ASP.Net中省市级联有关

public partial class City : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        if(!IsPostBack)
        {
            BindProv();
            BindCity();
        }
    }

    //绑定市
    private void BindCity()
    {
        ddlcity.Items.Clear();
        DataTable citydt = new CitySer().GetAllCityByProvId(int.Parse(ddlprov.SelectedValue.ToString()));
        foreach (DataRow dr in citydt.Rows)
        {
            ddlcity.Items.Add(new ListItem(dr["cityName"].ToString(), dr["id"].ToString()));
        }
    }
    //绑定省
    private void BindProv()
    {
        ddlprov.Items.Clear();
        DataTable dt = new CitySer().GetAllProv();
        foreach(DataRow dr in dt.Rows)
        {
            ddlprov.Items.Add(new ListItem(dr["provinceName"].ToString(),dr["id"].ToString()));
        }
    }
    //联动
    protected void ddlprov_SelectedIndexChanged(object sender, EventArgs e)
    {
        if (ddlprov.Items.Count != 0)
        {
            ddlcity.Items.Clear();
            DataTable citydt = new CitySer().GetAllCityByProvId(int.Parse(ddlprov.SelectedValue.ToString()));
            foreach (DataRow dr in citydt.Rows)
            {
                ddlcity.Items.Add(new ListItem(dr["cityName"].ToString(), dr["id"].ToString()));
            }
        }
    }
}