Databinding errors on ListView - What am I doing wrong?

[enjoysmath]

ListView ItemTemplate Data-binding currently gets these Errors at run-time and also the styling looks way off:

https://stackoverflow.com/q/77809597/7076615

I can't switch to CollectionView for unrelated / independent other error(s).

Discussed in #10277

^{Originally posted by danielcooper-hk September 22, 2022}
Hi everyone,

I am pulling what little hair I have left out over this - if someone can point me in the right direction I would be very grateful.

When the application runs there are no binding errors but when I click on the button to run the AddItemCommand the item appears in the list view but I get data binding errors on both Name and Description. What am I doing wrong in the ListView to cause this?

Thanks,

Dan.

I've written the following sample:

My MainPageModel:

namespace ListViewMVVM.Models;

public class MainPageModel
{
    public string Name { get; set; } = string.Empty;

    public string Description { get; set; } = string.Empty;
}

My MainPageViewModel:

namespace ListViewMVVM.ViewModels;

public class MainPageViewModel 
{
    public ICommand AddItemCommand { get; private set; }

    private ObservableCollection<MainPageModel> myItems;
    public ObservableCollection<MainPageModel> MyItems
    {
        get { return myItems; }
        set
        {
            if (myItems == value) return;

            myItems = value;
        }
    }

    public MainPageViewModel()
    {
        myItems = new()
        {
            new Models.MainPageModel { Name = "Item 1", Description = "Description 1" },
            new Models.MainPageModel { Name = "Item 2", Description = "Description 2" },
            new Models.MainPageModel { Name = "Item 3", Description = "Description 3" }
        };

        AddItemCommand = new Command(AddRecord);
    }

    public void AddRecord()
    {
        myItems.Add(new Models.MainPageModel
        {
            Name = "Item" + (myItems.Count + 1).ToString(), Description = "Description " + (myItems.Count + 1).ToString()
        }) ;

    }
}

My MainPage.xaml:

<?xml version="1.0" encoding="utf-8" ?>
<ContentPage xmlns="http://schemas.microsoft.com/dotnet/2021/maui"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             xmlns:viewmodels="clr-namespace:ListViewMVVM.ViewModels"
             xmlns:models="clr-namespace:ListViewMVVM.Models"
             x:Class="ListViewMVVM.MainPage">

   <ContentPage.BindingContext>
        <viewmodels:MainPageViewModel/>
    </ContentPage.BindingContext>
    
    <ScrollView>
        <VerticalStackLayout>

            <ListView x:Name="ListViewItems"
                      ItemsSource="{Binding MyItems}">
                <ListView.ItemTemplate>
                    <DataTemplate x:DataType="models:MainPageModel">
                        <TextCell Text="{Binding Name}"
                      Detail="{Binding Description}" />
                    </DataTemplate>
                </ListView.ItemTemplate>


            </ListView>

            <Button
                Text="Add Next"
                Command="{Binding AddItemCommand}"
                HorizontalOptions="Center" />

        </VerticalStackLayout>
    </ScrollView>

</ContentPage>

And finally the MainPage.xaml.cs:

namespace ListViewMVVM;

public partial class MainPage : ContentPage
{
	public MainPage()
	{
		InitializeComponent();
	}
}

[drasticactions]

If you're seeing errors in the Visual Studio UI but the actual MAUI UI looks fine, it could be an issue with the tooling. @spadapet What do you think?

[enjoysmath]

Well the whole structure of my app just got amended in design. So now we're doing everything with static pages, and a link to the parent view model is precisely what I need. So you can either fix or close this :)

[ghost]

Thanks for the issue report @enjoysmath! This issue appears to be a problem with Visual Studio, so we ask that you use the VS feedback tool to report the issue. That way it will get to the routed to the team that owns this experience in VS.

If you encounter a problem with Visual Studio, we want to know about it so that we can diagnose and fix it. By using the Report a Problem tool, you can collect detailed information about the problem, and send it to Microsoft with just a few button clicks.

1. Go to the Visual Studio for Windows feedback tool or Visual Studio for Mac feedback tool to report the issue
2. Close this bug, and consider adding a link to the VS Feedback issue so that others can follow its activity there.

[spadapet]

If you're seeing errors in the Visual Studio UI but the actual MAUI UI looks fine, it could be an issue with the tooling. @spadapet What do you think?

I think this is the same bug as:

• XAML bindings are flagging invalid binding failures in ListView - it is confused as to what the data context is... #8433

The binding failures UI in VS shows that MAUI's ListView is temporarily using the wrong data context when new items are added. The data context is supposed to be MainPageModel, not MainPageViewModel.

The correct data context will get set on the new items, but the initial error is still logged in the binding failures UI in VS. I'd guess it's a bug in ListView and not a problem with Visual Studio. Using the VS feedback tool isn't going to help more than the main MAUI issue.

cc: @drasticactions

[drasticactions]

Okay, I wasn't sure of the context. We can close this as a duplicate of #8433.