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Editorial Team
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Asked: 2026-06-05T14:50:46+00:00

I have an app which allows users to schedule alarms to sound at certain

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I have an app which allows users to schedule alarms to sound at certain times, repeating at intervals of their choosing. I am using JSON to persist the alarm details, using SharedPreferences as storage.

I am using AlarmManager to schedule when my app should be notified that an alarm should sound to notify the user. I am currently using the setRepeating() method of AlarmManager, supplying the interval provided by the user. This works well, and in theory the app would never need to update the JSon which stores the next alarm time, as AlarmManager will just reschedule the next alarm time using the interval.

However, my thinking is that when the device is rebooted, I will need to supply a up to date alarm time to AlarmManager to avoid AlarmManager thinking an alarm has been missed as this is not necessarily the case.

So, what’s the best way to do this?

  • update the JSon next alarm time when the alarm is sounded, even though this may not be necessary (setRepeating() handles this as long as there is no reboot)?
  • register for and listen for shutdown broadcasts and update JSon then (this raises questions – just how long will the app get to calculate and write alarm details to storage given that the phone is shutting down)?
  • don’t update the JSon but add logic to the object which is woken by the AlarmManager to decide if the alarm just broadcast is valid and the user should be alerted?

I’m sure any of the above will work, but I can’t decide which is the nicest way to do it.

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1 Answer

  1. Editorial Team

    This seems mostly a matter of choice. The problem you note parallels a general problem seen in Linux laptops and solved by anachrond. In my opinion, I would simply update the time and store it in SharedPreferences every time the event is received. Trying to listen for when the system shuts down might not be entirely reliable (what happens when your users — probably drunk college students — drop their device and the battery flies out?). Instead, I believe the best thing to do in this scenario would be to — each time the alarm fires — recalculate the time to send the next one, store it somewhere, and upon boot schedule appropriately.

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