Popup custom return raises an error

[erossini]

In my .NET 9 MAUI project, I use Popup from the Community Toolkit. I have created a generic component to display items in a List based on a ItemTemplate:

<?xml version="1.0" encoding="utf-8" ?>
<toolkit:Popup
		x:Class="LanguageInUse.Components.CustomPicker.PickerControlView"
		xmlns="http://schemas.microsoft.com/dotnet/2021/maui"
		xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
		xmlns:toolkit="http://schemas.microsoft.com/dotnet/2022/maui/toolkit"
		VerticalOptions="Center">
	<StackLayout Grid.Row="1" Background="White">
		<CollectionView
					x:Name="clPickerView"
					Margin="10,0,10,5"
					BackgroundColor="White"
					HorizontalOptions="FillAndExpand"
					SelectionChanged="clPickerView_SelectionChanged"
					SelectionMode="Single"
					VerticalOptions="FillAndExpand" />
	</StackLayout>
</toolkit:Popup>

In the code behind, I have this code:

public PickerControlView(IEnumerable itemSource, DataTemplate itemTemplate, 
    double pickerControlHeight = 200, string title = "")
{
    InitializeComponent();

    clPickerView.ItemsSource = itemSource;
    clPickerView.ItemTemplate = itemTemplate;
    grv.HeightRequest = pickerControlHeight;

    if (!string.IsNullOrEmpty(title))
        labelTitle.Text = title;
}

private async void clPickerView_SelectionChanged(object sender, 
    SelectionChangedEventArgs e)
{
    var currentItem = e.CurrentSelection.FirstOrDefault();
    await CloseAsync(currentItem);
}

To open the Popup and get the selection of the user, I have this code:

var pickerControlView = new MyPopupView(controls.ItemSource, controls.ItemTemplate, 
    controls.PickerHeightRequest, controls.Placeholder);
var response = await Application.Current.MainPage.ShowPopupAsync(pickerControlView, 
    new CancellationToken());

This code is working perfectly with .NET 8 MAUI: when there is a selection in the CollectionView, the value is returned to the called view.. With the new version of the Community Toolkit 12.1.0, Popup changed.

To open the popup, I use now something similar to this:

var response = await Application.Current.MainPage.ShowPopupAsync(pickerControlView, 
    PopupOptions.Empty, CancellationToken.None);

if (response != null)
    controls.SelectedItem = response;

But now what it returns is of type IPopupResult. If I know exactly what type it returns, I can write:

IPopupResult<LanguageModel> response = (IPopupResult<LanguageModel>)await
    Application.Current.MainPage.ShowPopupAsync(new LanguagePicker(), 
    PopupOptions.Empty, CancellationToken.None);

Because this is a generic view, I don't know what type of data I pass and receive back. I attempted to implement the Popup<T> as described in the Microsoft documentation.

So, I define the popup as:

public partial class PickerControlView : Popup<object>

and in the XAML

<toolkit:Popup
	x:Class="LanguageInUse.Components.CustomPicker.PickerControlView"
	xmlns="http://schemas.microsoft.com/dotnet/2021/maui"
	xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
	xmlns:popups="clr-namespace:LanguageInUse.Components.CustomPicker"
	xmlns:toolkit="http://schemas.microsoft.com/dotnet/2022/maui/toolkit"
	xmlns:system="clr-namespace:System;assembly=mscorlib"
	x:TypeArguments="system:Object"
	VerticalOptions="Center">

Now, the component opens the popup as expected but then I select an item in the CollectionView, the function clPickerView_SelectionChanged is called.

After the line

await CloseAsync(currentItem);

I get different issues depend on the platform. For example, in iOS I get this error.

ObjCRuntime.ObjCException: 'Objective-C exception thrown. Name: NSInternalInconsistencyException Reason: Attempted to modify the selection of an item in an out-of-bounds section (0) when there are only 0 sections. Collection view: <Microsoft_Maui_Controls_Handlers_Items_MauiCollectionView: 0x1520b7c00; baseClass = UICollectionView; frame = (0 0; 219 225); clipsToBounds = YES; autoresize = W+H; gestureRecognizers = <NSArray: 0x600000da1800>; backgroundColor = UIExtendedGrayColorSpace 0 0; layer = <CALayer: 0x6000008360c0>; contentOffset: {0, 0}; contentSize: {219, 0}; adjustedContentInset: {0, 0, 0, 0}; layout: <Microsoft_Maui_Controls_Handlers_Items_ListViewLayout: 0x14cdaa6e0>; dataSource: <Microsoft_Maui_Controls_Handlers_Items_ReorderableItemsViewController_1: 0x14cd508f0>>.

In Windows the reason of the error is always a mystery. I get there but I don't know the reason ("Select the type of word" is the popup).

In Android, just this error message

System.NullReferenceException: 'Object reference not set to an instance of an object.'

I don't understand how to fix this error or return the value.

Update

If I inspect the result from the Popup, I can see the IPopupResult has a Result property but I can access it.

[bijington]

For your latest code example you cannot access the Result property because you are declaring the type as IPopupResult you want to change this to IPopupResult<object> then you can access it.

In Windows if you inspect the e variable just above the System.Diagnostics.Debugger.Break(); line at the end of your gif you can find out the exception details

The error on iOS might be caused by this method:

private async void clPickerView_SelectionChanged(object sender, 
    SelectionChangedEventArgs e)
{
    var currentItem = e.CurrentSelection.FirstOrDefault();
    await CloseAsync(currentItem);
}

I would stick a breakpoint in this method as I suspect it will be called a second time when the popup is closing.