Android: Subtract minutes to my alarm

问题

I'm making an alarm, get the current time as follows:

public String getAlarmTimeStringFive2db() {

        String timef2db = "";
        if (alarmTime.get(Calendar.HOUR_OF_DAY) <= 9)
            timef2db += "0";
        timef2db += String.valueOf(alarmTime.get(Calendar.HOUR_OF_DAY));
        timef2db += ":";

        if (alarmTime.get(Calendar.MINUTE) <= 9)
            timef2db += "0";
        timef2db += String.valueOf(alarmTime.get(Calendar.MINUTE));

        return timef2db;

    }

...

public static long create(Alarm alarm) {
        ContentValues cv = new ContentValues();
        cv.put(COLUMN_ALARM_ACTIVE, alarm.getAlarmActive());
        cv.put(COLUMN_ALARM_TIME, alarm.getAlarmTimeStringFive2db());

...

public void setAlarmTime(String alarmTime) {

    String[] timePieces = alarmTime.split(":");

    Calendar newAlarmTime = Calendar.getInstance();
    newAlarmTime.set(Calendar.HOUR_OF_DAY,
            Integer.parseInt(timePieces[0]));
    newAlarmTime.set(Calendar.MINUTE, Integer.parseInt(timePieces[1]));
    newAlarmTime.set(Calendar.SECOND, 0);
    setAlarmTime(newAlarmTime);     
}

...

This works fine, for example returns 5:35 ... all right.

My problem is I want to subtract 5 minutes always on time. If the time is 5:35, I want the alarm time starts at 5:30.

My problem is I do not know how to subtract those 5 minutes. I tried

Calendar.MINUTE, Integer.parseInt(timePieces[1],5)

Calendar.MINUTE, -5)

...but nothing works

I read this link Set Alarm To Alert 5 Minutes Before a certian Time .. but I could not apply it to my code

Can anyone tell me as subtracting 5 minutes of my alarm?

thanks in advance

Regards

回答1:

I'm not sure if you are using the Calendar instance in the right way, but here is an example shows that time changes when use add -5 to the current calendar

Calendar cal = Calendar.getInstance();
    System.out.println("Before :" +  cal.get(Calendar.MINUTE));
    cal.add(Calendar.MINUTE, -5);
    System.out.println("After :" + cal.get(Calendar.MINUTE));

and the result will be something like this:

Before :37 
After :32

来源：https://stackoverflow.com/questions/18645074/android-subtract-minutes-to-my-alarm