Android timer updating a textview (UI)

Question

I'm using a timer to create a stop watch. The timer works by increasing a integer value. I want to then display this value in the activity by constantly updating a textview.

Here's my code from the service where I try and update the activity's textview:

protected static void startTimer() {
    isTimerRunning = true; 
    timer.scheduleAtFixedRate(new TimerTask() {
        public void run() {
            elapsedTime += 1; //increase every sec
            StopWatch.time.setText(formatIntoHHMMSS(elapsedTime)); //this is the textview
        }
    }, 0, 1000);
}

I got some kind of error about updating the UI in the wrong thread.

How can I adapt my code to accomplish this task of constantly updating the textview?

Answer 1

protected static void startTimer() {
    isTimerRunning = true; 
    timer.scheduleAtFixedRate(new TimerTask() {
        public void run() {
            elapsedTime += 1; //increase every sec
            mHandler.obtainMessage(1).sendToTarget();
        }
    }, 0, 1000);
}

public Handler mHandler = new Handler() {
    public void handleMessage(Message msg) {
        StopWatch.time.setText(formatIntoHHMMSS(elapsedTime)); //this is the textview
    }
};

Above code will work...

Note: Handlers must be created in your main thread so that you can modify UI content.

Answer 2

You should use Handler instead to update UI every X seconds. Here is another question that show an example: Repeat a task with a time delay?

Your approach doesn't work because you are trying to update UI from non-UI thread. This is not allowed.

Answer 3

StopWatch.time.post(new Runnable() {
    StopWatch.time.setText(formatIntoHHMMSS(elapsedTime));
});

this code block is based on Handler but you don't need to create your own Handler instance.

Answer 4

TimerTask implements Runnable, which would make it a thread. You can not update the main UI thread directly from a different thread without some work. One thing you could do is use Async Task to create the timer and publish an update every second that will update the UI.

Answer 5

I'm assuming StopWatch.time is some static or public reference to your TextView. Instead of doing this, you should implement a BroadcastReceiver to communicate between your timer (which runs from a separate thread) and your TextView.

Answer 6

You can use the following utility :

/**
 * Created by Ofek on 19/08/2015.
 */
public class TaskScheduler extends Handler {
    private ArrayMap<Runnable,Runnable> tasks = new ArrayMap<>();
    public void scheduleAtFixedRate(final Runnable task,long delay,final long period) {
        Runnable runnable = new Runnable() {
            @Override
            public void run() {
                task.run();
                postDelayed(this, period);
            }
        };
        tasks.put(task, runnable);
        postDelayed(runnable, delay);
    }
    public void scheduleAtFixedRate(final Runnable task,final long period) {
        Runnable runnable = new Runnable() {
            @Override
            public void run() {
                task.run();
                postDelayed(this, period);
            }
        };
        tasks.put(task, runnable);
        runnable.run();
    }
    public void stop(Runnable task) {
        Runnable removed = tasks.remove(task);
        if (removed!=null) removeCallbacks(removed);
    }

}

Then anywhere in code that runs by the UI Thread you can use it simply like this:

TaskScheduler timer = new TaskScheduler();
        timer.scheduleAtFixedRate(new Runnable() {
            @Override
            public void run() {
                time.setText(simpleDateFormat.format(GamePlay.instance().getLevelTime()));
            }
        },1000);

Answer 7

you can use Handler.

this code increase a counter every one second and show and update counter value on a textView.

public class MainActivity extends Activity {


    private Handler handler = new Handler();
    private TextView textView;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        textView = (TextView) findViewById(R.id.text);
        startTimer();
    }


    int i = 0;
    Runnable runnable = new Runnable() {
        @Override
        public void run() {
            i++;
            textView.setText("counter:" + i);
            startTimer();
        }
    };

    public void startTimer() {
        handler.postDelayed(runnable, 1000);
    }

    public void cancelTimer() {
        handler.removeCallbacks(runnable);
    }

    @Override
    protected void onStop() {
        super.onStop();
        handler.removeCallbacks(runnable);
    }
}