C# AJAX注册验证出错

Question

Reg.aspx中
function Customer_check(infobox)
{
var inputValue = document.getElementById('Register1_txtUsername').value;
//var cu = document.getElementById("userID").value;
//alert(cu);
if(!ValidateUserName(inputValue,infobox))
return false; showHint(inputValue)
}var xmlHttp
var urll;
function showHint(str)
{ 
if (str.length > 0 && str != null)
{ 
Customer.innerHTML="验证用户名....";
var url="DisposeEvent.aspx?CustomerID=" + str
xmlHttp=GetXmlHttpObject(stateChanged)
xmlHttp.open("GET", url , true)
xmlHttp.send(null)
} 
else
{ 
document.getElementById("Customer").innerHTML=""
} 
} 
DisposeEvent.aspx
  if (!this.IsPostBack)
        {
            string CustomerID = Request["CustomerID"] = null ? "" : Request["CustomerID"].ToString().Trim();
 if (CustomerID != "")
            {
                strcon.Open();
                string strSql = "select count(*) from tb_User where Userid = '" + CustomerID + "'";
                SqlCommand Use = new SqlCommand(strSql, strcon);
                if (Convert.ToInt32(Use.ExecuteScalar()) > 0)
                {
                    Response.Write("true");                    Response.End();
                }
                else
                {
                    Response.Write("false");                    Response.End();
                }
                strcon.Close();
            }
为什么一直提示用户名存在要不就是失败??DisposeEvent.aspx中哪出错???

Answer 1

string CustomerID = Request["CustomerID"] = null ? "" : Request["CustomerID"].ToString().Trim(); 
==
string CustomerID = Request["CustomerID"] == null ? "" : Request["CustomerID"].ToString().Trim();