“BindingExpression path error” using ItemsControl and VirtualizingStackPanel

Question

I\'m using Silverlight on Windows Phone 7.

Is it normal to get loads of \"BindingExpression path error\" debug messages when using a VirtualizingStackPanel? I think it

Answer 1

I know this post is pretty old, but a solution without creating the dummy properties is making sure the DataContext of the items can only be of the type you expect.

I do this with the following converter on the root of the data template:

public class SpecificTypeConverter : IValueConverter
{
    public string Type { get; set; }

    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
    {
        if (value == null || value.GetType().FullName == this.Type)
        {
            return value;
        }

        return DependencyProperty.UnsetValue;
    }

    public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
    {
        throw new NotImplementedException();
    }
}

Add a static resource like this:

<p:PhoneApplicationPage.Resources>
    <converters:SpecificTypeConverter x:Key="MustBeItem" Type="My.Namespace.MyListItemViewModel" /> 
</p:PhoneApplicationPage.Resources>

And in the data template, use the converter:

<DataTemplate>
    <StackPanel DataContext="{Binding Converter={StaticResource MustBeItem}}" >
        <TextBlock Tekst="{Binding Path=Name}" />
    </StackPanel>
</DataTemplate>

Now the Name property of the parent will never be checked.

Answer 2

I think your assessment of the situation is correct, but it sounds like a bug in the way the VirtualizingStackPanel works. It's not affecting the execution or bindings of your application at the points where you need it, but raising exceptions is a relatively expensive operation and so it would make sense to update the appropriate DataContext accordingly when unlinking the containers.

I think the best place to raise it as a potential bug would be on the App Hub forums