android - Using AsyncTask to implement API and updating result to UI -

i'm using asynctask in api carry out network operations. @ ui part there button, clicking on triggers api execute request/async task. api implementing callback updated onpostexecute() method. api gets right data populated once onpostexecute() passes data on callback. works good. i'm getting conceptual problem while updating ui. want achieve: 1- click "button" on ui 2- want update api's response string ui. response string after executing asynctask.

the problem api return null response in current thread of execution. once ui thread done, see api/asynctask data coming in. know i'm missing trivial, important. know whats right way update api response on ui?

[update]

here ui code includes clicking button triggering async task via api (just class implements callbacks getting server response)

button.setonclicklistener(new onclicklistener() {          public void onclick(view v) {                             api api = new api();             request request = new request();                     request.seturl("http://www.example.com/");                     api.fetch(request);              try { //it doesn't matter how wait here return response.  //response task doesn't return in thread.  //if click button "refresh" refresh data, api.getresponsestring() shows response server.                 thread.sleep(2000); //api.getresponsestring() returns null. expect return data retrieved server                 string text = api.getresponsestring();                 system.out.println("text: " + text);                 textview.settext(text);             } catch (interruptedexception e) {                 // todo auto-generated catch block                 e.printstacktrace();             }         }     }); 

api code

public class api implements responsecallbacks {  string responsestring = null;  public void fetch(request request) {     makerequest(request, this); }  public void makerequest(request request,         final responsecallbacks responsecallbacks) {     mytask asynctask = new mytask();     asynctask.setresponsecallbacks(responsecallbacks);     asynctask.execute(request); }  @override public void onsuccess(response response) throws ioexception {     if (response.issuccess()) {         responsestring = "success";     } else {         responsestring = "failed";     } }  public string getresponsestring() {     return responsestring; } } 

asynctask code

public class mytask extends asynctask { private responsecallbacks responsecallbacks;  public mytask() {}  public void setresponsecallbacks(responsecallbacks callbacks) {     this.responsecallbacks = callbacks; }  @override protected response doinbackground(request... params) {     request request = params[0];     response response = null;      try {         //make http call , gets response remote server here...     } catch (exception e) {      }      return response; }  protected void onpostexecute(response response) {     if (response.issuccess()) {         try {             if (response.issuccess()) {                 callbacks.onsuccess(response);             }         } catch (exception e) {             callbacks.onfailure(response);         }     } }   } 

what want update text returned server in textview after click button.

[update 2] apparently, found out if define 1 more callback uicallback , have activity register it, solves problem.

uicallback:

public interface uicallback { public void onfailure(string response); void onsuccess(string response) throws ioexception; } 

have activity implement it:

public class mainactivity extends activity implements uicallback {     .......     api = new netapi(); api.setuicallbacks(this);     .......      @override public void onsuccess(string response) throws ioexception {     string text = api.getresponsestring(); //works !     textview.settext(text);  } } 

does have better solution ? don't idea of activity implementing callback. have been awesome, if api deliver server response once done fetching data, api.getresponsestring().

my guess is, you're looking runonuithread.

if use in onpostexecute, can refresh ui data without registering callbacks , whatnot. this:

protected void onpostexecute(response response) {   if (response.issuccess()) {     try {         if (response.issuccess()) {               runonuithread(new runnable() {                 public void run() {                     textview.settext(text);                  }             });         }     } catch (exception e) {         callbacks.onfailure(response);     }   } } 

a synchronous alternative using runnable in main thread. you'd have redefine mytask implement runnable , join after. this

thread asynctask = new thread(mytask()); asynctask.start(); asynctask.join();//gets called task ends 

mytask be

public class mytask implements runnable{       public void run(){          //do whatever need      } }