getApplicationContext in AsyncTask class?

Question

I have a couple private AsyncTask methods that I'd like to break out into public external classes. In my application, I have a public class extending Application which holds some shared routines I want to access from different parts of my application. When I break out the AsyncTask class however, I'm no longer able to call getApplicationContext() to get a reference to my application library (the class does not inherit anything from Activity now). getBaseContext() will have problems as well. Should I be passing a context into the AsyncTask when it gets instantiated and build from there? Not sure if that was safe or not.

import java.util.ArrayList;
import android.os.AsyncTask;

public class DlTask extends AsyncTask
{
    long totalbytes = 0;
    long totalread = 0;
    ArrayList <String> data;

    @Override
    protected void onPreExecute ()
    {   
        AppLib lib = (AppLib) getApplicationContext();

        lib.saveStatusText ("Contacting " + lib.getServerAddress () + ":" + lib.getServerPort () + "...");
       super.onPreExecute ();
    }

      @Override
      protected Object doInBackground (Object... params)
      {
        data = lib.sendCommand (CMD_LIST);
         return true;
      }

      @Override
      protected void onPostExecute (Object result)
      {

         if (data != null)
         {
                    lib.saveStatusText (data.size () + " files found");
         }
         else
         {
            Log.d (TAG, "data is null");
            Toast.makeText (getBaseContext(), msg, Toast.LENGTH_SHORT).show ();                     
         }

         super.onPostExecute(result);
      }

}

Passing context in the constructor is not preferred as it leaks context object. [https://stackoverflow.com/questions/46797916/this-field-leaks-a-context-object] — Niaz Ahsan, Sep 20 '18 at 09:58

score 13 · Accepted Answer · answered Mar 07 '13 at 18:25

13

Should I be passing a context into the AsyncTask when it gets instantiated and build from there?

You do not have a choice, as you will be unable to get a Context by any other means.

answered Mar 07 '13 at 18:25

CommonsWare

986,068
189
2,389
2,491

Can you elaborate @CommonsWare ? Why does `getApplicationContext()` not work from the UI portions of `AsyncTask` ? (ex: `onPreExecute()` or `onPostExecute()`) This link 'suggests' it can work, But my reality shows it will not compile (Sdk 8 -- 17); http://www.daniweb.com/software-development/mobile-development/threads/449375/how-to-get-context-in-asynctask – donfede Apr 21 '13 at 17:10
2

@donfede: " Why does getApplicationContext() not work from the UI portions of AsyncTask ?" -- because `getApplicationContext()` is a method on `Context`, and `AsyncTask` does not inherit from `Context`. – CommonsWare Apr 21 '13 at 17:22
3

won't this cause a leak if the activity is destroyed before the asynctask finishes? – MikeIsrael Dec 19 '13 at 12:29
2

@MikeIsrael: For the duration of the task, yes. `AsyncTask` is designed for short operations. Anything that would take longer than a second or so should be handled by some other means, such as an `IntentService`. – CommonsWare Dec 19 '13 at 12:31
@CommonsWare thanks, as always the concise but precise answers are appreciated. – MikeIsrael Dec 19 '13 at 14:31

score 1 · Answer 2 · edited Oct 27 '17 at 09:14

You should do like this. In my case it works:

public class DlTask extends AsyncTask {
     private Context context;

     public DlTask(Context context) { this.context = context; }

     @Override
     protected void onPreExecute() {
         super.onPreExecute();
         ..........
     }

     @Override
     protected Object doInBackground (Object... params)
     {
        data = lib.sendCommand (CMD_LIST);

        return true;
     }

     @Override
     protected void onPostExecute (Object result)
     {

        if (data != null)
     {
         lib.saveStatusText (data.size () + " files found");
     }
     else
     {
        Log.d (TAG, "data is null");
        Toast.makeText (context, msg, Toast.LENGTH_SHORT).show ();              
        //You can use the CONTEXT like this (passing the context variable like parameter
     }

     super.onPostExecute(result);
  }

score 0 · Answer 3 · answered Mar 07 '13 at 18:26

0

Either pass a Context in the constructor of your AsyncTask, or use a static variable in your Application class to access it (set sMyInstace = this;). The first solution is preferable though.

answered Mar 07 '13 at 18:26

SimonSays

10,867
7
44
59

getApplicationContext in AsyncTask class?

3 Answers3

Linked