时间戳跟标准时间相互转换

本段代码的主要功能是取出装满标准时间的数组里边最大的值。并以标准时间输出

    NSMutableArray *arrayMSecond = [NSMutableArray arrayWithCapacity:2];
    for(NSString *date in arrayM){
        NSDateFormatter *formatter = [[NSDateFormatter alloc] init];
        [formatter setDateStyle:NSDateFormatterMediumStyle];
        [formatter setTimeStyle:NSDateFormatterShortStyle];
        [formatter setDateFormat:@"YYYY-MM-dd HH:mm:ss"];
        //设置时区,这个对于时间的处理有时很重要
        NSTimeZone* timeZone = [NSTimeZone timeZoneWithName:@"Asia/Beijing"];
        [formatter setTimeZone:timeZone];
        NSDate* dateSecond = [formatter dateFromString:date]; //------------将字符串按formatter转成nsdate
        //时间转时间戳的方法:
        NSInteger timeSp = [[NSNumber numberWithDouble:[dateSecond timeIntervalSince1970]] integerValue];
        [arrayMSecond addObject:@(timeSp)];
    }
    NSInteger max = [[arrayMSecond objectAtIndex:0] integerValue];
    for (int i=0; i