ajaxPro不刷新页面判断用户名是否存在

function checkLoginName11(str)
        {
            var flag=SchoolProject.Web.Leader.AddTeacherModify.CheckLoginName(str);
            if(flag.value==true)
            {
               document.getElementById("Tb_LoginName").innerText="";
               alert('用户名已经存在，请重新输入');
               document.getElementById("Tb_LoginName").focus();
            }
        }

 

 [AjaxPro.AjaxMethod]
        public bool CheckLoginName(string str)
        {
            SqlHelper sqlhelp = new SqlHelper();
            string sql = @" select count(*) from t_user where c_LoginName='"+str+"' ";
            DataTable dt=sqlhelp.GetDataSet(sql,"0").Tables[0];
            if (Convert.ToInt32(dt.Rows[0][0].ToString()) > 0)
            {
                return true;
            }
            else
            {
                return false;
            }
        }