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RadTreeViewPreviewExpanded Event
Occurs before a child TreeView item is expanded.

Namespace: Telerik.Windows.Controls
Assembly: Telerik.Windows.Controls.Navigation (in Telerik.Windows.Controls.Navigation.dll) Version: 2018.1.220.40 (2018.1.220.40)
public event EventHandler<RadRoutedEventArgs> PreviewExpanded


Type: SystemEventHandlerRadRoutedEventArgs
Following code fragment shows the basic usage.
void private void RadTreeView1_PreviewExpanded(object sender, RadRoutedEventArgs e)
    // get a reference to the item that will be expanded
    RadTreeViewItem itemToExpand = e.Source as RadTreeViewItem;

    // if the action should be canceled set Handled property to true
    e.Handled = true;
See Also