RadTreeView.PreviewCollapsed Event
Click or drag to resize
RadTreeViewPreviewCollapsed Event
Occurs before a child TreeView item is collapsed.

Namespace: Telerik.Windows.Controls
Assembly: Telerik.Windows.Controls.Navigation (in Telerik.Windows.Controls.Navigation.dll) Version: 2018.2.620.40 (2018.2.620.40)
public event EventHandler<RadRoutedEventArgs> PreviewCollapsed


Type: SystemEventHandlerRadRoutedEventArgs
Following code fragment shows the basic usage.
void private void RadTreeView1_PreviewCollapsed(object sender, RadRoutedEventArgs e)
    // get a reference to the item that will be collapsed
    RadTreeViewItem itemToCollapse = e.Source as RadTreeViewItem;

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