单表实现省市区三级菜单

简单的省市区三级菜单功能实现：

用的是单表做的如图：

控件作用描述：

DropDownList1：省级菜单

DropDownList2：市级菜单

DropDownList3：区级菜单

protected void Page_Load(object sender, EventArgs e)
        {
            if (!IsPostBack)
            {
                fun("0", DropDownList1);
            }
        }
        private void fun(string id,DropDownList dd)
        {
            string str = ConfigurationManager.ConnectionStrings["constr"].ConnectionString;
            using (SqlConnection con = new SqlConnection(str))
            {
                con.Open();
                using (SqlCommand cmd = con.CreateCommand())
                {
                    cmd.CommandText = "select A_Id,A_Name from T_Arear where A_ParentId=@id";
                    cmd.Parameters.Add("@id", id);
                    SqlDataAdapter ad = new SqlDataAdapter(cmd);
                    DataTable table = new DataTable();
                    ad.Fill(table);
                    dd.DataSource = table;
                    dd.DataTextField="A_Name";
                    dd.DataValueField = "A_Id";
                    dd.DataBind();
                    if (id=="0")//页面初次加载显示顶置内容
                    {
                        ListItem list = new ListItem("--select--", "0");
                        dd.Items.Insert(0, list);
                    }
                }
            }
        }
        protected void DropDownList1_SelectedIndexChanged(object sender, EventArgs e)
        {
            if (DropDownList1.SelectedItem.Value != "0")//判断是否选择省
            {
                fun(DropDownList1.SelectedItem.Value, DropDownList2);
                fun(DropDownList2.SelectedItem.Value, DropDownList3);
            }
            else//清空市、区下拉菜单内容
            {
                DropDownList2.Items.Clear();
                DropDownList3.Items.Clear();
            }
        }

        protected void DropDownList2_SelectedIndexChanged(object sender, EventArgs e)
        {
            fun(DropDownList2.SelectedItem.Value, DropDownList3);
        }