void LoadCbLichChieu()
{
cbLCPhim.DataSource = phim.LayDanhSachTenPhim();
cbLCRap.DataSource = rap.LayDanhSachTenRap();
cbLCGIoChieu.DataSource = giochieu.LayDanhSachMaGioChieu();
cbLCPhongChieu.DataSource = phongchieu.LayDanhSachTenPhongChieuTheoTenRap(cbLCRap.SelectedItem.ToString());
cbLCRap.SelectedIndexChanged += (s, e) => {
cbLCPhongChieu.DataSource = phongchieu.LayDanhSachTenPhongChieuTheoTenRap(cbLCRap.SelectedItem.ToString());
};
}