Develop Reference

How far (and why!) do Android alarms execute in the past?

I have had several frustrations with setting alarms in Android. I have tried setting repeating/non-repeating alarms and exact/inexact alarms but it does not matter, if the alarm is ever set for a time in the past, it executes as soon as it is set. I have tested this as far back as setting an alarm for 5 hours in the past and is still executes immediately.
For example:
The time is 7 AM and I set an alarm to execute at 2 AM. This is obviously meant for the next time the clock reads 2:00 AM but it does not matter, the alarm goes off at 7 AM, right after it is set.
The code below should select a random time between 1:00 AM and 3:59 AM to set/execute the alarm for the next calendar day and then the logic circles back around to set itself again after execution. The alarm will execute repeatedly, forever.
int randomHour = new Random().nextInt((3 - 1) + 1) + 1;
int randomMinute = new Random().nextInt((59 - 1) + 1) + 1;
Calendar calendar = Calendar.getInstance();
calendar.setTimeInMillis(System.currentTimeMillis());
calendar.set(Calendar.HOUR_OF_DAY, randomHour);
calendar.set(Calendar.MINUTE, randomMinute);
calendar.set(Calendar.SECOND, 0);
calendar.add(Calendar.DAY_OF_MONTH, 1);
alarmManager.setExact(AlarmManager.RTC_WAKEUP, calendar.getTimeInMillis(), pendingIntent);
Questions:
At what point does Android stop executing alarms in the past?
Is there any way to stop this?

"This is obviously meant for the next time" Does not work for computers, they will do exactly what you tell them to do.
calendar.getTimeInMillis() returns the number of milliseconds since January 1, 1970 at 00:00:00 GMT. You need to specify not just the time but also the date that you want the alarm to go off. Instead you are always calling calendar.add(Calendar.DAY_OF_MONTH, 1); (the first day of the current month)

Alarm goes off too early in android

I want to set alarm for a specific time, I tried the code below. The problem is, most of the time alarm goes off within 10 seconds. I tried getting value of time in a toast and that seems to be perfectly fine.
Calendar cur_cal = new GregorianCalendar();
cur_cal.setTimeInMillis(System.currentTimeMillis());//set the current time and date for this calendar
Calendar cal = new GregorianCalendar();
cal.add(Calendar.DAY_OF_YEAR, cur_cal.get(Calendar.DAY_OF_YEAR));
cal.set(Calendar.HOUR_OF_DAY, 1);
cal.set(Calendar.MINUTE, 54);
cal.set(Calendar.SECOND, 0);
cal.set(Calendar.MILLISECOND, 0);
cal.set(Calendar.DATE, cur_cal.get(Calendar.DATE));
cal.set(Calendar.MONTH, cur_cal.get(Calendar.MONTH));
long futureInMillis = SystemClock.elapsedRealtime() + delay;
long time = cal.getTimeInMillis()-(System.currentTimeMillis());
AlarmManager alarmManager = (AlarmManager) context.getSystemService(Context.ALARM_SERVICE);
alarmManager.setRepeating(AlarmManager.ELAPSED_REALTIME_WAKEUP, time, (1000*60*60*24) , pendingIntent);
Toast.makeText(context, "alarm set for" + time, Toast.LENGTH_SHORT).show();
I also tried,
alarmManager.set(AlarmManager.ELAPSED_REALTIME_WAKEUP, time, pendingIntent);
also,
alarmManager.setRepeating(AlarmManager.RTC_WAKEUP, cal.getTimeInMillis(), 24*60*60*1000, pendingIntent);
and,
alarmManager.set(AlarmManager.RTC_WAKEUP, cal.getTimeInMillis(), pendingIntent);

As I understand your question("I want to set alarm for a specific time"), you want the alarm to sound at--lets say 10 AM tomorrow. However, your code seems to be in contradiction to this statement, because you are calculating a time difference:
long time = cal.getTimeInMillis()-(System.currentTimeMillis());
You may also be experiencing an issue the AlarmManager has by with the setRepeating() method. The Android documentation says:
Note: as of API 19, all repeating alarms are inexact. If your
application needs precise delivery times then it must use one-time
exact alarms, rescheduling each time as described above. Legacy
applications whose targetSdkVersion is earlier than API 19 will
continue to have all of their alarms, including repeating alarms,
treated as exact.
So, if you do want to set an alarm for a specific time (and not a time difference) just try this:
long time = cal.getTimeInMillis();
You might also consider changing to the setExact() method and creating code to repeat as needed (there are examples on the Internet).
Link to Android documentation:
https://developer.android.com/reference/android/app/AlarmManager.html#setRepeating(int,%20long,%20long,%20android.app.PendingIntent)

AlarmsManager triggers whenever it wants

I want to trigger a notification each day at a specific time choosen by the user, like 6' / 7' / 8'.
For this, I created a WakefulBroadcastReceiver, that pass to an IntentService to create the notification.
And this is how I setup my AlarmsManager. timeInHours is an integer passed as parameter, between 6 and 12 :
Intent i = new Intent(context, StepCountNotifyBroadcast.class);
PendingIntent pi = PendingIntent.getBroadcast(context, 0, i, 0);
// Get the next day at timeInHours hours'.
Calendar cal = Calendar.getInstance();
cal.setTime(new Date()); // compute start of the day for the timestamp
cal.set(Calendar.HOUR_OF_DAY, timeInHours);
cal.set(Calendar.MINUTE, 0);
cal.set(Calendar.SECOND, 0);
cal.set(Calendar.MILLISECOND, 0);
cal.set(Calendar.AM_PM, Calendar.AM);
if (new Date().getTime() > cal.getTime().getTime())
cal.add(Calendar.DAY_OF_YEAR, 1);
long nextDay = cal.getTime().getTime();
// Setup the alarm.
long timeBetween = AlarmManager.INTERVAL_DAY; // Each day.
AlarmManager alarms = (AlarmManager) context.getSystemService(Context.ALARM_SERVICE);
alarms.cancel(pi);
alarms.setRepeating(AlarmManager.RTC_WAKEUP, nextDay, timeBetween, pi);
Date nextDayAsDate = new Date(nextDay);
GLog.d("AlarmUtils", "scheduleNotifiation for next date: " + nextDayAsDate.toString());
It works well 50% of the time, but still do crazy things like... Trigger the notification at 2:00 AM ?!
I know the system will not trigger the notification at the specific time I want and this is ok. But here we talk about approximately 18 hours later.
In logs, it seems that my IntentService code is effectively running in the middle of the night in some cases. So that's not an issue with the notification itself.
I can switch this line :
alarms.setRepeating(AlarmManager.RTC_WAKEUP, nextDay, timeBetween, pi);
to another line of code :
alarms.setExact(AlarmManager.RTC_WAKEUP, nextDay, pi);
But this is not good for the battery life I'm afraid.
Now my questions :
Can somebody tell me a reason about the way Android devices works with AlarmsManager ?
Do you find another solution than will not drain battery life and be sure the notification will be triggered in maximum 2 or 3 hours later?
Do you have any ideas, in this particular case, to debug and do code testing without waiting a day or two to detect issues?
Thanks in advance.

After API Level 23, Doze mode was introduced on the Android System to reduce battery consumption. Go through below link:
How to make Alarm Manager work when Android 6.0 in Doze mode?

Setting Notification using AlarmManager by passing calendar.getTimeInMillis(),triggers notification instantly not at the time intended

I have followed the following link https://developer.android.com/training/scheduling/alarms.html.
RTC examples first one, to set an alarm for a specific time on all days. Even after following the same code, the alarm is not triggered at the time it is suppose to get triggered. Instead the notification gets triggered immediately after setting the time which is done with the help of a time picker. Following is my code snippet,
AlarmManager alarmMgr = (AlarmManager) getSystemService(Context.ALARM_SERVICE);
Intent intent = new Intent(this, NotificationReceiver.class);
PendingIntent intentalarm = PendingIntent.getBroadcast(this, 1, intent, PendingIntent.FLAG_UPDATE_CURRENT);
Calendar calendar = Calendar.getInstance();
calendar.setTimeInMillis(System.currentTimeMillis());
calendar.set(Calendar.HOUR_OF_DAY,4);
calendar.set(Calendar.MINUTE, 30);
alarmMgr.setRepeating(AlarmManager.RTC_WAKEUP, calendar.getTimeInMillis(), AlarmManager.INTERVAL_DAY, intentalarm);
Instead of setRepeating I also tried setInexactRepeating but there was no luck.I would also like to add that when I changed the
calendar.getTimeInMillis() and used SystemClock.elapsedRealtime() + 120 * 1000 the alarm triggered exactly after 2 minutes from the time it was set.
But when calendar.getTimeInMillis() is being used the intended working does not happen instead immediate triggering occurs.
Would be indeed very helpful if anyone can help me out find a solution.Only for a note, I could learn if alarm is set before current device time the alarm would be triggered immediately but that is not the case here.
NotificationReceiver.class is working fine as it is generated and appears on the title. But the time it appears is the cause of concern.

You are using both setTimeInMillis and hourofday and minute.
If you want your alarm to be triggered at 4:30 just add hourofday and minute.
Calendar calendar = Calendar.getInstance();
calendar.set(Calendar.HOUR_OF_DAY,4);
calendar.set(Calendar.MINUTE, 30);`

I could Identify the issue I was facing. I was using a TimePicker with 24 hour format. But I used SimpleDateFormat "hh:mm". What 'h' stands for is as follows "h->Hour in am/pm (1-12) ". So any alarm that I set at AM triggers correctly. When I set a time at PM since I had used 1-12 'h' format, alarm gets set for a AM time and since that time is already passed when compared to the device time the alarm/notification got triggered immediately.The right format to use was "HH:MM" where 'H' stands for "H->Hour in day (0-23)". This resolved my issue.
Checking the TimeinMillis on online epoch time converter helped me identify this issue.Once again thanks for helping me.

android-can't run a code one a day

This is a code that i'm using for running a service once a day .
the problem is this , after 24h , the service keeps calling every 10 to 15 min .
Intent myIntent = new Intent(this, MyService.class);
pendingIntent = PendingIntent.getService(this, 0, myIntent, 0);
AlarmManager alarmManager = (AlarmManager) getSystemService(ALARM_SERVICE);
Calendar calendar = Calendar.getInstance();
calendar.setTimeInMillis(System.currentTimeMillis());
calendar.add(Calendar.HOUR, 24);
alarmManager.setRepeating(AlarmManager.RTC_WAKEUP,calendar.getTimeInMillis(), 86400, pendingIntent);
I think I'm using a bad code .Could you give me a better code for runnig a service once or twice a day
thanks you

The interval parameter to setRepeating represents millis. It should be 86400000 to get it right.
You are now programming an alarm to start first execution 24h past the current time, but with a period of 86400 millis (less than two minutes).
Morale of the story:
Always read the docs before using an API.
Use AlarmManager.INTERVAL_DAY instead of your own magic numbers