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I am displaying nodes in a TreeView control, and I am having issues with getting the data to display correctly with generics. More specifically, it seems that WPF is having trouble locating the data template. I'm guessing it is because the x:Type is declared to be NodeViewModel`1, and the actual type is NodeViewModel< INode>. However, the XAML will not compile if I try to use NodeViewModel< INode>.

I've got a HierachialDataTemplate that looks like the following:

<HierarchicalDataTemplate 
        ItemsSource="{Binding Path=Children}" 
        DataType="{x:Type viewModels:NodeViewModel`1}">
    <TextBlock Text="{Binding Path=Node.NodeDescription}" />                
</HierarchicalDataTemplate>

the NodeViewModel is declared as such:

public class NodeViewModel<T> where T : INode
{
    public T Node { get {...} set {...} }
}

the nodes interface looks as such:

public interface INode
{
    string NodeDescription { get; }
}
John Kraft
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1 Answers1

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I don't think that there what you're trying to do is supported. You could probably write a custom MarkupExtension to return a closed generic type, but it looks like you want to use the same DataTemplate for any NodeViewModel<T> where T : INode. In this case, WPF would need to support open generics as keys. Which it doesn't.

If that is the case, you're much better off just giving your HierarchicalDataTemplate a key, and applying it directly to the TreeView.

Or create a DataTemplateSelector and check the type of data item to select the proper template.

Abe Heidebrecht
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  • That is exactly what I am trying to do, Abe. I was afraid that was the case. This code started out much simpler; but keeps snowballing with every new requirement. I guess you could say I'm doing RAD (Requirements As-you-go Development). Thanks. I'll try as you suggested. – John Kraft Jul 08 '13 at 21:31