public void LoadDanhMucDocGia()
{
var docGia_BUS = new DocGia_BUS();
cbxLoaiDG.DisplayMember = "TenLoaiDocGia";
cbxLoaiDG.ValueMember = "MaLoaiDocGia";
cbxLoaiDG.DataSource = docGia_BUS.LoadComBoBoxLoaiDocGia("DocGiaLoai").Tables[0];
}