iOS中获取当前时间，设定时间，并算出差值

 NSDate *date = [NSDate date];//获取当前时间
         NSTimeZone *zone = [NSTimeZone systemTimeZone];//修改时区
         NSInteger interval1 = [zone secondsFromGMTForDate: date];//修改时区
         _localDate1 = [date  dateByAddingTimeInterval: interval1];//修改时区
         NSLog(@"~~~~~~~~~~~~~今天%@\n", _localDate1);

         NSCalendar *calendar = [NSCalendar currentCalendar];
         NSDateComponents *comp = [calendar components:NSYearCalendarUnit | NSMonthCalendarUnit | NSDayCalendarUnit | NSWeekdayCalendarUnit |    NSDayCalendarUnit fromDate:_localDate1];

         //获取当前年月日
         NSInteger year = [comp year];
         NSInteger month = [comp month];
         NSInteger day = [comp day];

         NSDateComponents * components = [[NSDateComponents alloc]init];

         //设定
         [components setYear:year];
         [components setMonth:month];
         [components setDay:day];
         [components setHour:];
         [components setMinute:];

         NSCalendar *current = [NSCalendar currentCalendar];

         NSDate *setDate1 = [current dateFromComponents:components];
         //默认的时区都是格林尼治0时区，我们在东8区
         NSTimeZone *zone2 = [NSTimeZone systemTimeZone];//修改时区
         NSInteger interval2 = [zone2 secondsFromGMTForDate: setDate1];//修改时区
         _localDate2 = [setDate1  dateByAddingTimeInterval: interval2];//修改时区

         NSLog(@"-----------%@\n",_localDate2);
 //_localDate1-_localDate2，得到的结果默认为秒，可以自己换算
 NSInteger lastTime = [_localDate2 timeIntervalSinceDate:_localDate1]/;
     NSLog(@"!!!!!!!!!!!!%ld\n",lastTime);

获取day的时候会多加一天，不知道是什么情况