Can a post be lost while rotating screen?

Question

Is that possible that when I click the button and then after waiting some time (~5sec) rotate the screen the post may be missed, because the activity didn't manage to re-register in time? I believe that I've managed to produce that. But it was like 1 from 50 tries:)

import android.os.Bundle;
import android.os.Handler;
import android.os.HandlerThread;
import android.util.Log;
import android.widget.Button;
import android.widget.TextView;

import org.greenrobot.eventbus.EventBus;
import org.greenrobot.eventbus.Subscribe;

import butterknife.BindView;
import butterknife.ButterKnife;
import butterknife.OnClick;

public class MainActivity extends BaseActivity {

    @BindView(R.id.post)
    Button mPost;

    @BindView(R.id.result)
    TextView mResult;

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

    @Override
    protected void onStart() {
        super.onStart();
        EventBus.getDefault().register(this);
    }

    @Override
    protected void onStop() {
        super.onStop();
        EventBus.getDefault().unregister(this);
    }

    @OnClick(R.id.post)
    void onPostClick() {

        HandlerThread handlerThread = new HandlerThread("MyThread");
        handlerThread.start();
        Handler handler = new Handler(handlerThread.getLooper());

        handler.post(new Runnable() {
            @Override
            public void run() {
                Log.e(TAG, Thread.currentThread().getName());
                try {
                    Thread.sleep(5000);
                    EventBus.getDefault().post(new MyObject("wow"));
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        });


    }

    @Subscribe(threadMode = ThreadMode.MAIN)
    public void onResult(MyObject object) {
        Log.e(TAG, "POST " + object);
    }

    static class MyObject {
        String val;

        public MyObject(String val) {
            this.val = val;
        }

        @Override
        public String toString() {
            return val;
        }
    }
}

Yes, of course. Because the Activity is restarted. This is the ABC of Android programming. — Phantômaxx, May 10 '16 at 07:39

Marcin Orlowski · Accepted Answer · 2016-07-09T12:32:54.070

There's a chance Activity code miss the event due to recreation, however if this is a problem then you most likely should be posting your events as sticky:

Some events carry information that is of interest after the event is posted. For example, an event signals that some initialization is complete. Or if you have some sensor or location data and you want to hold on the most recent values. Instead of implementing your own caching, you can use sticky events. EventBus keeps the last sticky event of a certain type in memory. The sticky event can be delivered to subscribers or queried explicitly. Thus, you don’t need any special logic to consider already available data.

http://greenrobot.org/eventbus/documentation/configuration/sticky-events/

Also, some suggests moving registration handling from onStart/onStop to onCreate/onDestroy. I think is is bad idea - you usually do not care the events if you are in background, therefore I'd also recommend moving reg/unreg code to onResume/onPause instead.

score 0 · Answer 2 · answered May 10 '16 at 07:37

0

Your Activity gets recreate while you rotate your device. You can set manifest attribute like. android:configChanges="orientation|keyboardHidden|screenSize"

answered May 10 '16 at 07:37

Javed Salat

526
4
10
26

It's a little bit hacky. – Guliash May 10 '16 at 07:46

score 0 · Answer 3 · answered May 10 '16 at 08:45

what you have to do is recreate your activity using onSaveInstanceState() method.

Save Your Activity State

static final String STATE_SCORE = "playerScore";
static final String STATE_LEVEL = "playerLevel";
...

@Override
public void onSaveInstanceState(Bundle savedInstanceState) {
// Save the user's current game state
savedInstanceState.putInt(STATE_SCORE, mCurrentScore);
savedInstanceState.putInt(STATE_LEVEL, mCurrentLevel);

// Always call the superclass so it can save the view hierarchy state
super.onSaveInstanceState(savedInstanceState);
}

Restore Your Activity State

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState); // Always call the superclass first

// Check whether we're recreating a previously destroyed instance
if (savedInstanceState != null) {
    // Restore value of members from saved state
    mCurrentScore = savedInstanceState.getInt(STATE_SCORE);
    mCurrentLevel = savedInstanceState.getInt(STATE_LEVEL);
} else {
    // Probably initialize members with default values for a new instance
}
...
}

score -1 · Answer 4 · answered May 10 '16 at 07:41

-1

You need to subsribe/unsubscribe the listener not in onStart and onStop, but in onCreate and onDestroy resp. Also, post the event in main thread. In this case there won't be the gap and new activity will receive the event if recteated

answered May 10 '16 at 07:41

Oleg Khalidov

5,108
1
28
29

Thanks. I see my mistake. I will add @Subscribe(threadMode = ThreadMode.MAIN). – Guliash May 10 '16 at 07:50

Can a post be lost while rotating screen?

4 Answers4