DropDownList 联动

public partial class _Default : System.Web.UI.Page
{
    private MyDBDataContext _Context = new MyDBDataContext();

    //绑定生产厂商
    private void FillProd()
    {
        List<Productor> list = _Context.Productor.ToList();
        ddlProd.DataSource = list;
        ddlProd.DataTextField = "Prod_Name";
        ddlProd.DataValueField = "Prod_Code" ;
        ddlProd.DataBind();
    }
    //绑定系列
    private void FillBrand()
    {
        string ProdCode = ddlProd.SelectedValue;
        List<Brand> list = _Context.Brand.Where(p=>p.Prod_Code == ProdCode).ToList ();
        ddlBrand.DataSource = list;
        ddlBrand.DataTextField = "Brand_Name";
        ddlBrand.DataValueField = "Brand_Code";
        ddlBrand.DataBind();
    }
    //绑定车
    private void FillCar()
    {
        string BrandCode = ddlBrand.SelectedValue;
        List<Car> list = _Context.Car.Where(p => p.Brand == BrandCode).ToList();
        ddlCar.DataSource = list;
        ddlCar.DataTextField = "Name";
        ddlCar.DataValueField = "Code";
        ddlCar.DataBind();

    }
    //加载
    protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
        {
            FillProd();
            FillBrand();
            FillCar();
        }
    }
    //点击生产厂商加载系列和车
    protected void ddlProd_SelectedIndexChanged(object sender, EventArgs e)
    {
        FillBrand();
        FillCar();
    }
    //点击系列加载车
    protected void ddlBrand_SelectedIndexChanged(object sender, EventArgs e)
    {
        FillCar();
    }
}