Question

The following is a stripped down version of a Fragment I’m using to display a simple stopwatch. The app is working perfectly on a tablet. However, on a phone, where an orientation change will cause the fragment to be re-created in a new activity, I’m getting a memory leak.

public class TimerFragment extends BaseFragment {

    private static final int MESSAGE_UPDATE_TEXT = 0;

    private TextView text;

    private static final String KEY_START_TIME = "KEY_START_TIME";
    private static final String KEY_ELAPSED_TIME = "KEY_ELAPSED";

    private long startTime;
    private long elapsedTime;

    private static boolean running;

    private final TimerHandler handler = new TimerHandler(this);

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {     
        setHasOptionsMenu(true);
        setUpHomeButton(false);

        View view = inflater.inflate(R.layout.fragment_timer, container, false);

        text = (TextView) view.findViewById(R.id.timerText);

        if(savedInstanceState != null) {
            startTime = savedInstanceState.getLong(KEY_START_TIME);
            elapsedTime = savedInstanceState.getLong(KEY_ELAPSED_TIME);
        }

        if(running) {
            handler.removeCallbacks(timer);
            handler.postDelayed(timer, 0);
        }

        updateText();

        return view;
    }

    private void updateText() {
        if(elapsedTime == 0L) {
            text.setText("0:00");
            return;
        }

        int sec = (int) (elapsedTime / 1000);
        int min = sec / 60;
        sec = sec % 60;

        text.setText(min + ":" + sec);

    }

    @Override
    public void onSaveInstanceState(Bundle outState) {
        super.onSaveInstanceState(outState);

        handler.removeCallbacks(timer);

        outState.putLong(KEY_START_TIME, startTime);
        outState.putLong(KEY_ELAPSED_TIME, elapsedTime);
    }

    private final Runnable timer = new Runnable() {

        @Override
        public void run() {
            long now = System.currentTimeMillis();
            elapsedTime = now - startTime;

            running = true;
            handler.postDelayed(this, 1000);
            handler.sendEmptyMessage(MESSAGE_UPDATE_TEXT);
        }
    };

    private static class TimerHandler extends Handler {
        private final WeakReference<TimerFragment> weakFragment;

        public TimerHandler(TimerFragment f) {
            weakFragment = new WeakReference<TimerFragment>(f);
        }

        @Override
        public void handleMessage(Message msg) {
            TimerFragment fragment = weakFragment.get();
            switch (msg.what) {
            case MESSAGE_UPDATE_TEXT:
                if(fragment != null) {
                    fragment.updateText();
                }
                break;

            default:
                break;
            }

        }
    }
}

Eclipse MAT even gives me this:

One instance of "android.os.MessageQueue" loaded by "<system class loader>" occupies 1     529 600 (14,19%) bytes. The memory is accumulated in one instance of "android.os.Message"     loaded by "<system class loader>".

Keywords
android.os.Message
android.os.MessageQueue

However, the above does not appear when I analyze memory when running on a tablet (single activity at all times).

Any ideas for how to fix this? If I understand the problem correctly, which I might not, I think there are multiple handlers getting created when an orientation change happens on a phone.

If my problem is hard to understand give me a hint and I will try to explain better.

Answer 1

There is a simple rule you should always follow when using Handler. Every time you write handler.postDelayed you should also write handler.removeCallbacks somewhere.

In your case you are calling handler.postDelayed(timer, 0) in onCreateView method so onDestroyView is the most appropriate place to call handler.removeCallbacks(timer)