Page_Load事件---IsPostBack属性 aspx代码 <%...@ Page Language="C#" AutoEventWireup="true" CodeFile="Default.aspx.cs" Inherits="_Default" %><!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml" ><head runat="server"> <title>无标题页</title></head><body> <form id="form1" runat="server"> <div style="text-align: left"> <br /> <br /> <br /> <br /> <asp:Label ID="Label1" runat="server" Height="31px" Text="用户名:" Width="95px"></asp:Label> <asp:TextBox ID="textUserName" runat="server" Height="24px" OnTextChanged="textUserName_TextChanged">textUserName</asp:TextBox><br /> <asp:Label ID="Label2" runat="server" Height="29px" Text="密码:" Width="93px"></asp:Label> <asp:TextBox ID="textUserPwd" runat="server" Height="22px">textUserPwd</asp:TextBox> <br /> <br /> <asp:Button ID="btnLogin" runat="server" OnClick="btnLogin_Click" Text="登录" /> <asp:Button ID="btnClear" runat="server" OnClick="btnClear_Click" Text="清空" /> <asp:Button ID="btnClose" runat="server" Text="关闭" /><br /> <br /> <asp:Label ID="lblMessage" runat="server" Height="66px" Text=" " Width="175px"></asp:Label></div> </form></body></html> aspx.cs代码 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;public partial class _Default : System.Web.UI.Page ...{ protected void Page_Load(object sender, EventArgs e) ...{ if (!Page.IsPostBack) //判断页面是否是第一次加载 ...{ this.textUserName.Text= " "; //将用户名框设置为空 this.textUserPwd.Text= " "; //将密码框设置为空 } this.btnClose.Attributes.Add("onclick", "window.close();");//关闭按纽设置,相当于在aspx文件的asp:label中添加onclick="window.close();" } protected void btnLogin_Click(object sender, EventArgs e) ...{ if (this.textUserName.Text == "zuo" && this.textUserPwd.Text == "zuo") ...{ this.lblMessage.Text = "登录成功"; } else ...{ this.lblMessage.Text = "登陆失败"; } } protected void btnClear_Click(object sender, EventArgs e) ...{ this.textUserName.Text = " "; //设置为空 this.textUserPwd.Text = " "; //设置为空 }}