Android 开发工具类 17_setAlarm

Alarm 是在应用程序生命周期之外设置的，所以它们十分适合于调度定时更新或者数据查询，从而避免了在后台持续运行 Service。但触发 Alarm 时，就会广播指定的 Pending Intent。

Alarm 类型：

1、RTC_WAKEUP：在指定的时间唤醒设备，并激活 Pending Intent。

2、RTC：在指定的时间点激活 Pending Intent，但是不会唤醒设备。

3、ELAPSED_REALTIME：根据设备启动之后经过的时间激活 Pending Intent，但是不会唤醒设备。经过的时间包含设备休眠的所有时间。

4、ELAPSED_REALTIME_WAKEUP：在设备启动并经过指定的时间之后唤醒设备和激活 Pending Intent。

 private void setAlarm() {
     /**
      * Listing 9-16: Creating a waking Alarm that triggers in 10 seconds
      */
     // Get a reference to the Alarm Manager
     AlarmManager alarmManager =
      (AlarmManager)getSystemService(Context.ALARM_SERVICE);

     // Set the alarm to wake the device if sleeping.
     int alarmType = AlarmManager.ELAPSED_REALTIME_WAKEUP;

     // Trigger the device in 10 seconds.
     long timeOrLengthofWait = 10000;

     // Create a Pending Intent that will broadcast and action
     String ALARM_ACTION = "ALARM_ACTION";
     Intent intentToFire = new Intent(ALARM_ACTION);
     PendingIntent alarmIntent = PendingIntent.getBroadcast(this, 0,
       intentToFire, 0);

     // Set the alarm
     alarmManager.set(alarmType, timeOrLengthofWait, alarmIntent);

     /**
      * Listing 9-17: Canceling an Alarm
      */
     alarmManager.cancel(alarmIntent);
   }

   private void setInexactRepeatingAlarm() {
     /**
      * Listing 9-18: Setting an inexact repeating alarm
      */
     //Get a reference to the Alarm Manager
     AlarmManager alarmManager =
     (AlarmManager)getSystemService(Context.ALARM_SERVICE);

     //Set the alarm to wake the device if sleeping.
     int alarmType = AlarmManager.ELAPSED_REALTIME_WAKEUP;

     //Schedule the alarm to repeat every half hour.
     long timeOrLengthofWait = AlarmManager.INTERVAL_HALF_HOUR;

     //Create a Pending Intent that will broadcast and action
     String ALARM_ACTION = "ALARM_ACTION";
     Intent intentToFire = new Intent(ALARM_ACTION);
     PendingIntent alarmIntent = PendingIntent.getBroadcast(this, 0,
      intentToFire, 0);

     //Wake up the device to fire an alarm in half an hour, and every
     //half-hour after that.
     alarmManager.setInexactRepeating(alarmType,
                               timeOrLengthofWait,
                               timeOrLengthofWait,
                               alarmIntent);
   }
 }