How to get the result of OnPostExecute() to main activity because AsyncTask is a separate class?

Question

I have this two classes. My main Activity and the one that extends the AsyncTask, Now in my main Activity I need to get the result from the OnPostExecute() in the AsyncTask. How can I pass or get the result to my main Activity?

Here is the sample codes.

My main Activity.

public class MainActivity extends Activity{      AasyncTask asyncTask = new AasyncTask();      @Override     public void onCreate(Bundle aBundle) {         super.onCreate(aBundle);                      //Calling the AsyncTask class to start to execute.           asyncTask.execute(a.targetServer);           //Creating a TextView.         TextView displayUI = asyncTask.dataDisplay;         displayUI = new TextView(this);         this.setContentView(tTextView);      }  } 

This is the AsyncTask class

public class AasyncTask extends AsyncTask<String, Void, String> {  TextView dataDisplay; //store the data   String soapAction = "http://sample.com"; //SOAPAction header line.  String targetServer = "https://sampletargeturl.com"; //Target Server.  //SOAP Request. String soapRequest = "<sample XML request>";        @Override protected String doInBackground(String... string) {  String responseStorage = null; //storage of the response  try {       //Uses URL and HttpURLConnection for server connection.      URL targetURL = new URL(targetServer);     HttpURLConnection httpCon = (HttpURLConnection) targetURL.openConnection();     httpCon.setDoOutput(true);     httpCon.setDoInput(true);     httpCon.setUseCaches(false);      httpCon.setChunkedStreamingMode(0);      //properties of SOAPAction header     httpCon.addRequestProperty("SOAPAction", soapAction);     httpCon.addRequestProperty("Content-Type", "text/xml; charset=utf-8");      httpCon.addRequestProperty("Content-Length", "" + soapRequest.length());     httpCon.setRequestMethod(HttpPost.METHOD_NAME);       //sending request to the server.     OutputStream outputStream = httpCon.getOutputStream();      Writer writer = new OutputStreamWriter(outputStream);     writer.write(soapRequest);     writer.flush();     writer.close();       //getting the response from the server     InputStream inputStream = httpCon.getInputStream();      BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(inputStream));     ByteArrayBuffer byteArrayBuffer = new ByteArrayBuffer(50);      int intResponse = httpCon.getResponseCode();      while ((intResponse = bufferedReader.read()) != -1) {         byteArrayBuffer.append(intResponse);     }      responseStorage = new String(byteArrayBuffer.toByteArray());       } catch (Exception aException) {     responseStorage = aException.getMessage();      }     return responseStorage; }  protected void onPostExecute(String result) {      aTextView.setText(result);  }         }    

Answer 1

Easy:

1. Create interface class, where String output is optional, or can be whatever variables you want to return.

    public interface AsyncResponse {      void processFinish(String output);  } 

2. Go to your AsyncTask class, and declare interface AsyncResponse as a field :

    public class MyAsyncTask extends AsyncTask<Void, Void, String> {    public AsyncResponse delegate = null;       @Override      protected void onPostExecute(String result) {        delegate.processFinish(result);      }   } 

3. In your main Activity you need to implements interface AsyncResponse.

    public class MainActivity implements AsyncResponse{    MyAsyncTask asyncTask =new MyAsyncTask();     @Override    public void onCreate(Bundle savedInstanceState) {        //this to set delegate/listener back to this class       asyncTask.delegate = this;        //execute the async task        asyncTask.execute();    }     //this override the implemented method from asyncTask    @Override    void processFinish(String output){       //Here you will receive the result fired from async class        //of onPostExecute(result) method.     }   } 

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UPDATE

I didn't know this is such a favourite to many of you. So here's the simple and convenience way to use interface.

still using same interface. FYI, you may combine this into AsyncTask class.

in AsyncTask class :

public class MyAsyncTask extends AsyncTask<Void, Void, String> {    // you may separate this or combined to caller class.   public interface AsyncResponse {         void processFinish(String output);   }    public AsyncResponse delegate = null;      public MyAsyncTask(AsyncResponse delegate){         this.delegate = delegate;     }      @Override     protected void onPostExecute(String result) {       delegate.processFinish(result);     } } 

do this in your Activity class

public class MainActivity extends Activity {       MyAsyncTask asyncTask = new MyAsyncTask(new AsyncResponse(){           @Override      void processFinish(String output){      //Here you will receive the result fired from async class       //of onPostExecute(result) method.      }   }).execute();   } 

Or, implementing the interface on the Activity again

public class MainActivity extends Activity      implements AsyncResponse{            @Override     public void onCreate(Bundle savedInstanceState) {          //execute the async task          new MyAsyncTask(this).execute();     }            //this override the implemented method from AsyncResponse     @Override     void processFinish(String output){         //Here you will receive the result fired from async class          //of onPostExecute(result) method.     } } 

As you can see 2 solutions above, the first and third one, it needs to create method processFinish, the other one, the method is inside the caller parameter. The third is more neat because there is no nested anonymous class.

Tip: Change String output, String response, and String result to different matching types in order to get different objects.

Answer 2

There are a few options:

• Nest the AsyncTask class within your Activity class. Assuming you don't use the same task in multiple activities, this is the easiest way. All your code stays the same, you just move the existing task class to be a nested class inside your activity's class.

  public class MyActivity extends Activity {     // existing Activity code     ...      private class MyAsyncTask extends AsyncTask<String, Void, String> {         // existing AsyncTask code         ...     } } 

• Create a custom constructor for your AsyncTask that takes a reference to your Activity. You would instantiate the task with something like new MyAsyncTask(this).execute(param1, param2).

  public class MyAsyncTask extends AsyncTask<String, Void, String> {     private Activity activity;      public MyAsyncTask(Activity activity) {         this.activity = activity;     }      // existing AsyncTask code     ... }