要求：
新建 ProvinceCity用户控件。在该控件 中增加一个Button1按钮。
在Demo1.aspx页面中引用 ProvincCity控件。并且加入button1和Lable1控件。
当点击Demo1中的button时，在lable1中显示用户在provinceCity控件中选择的省和市。
使用两种方法，实现当点击用户控件中的button1时，让demo1中的lable显示ProvinceCity控件中 drowpdownList2中选中的内容。
在Demo2中直接调用用户控件。
用户控件：
citySelect.ascx文件：
<%@ Control Xlanguage="C#" AutoEventWireup="true" CodeBehind="citySelect.ascx.cs" Inherits="用户自定义控件.citySelect" %>
省份：<asp:DropDownList ID="DropDownList1" runat="server" AutoPostBack="True" Xonselectedindexchanged="DropDownList1_SelectedIndexChanged"></asp:DropDownList>城市：<asp:DropDownList ID="DropDownList2" runat="server"></asp:DropDownList><asp:Button ID="Button1" runat="server" Text="获取页面中的label为其值" Xοnclick="Button1_Click" />citySelect.ascx.cs文件：
using System;
using System.Collections.Generic;using System.Linq;using System.Web;using System.Web.UI;using System.Web.UI.WebControls;using System.Data.SqlClient;using System.Data;namespace 用户自定义控件
{ public partial class citySelect : System.Web.UI.UserControl { public event CitySelectHandler GetCitySelect; //用委托定义对应类型的事件
public string GetProvinceCity
{ get { return "省份是：" + this.DropDownList1.SelectedItem.Text + " 城市是：" + this.DropDownList2.SelectedItem.Text; } }protected void Page_Load(object sender, EventArgs e)
{ if (!IsPostBack) { bindprovince(); } }private void bindprovince()
{ string constr = System.Configuration.ConfigurationManager.ConnectionStrings["con"].ConnectionString; using (SqlConnection con = new SqlConnection(constr)) {string sql = "select provinceID,province from province";
using (SqlCommand cmd = new SqlCommand(sql, con)) { SqlDataAdapter adapter = new SqlDataAdapter(cmd); DataTable dt = new DataTable(); adapter.Fill(dt); con.Open(); DropDownList1.DataSource = dt; DropDownList1.DataTextField = "province"; DropDownList1.DataValueField = "provinceID"; DropDownList1.DataBind(); } } }protected void DropDownList1_SelectedIndexChanged(object sender, EventArgs e)
{ this.DropDownList2.Items.Clear(); string Pid = this.DropDownList1.SelectedValue; string sql = "select cityId,city from city where "; SqlParameter P1 = new SqlParameter("@Pid", Pid);string constr = System.Configuration.ConfigurationManager.ConnectionStrings["con"].ConnectionString;
using (SqlConnection con = new SqlConnection(constr)) { using (SqlCommand cmd = new SqlCommand(sql, con)) { cmd.Parameters.Add(P1); SqlDataAdapter adapter = new SqlDataAdapter(cmd); DataTable dt = new DataTable(); adapter.Fill(dt); con.Open(); DropDownList2.DataSource = dt; DropDownList2.DataTextField = "city"; DropDownList2.DataValueField = "cityID"; DropDownList2.DataBind(); } }}
protected void Button1_Click(object sender, EventArgs e)
{ //Label lbl = this.Parent.FindControl("Label1") as Label; //lbl.Text = this.DropDownList2.SelectedItem.Text; //当用户控件中的button1按钮被单击的时候，激发GetCitySelect事件 if (GetCitySelect!=null) { GetCitySelect(this, DropDownList2.SelectedItem.Text); } } } public delegate void CitySelectHandler(object sender,string selectCity); //委托}Demo1.asox.cs文件：
using System;
using System.Collections.Generic;using System.Linq;using System.Web;using System.Web.UI;using System.Web.UI.WebControls;namespace 用户自定义控件
{ public partial class Demo1 : System.Web.UI.Page { protected void Page_Load(object sender, EventArgs e) { //增加用户控件citySelect.ascx的事件处理程序 this.citySelect1.GetCitySelect += new CitySelectHandler(citySelect1_GetCitySelect); }//按Tab建实例化委托，并生成一个方法。
void citySelect1_GetCitySelect(object sender, string selectCity) { this.Label1.Text = selectCity; this.TextBox1.Text = selectCity; }protected void Button1_Click(object sender, EventArgs e)
{ #region 方法一 FindControl方法 //DropDownList ddl1 = this.citySelect1.FindControl("DropDownList1") as DropDownList;//DropDownList ddl2 = this.citySelect1.FindControl("DropDownList2") as DropDownList;
//this.Label1.Text = "省份是：" + ddl1.SelectedItem.Text + " 城市是：" + ddl2.SelectedItem.Text; #endregion #region 方法二 在用户控件中定义属性，这里调用属性获取省市this.Label1.Text = this.citySelect1.GetProvinceCity;
#endregion
}
}}Demo2.aspx文件：
<%@ Page Xlanguage="C#" AutoEventWireup="true" CodeBehind="Demo2.aspx.cs" Inherits="用户自定义控件.Demo2" %>
<%@ Register src="citySelect.ascx" tagname="citySelect" tagprefix="uc1" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "">
<html xmlns="">
<head runat="server"> <title></title></head><body> <form id="form1" runat="server"> <div> <uc1:citySelect ID="citySelect1" runat="server" /> </div> </form></body></html>Demo2.aspx.cs文件：using System;
using System.Collections.Generic;using System.Linq;using System.Web;using System.Web.UI;using System.Web.UI.WebControls;namespace 用户自定义控件
{ public partial class Demo2 : System.Web.UI.Page { protected void Page_Load(object sender, EventArgs e) { this.citySelect1.GetCitySelect += new CitySelectHandler(citySelect1_GetCitySelect); }void citySelect1_GetCitySelect(object sender, string selectCity)
{ this.Response.Write(selectCity); } }}