三级联动下拉菜单

写个CS,AJAX也可以using System;using System.Data;using System.Configuration;using System.Web;using System.Web.Security;using System.Web.UI;using System.Web.UI.WebControls;using System.Web.UI.WebControls.WebParts;using System.Web.UI.HtmlControls;using System.Data.SqlClient;/// <summary>/// provcityservstat 的摘要说明/// 这个类主要是用来当省／城市／服务站都是下拉进判断，省和城市教师都是autopostback/// </summary>public class provcityservstat{    public DropDownList prov;    public DropDownList city;    public DropDownList servstat;    public string servstat_id;public provcityservstat(){//// TODO: 在此处添加构造函数逻辑//}    //绑定省的下拉    public void dataBindToProv()    {        SqlConnection con = db.createSqlConneciton();        con.Open();        SqlCommand cmd = new SqlCommand("select * from t_prov", con);        SqlDataReader sdr = cmd.ExecuteReader();        this.prov.DataSource = sdr;        this.prov.DataTextField = "prov_name";        this.prov.DataValueField = "prov_id";        this.prov.DataBind();        sdr.Close();        con.Close();    }

    //绑定城市下拉    public void dataBindToCity()    {        SqlConnection con = db.createSqlConneciton();        con.Open();        SqlCommand cmd = new SqlCommand("select * from t_city where city_provid = " + this.prov.SelectedValue, con);        SqlDataReader sdr = cmd.ExecuteReader();        this.city.DataSource = sdr;        this.city.DataTextField = "city_name";        this.city.DataValueField = "city_id";        this.city.DataBind();        sdr.Close();        con.Close();    }

    //绑定服务站    public void dataBindToServstat()    {        if (this.city.SelectedValue != "")        {            SqlConnection con = db.createSqlConneciton();            con.Open();            SqlCommand cmd = new SqlCommand("select * from t_servstat where servstat_cityid = " + this.city.SelectedValue, con);            SqlDataReader sdr = cmd.ExecuteReader();            this.servstat.DataSource = sdr;            this.servstat.DataTextField = "servstat_name";            this.servstat.DataValueField = "servstat_id";            this.servstat.DataBind();            sdr.Close();            con.Close();        }        else        {            this.servstat.Items.Clear();        }    }

    //一般用于新增时省，城市，服务站的下拉    public void dataBindAdd()    {        dataBindToProv();        dataBindToCity();        dataBindToServstat();    }

    //当省的下拉发生变化时    public void databinddropdownprov()    {        dataBindToCity();        dataBindToServstat();    }

    //下面开始是用于修改的,根据已知的servstat_id得出是哪个服务站，哪个城市，哪个省    public void dataBindMod()    {        SqlConnection con = db.createSqlConneciton();        con.Open();        SqlCommand cmd = new SqlCommand("select * from t_servstat,t_city,t_prov where prov_id = city_provid and city_id = servstat_cityid and servstat_id = " + servstat_id, con);        SqlDataReader sdr = cmd.ExecuteReader();        if (sdr.Read())        {            dataBindModProv(sdr["prov_id"].ToString());            dataBindModCity(sdr["prov_id"].ToString(), sdr["city_id"].ToString());            dataBindModServstat(sdr["city_id"].ToString(), sdr["servstat_id"].ToString());        }        sdr.Close();        con.Close();    }

    //绑定到修改时的省    public void dataBindModProv(string prov_id)    {        SqlConnection con = db.createSqlConneciton();        con.Open();        SqlCommand cmd = new SqlCommand("select * from t_prov", con);        SqlDataReader sdr = cmd.ExecuteReader();        this.prov.Items.Clear();        int i = 0;        while (sdr.Read())        {            this.prov.Items.Insert(i, new ListItem(sdr["prov_name"].ToString(), sdr["prov_id"].ToString()));            if (prov_id == sdr["prov_id"].ToString())            {                this.prov.Items[i].Selected = true;            }            i++;        }        sdr.Close();        con.Close();    }

    //绑定到修改时的城市    public void dataBindModCity(string prov_id, string city_id)    {        SqlConnection con = db.createSqlConneciton();        con.Open();        SqlCommand cmd = new SqlCommand("select * from t_city where city_provid = " + prov_id, con);        SqlDataReader sdr = cmd.ExecuteReader();        this.city.Items.Clear();        int i = 0;        while (sdr.Read())        {            this.city.Items.Insert(i, new ListItem(sdr["city_name"].ToString(), sdr["city_id"].ToString()));            if (city_id == sdr["city_id"].ToString())            {                this.city.Items[i].Selected = true;            }            i++;        }        sdr.Close();        con.Close();    }

    //绑定到修改时的服务站    public void dataBindModServstat(string city_id, string servstat_id)    {        SqlConnection con = db.createSqlConneciton();        con.Open();        SqlCommand cmd = new SqlCommand("select * from t_servstat where servstat_cityid = " + city_id, con);        SqlDataReader sdr = cmd.ExecuteReader();        this.servstat.Items.Clear();        int i = 0;        while (sdr.Read())        {            this.servstat.Items.Insert(i, new ListItem(sdr["servstat_name"].ToString(), sdr["servstat_id"].ToString()));            if (servstat_id == sdr["servstat_id"].ToString())            {                this.servstat.Items[i].Selected = true;            }            i++;        }        sdr.Close();        con.Close();    }}

参考一下我的,我这个是三级的注意,下拉的autopostback要先上