Android: How to update an UI from AsyncTask if AsyncTask is in a separate class?

Question

I hate inner class.

I\'ve a main activity who launches a \'short-life\' AsyncTask.

AsyncTask is in a separate file, is not an inner class of

Answer 1

Using Interface 1) Create one Interface

public interface OnDataSendToActivity {
    public void sendData(String str);
}

2) Implements it in your Activity

public class MainActivity extends Activity implements OnDataSendToActivity{

     @Override
     protected void onCreate(Bundle savedInstanceState) {
          new AsyncTest(this).execute(new String[]{"AnyData"}); // start your task
     }

     @Override
     public void sendData(String str) {
         // TODO Auto-generated method stub

     }

}

3) Create constructor in AsyncTask(Activity activity){} Register your Interface in AsyncTask file and call interface method as below.

public class AsyncTest extends AsyncTask {

    OnDataSendToActivity dataSendToActivity;
    public AsyncTest(Activity activity){
        dataSendToActivity = (OnDataSendToActivity)activity;
    }

    @Override
    protected void onPostExecute(String result) {
        super.onPostExecute(result);
        dataSendToActivity.sendData(result);
    }

}

Here, your OnPostExecute will call after all task done by AsyncTask and will get "result" as a parameter, returned by doInBackground(){ return "";}.

While "dataSendToActivity.sendData(result);" it will call activity's overrided method "public void sendData(String str) {}".

An edge case to remember: Be sure to pass this, i.e. you current activity's context to AsyncTask and not create another instance of your activity, otherwise your Activity will be destroyed and new one is created.