WPF HiercharchicalDataTemplate.DataType: How to react on interfaces?

Question

Problem

I've got a collection of IThings and I'd like to create a HierarchicalDataTemplate for a TreeView. The straightforward DataType={x:Type local:IThing} of course doesn't work, probably because the WPF creators didn't want to handle the possible ambiguities.

Since this should handle IThings from different sources at the same time, referencing the implementing class is out of question.

Current solution

For now I'm using a ViewModel which proxies IThing through a concrete implementation:

public interface IThing {
    string SomeString { get; }
    ObservableCollection<IThing> SomeThings { get; }
    // many more stuff
}

public class IThingViewModel
{
     public IThing Thing { get; }
     public IThingViewModel(IThing it) { this.Thing = it; }
}

<!-- is never applied -->
<HierarchicalDataTemplate DataType="{x:Type local:IThing}">

<!-- is applied, but looks strange -->
<HierarchicalDataTemplate
    DataType="{x:Type local:IThingViewModel}"
    ItemsSource="{Binding Thing.SomeThings}">
    <TextBox Text="{Binding Thing.SomeString}"/>
</HierarchicalDataTemplate>

Question

Is there a better (i.e. no proxy) way?

Answer 1

The reason for this is that the default template selector supports only concrete types, not interfaces. You need to create a custom DataTemplateSelector and apply it to the ItemTemplateSelector property of the TreeView. I can't find the URL where I found an example of it, but hopefully with this info, you can Google it.

Answer 2

Another solution is you give a key to the HierarchicalDataTemplate and put it in the Windows.Resources, and manually reference to it in the TreeView. <TreeView ItemDataTemplate={StaticResource templateKey}/>

But that limits the autoselection of data template according to data type, which is provided by WPF TreeView.