AlarmManager设置两次警报，而不是更新当前警报

Question

am setting an alarm at midnight and sometimes I set alarm again with the same id so why does alarm manager create another alarm instead of updating the present. I end up with 2 alarms instead 1. how can I change that so if this code executes while a current alarm is present it will update it instead creating a duplicate

    Intent intent = new Intent(con,MyReceiver.class);
    intent.setAction("ACTIVATE_MIDNIGHT_SERVICE");
    PendingIntent pendingIntent =  PendingIntent.getBroadcast(
            con, -1, intent, PendingIntent.FLAG_CANCEL_CURRENT);
    Date d = new Date();
    d.setDate(d.getDate()+1);
    d.setHours(0);
    d.setMinutes(0);
    d.setSeconds(0);  
    alarm.setRepeating(AlarmManager.RTC_WAKEUP, d.getTime(),AlarmManager.INTERVAL_DAY, pendingIntent);

Answer 1

I just had to deal with this same problem this week. At it's basic, the AlarmManager does 2 things: 1. sets a wake up reminder in the system's memory, so the device will wake up and perform a task, and 2. calls your app (via intent) to perform a task at a specific time.

With that being said, when you set up an Alarm you need to specify both parts, when you want the alarm to go off (via setRepeating ), and what to do (via Intent )

Notice that there is no indication in the setRepeating call to let the alarm manager know what to do if this call already exists, that is because you are allowed to create as many alarms as you need. PendingIntent.FLAG_CANCEL_CURRENT only tells the system what to do in case that the previous Intent is still active. Instead you need to cancel your existing alarm and set a new one. You do that by setting the request code to something distinct (ie a positive integer) and then cancelling when you set a new alarm

Intent intent = new Intent(con,MyReceiver.class);
intent.setAction("ACTIVATE_MIDNIGHT_SERVICE");
PendingIntent pendingIntent =  PendingIntent.getBroadcast(
            con, 300, intent, PendingIntent.FLAG_CANCEL_CURRENT);
Date d = new Date();
d.setDate(d.getDate()+1);
d.setHours(0);
d.setMinutes(0);
d.setSeconds(0);  

// This will cancel the existing alarm
alarm.cancel(pendingIntent);

alarm.setRepeating(AlarmManager.RTC_WAKEUP, d.getTime(),AlarmManager.INTERVAL_DAY, pendingIntent);

Answer 2

更换PendingIntent.FLAG_CANCEL_CURRENT与PendingIntent.FLAG_UPDATE_CURRENT创建时PendingIntent 。