getSystemService nullpointer异常

Question

我试图通过使用getSystemService从片段中使用一个intentService来设置发送intent的警报。但是由于null对象引用，我在getsystemservice上得到一个nullpointer异常。也请帮助我找到一个方法来传递时间设定为主要活动。

public class TimePickerFragment  extends DialogFragment implements TimePickerDialog.OnTimeSetListener{
      public int hour,minute,id;
    private AlarmManager alarmstart;
    private AlarmManager alarmstop;

    @Override
        public Dialog onCreateDialog(Bundle savedInstanceState){
        alarmstart = (AlarmManager) getActivity().getSystemService(Context.ALARM_SERVICE);
        alarmstop = (AlarmManager) getActivity().getSystemService(Context.ALARM_SERVICE);
            return new TimePickerDialog(getActivity(),this, hour, minute,
                    DateFormat.is24HourFormat(getActivity()));
        }

        public void identify(int identity){
            id=identity;
        }
        public void onTimeSet(TimePicker view, int hourOfDay, int minute){
            Calendar calendar = Calendar.getInstance();
            if(getActivity()!=null){
            Intent start =new Intent(getActivity(),starter.class);
            PendingIntent pi=PendingIntent.getService(getActivity(),0,start,0);
            Intent stop =new Intent(getActivity(),stopper.class);
            PendingIntent pi2=PendingIntent.getService(getActivity(),0,stop,0);
            switch (id) {
                case 1:
                    calendar.setTimeInMillis(0);
                    calendar.set(Calendar.DAY_OF_WEEK, Calendar.MONDAY);
                    calendar.set(Calendar.HOUR_OF_DAY, hourOfDay);
                    calendar.set(Calendar.MINUTE, minute);
                    alarmstart.set(AlarmManager.RTC_WAKEUP, calendar.getTimeInMillis(), pi);
                case 2:
                    calendar.setTimeInMillis(0);
                    calendar.set(Calendar.DAY_OF_WEEK, Calendar.MONDAY);
                    calendar.set(Calendar.HOUR_OF_DAY, hourOfDay);
                    calendar.set(Calendar.MINUTE, minute);
                    alarmstart.set(AlarmManager.RTC_WAKEUP, calendar.getTimeInMillis(), pi2);
                case 3:
                    calendar.setTimeInMillis(0);
                    calendar.set(Calendar.DAY_OF_WEEK, Calendar.TUESDAY);
                    calendar.set(Calendar.HOUR_OF_DAY, hourOfDay);
                    calendar.set(Calendar.MINUTE, minute);
                    alarmstart.set(AlarmManager.RTC_WAKEUP, calendar.getTimeInMillis(), pi);
                case 4:
                    calendar.setTimeInMillis(0);
                    calendar.set(Calendar.DAY_OF_WEEK, Calendar.TUESDAY);
                    calendar.set(Calendar.HOUR_OF_DAY, hourOfDay);
                    calendar.set(Calendar.MINUTE, minute);
                    alarmstart.set(AlarmManager.RTC_WAKEUP, calendar.getTimeInMillis(), pi2);
                case 5:
                    calendar.setTimeInMillis(0);
                    calendar.set(Calendar.DAY_OF_WEEK, Calendar.WEDNESDAY);
                    calendar.set(Calendar.HOUR_OF_DAY, hourOfDay);
                    calendar.set(Calendar.MINUTE, minute);
                    alarmstart.set(AlarmManager.RTC_WAKEUP, calendar.getTimeInMillis(), pi);
                case 6:
                    calendar.setTimeInMillis(0);
                    calendar.set(Calendar.DAY_OF_WEEK, Calendar.WEDNESDAY);
                    calendar.set(Calendar.HOUR_OF_DAY, hourOfDay);
                    calendar.set(Calendar.MINUTE, minute);
                    alarmstart.set(AlarmManager.RTC_WAKEUP, calendar.getTimeInMillis(), pi2);
                case 7:
                    calendar.setTimeInMillis(0);
                    calendar.set(Calendar.DAY_OF_WEEK, Calendar.THURSDAY);
                    calendar.set(Calendar.HOUR_OF_DAY, hourOfDay);
                    calendar.set(Calendar.MINUTE, minute);
                    alarmstart.set(AlarmManager.RTC_WAKEUP, calendar.getTimeInMillis(), pi);
                case 8:
                    calendar.setTimeInMillis(0);
                    calendar.set(Calendar.DAY_OF_WEEK, Calendar.THURSDAY);
                    calendar.set(Calendar.HOUR_OF_DAY, hourOfDay);
                    calendar.set(Calendar.MINUTE, minute);
                    alarmstart.set(AlarmManager.RTC_WAKEUP, calendar.getTimeInMillis(), pi2);
                case 9:
                    calendar.setTimeInMillis(0);
                    calendar.set(Calendar.DAY_OF_WEEK, Calendar.FRIDAY);
                    calendar.set(Calendar.HOUR_OF_DAY, hourOfDay);
                    calendar.set(Calendar.MINUTE, minute);
                    alarmstart.set(AlarmManager.RTC_WAKEUP, calendar.getTimeInMillis(), pi);
                case 10:
                    calendar.setTimeInMillis(0);
                    calendar.set(Calendar.DAY_OF_WEEK, Calendar.FRIDAY);
                    calendar.set(Calendar.HOUR_OF_DAY, hourOfDay);
                    calendar.set(Calendar.MINUTE, minute);
                    alarmstart.set(AlarmManager.RTC_WAKEUP, calendar.getTimeInMillis(), pi2);
                case 11:
                    calendar.setTimeInMillis(0);
                    calendar.set(Calendar.DAY_OF_WEEK, Calendar.SATURDAY);
                    calendar.set(Calendar.HOUR_OF_DAY, hourOfDay);
                    calendar.set(Calendar.MINUTE, minute);
                    alarmstart.set(AlarmManager.RTC_WAKEUP, calendar.getTimeInMillis(), pi);
                case 12:
                    calendar.setTimeInMillis(0);
                    calendar.set(Calendar.DAY_OF_WEEK, Calendar.SATURDAY);
                    calendar.set(Calendar.HOUR_OF_DAY, hourOfDay);
                    calendar.set(Calendar.MINUTE, minute);
                    alarmstart.set(AlarmManager.RTC_WAKEUP, calendar.getTimeInMillis(), pi2);
                case 13:
                    calendar.setTimeInMillis(0);
                    calendar.set(Calendar.DAY_OF_WEEK, Calendar.SUNDAY);
                    calendar.set(Calendar.HOUR_OF_DAY, hourOfDay);
                    calendar.set(Calendar.MINUTE, minute);
                    alarmstart.set(AlarmManager.RTC_WAKEUP, calendar.getTimeInMillis(), pi);
                case 14:
                    calendar.setTimeInMillis(0);
                    calendar.set(Calendar.DAY_OF_WEEK, Calendar.SUNDAY);
                    calendar.set(Calendar.HOUR_OF_DAY, hourOfDay);
                    calendar.set(Calendar.MINUTE, minute);
                    alarmstart.set(AlarmManager.RTC_WAKEUP, calendar.getTimeInMillis(), pi2);
            }
            }
        }


}