private void bindingNavigatorAddNewItem_Click(object sender, EventArgs e)
 {
     if (NhapHang == null || NhapHang.IsDisposed)
     {
         NhapHang = new frmNhapHang();
         NhapHang.Show();
     }
     else
     {
         NhapHang.Activate();
     }
 }
 private void dataGridView_DoubleClick(object sender, EventArgs e)
 {
     if (NhapHang == null || NhapHang.IsDisposed)
     {
         NhapHang = new frmNhapHang(ctrl);
         NhapHang.Show();
     }
     else
     {
         NhapHang.Activate();
     }
 }