Schedule TextView update

Question

In my application in every activity at the top I have a fragment with TextView showing the current event that is taking place. It looks something like this:

--------------------
|    Event name    |
|------------------|
|                  |
|                  |
|                  |
|     Activity     |
|     content      |
|                  |
|                  |
|                  |
|                  |
|                  |
--------------------

I want to update the event name when the next event starts. I'm using singleton pattern and in my Application I have the currentEvent string that I show at every activity start. I keep the events in database and every event has start time. What is the best way to update the event name. How can I schedule event that will update the text view based on the start time for the next event?

Answer 1

I did it something like @Jeffrey said but with some changes:

• In the Application class, in onCreate() I get the current and the next event and create the handler just like @Jeffrey said, but in the run() of the handler's Runnable I send a broadcast.

• I register a BroadcastReceiver with the same IntentFilter in each CurrentEvent fragment. And in the onReceive() method of the receiver I update the TextView.

Answer 2

I think something like this should work. The AsyncTask gets the current event name and next event start time from the database. When it found those, the current event name is set, and a runnable is posted, and executed when the next event starts. At that point you obtain that event name again and set it, and post a new delayed runnable. This way, the current event name is set when the fragment is created, or when it starts while the user has the fragment is open.

Note that you do not want to use the AlarmManager for this. From the documentation:

The Alarm Manager is intended for cases where you want to have your application code run at a specific time, even if your application is not currently running. For normal timing operations (ticks, timeouts, etc) it is easier and much more efficient to use Handler.

Also note that I did not test this code thoroughly, so there might be some issues when the activity gets killed etc. This example seems to work though, as it shows a Toast message every 10 seconds.

public class MyFragment extends Fragment implements Runnable {

    TextView currentEventTextView;
    Handler handler;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        handler = new Handler();
    }

    @Override
    public void onStart() {
        super.onStart();
        new GetEventTask().execute();
    }

    @Override
    public void onStop() {
        handler.removeCallbacks(this);
        super.onStop();
    }

    @Override
    public void run() {
        // next event is starting, so obtain it
        new GetEventTask().execute();
    }

    private class GetEventTask extends AsyncTask<Void, Void, Event>{
        @Override
        protected Event doInBackground(Void... params) {
            try {
                Thread.sleep(1000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }

            // TODO get current name and next start time from db
            Event event = new Event();
            event.name = "Google I/O " + System.currentTimeMillis();
            event.nextStartTime = System.currentTimeMillis() + 10000;

            return event;
        }

        @Override
        protected void onPostExecute(Event event) {
            currentEventTextView.setText(event.name);
            handler.postDelayed(MyFragment.this, event.nextStartTime - System.currentTimeMillis());
        }
    }


    private class Event {
        public String name;
        public long nextStartTime;
    }
}