Android重复闹钟无效

Question

This works fine:

Intent intent = new Intent(HelloAndroid2.this, AlarmReceiver.class);

    PendingIntent pendingIntent = PendingIntent.getBroadcast(HelloAndroid2.this, 0,
    intent, PendingIntent.FLAG_ONE_SHOT);

    AlarmManager alarmManager = (AlarmManager) getSystemService(ALARM_SERVICE);
    alarmManager.set(AlarmManager.RTC_WAKEUP, System.currentTimeMillis() + (12 * 1000), pendingIntent);

This doesn't work. I hear the alarm only time.

alarmManager.setRepeating(AlarmManager.RTC_WAKEUP, System.currentTimeMillis() + (12 * 1000), 3 * 1000, pendingIntent);

I have also tried this, no luck:

Calendar calendar = Calendar.getInstance();
    calendar.setTimeInMillis(System.currentTimeMillis());
    calendar.add(Calendar.SECOND, 5);

    alarmManager.setRepeating(AlarmManager.RTC_WAKEUP, calendar.getTimeInMillis(), 7000, pendingIntent);

What is the problem?

Answer 1

From the PendingIntent doc for FLAG_ONE_SHOT:

this PendingIntent can only be used once. If set, after send() is called on it, it will be automatically canceled for you and any future attempt to send through it will fail.

So after the pendingIntent is fired the first time, it will be cancelled and the next attempt to send it via the alarm manager will fail

Try using FLAG_UPDATE_CURRENT

Answer 2

Looking at your code samples in order:

In your first sample you are using AlarmManager.set - this is strictly for one-off alarms so yes, it will only fire once. If you want to use AlarmManager.set then the last thing the code triggered should do is to set a fresh alarm (which should also use a fresh PendingIntent).

In your second example you are using a repeating alarm. You do not need to create a fresh PendingIntent each time this fires as the OS takes care of the repeating aspect of the alarm.

There is no reason why your alarm should not repeat every 3 seconds, so I would start looking at the BroadcastReceiver implementation you have written to handle the alarm.

Check that you've implemented it properly. Comment out all the code in the onReceive() method and instead just have it writing a log message. Once you see your log message appearing in the logcat every time the alarm fires, add your code back in (keeping the log message), and another log message to the end of the method. This allows you to see how long the method takes to execute - you want it to be finished before the alarm fires again to avoid any unexpected side effects.

As an aside, if you want a repeating alarm, android.os.Handler is a much more efficient approach although alarms set through AlarmManager do fire very accurately.