AsyncTask passing custom objects

Question

[I have a custom parcelable object Vehicle]

I have looked at AsyncTask but it wasn't too clear on this topic:

I would like to pass a String(which is the Vehicle ID of the Vehicle) into an AsyncTask, then in doInBackground() I have a method

mRemoteInterface.getTrackHistory();

which gives me an ArrayList. I would like to then, in onPostExecute() start an activity where both the Vehicle ID and ArrayList are extras.

This is an outline of what I wan't to be able to do. The issue is that I don't understand passing objects INTO the asynctask, and then from doInBackground() to onPostExecute() and from onPostExecute() back to the original execute call.

getTrackHistory.execute(WHAT SHOULD GO HERE?);

private class getTrackHistory extends
AsyncTask<String, Integer, Boolean **WHAT SHOULD GO HERE?**> {

    @Override
    protected Boolean doInBackground(
            String... params) {
        try {
            String vehicleID = params[0];
            listVehicleHistory = (ArrayList<Vehicle>) mRemoteInterface.getVehicleHistory(vehicleID);
        } catch (Exception e) {

            e.printStackTrace();
        }


    }




    @Override
    protected void onProgressUpdate(Integer... progress) {

    }

    @Override
    protected void onPostExecute(Boolean worked) {

        super.onPostExecute(worked);

        Intent intent = new Intent(MainActivity.this,VehicleInfo.class);

        intent.putExtra("Vehicle ID", toReturn);
        intent.putParcelableArrayListExtra("VehicleHistory", listVehicleHistory);

        startActivity(intent);
    }

}

Just create a constructor for your async task. its much easier than atte,pting to pass in the details as params. — r2DoesInc, Aug 12 '13 at 16:00

score 5 · Accepted Answer · edited Jul 19 '19 at 20:32

You can pass the string to the constructor of asynctask or to doInbackground

   new getTrackHistory(mystringvalue).execute();

Then in the constructor

  private class getTrackHistory extends AsyncTask<String, Integer, Boolean> {  

  String value; 
  public getTrackHistory(String mystring) {
      value = mystring;
  }

Edit:

You can also pass value to doInbackground()

   new TheTask().execute("mystring");
   class TheTask extends AsyncTask <String,Void,Void> { 
     @Override
     protected void onPreExecute() {
       super.onPreExecute();
     }
     @Override
     protected void onPostExecute(Void result) {
      super.onPostExecute(result);
     }
     @Override
     protected Void doInBackground(String... params) {
      String value = params[0];
     return null;
     }
   }

To the question in the comment

  new getTrackHistory(mystringvalue,ActivityName.this).execute();

In the Constructor

  String value; 
  TheInterface listener;
  public getTrackHistory(String mystring,Context context) {
      value= mystring;
      listener = (TheInterface) context; 
  }

Interface

public interface TheInterface {

public void theMethod(ArrayList<String> result); // your result type

}

Then

In your doInbackground return the result. I am assuming its ArrayList of type String. Change the arraylist to what suits your requirement.

In your onPostExecute

if (listener != null) {
  listener.theMethod(result); // result is the ArrayList<String>
  // result returned in doInbackground 
  // result of doInbackground computation is a parameter to onPostExecute 
}

In your activity class implement the interface

  public class ActivityName implements getTrackHistory.TheInterface

Then

 @Override
 public void theMethod(ArrayList<String> result) { // change the type of result according yo your requirement
 // use the arraylist here
 }

Similar post using interface

Android Parse JSON stuck on get task.

Thank you, that makes sense. Could you elaborate on passing from onPostExecute() back to where new getTrackhistory(mystringvalue).execute() was called?(is this possible) — benzabill, Aug 12 '13 at 16:03
@bent you can do that with the help of a interface. i have answered a similar one. i will find the link — Raghunandan, Aug 12 '13 at 16:04
Ah, thank you. So I can pass a value to either doInBackground() or to a constructor. Effectively the same. Thanks @Raghunandan!!! — benzabill, Aug 12 '13 at 16:12
I am having an issue that I am hoping you can help me with. Could you take a look? http://stackoverflow.com/questions/18448216/unable-to-execute-dex-multiple-dex-files-define-lcom-shared-classes Thank you! — benzabill, Aug 26 '13 at 16:06

Marcin Orlowski · Answer 2 · 2013-08-29T19:28:40.763

Common approach to this is to pass your arguments/objects to constructor of your AsyncTask, store as member and then reference from doInBackground(). For example:

private class getTrackHistory extends AsyncTask<String, Integer, Boolean> {

    Vehicle mVehicle;

    public getTrackHistory( Vehicle v) {
       mVehicle = v;
    }

    @Override
    protected Boolean doInBackground() {

          // use mVehicle member here

    }
}

score 0 · Answer 3 · answered Aug 12 '13 at 16:01

0

An Asynctask is just a class like any other, use a constructor, or populate the instantiated object through a setter, public members, etc.

answered Aug 12 '13 at 16:01

Sam Dozor

40,335
6
42
42

AsyncTask passing custom objects

3 Answers3

Linked