How to data-bind TreeViewItem.IsExpanded to a node data objects

Question

I have a hierarchical data classes like

public class MyNode 
{
   public string Name { get; set;}
   public bool IsExpanded { get; set;}
   public List<MyNode> Nodes { get; set;}
}

I could define a HierarchicalDataTemplate to bind MyNode classes to the TreeView.

<sdk:TreeView ItemsSource="{Binding RootNodes}">
  <sdk:TreeView.ItemTemplate>
    <sdk:HierarchicalDataTemplate ItemsSource="{Binding Nodes}">
      <TextBlock Text="{Binding Name}" />
    </sdk:HierarchicalDataTemplate>
  </sdk:TreeView.ItemTemplate>
</sdk:TreeView>

The question is how to data-bind IsExpanded property of TreeViewItem to corresponding MyNode.IsExpanded property, so I could persist this information.

Thank you in advance, Lex

Answer 1

It is possible, if we override TreeView & TreeViewItem classes like this:

public class ExTreeView : System.Windows.Controls.TreeView
{
  protected override DependencyObject GetContainerForItemOverride()
  {
    return new ExTreeViewItem();
  }
}


public class ExTreeViewItem : System.Windows.Controls.TreeViewItem
{
  public ExTreeViewItem()
  {
    SetBinding(IsExpandedProperty, new Binding("IsExpanded") { Mode = BindingMode.TwoWay });
  }

protected override DependencyObject GetContainerForItemOverride()
  {
    return new ExTreeViewItem();
  }
}

Then use ExTreeView instead of TreeView, it will automatically data bind to IsExpanded property of hierarchical data item.