Asp.Net文本框失去焦点检查用户名是否存在

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DAL层

using System;
using System.Collections.Generic;
using System.Text;
using MODEL;
using System.Data;

namespace DAL
{
    public static class UserService
    {
        //检查用户名是否存在
        public static bool CheckUserName(string username)
        {
            string sql = "select count(*) from My_UserMessage where uname = '" + username + "'";
            try
            {
                int count = DBHelper.GetScalar(sql);
                if (count > 0)
                {
                    return false;
                }
                else
                {
                    return true;
                }
            }
            catch (Exception ex)
            {
                Console.WriteLine(ex.Message);
                return false;
            }
        }
    }
}

BLL层

using System;
using System.Collections.Generic;
using System.Text;
using DAL;

namespace BLL
{
    public static class UserManager
    {
        //检查用户是否存在
        public static bool CheckUserName(string username)
        {
            return UserService.CheckUserName(username);
        }

}
}

MODEL层

using System;
using System.Collections.Generic;
using System.Text;

namespace MODEL
{
    public class UserMessage
    {
        private int id;

        public int Id
        {
            get { return id; }
            set { id = value; }
        }
        private string uname;

        public string Uname
        {
            get { return uname; }
            set { uname = value; }
        }

private string password;

        public string Password
        {
            get { return password; }
            set { password = value; }
        }
    }
}

Web层

CheckUserName.aspx代码

（*注：文本框的AutoPostBack="true"的属性）

<%@ Page Language="C#" AutoEventWireup="true" CodeFile="CheckUserName.aspx.cs" Inherits="CheckUserName" %>

<!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>检查用户名是否存在</title>
</head>
<body>
    <form id="form1" runat="server">
    <div>
        <asp:TextBox ID="txtCheck" runat="server" OnTextChanged="txtCheck_TextChanged" AutoPostBack="true"></asp:TextBox>
        <asp:Label ID="lblMessage" runat="server" Text="Label"></asp:Label>
        <asp:TextBox ID="TextBox1" runat="server"></asp:TextBox>
        <asp:Button ID="Button1" runat="server" Text="Button" /></div>
    </form>
</body>
</html>

CheckUserName.aspx.cs代码

using System;
using System.Data;
using System.Configuration;
using System.Collections;
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 BLL;
using MODEL;

public partial class CheckUserName : System.Web.UI.Page
{
protected void Page_Load(object sender, EventArgs e)
{

    }
    //文本框改变事件
    protected void txtCheck_TextChanged(object sender, EventArgs e)
    {
        bool result = UserManager.CheckUserName(txtCheck.Text.Trim());
        if (result == true)
        {
            lblMessage.Text = "恭喜您，此用户名可以使用！";
            Button1.Enabled = true;
        }
        if (result == false)
        {
            lblMessage.Text = "该用户名已存在，请更换用户名！";
            Button1.Enabled = false;
        }
    }
}