Alarm manager triggered immediately

问题:

Hi I am currently working with AlarmManager. I have written a code given below. As per code the AlarmManager should be triggered after 10 Sec, but here in my code the alarm manager triggers immediately. Please help.

public class MainActivity extends Activity {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        AlarmManager alarmManager = (AlarmManager)getSystemService(Context.ALARM_SERVICE);
        int alarmType = AlarmManager.ELAPSED_REALTIME_WAKEUP;
        long timeOrLengthofWait = 10000;
        Intent intentToFire = new Intent(this, AlarmReciever.class);
        PendingIntent alarmIntent = PendingIntent.getBroadcast(this, 0, intentToFire, 0);
        alarmManager.set(alarmType, timeOrLengthofWait, alarmIntent);
    }
}

And My AlarmReciever Class

public class AlarmReciever extends BroadcastReceiver {
    @Override
    public void onReceive(Context context, Intent intent) {

        String phoneNumberReciever="5556";
        String message="Alarm Triggered";
        SmsManager sms = SmsManager.getDefault(); 
        sms.sendTextMessage(phoneNumberReciever, null, message, null, null);
        Toast.makeText(context," A message has been sent", Toast.LENGTH_LONG).show();

        Log.d("Alarm ", "Alarm Has been triggered and sms send");
    }
}

I have Already added required permissions in manifest.

回答1:

You are using an alarm type of ELAPSED_REALTIME_WAKEUP. That means that the second parameter to set() must be the number of milliseconds from now, where now is expressed as SystemClock.elapsedRealtime().

If your goal is to have this occur 10000 milliseconds from the time you make the set() call, that set() call should be:

alarmManager.set(alarmType, SystemClock.elapsedRealtime()+timeOrLengthofWait, alarmIntent);

回答2:

If you are creating PendingIntent of an alarm for past time it will be fired immediately. Example - Schedule alarm for today 8AM but executing code around 11AM will fire immediately.

Solution:

cal.add(Calendar.DATE, 1);

long delay = 24 * 60 * 60 * 1000;
alarmManager.setRepeating(AlarmManager.RTC_WAKEUP, cal.getTimeInMillis(), delay,pendingIntent);` 

This will fire the event on next day at specified time (i.e 8AM);