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);
  }
}