Why can't get responseHeaders by WWW in ios ?

Hi everyone !
I need get response code from my request. My code work in Unity. But when i build to Xcode. It can't work.
Pls help me fix it
Thank you so much

Code (CSharp):

1. public  int getResponseCode(WWW request) {
2.         int ret = 0;
3.         if (request.responseHeaders == null) {
4.             Debug.LogError("no response headers.");
5.         }
6.         else {
7.             if (!request.responseHeaders.ContainsKey("STATUS")) {
8.                 Debug.LogError("response headers has no STATUS.");
9.             }
10.             else {
11.                 ret = parseResponseCode(request.responseHeaders["STATUS"]);
12.             }
13.         }
14.         Debug.Log ("RESPONSE CODE : " +ret);
15.         return ret;
16.     }
17.    
18.     public  int parseResponseCode(string statusLine) {
19.         int ret = 0;
20.        
21.         string[] components = statusLine.Split(' ');
22.         if (components.Length < 3) {
23.             Debug.LogError("invalid response status: " + statusLine);
24.         }
25.         else {
26.             if (!int.TryParse(components[1], out ret)) {
27.                 Debug.LogError("invalid response code: " + components[1]);
28.             }
29.         }
30.        
31.         return ret;
32.     }

Code (CSharp):

1. public IEnumerator GetEndLinks(string url_redirect)
2.     {
3.             WWW request = new WWW (url_redirect);
4.             yield return request;
5.  
6.          int CODE = getResponseCode (request);   //=> Not work when build to xcode and run with iphone
7.              Debug.Log("v-------------new--------------v");
8.             foreach(var cKey in request.responseHeaders.Keys)
9.             {
10.              Debug.Log(cKey + " : " + request.responseHeaders[cKey]);
11.            }
12.  
13.            if (CODE == 301 || CODE == 302 || CODE == 303 || CODE == 304 || CODE == 305 || CODE == 306 || CODE == 307)
14.                {
15.                   string redirection = request.responseHeaders ["LOCATION"];
16.                    Debug.Log (redirection);
17.                    //Open redirect links
18.                    Application.OpenURL (redirection);
19.                }
20.     }