三级联动

新建ChinaStates类

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;

/// <summary>
/// ChinaStatesDA 的摘要说明
/// </summary>
public class ChinaStatesDA
{
    private DataClassesDataContext Context;
    public ChinaStatesDA()
    {
        //
        // TODO: 在此处添加构造函数逻辑
        //
        Context = new DataClassesDataContext();
    }
    public List<ChinaStates> select(string parentcode)
    {
        return Context.ChinaStates.Where(r=>r.ParentAreaCode==parentcode).ToList();
    }
}

后端代码

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;

public partial class Default2 : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
        {
            binddl(DropDownList1,"0001");
        }
    }
    private void binddl(DropDownList ddl, string code)
    {
        ddl.Items.Clear();
        ddl.Items.Add("--请选择--");
        foreach (ChinaStates data in new ChinaStatesDA().select(code))
        {
            ListItem it = new ListItem(data.AreaName, data.AreaCode);
            ddl.Items.Add(it);
        }
      }
    protected void DropDownList1_SelectedIndexChanged(object sender, EventArgs e)
    {
        binddl(DropDownList2, DropDownList1.SelectedValue); ;
    }
    protected void DropDownList2_SelectedIndexChanged(object sender, EventArgs e)
    {
        binddl(DropDownList3,DropDownList2.SelectedValue);
    }
}