Return an object from onPostExecute() method

Issue

I have the following AsyncTask class which I want to handle multiple api calls and return a List back to my activity. I am having a problems trying to make this work.

How can I return an object back to my activity when onPostExecute() method does not return anything?

public class NetworkCall extends AsyncTask<Call, Void, List<Student>> {

@Override
protected List<Students> doInBackground(Call... calls) {
    try {
        Call<Students> call = calls[0];
        Response<Students> response = call.execute();
        return response.body().getStudents();

    } catch (IOException e) {
        e.printStackTrace();
    }

    return null;
    }

    @Override
    protected void onPostExecute(List<Students> students) { 

    }
}

Solution

One of the options is to create interface and use as callback. In async task class :

public class NetworkCall extends AsyncTask<Call, Void, List<Student>> {

public interface NetworkCallback{
    void onResponse(List<Students> students);
}

private NetworkCallback callback;

public void setCallback(NetworkCallback callback){
    this.callback = callback;
}

@Override
protected List<Students> doInBackground(Call... calls) {
    try {
        Call<Students> call = calls[0];
        Response<Students> response = call.execute();
        return response.body().getStudents();

    } catch (IOException e) {
        e.printStackTrace();
    }

    return null;
    }

    @Override
    protected void onPostExecute(List<Students> students) { 
        callback.onResponse(students)
    }
} 

and now in your activity implement the interface and provide to the async task via setter.

public class StudentsActivity extends AppCompatActivity {
  @Override
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    //.... you setup for activity

    NetworkCall networkCall = new NetworkCall();
    networkCall.setCallback(new NetworkCall.NetworkCallback() {
      @Override
      public void onResponse(List<Students> students) {
        //update your UI here
      }
    });
  }
}

Based on the Docs onPostExecute runs on the main UI thread so no need to the runOnUiThread and Runnable

Answered By - Maksim Novikov