重新打开应用程序时恢复计时器

Question

I am trying to find a way to start a count-up timer from a particular time (eg 01:34:22). At the moment I have a button which can be tapped to start the timer, but I need the timer to 'continue' when the app is closed.

Therefore I need to find a way to save the start time of the timer, and then resume when the app is reopened using the start time and the current time.

This is the code for the timer:

public abstract class CountUpTimer {
private final long interval;
private long base;

public CountUpTimer(long interval) {
    this.interval = interval;
}

public void start() {
    base = SystemClock.elapsedRealtime();
    handler.sendMessage(handler.obtainMessage(MSG));
}

public void stop() {
    handler.removeMessages(MSG);
}

public void reset() {
    synchronized (this) {
        base = SystemClock.elapsedRealtime();
    }
}

abstract public void onTick(long elapsedTime);

private static final int MSG = 1;

private Handler handler = new Handler() {
    @Override
    public void handleMessage(Message msg) {
        synchronized (CountUpTimer.this) {
            long elapsedTime = SystemClock.elapsedRealtime() - base;
            onTick(elapsedTime);
            sendMessageDelayed(obtainMessage(MSG), interval);
        }
    }
};

}

And this is the code I am using to setup the timer:

    private void setupTimer() {
    timerTextView = (TextView) findViewById(R.id.timerTextView);
    timer = new CountUpTimer(1) {
        @Override
        public void onTick(long elapsedTime) {
            timerCount = elapsedTime;
            String finalTimer = String.format("%02d:%02d:%02d",
                    TimeUnit.MILLISECONDS.toHours(elapsedTime),
                    TimeUnit.MILLISECONDS.toMinutes(elapsedTime),
                    TimeUnit.MILLISECONDS.toSeconds(elapsedTime) - TimeUnit.MINUTES.toSeconds(TimeUnit.MILLISECONDS.toMinutes(elapsedTime))
            );

            timerTextView.setText(finalTimer);
        }
    };

    timer.stop();
}

That's called when the view is created.

And this is the code for when the start button is tapped:

    private void addTimerLister() {
    startTimerButton.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View arg0) {
            timer.start();

            DateTime startTime = DateTime.now();
            long startTimeMilliseconds = startTime.getMillis();

            SharedPreferences sharedPreferences = PreferenceManager.getDefaultSharedPreferences(getApplicationContext());
            SharedPreferences.Editor editor = sharedPreferences.edit();
            editor.putString("attractionTimerName", currentAttraction.name);
            editor.putLong("attractionTimerStart", startTimeMilliseconds);
            editor.putBoolean("attractionTimerRunning", true);
            editor.commit();

            animateFade();
        }
    });
}

As you can see, I've made a start to saving the start time, but I need a way to resume the timer when the app is reopened. I can use JodaTime if necessary.

Anyone have any suggestions?

Answer 1

Use SharedPreferences to store the current time in onPause and retrieve this time in onResume . Remove handler messages in onPause and post message in onResume when you have retrieved the time.

Reset the timer in onPause and reinitialize it in onResume with the retrieved time.

timer = new CountUpTimer(retrievedTime) {
        @Override
        public void onTick(long elapsedTime) {
            timerCount = elapsedTime;
            String finalTimer = String.format("%02d:%02d:%02d",
                    TimeUnit.MILLISECONDS.toHours(elapsedTime),
                    TimeUnit.MILLISECONDS.toMinutes(elapsedTime),
                    TimeUnit.MILLISECONDS.toSeconds(elapsedTime) - TimeUnit.MINUTES.toSeconds(TimeUnit.MILLISECONDS.toMinutes(elapsedTime))
            );

            timerTextView.setText(finalTimer);
        }
    };

If you don't want to reinitialize the timer again, send a message to the handler instead.

   Bundle b = new Bundle();
   b.putLong(YourClass.COUNTER_TIME, retrievedTime); // YourClass.COUNTER_TIME is a public static string
   Message msg = getHandler().obtainMessage(); // Write getHandler() in CountUpTimer
   msg.setData(b);
   mHandler.sendMessage(msg);

and then retrieve it in handleMessage()

@Override
    public void handleMessage(Message msg) {
        synchronized (CountUpTimer.this) {
            long retrievedTime = msg.getData().getLong(YourClass.COUNTER_TIME, 0)
        }
    }

If you want the timer to be running even after the app is closed or the system kills the app, use a service.