OnExpanded event for any item in a treeview

Question

I'd like to get an event for any expansion of a treeviewitem in my treeview.

The reason for this, a bit unrelated to the original question: I am creating a tree that relates closely to an xml file tree, but I am allowing an include element in the xml so the tree can go across multiple files. I'd like to set the itemssource property of treeviewitems within my treeview upon expansion.

Answer 1

You can use the TreeViewItem.Expanded event as an attached event :

<TreeView TreeViewItem.Expanded="TreeViewItem_Expanded"
          ItemsSource="{Binding}">
    ...
</TreeView/>

In code-behind, you can identify the TreeViewItem that initiated the event using the OriginalSource property :

    private void TreeViewItem_Expanded(object sender, RoutedEventArgs e)
    {
        TreeViewItem tvi = e.OriginalSource as TreeViewItem;
        if (tvi != null)
        {
            MessageBox.Show(string.Format("TreeNode '{0}' was expanded", tvi.Header));
        }
    }