后台代码:
DB cn = new DB(); 
Page_Load#region Page_Load 
private void Page_Load(object sender, System.EventArgs e) 
{ 
if (!this.IsPostBack) 
{ 
this.down1_bind(); 
this.ListBox1.Attributes.Add("onchange", "XmlPost2(this);"); 
this.ListBox2.Attributes.Add("onchange", "XmlPost3(this);"); 
} 
if (povinceid != "") 
{ 
this.down2_bind(povinceid); 
} 
if (cityid != "") 
{ 
this.down3_bind(cityid); 
} 
} 
#endregion 
property#region property 
private string povinceid 
{ 
get 
{ 
if (ViewState["povinceid"] != null && ViewState["povinceid"].ToString() != "") 
{ 
return ViewState["povinceid"].ToString(); 
} 
else 
{ 
if (Request["povinceid"] != null && Request["povinceid"].ToString() != "") 
{ 
return Request["povinceid"]; 
} 
else 
{ 
return ""; 
} 
} 
} 
set 
{ 
ViewState["povinceid"] = value; 
} 
} 
private string cityid 
{ 
get 
{ 
if (ViewState["cityid"] != null && ViewState["cityid"].ToString() != "") 
{ 
return ViewState["cityid"].ToString(); 
} 
else 
{ 
if (Request["cityid"] != null && Request["cityid"].ToString() != "") 
{ 
return Request["cityid"]; 
} 
else 
{ 
return ""; 
} 
} 
} 
set 
{ 
ViewState["povinceid"] = value; 
} 
} 
#endregion 
down2_bind#region down2_bind 
private void down2_bind(string id) 
{ 
string mystr = ""; 
string sql = "select cityID,city from city where father = ’" + id + "’"; 
DataTable dt = cn.ReturnTable2(sql); 
if (dt.Rows.Count != 0) 
{ 
for (int i = 0; i < dt.Rows.Count; i++) 
{ 
mystr += "," + dt.Rows[i][0].ToString() + "|" + dt.Rows[i][1].ToString(); 
} 
mystr = mystr.Substring(1); 
} 
this.Response.Write(mystr); 
this.Response.End(); 
} 
#endregion 
down3_bind#region down3_bind 
private void down3_bind(string id) 
{ 
string mystr = ""; 
string sql = "select areaID,area from area where father = ’" + id + "’"; 
DataTable dt = cn.ReturnTable2(sql); 
if (dt.Rows.Count != 0) 
{ 
for (int i = 0; i { 
mystr += "," + dt.Rows[i][0].ToString() + "|" + dt.Rows[i][1].ToString(); 
} 
mystr = mystr.Substring(1); 
} 
this.Response.Write(mystr); 
this.Response.End(); 
} 
#endregion 
down1_bind#region down1_bind 
private void down1_bind() 
{ 
string sql = "select provinceID,province from povince"; 
DataTable dt = cn.ReturnTable2(sql); 
this.ListBox1.DataSource = dt.DefaultView; 
this.ListBox1.DataValueField = "provinceID"; 
this.ListBox1.DataTextField = "province"; 
this.ListBox1.DataBind(); 
} 
#endregion 
以上是实现listbox的方法,DropDownList的方法与它一样,只要替换下就可以了. 
数据库这里上传不了,我把它放到我的资源里,你们要是想要的话,就到我的资源里去下载下来,或者你们自己建表看效果.地址是:http://download.csdn.net/user/ainir1314520;数据库是access的,你们转换下就可以了 
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