NRE in CarouselViewController on iOS 15.5 & 16.4

[mypp74]

Description

2025-03-21 22:38:28.494272+0100 Dopnet.YourDive.Maui[49904:537114] Unhandled managed exception: Value cannot be null. (Parameter 'key') (System.ArgumentNullException) at System.Collections.Generic.Dictionary2[[System.Object, System.Private.CoreLib, Version=9.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e],[Microsoft.Maui.Controls.Handlers.Items.TemplatedCell, Microsoft.Maui.Controls, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null]].FindValue(Object key) at System.Collections.Generic.Dictionary2[[System.Object, System.Private.CoreLib, Version=9.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e],[Microsoft.Maui.Controls.Handlers.Items.TemplatedCell, Microsoft.Maui.Controls, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null]].TryGetValue(Object key, TemplatedCell& value) at Microsoft.Maui.Controls.Handlers.Items.ItemsViewController1[[Microsoft.Maui.Controls.CarouselView, Microsoft.Maui.Controls, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null]].UpdateTemplatedCell(TemplatedCell cell, NSIndexPath indexPath) at Microsoft.Maui.Controls.Handlers.Items.ItemsViewController1[[Microsoft.Maui.Controls.CarouselView, Microsoft.Maui.Controls, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null]].GetCell(UICollectionView collectionView, NSIndexPath indexPath) at Microsoft.Maui.Controls.Handlers.Items.CarouselViewController.GetCell(UICollectionView collectionView, NSIndexPath indexPath) at UIKit.UICollectionView.ReloadItems(NSIndexPath[] indexPaths) in /Users/builder/azdo/_work/1/s/xamarin-macios/src/build/dotnet/ios/generated-sources/UIKit/UICollectionView.g.cs:line 753 at Microsoft.Maui.Controls.Handlers.Items.ObservableItemsSource.<>c__DisplayClass45_0.<Replace>b__0(UICollectionView c) at Microsoft.Maui.Controls.Handlers.Items.ObservableItemsSource.Update(Action1 update, NotifyCollectionChangedEventArgs args) at Microsoft.Maui.Controls.Handlers.Items.ObservableItemsSource.Replace(NotifyCollectionChangedEventArgs args) at Microsoft.Maui.Controls.Handlers.Items.ObservableItemsSource.CollectionChanged(NotifyCollectionChangedEventArgs args) at Microsoft.Maui.Controls.Handlers.Items.ObservableItemsSource.CollectionChanged(Object sender, NotifyCollectionChangedEventArgs args) at System.Collections.ObjectModel.ObservableCollection1[[Dopnet.YourDive.Services.DiveInfo, Dopnet.YourDive.Services, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null]].OnCollectionChanged(NotifyCollectionChangedEventArgs e) at System.Collections.ObjectModel.ObservableCollection1[[Dopnet.YourDive.Services.DiveInfo, Dopnet.YourDive.Services, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null]].OnCollectionChanged(NotifyCollectionChangedAction action, Object oldItem, Object newItem, Int32 index) at System.Collections.ObjectModel.ObservableCollection1[[Dopnet.YourDive.Services.DiveInfo, Dopnet.YourDive.Services, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null]].SetItem(Int32 index, DiveInfo item) at System.Collections.ObjectModel.Collection1[[Dopnet.YourDive.Services.DiveInfo, Dopnet.YourDive.Services, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null]].set_Item(Int32 index, DiveInfo value) at Dopnet.YourDive.UI.ViewModels.DiveDetailViewModel.UpdateDive(DiveInfo dive) in C:\Users\MarcPERROT\source\repos\YourDive\Dopnet.YourDive.UI.Logic\YourDive.UI.ViewModels\DiveDetailViewModel.cs:line 614 at Dopnet.YourDive.UI.ViewModels.DiveDetailViewModel.OnDiveChanged(Object sender, ChangedEventArgs1 e) in C:\Users\MarcPERROT\source\repos\YourDive\Dopnet.YourDive.UI.Logic\YourDive.UI.ViewModels\DiveDetailViewModel.cs:line 553 at Dopnet.YourDive.UI.ViewModels.ChangedEventSource1[[Dopnet.YourDive.Services.DiveInfo, Dopnet.YourDive.Services, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null]].Raise(ChangedEventArgs1 e) in C:\Users\MarcPERROT\source\repos\YourDive\Dopnet.YourDive.UI.Logic\YourDive.UI.ViewModels\ChangedEventSource.cs:line 11 at Dopnet.YourDive.UI.ViewModels.IChangedEventSourceExtensions.RaiseUpdate[DiveInfo](IChangedEventSource1 source, String id, DiveInfo value) in C:\Users\MarcPERROT\source\repos\YourDive\Dopnet.YourDive.UI.Logic\YourDive.UI.ViewModels\IChangedEventSourceExtensions.cs:line 62 at Dopnet.YourDive.UI.ViewModels.IChangedEventSourceExtensions.RaiseUpdate(IChangedEventSource1 source, DiveInfo value) in C:\Users\MarcPERROT\source\repos\YourDive\Dopnet.YourDive.UI.Logic\YourDive.UI.ViewModels\IChangedEventSourceExtensions.cs:line 24 at Dopnet.YourDive.UI.ViewModels.StampsRequestViewModel.RequestStampsAsync() in C:\Users\MarcPERROT\source\repos\YourDive\Dopnet.YourDive.UI.Logic\YourDive.UI.ViewModels\StampsRequestViewModel.cs:line 97 at Dopnet.Maui.CommandFactory.<>c__DisplayClass7_0.<<CreateCommand>b__0>d.MoveNext() in C:\Users\MarcPERROT\source\repos\YourDive\Dopnet.Maui\CommandFactory.cs:line 48 --- End of stack trace from previous location --- at System.Threading.Tasks.Task.<>c.<ThrowAsync>b__128_0(Object state) at Foundation.NSAsyncSynchronizationContextDispatcher.Apply() in /Users/builder/azdo/_work/1/s/xamarin-macios/src/Foundation/NSAction.cs:line 179 --- End of stack trace from previous location --- at ObjCRuntime.Runtime.ThrowException(IntPtr gchandle) in /Users/builder/azdo/_work/1/s/xamarin-macios/src/ObjCRuntime/Runtime.cs:line 2742 at UIKit.UIApplication.UIApplicationMain(Int32 argc, String[] argv, IntPtr principalClassName, IntPtr delegateClassName) in /Users/builder/azdo/_work/1/s/xamarin-macios/src/UIKit/UIApplication.cs:line 64 at UIKit.UIApplication.Main(String[] args, Type principalClass, Type delegateClass) in /Users/builder/azdo/_work/1/s/xamarin-macios/src/UIKit/UIApplication.cs:line 96 at Dopnet.YourDive.Maui.Program.Main(String[] args) in C:\Users\MarcPERROT\source\repos\YourDive\Dopnet.YourDive.Maui\Platforms\iOS\Program.cs:line 13

Steps to Reproduce

CrashCarouselView.zip

Link to public reproduction project repository

No response

Version with bug

9.0.50 SR5

Is this a regression from previous behavior?

Not sure, did not test other versions

Last version that worked well

No response

Affected platforms

iOS

Affected platform versions

iOS 15.5

Did you find any workaround?

No response

Relevant log output

[malsabi]

I'm also having this exception, it's really unfortunate that this only happens in iOS. This used to be "Index was out of range. Must be non-negative and less than the size of the collection. (Parameter 'index')." and now we are getting this new exception. @PureWeen If there is any workaround please notify us or if there is a proper way for using CollectionView in iOS. I tried dispatching it on UI Thread, tried concurrency but still the exception happens.

[sheiksyedm]

@malsabi Would it be possible for you to share a replication sample for this issue? I'm not sure in which scenario it occurs, making it difficult to reproduce. If you provide a sample, it would be really helpful in tracking the issue more effectively.

[malsabi]

@sheiksyedm Thank you for your reply. I couldn't replicate this issue in another repository, but It still happens in my app and I cannot share for privacy reasons. However I will provide the exception log that I'm getting maybe It can help to figure out the issue.

  at System.Collections.Generic.Dictionary2[[System.Object, System.Private.CoreLib, Version=9.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e],[Microsoft.Maui.Controls.Handlers.Items.TemplatedCell, Microsoft.Maui.Controls, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null]].FindValue(Object key)
   at System.Collections.Generic.Dictionary2[[System.Object, System.Private.CoreLib, Version=9.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e],[Microsoft.Maui.Controls.Handlers.Items.TemplatedCell, Microsoft.Maui.Controls, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null]].TryGetValue(Object key, TemplatedCell& value)
   at Microsoft.Maui.Controls.Handlers.Items.ItemsViewController1[[Microsoft.Maui.Controls.ReorderableItemsView, Microsoft.Maui.Controls, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null]].UpdateTemplatedCell(TemplatedCell cell, NSIndexPath indexPath)
   at Microsoft.Maui.Controls.Handlers.Items.ItemsViewController1[[Microsoft.Maui.Controls.ReorderableItemsView, Microsoft.Maui.Controls, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null]].CreateMeasurementCell(NSIndexPath indexPath)
   at Microsoft.Maui.Controls.Handlers.Items.ItemsViewController1[[Microsoft.Maui.Controls.ReorderableItemsView, Microsoft.Maui.Controls, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null]].GetPrototypeForIndexPath(NSIndexPath indexPath)
   at Microsoft.Maui.Controls.Handlers.Items.ItemsViewController1[[Microsoft.Maui.Controls.ReorderableItemsView, Microsoft.Maui.Controls, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null]].GetPrototype()
   at Microsoft.Maui.Controls.Handlers.Items.ItemsViewLayout.DetermineCellSize()
   at Microsoft.Maui.Controls.Handlers.Items.ListViewLayout.ConstrainTo(CGSize size)
   at Microsoft.Maui.Controls.Handlers.Items.ItemsViewLayout.UpdateConstraints(CGSize size)
   at Microsoft.Maui.Controls.Handlers.Items.ItemsViewController1[[Microsoft.Maui.Controls.ReorderableItemsView, Microsoft.Maui.Controls, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null]].ConstrainItemsToBounds()
   at Microsoft.Maui.Controls.Handlers.Items.ItemsViewController1[[Microsoft.Maui.Controls.ReorderableItemsView, Microsoft.Maui.Controls, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null]].ViewWillLayoutSubviews()
   at Microsoft.Maui.Controls.Handlers.Items.StructuredItemsViewController1[[Microsoft.Maui.Controls.ReorderableItemsView, Microsoft.Maui.Controls, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null]].ViewWillLayoutSubviews()
   at UIKit.UIApplication.UIApplicationMain(Int32 argc, String[] argv, IntPtr principalClassName, IntPtr delegateClassName) in /Users/builder/azdo/_work/5/s/xamarin-macios/src/UIKit/UIApplication.cs:line 61
   at UIKit.UIApplication.Main(String[] args, Type principalClass, Type delegateClass) in /Users/builder/azdo/_work/5/s/xamarin-macios/src/UIKit/UIApplication.cs:line 96

[mypp74]

still present in 9.0.70 SR7

[mypp74]

The scenario in which the bug occurs is as follows. I have a CarouselView on a first page. I navigate to a second page. On this second page, an event causes an update of the ObservableCollection linked to the CarouselView of the first page, which is therefore not in the foreground at that moment. The crash then occurs, frequently, but not systematically

[mypp74]

The problem also exists on iPhone 14 and iOS 16.4

[mypp74]

Here is a way to reproduce the crash. Is it possible to include this issue in the SR8?

CrashCarouselView.zip

[mypp74]

@sheiksyedm

@malsabi Would it be possible for you to share a replication sample for this issue? I'm not sure in which scenario it occurs, making it difficult to reproduce. If you provide a sample, it would be really helpful in tracking the issue more effectively.

CrashCarouselView.zip

[bnoffer]

I am running into the same exception as well, however using a regular CollectionView in combination with a ObservableCollection when testing on a iOS Simulator with iOS 15.5. iOS 18.4 is fine though.

[mypp74]

still present in 9.0.80 SR8

[LogishaSelvarajSF4525]

This issue has been verified in Visual Studio Code 1.100.3 with MAUI versions (9.0.80, 9.0.70, 9.0.60, 9.0.50, 9.0.40 & 9.0.0). It can be reproduced on the iOS 15.5 platform. It works fine on the iOS 18.4 platform.

[PureWeen]

Does this issue reproduce if you use CollectionView2/CarouselView2?

https://learn.microsoft.com/en-us/dotnet/maui/whats-new/dotnet-9?view=net-maui-9.0#collectionview-and-carouselview

[mypp74]

The issue only occurs when using CarouselView 1. But for now there are other issues with CarouselView 2

[UserMiha]

I have similar issue with CollectionView and ObservableCollection. In my case after clearing the ObservableCollection app crashes with such exception:

 at System.Collections.Generic.Dictionary`2[[System.Object, System.Private.CoreLib, Version=9.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e],[Microsoft.Maui.Controls.Handlers.Items.TemplatedCell, Microsoft.Maui.Controls, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null]].FindValue(Object key)
   at System.Collections.Generic.Dictionary`2[[System.Object, System.Private.CoreLib, Version=9.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e],[Microsoft.Maui.Controls.Handlers.Items.TemplatedCell, Microsoft.Maui.Controls, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null]].TryGetValue(Object key, TemplatedCell& value)
   at Microsoft.Maui.Controls.Handlers.Items.ItemsViewController`1[[Microsoft.Maui.Controls.ReorderableItemsView, Microsoft.Maui.Controls, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null]].UpdateTemplatedCell(TemplatedCell cell, NSIndexPath indexPath)
   at Microsoft.Maui.Controls.Handlers.Items.ItemsViewController`1[[Microsoft.Maui.Controls.ReorderableItemsView, Microsoft.Maui.Controls, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null]].GetCell(UICollectionView collectionView, NSIndexPath indexPath)
   at UIKit.UIApplication.UIApplicationMain(Int32 argc, String[] argv, IntPtr principalClassName, IntPtr delegateClassName) in /Users/builder/azdo/_work/1/s/macios/src/UIKit/UIApplication.cs:line 69
   at UIKit.UIApplication.Main(String[] args, Type principalClass, Type delegateClass) in /Users/builder/azdo/_work/1/s/macios/src/UIKit/UIApplication.cs:line 104
   at MyApp.iOS.Program.Main

I have a dirty workaround. It works for me, but for other cases it will need to be adapted locally. The idea of ​​the fix is ​​to intercept the place where an index comes that is not in the collection and return an empty object instead of null. It happens in ItemsViewController.UpdateTemplatedCell.

To fix it, you need to create your own handler for the collection view.

public class CustomCollectionViewHandler : CollectionViewHandler
{
    protected override ItemsViewController<ReorderableItemsView> CreateController(ReorderableItemsView itemsView,
        ItemsViewLayout layout)
    {
        return new CustomReorderableItemsViewController(itemsView, layout);
    }
}

public class CustomReorderableItemsViewController : ReorderableItemsViewController<ReorderableItemsView>
{
    public CustomReorderableItemsViewController(ReorderableItemsView itemsView, ItemsViewLayout layout) : base(
        itemsView,
        layout)
    {
    }

    protected override IItemsViewSource CreateItemsViewSource()
    {
        if (ItemsView.ItemsSource == null)
            return base.CreateItemsViewSource();

        return new ObservableItemsSource(ItemsView.ItemsSource, this);
    }
}

I'm using ObservableCollection as ItemSource and patched the original ObservableItemsSource

with next code:

public static readonly object EmptyItem = new object();

internal object ElementAt(int index)
{
   if (_itemsSource is IList list)
       return (index >= 0 && index < list.Count) ? list[index] : EmptyItem;

   int count = 0;
   foreach (var item in _itemsSource)
   {
       if (count == index)
           return item;
       count++;
   }

   return EmptyItem;
}

and don't forget to register the new handler in MauiProgram.CreateMauiApp

builder.ConfigureMauiHandlers(handlers =>
{
    handlers.AddHandler(typeof(CollectionView), typeof(CustomCollectionViewHandler));
});

WorkaroundFiles.zip

[malsabi]

Why its still being in the backlog?

[jaimeatsherpa]

Indeed, we need a fix to this issue as soon as possible... CarouselView and CollectionView are one of the most common components. Does someone have any updates on this?

[jaimeatsherpa]

@UserMiha I've tried your solution but I still get the same exception with a CollectionView and an ObservableCollection, can you send me a working example? Maybe I did something wrong

[malsabi]

@Ahamed-Ali Can you please also check for the "CollectionView" I'm getting similar exception and here are the logs I'm not sure if they are useful.

Unhandled managed exception: Value cannot be null. (Parameter 'key') (System.ArgumentNullException) at System.Collections.Generic.Dictionary2[[System.Object, System.Private.CoreLib, Version=9.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e],[Microsoft.Maui.Controls.Handlers.Items.TemplatedCell, Microsoft.Maui.Controls, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null]].FindValue(Object key) at System.Collections.Generic.Dictionary2[[System.Object, System.Private.CoreLib, Version=9.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e],[Microsoft.Maui.Controls.Handlers.Items.TemplatedCell, Microsoft.Maui.Controls, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null]].TryGetValue(Object key, TemplatedCell& value) at Microsoft.Maui.Controls.Handlers.Items.ItemsViewController1[[Microsoft.Maui.Controls.ReorderableItemsView, Microsoft.Maui.Controls, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null]].UpdateTemplatedCell(TemplatedCell cell, NSIndexPath indexPath) at Microsoft.Maui.Controls.Handlers.Items.ItemsViewController1[[Microsoft.Maui.Controls.ReorderableItemsView, Microsoft.Maui.Controls, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null]].CreateMeasurementCell(NSIndexPath indexPath) at Microsoft.Maui.Controls.Handlers.Items.ItemsViewController1[[Microsoft.Maui.Controls.ReorderableItemsView, Microsoft.Maui.Controls, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null]].GetPrototypeForIndexPath(NSIndexPath indexPath) at Microsoft.Maui.Controls.Handlers.Items.ItemsViewController1[[Microsoft.Maui.Controls.ReorderableItemsView, Microsoft.Maui.Controls, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null]].GetPrototype() at Microsoft.Maui.Controls.Handlers.Items.ItemsViewLayout.DetermineCellSize() at Microsoft.Maui.Controls.Handlers.Items.ListViewLayout.ConstrainTo(CGSize size) at Microsoft.Maui.Controls.Handlers.Items.ItemsViewLayout.UpdateConstraints(CGSize size) at Microsoft.Maui.Controls.Handlers.Items.ItemsViewController1[[Microsoft.Maui.Controls.ReorderableItemsView, Microsoft.Maui.Controls, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null]].ConstrainItemsToBounds() at Microsoft.Maui.Controls.Handlers.Items.ItemsViewController1[[Microsoft.Maui.Controls.ReorderableItemsView, Microsoft.Maui.Controls, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null]].ViewWillLayoutSubviews() at Microsoft.Maui.Controls.Handlers.Items.StructuredItemsViewController1[[Microsoft.Maui.Controls.ReorderableItemsView, Microsoft.Maui.Controls, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null]].ViewWillLayoutSubviews() at UIKit.UIApplication.UIApplicationMain(Int32 argc, String[] argv, IntPtr principalClassName, IntPtr delegateClassName) in /Users/builder/azdo/_work/5/s/xamarin-macios/src/UIKit/UIApplication.cs:line 61 at UIKit.UIApplication.Main(String[] args, Type principalClass, Type delegateClass) in /Users/builder/azdo/_work/5/s/xamarin-macios/src/UIKit/UIApplication.cs:line 96

[Markus-Zoennchen]

We have the same issue on iOS. We clear an ObservableCollection and while this, we get this error.