private void btnOkSua_Click(object sender, EventArgs e)
 {
     if ((txtMaNXB.Text != "") && (txtTenNXB.Text != ""))
     {
         try
         {
             NXB_DTO nxb = new NXB_DTO(txtMaNXB.Text, txtTenNXB.Text, rtbThongTinNXB.Text);
             BUS_OBJ.suaNXB(nxb);
             HienThiDuLieu();
         }
         catch (Exception ex)
         {
             MessageBox.Show(ex.Message);
         }
         finally
         {
             btnCancel_Click(sender, e);
             //if (conn.State == ConnectionState.Open) conn.Close();
         }
     }
     else
     {
         MetroFramework.MetroMessageBox.Show(this, "Nhập thiếu dữ liệu.", "Lỗi.", MessageBoxButtons.OK, MessageBoxIcon.Warning);
         if (txtTenNXB.Text == "")
         {
             txtTenNXB.Focus();
         }
         if (txtMaNXB.Text == "")
         {
             txtMaNXB.Focus();
         }
     }
 }