private void btnSua_Click(object sender, RoutedEventArgs e)
 {
     if (Danhsachdonvi.SelectedItem != null)
     {
         ThemSuaDonVi ts = new ThemSuaDonVi(Danhsachdonvi.SelectedItem as Donvi);
         (this.Parent as StackPanel).Children.Add(ts);
     }
 }
 private void btnThem_Click(object sender, RoutedEventArgs e)
 {
     ThemSuaDonVi ts = new ThemSuaDonVi();
     (this.Parent as StackPanel).Children.Add(ts);
 }