I have an android app where I try to set an alarm. My code inside activity:

fun setAlarm() {
    alarmManager = getSystemService(Context.ALARM_SERVICE) as AlarmManager
    val intent = Intent(this, NotificationReceiver::class.java)
    pendingIntent = PendingIntent.getBroadcast(this, 0, intent, PendingIntent.FLAG_IMMUTABLE)

    alarmManager!!.set(AlarmManager.RTC_WAKEUP, /*calculateAlarmTime()*/1, pendingIntent)

    Timber.i("setAlarm executed")
}

I set this alarm, calling setAlarm method. This is my NotificationReceiver class:

public class NotificationReceiver extends BroadcastReceiver {

    @Override
    public void onReceive(Context context, Intent intent) {
        Timber.i("onReceive called");
    }
}

Why I have only "setAlarm executed" in logcat, and not "onReceive called"? I set alarm to 1 millisecond and it should trigger immeditately. Why nothing happens?

CodePudding user response：

You set the AlarmManager with RTC_WAKEUP, so you should supply the exact date and time. Instead you set the time to 1 ms, which is interpreted as 1ms after 1-1-1970, 00h00m00s. If you want to use an relative time from setting the alarmManager you should get the current RTC time, add a few seconds and set the alarmManager with that time. As this method is inexact, allow a few seconds leeway. See here for description RTC_WAKEUP

CodePudding user response：

Your second parameter is wrong. It isn't how long from now you want the alarm to occur, it's the Unix timestamp of when you want it to occur. So 1 would have happened back in 1970. You would need to, at minimum, go System.currentTimeMillis() 1. Although that may well cause race conditions, I wouldn't count on an alarm being set for less than a second in the future working.