IOS日期转为今天昨天形式

近期项目有类似QQ空间展示动态的UI，模仿了QQ空间的时间显示。在此记录，以备查阅。

这是QQ空间的ui：

时间显示为：

1.今天－－>今天 xx:xx(今天 15:39)

2.昨天－－>昨天 xx:xx(昨天 06:00)

3.前天－－>前天 xx:xx(前天 19:00)

4.同一年, 比如:同一年的一月三号－－>01-03 xx:xx(01-03 12:29)

5.不在同一年 －－> xxxx-xx-xx(2014-12-12)

程序执行效果例如以下。下面为简单的測试。没有ui界面:

以下的代码是在网上已有代码的基础上更改而来，原代码点此查看

/**
 *  仿QQ空间时间显示
 *  @param string eg:2015年5月24日 02时21分30秒
 */
- (NSString *)format:(NSString *)string{
    NSDateFormatter *inputFormatter= [[NSDateFormatter alloc] init];
    [inputFormatter setLocale:[[NSLocale alloc] initWithLocaleIdentifier:@"en_US"] ];
    [inputFormatter setDateFormat:@"yyyy年MM月dd日 HH时mm分ss秒"];
    NSDate*inputDate = [inputFormatter dateFromString:string];
    //NSLog(@"startDate= %@", inputDate);

    NSDateFormatter *outputFormatter= [[NSDateFormatter alloc] init];
    [outputFormatter setLocale:[NSLocale currentLocale]];
    [outputFormatter setDateFormat:@"yyyy-MM-dd HH:mm:ss"];
    //get date str
    NSString *str= [outputFormatter stringFromDate:inputDate];
    //str to nsdate
    NSDate *strDate = [outputFormatter dateFromString:str];
    //修正8小时的差时
    NSTimeZone *zone = [NSTimeZone systemTimeZone];
    NSInteger interval = [zone secondsFromGMTForDate: strDate];
    NSDate *endDate = [strDate  dateByAddingTimeInterval: interval];
    //NSLog(@"endDate:%@",endDate);
    NSString *lastTime = [self compareDate:endDate];
    NSLog(@"lastTime = %@",lastTime);
    return str;
}

-(NSString *)compareDate:(NSDate *)date{

    NSTimeInterval secondsPerDay = 24 * 60 * 60;

    //修正8小时之差
    NSDate *date1 = [NSDate date];
    NSTimeZone *zone = [NSTimeZone systemTimeZone];
    NSInteger interval = [zone secondsFromGMTForDate: date1];
    NSDate *localeDate = [date1  dateByAddingTimeInterval: interval];

    //NSLog(@"nowdate=%@\nolddate = %@",localeDate,date);
    NSDate *today = localeDate;
    NSDate *yesterday,*beforeOfYesterday;
    //今年
    NSString *toYears;

    toYears = [[today description] substringToIndex:4];

    yesterday = [today dateByAddingTimeInterval: -secondsPerDay];
    beforeOfYesterday = [yesterday dateByAddingTimeInterval: -secondsPerDay];

    // 10 first characters of description is the calendar date:
    NSString *todayString = [[today description] substringToIndex:10];
    NSString *yesterdayString = [[yesterday description] substringToIndex:10];
    NSString *beforeOfYesterdayString = [[beforeOfYesterday description] substringToIndex:10];

    NSString *dateString = [[date description] substringToIndex:10];
    NSString *dateYears = [[date description] substringToIndex:4];

    NSString *dateContent;
    if ([dateYears isEqualToString:toYears]) {//同一年
        //今 昨 前天的时间
        NSString *time = [[date description] substringWithRange:(NSRange){11,5}];
        //其它时间
        NSString *time2 = [[date description] substringWithRange:(NSRange){5,11}];
        if ([dateString isEqualToString:todayString]){
            dateContent = [NSString stringWithFormat:@"今天 %@",time];
            return dateContent;
        } else if ([dateString isEqualToString:yesterdayString]){
            dateContent = [NSString stringWithFormat:@"昨天 %@",time];
            return dateContent;
        }else if ([dateString isEqualToString:beforeOfYesterdayString]){
            dateContent = [NSString stringWithFormat:@"前天 %@",time];
            return dateContent;
        }else{
            return time2;
        }
    }else{
        return dateString;
    }
}