asp中怎样实现注册时自动检测用户名是否已存在的问题

[堵刻]

本人刚学.net，做了个注册表，想实现用户名自动检测存在在数据库中的用户名是否会重复，重复就提示用户名已存在，就像现在很多网站注册页面一样。求高手解答

[暖枫无敌]

在插入数据前，以这个用户名到数据库中查询，如果查询到有的话，就提示已经存在，如果没有就说明该用户名可用。

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using USTC;
using System.Data;

public partial class Admin_user_Registration : System.Web.UI.Page
{
    DM dm = new DM();
    protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
        {
            BindDropDownList();
            this.msg.Visible = false;
            this.msg2.Visible = false;
        }
    }

    protected void btnRegister_Click(object sender, EventArgs e)
    {
        string name = this.tbUserName.Text.Trim(); //用户名
        string pwd = Common.MD5.ToMD5(this.tbUserPwd.Text.Trim()); //密码
        string realname = this.tbRealName.Text.Trim(); //真实姓名
        string inclass = string.Empty; //所在班级
        if (this.ddlClass.SelectedItem.Text == "--请选择--")
        {
            this.msg2.Visible = true;
            this.msg2.InnerText = "(*)请选择班级！";
        }
        else
        {
            inclass = this.ddlClass.SelectedItem.Text.Trim();
            if (IsUserNameValid(name))
            {
                //用户名已经存在
                this.msg.Visible = true;
                this.msg.InnerText = "(*)该用户名已经存在！";
            }
            else
            {
                try
                {
                    //用户名不存在，可以添加
                    string strSQL = "insert into tb_Users(RealName,InClass,Question,Answer) values('" + realname + "','" + inclass + "','" + name + "','" + pwd + "')";
                    dm.execsql(strSQL);

                    ClientScript.RegisterClientScriptBlock(GetType(), "", "<script>alert('注册成功!');setTimeout('window.close();',2000);</script>");
                }
                catch (Exception)
                {
 
                }
            }
        }
    }

    /// <summary>
    /// 绑定所在班级
    /// </summary>
    public void BindDropDownList()
    {
        string strSQL = "select * from tb_Class";
        DataSet ds = dm.getsql(strSQL);
        this.ddlClass.DataSource = ds;
        this.ddlClass.DataTextField = "ClassName";
        this.ddlClass.DataValueField = "ClassID";
        this.ddlClass.DataBind();
        this.ddlClass.Items.Insert(0,"--请选择--");
    }

    protected void btnReset_Click(object sender, EventArgs e)
    {
        this.tbUserName.Text = "";
        this.tbUserPwd.Text = "";
        this.tbRealName.Text = "";
        this.ddlClass.SelectedIndex = 0;
    }

    /// <summary>
    /// 
    /// </summary>
    /// <param name="name"></param>
    /// <returns></returns>
    public bool IsUserNameValid(string name)
    {
        bool flag = false;
        string strSQL = "select count(Question) as counter from tb_Users where Question='" + name.Trim() + "'";
        DataSet ds = dm.getsql(strSQL);
        if (ds.Tables[0].Rows[0]["counter"].ToString() != "0")
        {
            flag = true;
        }
        return flag;
    }
}

[fangyuantdy]

这个就复杂了，设计到ajax请求后台方法，获取返回值后DOM操作，刚学.NET别搞那么花哨的了，把基本的注册，登录，发布留言什么，管理等等搞定了再说吧

[ljs0203]

设置文本框的失去焦点事件，通过AJAX发送到后台，判断是否存在，然后返回信息，赋值给提示Lable。就可以了

[SomethingJack]

工作了1年多最近转WEB慢慢开始接触前端的技术 楼主刚学就AJAX JQ- -强悍 你先搞清楚一些原理吧- -

[弦弦]

    <script type="text/javascript" src="Scripts/jquery-1.4.1-vsdoc.js"></script>
    <script type="text/javascript">
        $(function () {
            $(document).ready(function () {
                $("#btt").click(function () {
                    $.ajax({
                        url: "Handler1.ashx",
                        type: "post",
                        datatype: "html",
                        data: {userName: $("#TextBox1").val()},
                        success: function (msg) {
                            if (msg != null) {
                                $("#div1").html("<font color='red'>" + msg + "</font>");
                            }
                        }
                    });
                });
            });
        });
    </script>

<body>
    <form id="form1" runat="server">
    <div id="div1">
        <asp:TextBox ID="TextBox1" runat="server"></asp:TextBox>
        <input type="button" value="点击我" id="btt" />
    </div>
    </form>
</body>

[code=C#]
        public void ProcessRequest(HttpContext context)
        {
            string userName = context.Request["userName"];
            if (userName != "HelloAccp")
            {
                string title = "用户名可以用";
                context.Response.Write(title);
            }
            else
            {
                context.Response.Write("该用户名已经存在，不可以使用");
            }
        }

[/code]