下拉框二级联动的功能在我们在网站开发中经常使用到的，下面提供的实现文法是在ASP.NET中进行开发的，并附有数据库设计，有需要的同志们看一下了！
namespace WebApplicationDlh
{
using System;
using System.Data;
using System.Drawing;
using System.Web;
using System.Web.UI.WebControls;
using System.Web.UI.HtmlControls;
using System.Data.SqlClient;
using Db;
/// <summary>
/// Area 的摘要说明。
/// </summary>
public class Area : System.Web.UI.UserControl
{
protected System.Web.UI.WebControls.DropDownList ddlProvince;
protected System.Web.UI.WebControls.DropDownList ddlCity;
public string strProvince
{
get
{
return ddlProvince.SelectedItem.Value;
}
set
{
ddlProvince.SelectedItem.Value = value;
}
}
public string strCity
{
get
{
return ddlCity.SelectedItem.Value;
}
set
{
ddlCity.SelectedItem.Value = value;
}
}
private void Page_Load(object sender, System.EventArgs e)
{
if(!IsPostBack)
{
ddlProvinceBind();
ddlCity.Items.Insert(0,"-请选择城市-");
}
}
private void ddlProvinceBind()
{
Db.Area myArea = new Db.Area();
SqlDataReader dr = myArea.GetAllProvince();
if(dr.Read())
{
ddlProvince.DataSource = dr;
ddlProvince.DataTextField = "Province";
ddlProvince.DataValueField = "Province";
ddlProvince.DataBind();
ddlProvince.Items.Insert(0,"-请选择省份-");
}
}
#region Web 窗体设计器生成的代码
override protected void OnInit(EventArgs e)
{
//
// CODEGEN: 该调用是 ASP.NET Web 窗体设计器所必需的。
//
InitializeComponent();
base.OnInit(e);
}

/// <summary>
/// 设计器支持所需的方法 - 不要使用代码编辑器
/// 修改此方法的内容。
/// </summary>
private void InitializeComponent()
{
this.ddlProvince.SelectedIndexChanged += new System.EventHandler(this.ddlProvince_SelectedIndexChanged);
this.Load += new System.EventHandler(this.Page_Load);
}
#endregion
private void ddlProvince_SelectedIndexChanged(object sender, System.EventArgs e)
{
if(ddlProvince.SelectedItem.Value == "-请选择省份-")
{
ddlCity.Items.Clear();
ddlCity.Items.Insert(ddlProvince.SelectedIndex,"-请选择城市-");
}
else
{
Db.Area myArea = new Db.Area();
SqlDataReader dr = myArea.GetAllCityWhereProvince(ddlProvince.SelectedItem.Value);
if(dr.Read())
{
ddlCity.DataSource = dr;
ddlCity.DataTextField = "City";
ddlCity.DataValueField = "ID";
ddlCity.DataBind();
} } } } }