省市联动

string strCon = "server=.;database=test;user=sa;pwd=123";
    protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
        {
            BindPro();
            BindCity();
        }
    }

    void BindPro()//加载省份
    {
        SqlConnection con = new SqlConnection(strCon);
        SqlCommand cmd = new SqlCommand("select * from Table_1 where proid=0", con);
        SqlDataAdapter sda = new SqlDataAdapter(cmd);
        DataTable dt = new DataTable();
        sda.Fill(dt);

        ddlPro.DataSource = dt;
        ddlPro.DataTextField = "city";
        ddlPro.DataValueField = "num";
        ddlPro.DataBind();
    }
    void BindCity()//加载特定市
    {
        SqlConnection con = new SqlConnection(strCon);
        SqlCommand cmd = new SqlCommand("select * from Table_1 where proid=@id", con);
        cmd.Parameters.Add("@id", SqlDbType.Int).Value = Convert.ToInt32(ddlPro.SelectedValue);
        SqlDataAdapter sda = new SqlDataAdapter(cmd);
        DataTable dt = new DataTable();
        sda.Fill(dt);

        ddlCity.DataSource = dt;
        ddlCity.DataTextField = "city";
        ddlCity.DataValueField = "num";
        ddlCity.DataBind();
    }
    protected void ddlPro_SelectedIndexChanged(object sender, EventArgs e)
    {
        BindCity();
    }