如何在iPhone目标c中显示昨天（相对于日期，但不是24小时的时间间隔）访问过的项目

Question

我有一个带有联系人的表格视图。 因为当我选择联系人时，必须将该联系人添加到另一个表：RecentsTable 中。作为最近访问过的项目。为此，我使用了这样的代码，它可以工作，但是。 就昨天而言，它考虑的是 24 小时。但我想在日期更改时显示昨天的项目，然后自动将其添加到昨天的列表中。请指导我。

     NSDate *date = self.lastviewed;
                double time = [date timeIntervalSinceNow];

                NSString *tmpValue = nil;
                time *= -1;


                if(time < 3600*24) {
                    tmpValue = @"Today";
                }

                else {
                    int div = round(time / 60 / 60 / 24);

             // I want solution wth respect to yesterday's date date but not as follows
                     if(div == 1)
                          tmpvalue = @ "Yester Day";


                if (div >1 && div <7)
                        //tmpValue= [NSString stringWithFormat:@"%d days ago", div];
                        tmpValue = @"This Week";

                    else if(div <30)
                        tmpValue = @"This Month";
                    else 
                        tmpValue = @"Earlier"; 
                } 

提前致谢..

Answer 1

您应该使用 NSDateComponents< /a> 处理日期时。它将处理夏令时等问题。NSDate 上的 StackOverflow 上有很多问题，这个 例如，可以通过将日期部分更改为 -1 天来解决您的问题。

NSCalendar *gregorian = [[NSCalendar alloc] initWithCalendarIdentifier:NSGregorianCalendar];
NSDate *today = [NSDate date];

NSDateComponents *dayComponent = [[NSDateComponents alloc] init];
dayComponent.day = -1;
NSDate *yesterday = [gregorian dateByAddingComponents:dayComponent 
                                               toDate:today 
                                              options:0];

Answer 2

我认为你不仅要改变“昨天”的情况，还要改变月、年和周的其他计算。

NSDate *date = self.lastviewed;
// double time = [date timeIntervalSinceNow];
NSCalendar *currentCalendar = [NSCalendar currentCalendar];
NSDateComponents * componentsOfDate = [currentCalendar 
                                        components: (NSYearCalendarUnit|NSMonthCalendarUnit|
                                                   NSDayCalendarUnit|NSWeekCalendarUnit)
                                       fromDate:date];
NSDateComponents * componentsOfToday = [currentCalendar 
                                         components:(NSYearCalendarUnit|NSMonthCalendarUnit|
                                         NSDayCalendarUnit|NSWeekCalendarUnit) 
                                       fromDate:[NSDate date]];

if ([componensOfDate year] == [componentsOfToday year])
    if ([componentsOfDate month] == [componentsOfToday month])
        if([componentsOfDate day] == [componentsOfToday day])
            tmpvalue = @"Today" ;
         else
             tmpvalue = @"This Month" ;
    else
        tmpvalue = @"This Year" ;

// This week calculation, the easy way.
if([componentsOfDate week] == [componentsOfToday week] && 
   abs([date timeIntervalSinceNow]) <= (7*24*60*60))
    tmpvalue = @"This Week" ;

// Yesterday calculation
NSDate * yesterday = [NSDate dateWithTimeInterval:(-24*7*60*60) sinceDate:[NSDate date]];
NSComponents *componentsOfYesterday = [currentCalendar 
                                        components: (NSYearCalendarUnit|NSMonthCalendarUnit|
                                                   NSDayCalendarUnit)
                                       fromDate:yesterday];

// check this, as I'm not sure you can use compare: on components object
if([componentsOfDate compare:componentsOfYesterday] == NSOrderedSame)
  tmpvalue = @"Yesterday";

Answer 3

如果您使用 NSCalendar 获取日和月单位。

请参阅此和这个一些例子。

如果您获得当天和给定的最后查看日期的日、月单位，您可以通过比较两者找到所需的值。

编辑：

NSDate *todate = [NSDate date];
NSDate *lastViewedDate = self.lastviewed; 

NSCalendar *gregorian = [[NSCalendar alloc] 
                         initWithCalendarIdentifier:NSGregorianCalendar]; 

NSUInteger unitFlags = NSMonthCalendarUnit | NSDayCalendarUnit; 

NSDateComponents *components = [gregorian components:unitFlags 
                                            fromDate:lastViewedDate 
                                              toDate:todate options:0]; 
NSInteger months = [components month]; 
NSInteger days = [components day]; 

NSString *tmpValue = nil;

if ( days == 0 ) {
    tmpValue = @"Today";
}
else
{
    if(days == 1)
        tmpValue = @"Yesterday";

    else if (days >1 && days <7)
        //tmpValue= [NSString stringWithFormat:@"%d days ago", div];
        tmpValue = @"This Week";

    else if(days <30)
        tmpValue = @"This Month";
    else 
        tmpValue = @"Earlier";
}