Why alarmmanager not exactly repeats an event android

Question

Please help me. Why does AlarmManager not exactly repeats an event when the repetition period of more than one day?

Here is my code to run AlarmManager. The variable time_period contains the following value 60*1000*60*24*7 which is equal to 7 days. In the end, if I change the date on your phone, the event is triggered by 6-4-7-7-7-7 days.

This can be seen in the logs of the application (See link http://prntscr.com/7kdqbw ) Thanks in advance for your reply.

Intent notification = new Intent(this , ServiceReminders.class);     
notification.putExtra("backup", "backup");
AlarmManager alarmManagerBackup = (AlarmManager)getSystemService(ALARM_SERVICE);
PendingIntent pibackup = PendingIntent.getService(this, 3, notification, 10);

if (sdkVersion < 19) {
    alarmManagerBackup.setRepeating(AlarmManager.RTC_WAKEUP, 0, time_period, pibackup);
}
else if (sdkVersion >= 19) {
    alarmManagerBackup.setInexactRepeating(AlarmManager.RTC_WAKEUP, 0, time_period, pibackup);
}

Log.d("ServiceManagerNotification", "AlarmBackup sdkVersion = "+sdkVersion);

Answer 1

You are explicitly leveraging the inexact alarms by calling setInexactRepeating(). Unsurprisingly, this results in your alarms being set at inexact intervals.

The problem is further compounded by the fact that you are supplying a custom period. If you do not use one of the pre-defined intervals, then the framework will simply call setRepeating() using your interval instead of using setInexactRepeating().

From the documentation for the intervalMillis parameter:

interval in milliseconds between subsequent repeats of the alarm. Prior to API 19, if this is one of INTERVAL_FIFTEEN_MINUTES, INTERVAL_HALF_HOUR, INTERVAL_HOUR, INTERVAL_HALF_DAY, or INTERVAL_DAY then the alarm will be phase-aligned with other alarms to reduce the number of wakeups. Otherwise, the alarm will be set as though the application had called setRepeating(int, long, long, PendingIntent). As of API 19, all repeating alarms will be inexact and subject to batching with other alarms regardless of their stated repeat interval.

In the end, regardless of how you set this alarm, it will be inexact if you set it as a repeating alarm and there isn't a whole lot you can do about it.

If you need more precision, you should use either setWindow() or setExact() and set the next alarm every time your alarm triggers. Although if you are only performing an action once a week, it is likely that in the end you don't need that precision.