void btn_Click(object sender, RoutedEventArgs e)
 {
     Button b = sender as Button;
     Nhanvien nv = b.DataContext as Nhanvien;
     ThemSuaNhanVien tsnv = new ThemSuaNhanVien(nv);
     (this.Parent as StackPanel).Children.Add(tsnv);
 }
 private void btnThem_Click(object sender, RoutedEventArgs e)
 {
     ThemSuaNhanVien ts = new ThemSuaNhanVien();
     (this.Parent as StackPanel).Children.Add(ts);
 }