java - OnPostExecute result null -

i'm sending data app external server.

public class postkey extends asynctask<string, string, string> {     public asyncresponse delegate = null;      @override     protected string doinbackground(string... params) {         postdata(params[0]);         return null;     }      @override     protected void onpostexecute(string result){         log.d(string.valueof(result), " result?");         delegate.processfinish(result); // returns nullpointerexception     }      public void postdata(string valueiwanttosend) {         httpclient httpclient = new defaulthttpclient();         httppost httppost     = new httppost("http://domain.com/post.php");          try {             list<namevaluepair> namevaluepairs = new arraylist<namevaluepair>();             namevaluepairs.add(new basicnamevaluepair("hoi", "test"));             httppost.setentity(new urlencodedformentity(namevaluepairs));              httpresponse response = httpclient.execute(httppost);             string responsestr = entityutils.tostring(response.getentity());              log.d(responsestr, "");         } catch (clientprotocolexception e) {             // todo auto-generated catch block         } catch (ioexception e) {             // todo auto-generated catch block         }     }      public interface asyncresponse {         void processfinish(string output);     } } 

log.d(responsestr, ""); return true or false, depending on data send, , logs it.

delegate.processfinish(result); returns nullpointerexception mentioning public class postkey extends asynctask<string, string, string> eventhough parameters declared strings.

i've tried replacing result responsestr didn't work either.

problem method call delegate.processfinish(result); delegate not initialized. calling method on null object.