ASP.NET自动检测用户名是否注册

Question

<asp:TextBox ID="txtUserName" runat="server" onBlur="send_request('addAdmin');"></asp:TextBox>  <script language="javascript" type="text/javascript">
          function send_request(flag)
          {
              //创建XMLHttpRequest;
              http_request = false;
              if(window.XMLHttpRequest)
              {
                  //　非IE　浏览器
                  http_request = new XMLHttpRequest();
              }
              else if(window.ActiveXObject)
              {
                  //IE
                  try
                  {
                      http_request = new ActiveXObject("Msxml2.XMLHTTP");//较新版本的IE
                  }catch(e)
                  {
                      try
                      {
                          http_request = new ActiveXOBject("Microsoft.XMLHTTP");//旧版本IE
                      }catch(e){}                    
                  }
              }
              else
              {
                  window.alert("不能创建　XMLHttpRequest对象，无法应用Ajax");
                  return false;
              }
              //指定回调函数
              if(flag == "addAdmin")
              {
                   http_request.onreadystatechange = addAdmin;
                    //创建HTTP请求
                   http_request.open("get","Handler.ashx?flag=addAdmin&userName="+document.getElementById("txtUserName").value,true);
            
              }
               else if(flag == "updateTitle")
               {
                  http_request.onreadystatechange = updateTitle;
                   //创建HTTP请求
                   i = document.getElementById("ddlVoteTitle").selectedIndex;//选择的索引
                   id = document.form1.ddlVoteTitle.options[i].value;
                   http_request.open("get","Handler.ashx?flag=updateTitle&id="+id,true);
            
               }
           
           
              //发送上面创建的HTTP请求
              http_request.send(null);  
          }
          function addAdmin()
          {  
              if(http_request.readyState == 4)//发送成功
              {
                  if(http_request.status == 200)//交易成功
                  { 
                      //正式处理有信息
                      if(http_request.responseText == "该用户已经存在")
                      {
                          //隐藏提交按扭
                          document.getElementById("Button1").style.display ="none";
                      }
                      else
                      {
                          document.getElementById("Button1").style.display="";
                      }
                   
                      document.getElementById("lblShow").innerText=http_request.responseText;
                  }
              }
          }
          function updateTitle()
          {
              if(http_request.readyState == 4)//发送成功
              {
                  if(http_request.status == 200)//交易成功
                  { 
                      //正式处理有信息
                   
                      document.getElementById("lblTitle").innerText=http_request.responseText;
                  }
              }
          }
      </script>
为什么在表单里输入数字没反应呢?

Answer 1

调试页面Handler.ashx的后台代码程序，断点设在窗体加载事件的if(!IsPostback)中