Issue with bindings in ListView

[cntseesharp]

Description

Command="{Binding BindingContext.DeleteNoteCommand, Source={RelativeSource AncestorType={x:Type vm:NotesOverviewViewModel}}}" 
CommandParameter="{Binding .}"

[RelayCommand]
private async Task DeleteNote(NoteModel note)

This binding completely crashes element creation when CommandParameter is used, because ListView on initializing a ViewCell sets its BindingContext from the parent, instead of the ItemsSource element.

Step by step:

1. ViewCell is created.
2. Its BindingContext is set to the ListView BindingContext.
   --- During this step binding a command to a VM property will crash due to the wrong CommandParameter type.
3. Something happens and BindingContext is changed to the item from ItemsSource.

This mistake is also the reason why everyone sees binding errors even though their bindings are working in the end.

Steps to Reproduce

1. New MAUI app or existing one
2. Create a data model

public partial class NoteModel : ObservableObject
{
    [ObservableProperty]
    private Guid _id;
}

3. In your ViewModel create a collection of your model

private ObservableCollection<NoteModel> _notes = [];
public ObservableCollection<NoteModel> Notes => _notes;

4. In your ViewModel create a method that takes your model as an argument

[RelayCommand]
private async Task DeleteNote(NoteModel note)
{
    Notes.Remove(note);
}

5. In your XAML create binding to the method inside the ViewCell

<ListView ItemsSource="{Binding Notes}" HasUnevenRows="True">
    <ListView.ItemTemplate>
        <DataTemplate x:DataType="notes:NoteModel">
            <ViewCell>
                <Grid>
                    <Button Command="{Binding DeleteNoteCommand, Source={RelativeSource AncestorType={x:Type vm:NotesOverviewViewModel}}}" CommandParameter="{Binding .}" />
                </Grid>
            </ViewCell>
        </DataTemplate>
    </ListView.ItemTemplate>
</ListView>

6. Get the following exception.
   

HOTFIX:

Use objects as arguments, to prevent the exception, cast your data manually

[RelayCommand]
private async Task DeleteNote(object? obj)
{
    if (obj is not NoteModel selectedNote)
        return;

    Notes.Remove(selectedNote);
}

Link to public reproduction project repository

No response

Version with bug

8.0.6 SR1

Is this a regression from previous behavior?

Not sure, did not test other versions

Last version that worked well

Unknown/Other

Affected platforms

Windows

Affected platform versions

19045.3930

Did you find any workaround?

Use object as arguments, to prevent the exception, and cast your data manually

[RelayCommand]
private async Task DeleteNote(object? obj)
{
    if (obj is not NoteModel selectedNote)
        return;

    Notes.Remove(selectedNote);
}

Relevant log output

No response

[hugebug4ever]

I had the same problem.
It seems caused by the CommandParameter.
And the same code works on iOS. It's should be windows specific problem.

I think this problem is related.
#14234

[kevinxufei]

Verified this issue with Visual Studio 17.10.0 Preview 2(maui version 8.0.10). Cannot repro this issue.
MauiApp15.zip

[dotnet-policy-service]

Hi @cntseesharp. We have added the "s/try-latest-version" label to this issue, which indicates that we'd like you to try and reproduce this issue on the latest available public version. This can happen because we think that this issue was fixed in a version that has just been released, or the information provided by you indicates that you might be working with an older version.

You can install the latest version by installing the latest Visual Studio (Preview) with the .NET MAUI workload installed. If the issue still persists, please let us know with any additional details and ideally a reproduction project provided through a GitHub repository.

This issue will be closed automatically in 7 days if we do not hear back from you by then - please feel free to re-open it if you come back to this issue after that time.