WPF TreeView databinding follow up

Question

As a follow up to my first TreeView question on SO, I'm unable to bind a TreeView control to the Id property of my Commission object and its Products collection in the same TreeView control. Here's my simplified model:

internal class Contract
{
    public string Name { get; set; }
    public ObservableCollection<Commission> Commissions { get; set; }
}

internal class Commission
{
    public string Id { get; set; }
    public ObservableCollection<Product> Products { get; set; }
}

internal class Product
{
   public string Code { get; set; }
}

Here's my problem XAML. Contract returns a collection of Commission objects (Commissions). I've commented out the HierarchicalDataTemplate for returning Products. Either HierarchicalDataTemplate will work individually, but not if both are uncommented:

<TreeView ItemsSource="{Binding Contract.Commissions}">
                    <TreeView.Resources>
                        <HierarchicalDataTemplate DataType="{x:Type m:Commission}">
                            <TextBlock Text="{Binding Id}" />
                        </HierarchicalDataTemplate> 
                    <!--<HierarchicalDataTemplate DataType="{x:Type m:Commission}" ItemsSource="{Binding Products}">
                            <TextBlock Text="{Binding Code}" />
                        </HierarchicalDataTemplate>-->
                    </TreeView.Resources>
                </TreeView>

If both HierarchicalDataTemplates are uncommented, an error is thrown because I'm using a unique (Commission Type) twice, but I don't know how to make either HierarchicalDataTemplate work without using Commission Type as the template's DataType.

Answer 1

You are jumbling up things here. I assume you want to show Commission's Id and beneath each Commission node, child Product's code value.

Only one HierarchicalDataTemplate of Commission is required and one DataTemplate for Product:

<TreeView.Resources>
  <HierarchicalDataTemplate DataType="{x:Type m:Commission}"
                            ItemsSource="{Binding Products}">
      <TextBlock Text="{Binding Id}" />
   </HierarchicalDataTemplate>
   <DataTemplate DataType="{x:Type m:Product}">
      <TextBlock Text="{Binding Code}" />
   </DataTemplate> 
</TreeView.Resources>

Explanation:

• Declare HierarchicalDataTemplate for nodes which needs to contain child nodes. In your case Commission.
• Set ItemsSource to child collection which you need to shown beneath those nodes. In your case Products.
• Lastly, declare DataTemplate for node which won't contain any child nodes. In your case Product.