void loadData()
{
DanhSachPhieuThuePhong.Rows[index].Cells[0].Value = index + 1;
DataGridViewComboBoxCell cbMaKhachHang = DanhSachPhieuThuePhong.Rows[index].Cells[1] as DataGridViewComboBoxCell;
cbMaKhachHang.DataSource = khachHangBLL.loadKhachHang();
cbMaKhachHang.DisplayMember = "TenKhachHang";
cbMaKhachHang.ValueMember = "MaKhachHang";
cbMaKhachHang.ValueType = typeof(string);
cbMaPhong.DataSource = phongBLL.loadPhongChuaThue();
cbMaPhong.DisplayMember = "TenPhong";
cbMaPhong.ValueMember = "MaPhong";
index++;
}