比较NSDate今天或昨天

Question

嗯,我想这已被问了一千次,但由于某种原因,答案真的不起作用或有其他问题,....

无论如何这里是我"工作":

    NSCalendar *calendar = [NSCalendar currentCalendar];    
    NSDate *currentDate = [NSDate date];
    NSDateComponents *comps = [[NSDateComponents alloc] init];
    // set tomorrow (0: today, -1: yesterday)
    [comps setDay:0];
    NSDate *dateToday = [calendar dateByAddingComponents:comps toDate:currentDate options:0];
    [comps setDay:-1];
    NSDate *dateYesterday = [calendar dateByAddingComponents:comps toDate:currentDate options:0];
    [comps release];


NSString *todayString = [self.dateFormatter stringFromDate:dateToday] ;
NSString *yesterdayString = [self.dateFormatter stringFromDate:dateYesterday] ;
NSString *refDateString = [self.dateFormatter stringFromDate:info.date];

if ([refDateString isEqualToString:todayString]) 
{
    cell.title.text =  @"Today";
} else if ([refDateString isEqualToString:yesterdayString]) 
{
    cell.title.text =  @"Yesterday";
} else 
{
    cell.title.text =  [self.dateFormatter stringFromDate:info.date];
}

现在问题:

对于日期比较而言,这似乎是一个非常多的代码,有更简单的方法吗？

最重要的问题是所有对象的发布.可能已经猜到了,我在UITableViewController中使用它.我的代码中也有这些行:

//[calendar release];
//[currentDate release];
//[dateToday release];
//[dateYesterday release];
//[todayString release];
//[yesterdayString release];
//[refDateString release];

问题是,一旦我取消注释其中一行,我的应用程序崩溃了,我不明白为什么？!我希望有人能在这里启发我.

非常感谢.

Answer 1

最简单的方法是只比较description日期:

// Your dates:
NSDate * today = [NSDate date];
NSDate * yesterday = [NSDate dateWithTimeIntervalSinceNow:-86400]; //86400 is the seconds in a day
NSDate * refDate; // your reference date

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

if ([refDateString isEqualToString:todayString]) 
{
    cell.title.text =  @"Today";
} else if ([refDateString isEqualToString:yesterdayString]) 
{
    cell.title.text =  @"Yesterday";
} else 
{
    cell.title.text =  refDateString;
}

如果要更改可以使用的日期字符串的格式descriptionWithLocale:.

Answer 2

我知道这是一个古老的问题,但我自己也做了类似的事情并且发现了它.

首先,自iOS 4.0(和Mac OS 10.6)以来,NSDateFormatter可以做相对日期,这会自动给你"今天"和"昨天".

NSDateFormatter* formatter = [[NSDateFormatter alloc] init];
[formatter setTimeStyle:NSDateFormatterNoStyle];
[formatter setDateStyle:NSDateFormatterShortStyle];
[formatter setDoesRelativeDateFormatting:YES];

NSString* dateString = [formatter stringFromDate:[NSDate date]];    
NSLog( @"date = %@", dateString );

哪个输出:

2014-03-15 15:26:37.683 TestApp[1293:303] date = Today

然而,OP正在询问如何比较NSDate今天或昨天,我也想做的事情,相对日期格式除外.这是我提出的,作为一个类别实现NSDate:

@implementation NSDate (IsToday)

- (BOOL) isToday
{
    NSCalendar* calendar = [NSCalendar currentCalendar];

    // Components representing the day of our date.
    NSDateComponents* dateComp = [calendar components:NSYearCalendarUnit | NSMonthCalendarUnit | NSDayCalendarUnit
                                             fromDate:self];
    NSDate* date = [calendar dateFromComponents:dateComp];

    // Components representing today.
    NSDateComponents* todayComp = [calendar components:NSYearCalendarUnit | NSMonthCalendarUnit | NSDayCalendarUnit
                                              fromDate:[NSDate date]];
    NSDate* todayDate = [calendar dateFromComponents:todayComp];

    // If the dates are equal, then our date is today.
    return [date isEqualToDate:todayDate];
}

@end

我想这样做的原因是,我可以显示今天创建的内容的时间,以及今天没有创建的日期 - 类似于Mail.app显示消息上的日期.它看起来像这样:

- (NSString*) postDateToString:(NSDate*)aDate
{
    static NSDateFormatter* todayFormatter = nil;
    if( todayFormatter == nil ) {
        todayFormatter = [[NSDateFormatter alloc] init];
        [todayFormatter setTimeStyle:NSDateFormatterShortStyle];
        [todayFormatter setDateStyle:NSDateFormatterNoStyle];
    }

    static NSDateFormatter* notTodayFormatter = nil;
    if( notTodayFormatter == nil ) {
        notTodayFormatter = [[NSDateFormatter alloc] init];
        [notTodayFormatter setTimeStyle:NSDateFormatterNoStyle];
        [notTodayFormatter setDateStyle:NSDateFormatterShortStyle];
        [notTodayFormatter setDoesRelativeDateFormatting:YES];
    }

    NSDateFormatter* formatter = notTodayFormatter;

    if( [aDate isToday] ) {
        formatter = todayFormatter;
    }

    return [formatter stringFromDate:aDate];
}