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<arrayMSecond.count-1; i++) {
        if(max < [[arrayMSecond objectAtIndex:i+1] integerValue]){
            max = [[arrayMSecond objectAtIndex:i+1] integerValue];
        }
    }
    
    NSDateFormatter *formatter = [[NSDateFormatter alloc] init];
    [formatter setDateStyle:NSDateFormatterMediumStyle];
    [formatter setTimeStyle:NSDateFormatterShortStyle];
    [formatter setDateFormat:@"YYYY-MM-dd HH:mm:ss"]; //----------设置你想要的格式,hh与HH的区别:分别表示12小时制,24小时制
    //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 *confromTimesp = [NSDate dateWithTimeIntervalSince1970:max];
    NSString *confromTimespStr = [formatter stringFromDate:confromTimesp];
    self.presellEndDate = confromTimespStr;