Question

Given that:

1. DataTemplates cannot be assigned by TargetType
2. StaticResource references can only reference previously

How does one template the following situation in a TreeView?

class Resource {
  public string Name {get;}
  public IEnumerable<Property> Properties {get;}
}

class Property {
  public string Name {get;}
  public IEnumerable<Resource> Values {get;}
}

That structure lends itself well to a tree which would look like:

Resource 1
|- Property A
   | - Resource 2
   | - Resource 3
|- Property B
   |- Resource 4

This would trivial to template in WPF because of the TargetType property of HierarchicalDataTemplate. In Silverlight, we would have to do something more like:

<HierarchicalDataTemplate x:Key="ResourceTemplate"
                          ItemSource="{Binding Properties}"
                          ItemTemplate={StaticResource PropertyTemplate}" />

<HierarchicalDataTemplate x:Key="PropertyTemplate"
                          ItemSource="{Binding Values}"
                          ItemTemplate="{StaticResource ResourceTemplate}" />

Which obviously can’t work because ResourceTemplate can’t reference PropertyTemplate because it is defined after it in the XAML document. So, how do you solve this chicken-and-egg problem?

Answer 1

The only reasonable solution I’ve found is to create a third ViewModel type which would wrap either of the first two types (Resource or Property) and provide common properties to bind to: (e.g. children). This still is not very optimal, though, if the two types need very different templates because at that point, I am using the VisualStateManager to switch between templates for the data.

<HierarchicalDataTemplate x:Key="TreeItemTemplate"
                          ItemSource="{Binding Children}">
  <ContentPresenter Content="{Binding}">
    <VisualStateManager.Groups>
      <VisualStateGroup>
        <VisualState Name="IsResource">
          <!-- set resource template -->
        </VisualState>
        <VisualState Name="IsProperty">
          <!-- set property template -->
        </VisualState>
      </VisualStateGroup>
    </VisualStateManager.Groups>
  </ContentPresenter>
</HierarchicalDataTemplate>