private void btnThem_Click(object sender, EventArgs e)
        {
            luu = true;
            frmKhachHang_Sua frm = new frmKhachHang_Sua(this.grdKH);

            frm.Text = "Thêm khách hàng";
            frm.ShowDialog();
        }
        private void btnSua_Click(object sender, EventArgs e)
        {
            DataGridViewRow row = this.grdKH.Rows[grdKH.CurrentCell.RowIndex];

            luu = false;
            frmKhachHang_Sua frm = new frmKhachHang_Sua(this.grdKH);

            MaKH        = row.Cells[0].Value.ToString();
            TenKH       = row.Cells[1].Value.ToString();
            SoDienThoai = row.Cells[2].Value.ToString();
            DiaChi      = row.Cells[3].Value.ToString();
            frm.Text    = "Sửa khách hàng";
            frm.ShowDialog();
        }