private void btnThem_Click(object sender, EventArgs e)
        {
            FormThem_CapNhatKH newForm = new FormThem_CapNhatKH();

            this.Visible = false;
            newForm.Show();
            newForm.Disposed += NewForm_Disposed;
        }
        private void btnSua_Click(object sender, EventArgs e)
        {
            DataGridViewRow row = dataGVKhachHang.SelectedRows.Count >= 1 ? dataGVKhachHang.SelectedRows[0] : null;

            if (row != null)
            {
                string             maKH     = row.Cells["colMaKH"].Value.ToString();
                string             tenKH    = row.Cells["colTenKH"].Value.ToString();
                string             email    = row.Cells["colEmail"].Value.ToString();
                string             sdt      = row.Cells["colSDT"].Value.ToString();
                string             diaChi   = row.Cells["colDC"].Value.ToString();
                string             gioiTinh = row.Cells["colGioiTinh"].Value.ToString();
                DateTime           ngaySinh = (DateTime)row.Cells["colNgaySinh"].Value;
                FormThem_CapNhatKH newForm  = new FormThem_CapNhatKH(maKH, tenKH, sdt, email, diaChi, gioiTinh, ngaySinh);
                this.Visible = false;
                newForm.Show();
                newForm.Disposed += NewForm_Disposed;
            }
            else
            {
                MessageBox.Show("Bạn chưa chọn khách hàng để sửa");
                ;
            }
        }