CODEWITHSUNDEEP
winrt-xaml
SOReader
SOReader

Reputation: 6047

Type-Qualified binding in WinRt?

Is it possible to bind data using Type-Qualified (see Single Property, Attached or Otherwise Type-Qualified section) syntax in WinRT?

What I want to get is to have possibility to bind to an item of my ViewModel which is an interface:

public interface IViewModel {
     INewsContainer ItemHost {get;}
}

public interface INewsContainer {
     ObservableCollection<INews> News {get;}
}

class ViewModel: IViewModel, INewsContainer {
     // ....
     public INewsContainer ItemHost { get { return this; } }

     // ...
     ObservableCollection<INews> news;
     ObservableCollection<INews> INewsContainer.News { get { return news; } }
}

Normally, in WPF binding like the following one works fine (assuming DataContext is an instance of ViewModel): 

    <ListView Grid.Column="1"
         ItemsSource="{Binding Path=ItemHost.(vm:INewsContainer.News)}" />

But if I try doing so in WinRT it fails with log in Immediate Window:

 A first chance exception of type 'Windows.UI.Xaml.Markup.XamlParseException' occurred (...) Failed to assign to property 'Windows.UI.Xaml.Data.Binding.Path'. [Line: 35 Position: 17]

"Regular" binding, i.e. Path=ItemHost.News doesn't work either. It states that News property cannot be found in an instance of class ViewModel.

Workaround
This workaround works fine but I really hate having a converter over here :(

Upvotes: 2

Views: 85

Answers (1)

Jerry Nixon
Jerry Nixon

Reputation: 31831

If you want to do that, you need to implement the interface both explicitly and implicitly.

Like this:

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

public class ViewModel : IViewModel
{
    public ViewModel()
    {
        (this as IViewModel).Name = "Jerry";
    }
    public string Name
    {
        get { return (this as IViewModel).Name; }
        set { (this as IViewModel).Name = value; }
    }
    string IViewModel.Name { get; set; }
}

Then you can do this

<Grid Background="Black">

    <Grid.DataContext>
        <local:ViewModel/>
    </Grid.DataContext>

    <TextBlock Text="{Binding Name}" />

</Grid>

Read: http://msdn.microsoft.com/en-us/library/aa288461(v=vs.71).aspx

Best of luck.

Upvotes: 1

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