Timer in Android - how to keep counting even when phone or app is off

Question

I am trying to implement a timer that just counts the time passed since pressed start. I need to keep this counter even if the app/phone is off. How do I achieve this? Store the current time somewhere when the app is turned off, and then retrieve this data when the app is on again? And if this is a good way to do it, how do I implement this solution? I hope someone has some input.

I have implemented my timer/counter using Handler (I saw this solution in an answer here on StackOverflow)

score 2 · Accepted Answer · edited May 23 '17 at 12:14

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One method of doing this would be to save the system Time when the counter begins and then again save the Time when it ends.

You can compare the start time with the end time to find out how much time has passed.

It might look something like this:

Calendar c = Calendar.getInstance();
int startTime = c.get(Calendar.SECOND);

...

Calendar c = Calendar.getInstance();
int endTime = c.get(Calendar.SECOND);

int secondsElapsed = endTime - startTime;

Edit: The main downside of this method is that it does not account for timezone changes or changes to system time. If neither of those concern you, it works fine.

Edit 2: To save the startTime so it isn't lost when the app is closed, use SharedPreferences. An example of storing and retrieving values with SharedPreferences can be seen here.

edited May 23 '17 at 12:14

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answered Aug 14 '15 at 18:01

Alex Crist

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Although this may work, it does not account for timezone changes or user manipulation of the clock, so if that does not concern you then it's good. – Jim Aug 14 '15 at 18:31
@Jim True, I'll add that to my answer. – Alex Crist Aug 14 '15 at 18:32
How would I save the information so that it doesn't get lost each time the app is restarted? – user16655 Aug 14 '15 at 21:36
@user16655 Good question, I'll add that to the answer. – Alex Crist Aug 14 '15 at 21:39

score 1 · Answer 2 · edited May 23 '17 at 12:14

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if you are really worried about the time since "start" was pressed, you need probably need elapsedRealtime - system clock can be manipulated, but even elapsed time is reset with the restart of the phone, so be cautious, but that should do most of what you need.

See this post: Know if uptime timer is reset or Android has been rebooted

edited May 23 '17 at 12:14

Community

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answered Aug 14 '15 at 17:43

Jim

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score 0 · Answer 3 · answered Aug 14 '15 at 17:43

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You should use Alarm Manager. It utilize PendingIntent to send notification to your app's components, for example to BroadcastReceiver where you can process delayed job.

answered Aug 14 '15 at 17:43

Viacheslav

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Timer in Android - how to keep counting even when phone or app is off

3 Answers3