsuarezruiz suggested changes Jul 29, 2025

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Ahamed-Ali added 5 commits October 21, 2025 07:57

Fixed the ArgumentNullException crash in iOS15 and iOS 16 versions in…

672bdd1

… CarouselView1

Added the test for the issue

5ff427d

restricted the test on windows

2ccff16

spell error

8403978

Added the comment

4868c3c

github-actions bot force-pushed the fix-28557 branch from 14a0bf0 to 4868c3c Compare October 21, 2025 07:58

rmarinho approved these changes Dec 4, 2025

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rmarinho changed the base branch from main to inflight/current December 4, 2025 13:56

rmarinho merged commit a499756 into dotnet:inflight/current Dec 4, 2025
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PureWeen mentioned this pull request Dec 18, 2025

December 22nd, Candidate #33185

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Ahamed-Ali commented Jul 25, 2025

Root Cause of the issue

Description of Change

Issues Fixed

Tested the behaviour in the following platforms

Tested Version

Screenshot

iOS 15.5

iOS 16.0

iOS 17.4 && iOS 18.4

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Pull Request Overview

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