Android -如何设置特定日期前X天的闹钟

Question

我已经看过很多关于创建AlarmManager和在特定日期弹出通知的教程，但我想知道如何在X天前做到这一点。

例如，如果我在2014年1月8日有一个活动，我想将其提前一周设置为2014年1月1日，我只需将闹钟设置为：

Calendar calendar = Calendar.getInstance();

calendar.set(Calendar.MONTH, 1);
calendar.set(Calendar.YEAR, 2013);
calendar.set(Calendar.DAY_OF_MONTH, Day-7);

calendar.set(Calendar.HOUR_OF_DAY, 0);
calendar.set(Calendar.MINUTE, 0);
calendar.set(Calendar.SECOND, 0);
calendar.set(Calendar.AM_PM,Calendar.AM);

Intent myIntent = new Intent(MainActivity.this, MyReceiver.class);
pendingIntent = PendingIntent.getBroadcast(MainActivity.this, 0, myIntent, 0);

AlarmManager alarmManager = (AlarmManager)getSystemService(ALARM_SERVICE);
alarmManager.set(AlarmManager.RTC_WAKEUP, calendar.getTimeInMillis(), pendingIntent);

但是，如果活动是在2014年1月4日，那么我想将日期设置为2013年12月28日。有没有可以做到这一点的函数？或者我必须写很多案例？

Answer 1

活动时间为2014年1月4日：

Calendar calendar = Calendar.getInstance();
calendar.set(Calendar.MONTH, 0);
calendar.set(Calendar.YEAR, 2014);
calendar.set(Calendar.DAY_OF_MONTH, 4);
calendar.set(Calendar.HOUR_OF_DAY, 0);
calendar.set(Calendar.MINUTE, 0);
calendar.set(Calendar.SECOND, 0);
long eventTime=calendar.getTimeInMillis();//Returns Time in milliseconds

long oneDay=AlarmManager.INTERVAL_DAY;//Converts 24 Hrs(1 Day) to milliseconds
int noOfDays=4
long reminderTime=eventTime-(noOfDays*oneDay);//Time in milliseconds when the alarm will shoot up & you do not need to concider month/year with this approach as time is already in milliseconds.

//Set alarm
Intent myIntent = new Intent(MainActivity.this, MyReceiver.class);
pendingIntent = PendingIntent.getBroadcast(MainActivity.this, 0, myIntent,0);
AlarmManager alarmManager = (AlarmManager)getSystemService(ALARM_SERVICE);
alarmManager.set(AlarmManager.RTC_WAKEUP, reminderTime, pendingIntent);

希望这能有所帮助！

Answer 2

以毫秒为单位获取当前时间，然后减去no。天数，这里1 day= 24*60*60*1000 = 86400000

AlarmManager alarmManager = (AlarmManager)getSystemService(ALARM_SERVICE);
  alarmManager.set(AlarmManager.RTC_WAKEUP, (calendar.getTimeInMillis()-(no. of days * 86400000)), pendingIntent);