private void Attach(FrameworkElement element)
{
element.MouseLeftButtonDown += this.OnHeaderMouseLeftButtonDown;
this.dataSource = element.ParentOfType<RadGanttView>().DataContext as TasksDataSource;
}
private void Detach(FrameworkElement element)
{
element.MouseLeftButtonDown -= this.OnHeaderMouseLeftButtonDown;
this.dataSource = null;
this.proxy = null;
}