如何从年月日的总和中提取日期分量乘以iOS中的某个整数？

Posted 2023-03-16

【中文标题】如何从年月日的总和中提取日期分量乘以iOS中的某个整数？

【英文标题】：how to extract date components from sum of year month day weekday multiply by certain integer in iOS?

【发布时间】：2015-03-13 12:25:44

【问题描述】：

Apple 示例项目DateSectionTitles 演示了如何按年和月对部分进行分组，如何扩展它以支持年月日和工作日？

sectionIdentifier 是一个临时属性，派生自持久日期属性timestamp。

- (NSString *)sectionIdentifier 

    // Create and cache the section identifier on demand.

    [self willAccessValueForKey:@"sectionIdentifier"];
    NSString *tmp = [self primitiveSectionIdentifier];
    [self didAccessValueForKey:@"sectionIdentifier"];

    if (!tmp) 
        /*
         Sections are organized by month and year. Create the section identifier
         as a string representing the number (year * 1000 + month);
         this way they will be correctly ordered chronologically regardless of
         the actual name of the month.
         */
        NSCalendar *calendar = [NSCalendar currentCalendar];

        NSDateComponents *components = [calendar components:(NSYearCalendarUnit | NSMonthCalendarUnit)
                               fromDate:[self timeStamp]];
        tmp = [NSString stringWithFormat:@"%d", [components year] * 1000 + [components month]];
        [self setPrimitiveSectionIdentifier:tmp];
    
    return tmp;


- (NSString *)tableView:(UITableView *)tableView titleForHeaderInSection:(NSInteger)section

    id <NSFetchedResultsSectionInfo> theSection = [[self.fetchedResultsController sections] objectAtIndex:section];

    /*
     Section information derives from an event's sectionIdentifier, which is a string representing the number (year * 1000) + month.
     To display the section title, convert the year and month components to a string representation.
     */
    static NSDateFormatter *formatter = nil;

    if (!formatter)
    
        formatter = [[NSDateFormatter alloc] init];
        [formatter setCalendar:[NSCalendar currentCalendar]];

        NSString *formatTemplate = [NSDateFormatter dateFormatFromTemplate:@"MMMM YYYY" options:0 locale:[NSLocale currentLocale]];
        [formatter setDateFormat:formatTemplate];
    

    NSInteger numericSection = [[theSection name] integerValue];
    NSInteger year = numericSection / 1000;
    NSInteger month = numericSection - (year * 1000);

    NSDateComponents *dateComponents = [[NSDateComponents alloc] init];
    dateComponents.year = year;
    dateComponents.month = month;
    NSDate *date = [[NSCalendar currentCalendar] dateFromComponents:dateComponents];

    NSString *titleString = [formatter stringFromDate:date];

    return titleString;

我不知道计算年月日和工作日的确切算法，如下面的代码。

tmp = [NSString stringWithFormat:@"%d", [components year] * 1000 + [components month]];

以及数据源方法的计算。

id <NSFetchedResultsSectionInfo> theSection = [[self.fetchedResultsController sections] objectAtIndex:section];

NSInteger numericSection = [[theSection name] integerValue];
NSInteger year = numericSection / 1000;
NSInteger month = numericSection - (year * 1000);

【参考方案1】：

您需要一个“算法”来为每一天创建不同的结果（工作日与一天相同。没有“2015 年 3 月 13 日，星期四”）。

假设您有 2015 年 3 月 13 日。一个很好的唯一字符串是 20150313。或 year * 10000 + month * 100 + day。

例如：

NSDateComponents *components = [calendar components:(NSCalendarUnitYear | NSCalendarUnitMonth | NSCalendarUnitDay)
                                               fromDate:[self timeStamp]];
tmp = [NSString stringWithFormat:@"%d", [components year] * 10000 + [components month] * 100 + [components day]];

然后反转计算以取回各个组件：

NSInteger numericSection = [[theSection name] integerValue];
NSInteger year = numericSection / 10000;
NSInteger month = (numericSection - (year * 10000))/100;
NSInteger day = (numericSection - (year * 10000 + month * 100))

或者只是从该部分中的一个对象中获取 NSDate：

- (NSString *)tableView:(UITableView *)tableView titleForHeaderInSection:(NSInteger)section

    id <NSFetchedResultsSectionInfo> theSection;// = [[self.fetchedResultsController sections] objectAtIndex:section];
    static NSDateFormatter *formatter = nil;

    if (!formatter)
    
        formatter = [[NSDateFormatter alloc] init];
        [formatter setCalendar:[NSCalendar currentCalendar]];

        NSString *formatTemplate = [NSDateFormatter dateFormatFromTemplate:@"MMMM yyyy dd EEEE" options:0 locale:[NSLocale currentLocale]];
        [formatter setDateFormat:formatTemplate];
    

    APLEvent *event = [[theSection objects] firstObject];
    if (event) 
        NSDate *date = [event timeStamp];
        return [formatter stringFromDate:date];
    
    return nil;