return value after run another AsyncTask in onPostExecute()

Issue

How to return value to main activity after run another AsyncTask in onPostExecute()?

I have written function in 2nd Asynctask to return ArrayList back to 1st Asynctask. However, I don't know how to return the ArrayList from 1st Asynctask back to main activity.

//Main Activity:
DownloaderGet downloaderGet = new DownloaderGet(getActivity(), "http://xxxxx.php");
downloaderGet.execute();

//1st AsyncTask(DownloaderGet)
@Override
    protected void onPostExecute(String jsonData) {
        super.onPostExecute(jsonData);
        new DataParserGet(c, jsonData).execute();
    }

//2nd Asynctask(DataParserGet)
@Override
    protected void onPostExecute(Boolean result) {
        super.onPostExecute(result);

        pd.dismiss();
        if(result)
        {
            myNewArrayList = spacecrafts;
            passToClass();
        }
    }

Solution

Problem: You want to pass the array list from the second AsyncTask back to MainActivity.

Solution: Passing activity instance to the first AsyncTask, then forward the instance to the second AsyncTask.

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        // Pass `this` as activity instance to the first AsyncTask.
        DownloaderGet downloaderGet = new DownloaderGet(this, "http://xxxxx.php");
        downloaderGet.execute();
    }

    public void onDataAvailable(List<String> arrauList) {
        // Process array list here.

    }
}

// The first AsyncTask.
class DownloaderGet extends AsyncTask<Void, Void, String> {
    private WeakReference<MainActivity> activity;
    private String url;

    DownloaderGet(MainActivity activity, String url) {
        this.activity = new WeakReference<>(activity);
        this.url = url;
    }

    @Override
    protected String doInBackground(Void... voids) {
        // Your code here
        // ...
        return null;
    }

    @Override
    protected void onPostExecute(String jsonData) {
        // Forward the instance to the second AsyncTask.
        new DataParserGet(activity.get(), jsonData).execute();
    }
}

class DataParserGet extends AsyncTask<Void, Void, Boolean> {
    private WeakReference<MainActivity> activity;
    private String jsonData;

    DataParserGet(MainActivity activity, String jsonData) {
        this.activity = new WeakReference<>(activity);
        this.jsonData = jsonData;
    }

    @Override
    protected Boolean doInBackground(Void... voids) {
        // Your code here
        // ...
        return null;
    }

    @Override
    protected void onPostExecute(Boolean result) {
        if (result) {
            myNewArrayList = spacecrafts;
            if (activity.get() != null) {
                // Pass the array list back to main activity.
                activity.get().onDataAvailable(myNewArrayList);
            }
        }
    }
}

Answered By - Son Truong