Objectivec 如何将 NSDate 转换为今天、昨天、一周前、一个月前、一年前等相对格式

For simplicity I'm assuming that the dates you are formatting are all in the past (no "tomorrow" or "next week"). It's not that it can't be done but it would be more cases to deal with and more strings to return.

你可以将components:fromDate:toDate:options:与你想要的任何日期组件组合使用，以获得两个日期之间的年数、月数、周数、日数、小时数等.然后按照从最重要(例如年)到最不重要(例如天)的顺序遍历它们，您可以仅基于最重要的部分来设置字符串的格式.

例如:1周、2天和7小时前的日期将被格式化为"1周".

如果要为单位的特殊编号创建特殊字符串，如"1天前"的"明天"，则可以在确定该分量是最重要的分量后判断该分量的值.

代码如下所示:

- (NSString *)relativeDateStringForDate:(NSDate *)date
{
    NSCalendarUnit units = NSCalendarUnitDay | NSCalendarUnitWeekOfYear | 
                           NSCalendarUnitMonth | NSCalendarUnitYear;

    // if `date` is before "now" (i.e. in the past) then the components will be positive
    NSDateComponents *components = [[NSCalendar currentCalendar] components:units
                                                                   fromDate:date
                                                                     toDate:[NSDate date]
                                                                    options:0];

    if (components.year > 0) {
        return [NSString stringWithFormat:@"%ld years ago", (long)components.year];
    } else if (components.month > 0) {
        return [NSString stringWithFormat:@"%ld months ago", (long)components.month];
    } else if (components.weekOfYear > 0) {
        return [NSString stringWithFormat:@"%ld weeks ago", (long)components.weekOfYear];
    } else if (components.day > 0) {
        if (components.day > 1) {
            return [NSString stringWithFormat:@"%ld days ago", (long)components.day];
        } else {
            return @"Yesterday";
        }
    } else {
        return @"Today";
    }
}

如果日期也可能在future ，则可以按相同顺序判断组件的绝对值，然后判断其是否为正或负，以返回相应的字符串.我只展示以下年份:

if ( abs(components.year > 0) ) { 
    // year is most significant component
    if (components.year > 0) {
        // in the past
        return [NSString stringWithFormat:@"%ld years ago", (long)components.year];
    } else {
        // in the future
        return [NSString stringWithFormat:@"In %ld years", (long)components.year];
    }
}