iOS-NSDate (Extension)

/**
 *  判断某个时间是否为今年
 */
- (BOOL)isThisYear
{
    NSCalendar *calendar = [NSCalendar currentCalendar];
    // 获得某个时间的年月日时分秒
    NSDateComponents *dateCmps = [calendar components:NSCalendarUnitYear fromDate:self];
    NSDateComponents *nowCmps = [calendar components:NSCalendarUnitYear fromDate:[NSDate date]];
    return dateCmps.year == nowCmps.year;
}

/**
 *  判断某个时间是否为昨天
 */
- (BOOL)isYesterday
{
    NSDate *now = [NSDate date];

    // date ==  2014-04-30 10:05:28 --> 2014-04-30 00:00:00
    // now == 2014-05-01 09:22:10 --> 2014-05-01 00:00:00
    NSDateFormatter *fmt = [[NSDateFormatter alloc] init];
    fmt.dateFormat = @"yyyy-MM-dd";

    // 2014-04-30
    NSString *dateStr = [fmt stringFromDate:self];
    // 2014-10-18
    NSString *nowStr = [fmt stringFromDate:now];

    // 2014-10-30 00:00:00
    NSDate *date = [fmt dateFromString:dateStr];
    // 2014-10-18 00:00:00
    now = [fmt dateFromString:nowStr];

    NSCalendar *calendar = [NSCalendar currentCalendar];

    NSCalendarUnit unit = NSCalendarUnitYear | NSCalendarUnitMonth | NSCalendarUnitDay;
    NSDateComponents *cmps = [calendar components:unit fromDate:date toDate:now options:0];

    return cmps.year == 0 && cmps.month == 0 && cmps.day == 1;
}

/**
 *  判断某个时间是否为今天
 */
- (BOOL)isToday
{
    NSDate *now = [NSDate date];
    NSDateFormatter *fmt = [[NSDateFormatter alloc] init];
    fmt.dateFormat = @"yyyy-MM-dd";

    NSString *dateStr = [fmt stringFromDate:self];
    NSString *nowStr = [fmt stringFromDate:now];

    return [dateStr isEqualToString:nowStr];
}
@end



- (NSString *)created_at
{
    NSDateFormatter *fmt = [[NSDateFormatter alloc] init];
    // 如果是真机调试，转换这种欧美时间，需要设置locale
    fmt.locale = [[NSLocale alloc] initWithLocaleIdentifier:@"en_US"];

    // 设置日期格式（声明字符串里面每个数字和单词的含义）
    // E:星期几
    // M:月份
    // d:几号(这个月的第几天)
    // H:24小时制的小时
    // m:分钟
    // s:秒
    // y:年
    fmt.dateFormat = @"EEE MMM dd HH:mm:ss Z yyyy";
//    _created_at = @"Tue Sep 30 17:06:25 +0800 2014";

    // 微博的创建日期
    NSDate *createDate = [fmt dateFromString:_created_at];
    // 当前时间
    NSDate *now = [NSDate date];

    // 日历对象（方便比较两个日期之间的差距）
    NSCalendar *calendar = [NSCalendar currentCalendar];
    // NSCalendarUnit枚举代表想获得哪些差值
    NSCalendarUnit unit = NSCalendarUnitYear | NSCalendarUnitMonth | NSCalendarUnitDay | NSCalendarUnitHour | NSCalendarUnitMinute | NSCalendarUnitSecond;
    // 计算两个日期之间的差值
    NSDateComponents *cmps = [calendar components:unit fromDate:createDate toDate:now options:0];

    if ([createDate isThisYear]) { // 今年
        if ([createDate isYesterday]) { // 昨天
            fmt.dateFormat = @"昨天 HH:mm";
            return [fmt stringFromDate:createDate];
        } else if ([createDate isToday]) { // 今天
            if (cmps.hour >= 1) {
                return [NSString stringWithFormat:@"%d小时前", cmps.hour];
            } else if (cmps.minute >= 1) {
                return [NSString stringWithFormat:@"%d分钟前", cmps.minute];
            } else {
                return @"刚刚";
            }
        } else { // 今年的其他日子
            fmt.dateFormat = @"MM-dd HH:mm";
            return [fmt stringFromDate:createDate];
        }
    } else { // 非今年
        fmt.dateFormat = @"yyyy-MM-dd HH:mm";
        return [fmt stringFromDate:createDate];
    }
}