用AlarmManager设置的闹铃取消不了

Question

删除闹铃代码如下：
Intent intent = new Intent(deleteAlarmFromDatabase.this,AlarmReceiver.class);
PendingIntent pendingIntent = PendingIntent.getBroadcast(deleteAlarmFromDatabase.this, id, intent, 0);
//获取闹钟管理器
AlarmManager alarmManager = (AlarmManager)getSystemService(ALARM_SERVICE);
alarmManager.cancel(pendingIntent);

                    取消不了，为什么？？