iOS:判断昨天，今天，今年

- (BOOL)isThisYear
{
    // 日历
    NSCalendar *calendar = [NSCalendar currentCalendar];

    NSInteger nowYear = [calendar component:NSCalendarUnitYear fromDate:[NSDate date]];
    NSInteger selfYear = [calendar component:NSCalendarUnitYear fromDate:self];

    return nowYear == selfYear;
}

//- (BOOL)isToday
//{
//    // 日历
//    NSCalendar *calendar = [NSCalendar currentCalendar];
//
//    NSCalendarUnit unit = NSCalendarUnitYear | NSCalendarUnitMonth | NSCalendarUnitDay;
//
//    NSDateComponents *nowCmps = [calendar components:unit fromDate:[NSDate date]];
//    NSDateComponents *selfCmps = [calendar components:unit fromDate:self];
//
//    return nowCmps.year == selfCmps.year
//    && nowCmps.month == selfCmps.month
//    && nowCmps.day == selfCmps.day;
//}

- (BOOL)isToday
{
    NSDateFormatter *fmt = [[NSDateFormatter alloc] init];
    fmt.dateFormat = @"yyyy-MM-dd";

    NSString *nowString = [fmt stringFromDate:[NSDate date]];
    NSString *selfString = [fmt stringFromDate:self];

    return [nowString isEqualToString:selfString];
}

- (BOOL)isYesterday
{
    // 2014-12-31 23:59:59 -> 2014-12-31
    // 2015-01-01 00:00:01 -> 2015-01-01

    // 日期格式化类
    NSDateFormatter *fmt = [[NSDateFormatter alloc] init];
    fmt.dateFormat = @"yyyy-MM-dd";

    NSDate *nowDate = [fmt dateFromString:[fmt stringFromDate:[NSDate date]]];
    NSDate *selfDate = [fmt dateFromString:[fmt stringFromDate:self]];

    NSCalendar *calendar = [NSCalendar currentCalendar];
    NSDateComponents *cmps = [calendar components:NSCalendarUnitDay | NSCalendarUnitMonth | NSCalendarUnitYear fromDate:selfDate toDate:nowDate options:];

    return cmps.year ==
    && cmps.month ==
    && cmps.day == ;
}

发帖时间的判断：

- (NSString *)create_time
{
    // 日期格式化类
    NSDateFormatter *fmt = [[NSDateFormatter alloc] init];
    // 设置日期格式(y:年,M:月,d:日,H:时,m:分,s:秒)
    fmt.dateFormat = @"yyyy-MM-dd HH:mm:ss";
    // 帖子的创建时间
    NSDate *create = [fmt dateFromString:_create_time];

    if (create.isThisYear) { // 今年
        if (create.isToday) { // 今天
            NSDateComponents *cmps = [[NSDate date] deltaFrom:create];

            if (cmps.hour >= ) { // 时间差距 >= 1小时
                return [NSString stringWithFormat:@"%zd小时前", cmps.hour];
            } else if (cmps.minute >= ) { // 1小时 > 时间差距 >= 1分钟
                return [NSString stringWithFormat:@"%zd分钟前", cmps.minute];
            } else { // 1分钟 > 时间差距
                return @"刚刚";
            }
        } else if (create.isYesterday) { // 昨天
            fmt.dateFormat = @"昨天 HH:mm:ss";
            return [fmt stringFromDate:create];
        } else { // 其他
            fmt.dateFormat = @"MM-dd HH:mm:ss";
            return [fmt stringFromDate:create];
        }
    } else { // 非今年
        return _create_time;
    }
}