UWP XAML x:Bind inherited interfaces are not recognized

Question

When using x:Bind in a UWP XAML application consider the following:

interface IBaseInterface
{
    string A { get; set; }
}
interface ISubInterface : IBaseInterface
{
    string B { get; set; }
}
class ImplementationClass : ISubInterface
{
    public string A { get; set; }
    public string B { get; set; }
}

In the Page class we have the following:

public partial class MainPage : Page
{
    public ISubInterface TheObject = new ImplementationClass { A = "1", B = "2" };
    //All the rest goes here
}

In the MainPage XAML we have the following snippet:

<TextBlock Text={x:Bind Path=TheObject.A}></TextBlock>

Which causes the following compiler error: XamlCompiler error WMC1110: Invalid binding path 'A' : Property 'A' can't be found on type 'ISubInterface'

The following does work however:

<TextBlock Text={x:Bind Path=TheObject.B}></TextBlock>

Does anybody know if it is a known limitation of the UWP XAML platform that inherited interface-properties are not recognized by the compiler? Or should this be considered a bug? Are there any known workarounds?

Help is greatly appreciated. Thanks in advance!

Harakiri

Can you try to define TheObject as IBaseInterface rather than ISubInterface and see if the Compiler then accepts TheObject.A? – Folie

Answer 1

Yes, after doing some test and reseach, it seems that inherited interface-properties are not recognized by the compiler when using the X:Bind.

As a workaround we can use the traditional Binding instead of the X:Bind as following:

In the .xaml:

<Grid Name="MyRootGrid">
         <TextBlock Text="{Binding A}"></TextBlock>
</Grid>

In the xaml.cs:

MyGrid.DataContext = TheObject;

Eubanks

Thanks for trying and coming to the same conclusion as I did. I did submit a bug via Connect: connect.microsoft.com/VisualStudio/feedback/details/1770944 – Harakiri

Answer 2

If you write a class Foo inherited IFoo.

public class Foo : INotifyPropertyChanged, IF1
{
    public Foo(string name)
    {
        _name = name;
    }

    private string _name;
    public event PropertyChangedEventHandler PropertyChanged;

    protected virtual void OnPropertyChanged([CallerMemberName] string propertyName = null)
    {
        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
    }

    string IF1.Name
    {
        get { return _name; }
        set { _name = value; OnPropertyChanged(); }
    }

}

public interface IF1
{
    string Name { set; get; }
}

And when you write a list in page

  public ObservableCollection<Foo> Foo { set; get; } = new ObservableCollection<Foo>()
    {
        new Foo("jlong"){}
    };

How can you bind it in xaml?

I find a way to bind it. You should use x:bind and use Path=(name:interface.xx) to bind it in xaml.

    <ListView ItemsSource="{x:Bind Foo}">
        <ListView.ItemTemplate>
            <DataTemplate x:DataType="local:Foo">
                <TextBlock Text="x:Bind Path=(local:IFoo.Name)"></TextBlock>
            </DataTemplate>
        </ListView.ItemTemplate>
    </ListView>

Wain

Answer 3

Add the namespace of the base class via a xmlns at the top of the file:

xmlns:base="using:Namespace.Of.Base.Class"

Blabbermouth