一些考虑语言环境设置等的 NSDate 问题答案

【问题标题】：Some NSDate questions considering locale settings etc一些考虑语言环境设置等的 NSDate 问题
【发布时间】：2014-02-16 13:31:17
【问题描述】：

我对 iOS 还是有点陌生，并且在使用 NSDate 时遇到了一些困难。基本上我的应用中有特定的 CostPeriods：

CostPeriodDaily
CostPeriodWeekly
CostPeriodMonthly
CostPeriodSemiAnnually
CostPeriodAnnually

根据 CostPeriod，我想要那个特定时期的开始和结束日期。 CostPeriodDaily 当然是从（即今天）2014 年 2 月 16 日 00:00:00（当地时间）- 2014 年 2 月 16 日 23:59:59（当地时间）。每月将从 2014 年 2 月 1 日 00:00:00 到 2014 年 2 月 28 日 23:59:59 等。

我首先有两个具体问题：

NSWeekdayCalendarUnit：1 总是星期日和 7 星期六？不管设置了什么语言环境？
如果我 NSLog 我的 endDate（如下面的代码）或开始日期，它通常是日期和 23:00:00，因为我生活在时区格林威治标准时间+1。这是正确的吗？

现在到我的 endDate 函数，还有两个问题:-)

这个功能一般可以吗？或者我会根据特定的语言环境设置出现一些问题？
我的 CostPeriodWeekly 案例给了我今天的错误日期 2014-02-15 23:00:00 +0000。我不知道为什么...？

+(NSDate *)endDateForCurrentCostPeriod:(CostPeriod)costPeriod{ NSCalendar *gregorian = [[NSCalendar 分配] initWithCalendarIdentifier:NSGregorianCalendar];

NSDateComponents *todayComponents =
[gregorian components:(NSDayCalendarUnit | NSWeekdayCalendarUnit | NSMonthCalendarUnit | NSYearCalendarUnit ) fromDate:[NSDate date]];
NSRange daysOfCurrentMonth = [gregorian rangeOfUnit:NSDayCalendarUnit inUnit:NSMonthCalendarUnit forDate:[NSDate date]];


NSDateComponents *endDateComponents = [[NSDateComponents alloc] init];

switch (costPeriod) {
    case CostPeriodDaily:
        [endDateComponents setDay:[todayComponents day]];
        [endDateComponents setMonth:[todayComponents month]];
        [endDateComponents setYear:[todayComponents year]];
        break;

    case CostPeriodWeekly:
        //Weekday 1 = sunday, 2 = monday
        if([todayComponents weekday] == 1){
            //Sunday -> do nothing, we have the end date
            [endDateComponents setDay:[todayComponents day]];
            [endDateComponents setMonth:[todayComponents month]];
            [endDateComponents setYear:[todayComponents year]];

        } else {
            // all other days of current week, so 8- weekday (if Friday: 8 - 6 = + 2 -> Sunday)
            NSDateComponents *componentsToAdd = [[NSDateComponents alloc] init];
            [componentsToAdd setDay: 8 - [todayComponents weekday]];
            NSDate *endOfWeek = [gregorian dateByAddingComponents:componentsToAdd
                                                                 toDate:[NSDate date] options:0];

            NSDateComponents *endOfWeekComponents = [gregorian components:(NSDayCalendarUnit | NSMonthCalendarUnit | NSYearCalendarUnit) fromDate:endOfWeek];

            [endDateComponents setDay:[endOfWeekComponents day]];
            [endDateComponents setMonth:[endOfWeekComponents month]];
            [endDateComponents setYear:[endOfWeekComponents year]];
        }
        break;

    case CostPeriodMonthly:
        [endDateComponents setDay:daysOfCurrentMonth.length];
        [endDateComponents setMonth:[todayComponents month]];
        [endDateComponents setYear:[todayComponents year]];
        break;

    case CostPeriodSemiAnnually:
        [endDateComponents setYear:[todayComponents year]];

        if([todayComponents month] <= 6){
            [endDateComponents setDay:30];
            [endDateComponents setMonth:6];
        } else {
            [endDateComponents setDay:31];
            [endDateComponents setMonth:12];
        }
        break;

    case CostPeriodAnnually:
        [endDateComponents setDay:31];
        [endDateComponents setMonth:12];
        [endDateComponents setYear:[todayComponents year]];
        break;

    default:
        [endDateComponents setDay:daysOfCurrentMonth.length];
        [endDateComponents setMonth:[todayComponents month]];
        [endDateComponents setYear:[todayComponents year]];
        break;
}

NSDate *endDate = [gregorian dateFromComponents:endDateComponents];
return endDate;

}

【问题讨论】：

标签： ios localization nsdate

【解决方案1】：

NSWeekdayCalendarUnit：1 总是星期日和 7 星期六？无论设置什么语言环境？

没错。但这并不意味着 1=Sunday 总是被认为是一周中的第一天。 NSCalendar 有一个 firstWeekDay 方法，那个取决于语言环境。（例如，在德国，星期一是一周的第一天。）

如果我 NSLog 我的 endDate（如下代码所示）或开始日期通常是日期和 23:00:00，因为我住在时区格林威治标准时间+1。这是正确的吗？

没错。

这个功能一般都可以吗，或者我会在一些问题中运行取决于特定的区域设置？

您的方法看起来过于复杂。要确定您可以使用的时间段

NSDate *now = [NSDate date];
NSCalendar *cal = [NSCalendar currentCalendar];
NSDate *startOfPeriod, *endOfPeriod;
NSTimeInterval lengthOfPeriod;

NSCalendarUnit unit = NSDayCalendarUnit; // or NSWeekCalendarUnit, NSMonthCalendarUnit, ...
[cal rangeOfUnit:unit startDate:&startOfPeriod interval:&lengthOfPeriod forDate:now];
endOfPeriod = [startOfPeriod dateByAddingTimeInterval:lengthOfPeriod]

根据您的语言环境，这应该可以正常工作。对于今天的当前一周（2 月 16 日星期日）在德国会给出结果

startOfPeriod =  2014-02-10 00:00:00 CET
endOfPeriod   =  2014-02-17 00:00:00 CET

因为这里的一周从星期一开始。（所以实际上endOfPeriod并不是结束期间的开始，但下一个期间的开始。）

半年期 没有对应的NSCalendarUnit，可以这样处理：

NSDate *now = [NSDate date];
NSCalendar *cal = [NSCalendar currentCalendar];

// Compute start and end of the current year (as above):
NSDate *startOfYear, *endOfYear;
NSTimeInterval lengthOfYear;
NSCalendarUnit unit = NSYearCalendarUnit;
[cal rangeOfUnit:unit startDate:&startOfYear interval:&lengthOfYear forDate:now];
endOfYear = [startOfYear dateByAddingTimeInterval:lengthOfYear];

// Compute middle of the year:
NSDateComponents *halfYear = [[NSDateComponents alloc] init];
NSRange range = [cal rangeOfUnit:NSMonthCalendarUnit inUnit:NSYearCalendarUnit forDate:now];
halfYear.month = range.length/2;
NSDate *middleOfYear = [cal dateByAddingComponents:halfYear toDate:startOfYear options:0];

// Compare current date with middle of the year and set start/end of period:
NSDate *startOfPeriod, *endOfPeriod;
if ([now compare:middleOfYear] == NSOrderedAscending) {
    startOfPeriod = startOfYear;
    endOfPeriod = middleOfYear;
} else {
    startOfPeriod = middleOfYear;
    endOfPeriod = endOfYear;
}

编辑：在 Martin 的帮助下改变了一切。有效，但仍然对结束日期 +1 天 +1 小时的必要性感到困惑......

+ (NSDate *)startDateForCostPeriod:(CostPeriod)costPeriod withDate:(NSDate *)date
{
    NSCalendar *calender = [NSCalendar currentCalendar];
    NSDate *startOfPeriod;
    NSTimeInterval lengthOfPeriod;
    //If unit is not initialized here, semi annual throws always a caution message since no unit is initialized there
    NSCalendarUnit unit = NSMonthCalendarUnit;

    //For the SemiAnnual period we need date components
    NSDateComponents *todayComponents =
    [calender components:(NSDayCalendarUnit | NSMonthCalendarUnit | NSYearCalendarUnit ) fromDate:date];
    NSDateComponents *startDateComponents = [[NSDateComponents alloc] init];

    switch (costPeriod) {
        case CostPeriodDaily:
            unit = NSDayCalendarUnit;
            break;

        case CostPeriodWeekly:
            unit = NSWeekCalendarUnit;
            break;

        case CostPeriodMonthly:
            unit = NSMonthCalendarUnit;
            break;

        case CostPeriodSemiAnnually:
            [startDateComponents setDay:1];
            [startDateComponents setYear:[todayComponents year]];

            if([todayComponents month] <= 6){
                [startDateComponents setMonth:1];
            } else {
                [startDateComponents setMonth:7];
            }
            break;

        case CostPeriodAnnually:
            unit = NSYearCalendarUnit;
            break;

        default:
            unit = NSMonthCalendarUnit;
            break;
    }

    if(costPeriod != CostPeriodSemiAnnually){
        [calender rangeOfUnit:unit startDate:&startOfPeriod interval:&lengthOfPeriod forDate:date];
        return startOfPeriod;
    } else {
        return [calender dateFromComponents:startDateComponents];
    }
}

+ (NSDate *)endDateForCostPeriod:(CostPeriod)costPeriod withDate:(NSDate *)date
{
    NSCalendar *calender = [NSCalendar currentCalendar];
    NSDate *startOfPeriod;
    NSTimeInterval lengthOfPeriod;
    //If unit is not initialized here, semi annual throws always a caution message since no unit is initialized there
    NSCalendarUnit unit = NSMonthCalendarUnit;

    //For the SemiAnnual period we need date components
    NSDateComponents *todayComponents =
    [calender components:(NSDayCalendarUnit | NSMonthCalendarUnit | NSYearCalendarUnit ) fromDate:date];
    NSDateComponents *endDateComponents = [[NSDateComponents alloc] init];

    switch (costPeriod) {
        case CostPeriodDaily:
            unit = NSDayCalendarUnit;
            break;

        case CostPeriodWeekly:
            unit = NSWeekCalendarUnit;
            break;

        case CostPeriodMonthly:
            unit = NSMonthCalendarUnit;
            break;

        case CostPeriodSemiAnnually:
            [endDateComponents setYear:[todayComponents year]];

            if([todayComponents month] <= 6){
                [endDateComponents setDay:30];
                [endDateComponents setMonth:6];
            } else {
                [endDateComponents setDay:31];
                [endDateComponents setMonth:12];
            }
            break;

        case CostPeriodAnnually:
            unit = NSYearCalendarUnit;
            break;

        default:
            unit = NSMonthCalendarUnit;
            break;
    }

    if(costPeriod != CostPeriodSemiAnnually){
        [calender rangeOfUnit:unit startDate:&startOfPeriod interval:&lengthOfPeriod forDate:date];
        return [startOfPeriod dateByAddingTimeInterval:lengthOfPeriod];
    } else {
        //somehow if you take the date without a time it is always 1 day and 1 hour before. i.e. 16.2.2014 is 15.2.2014 22:00:00
        //thats why you need to add 1 day and 1 hour!
        NSDate *endDate = [calender dateFromComponents:endDateComponents];
        NSDateComponents *componentsToAdd = [[NSDateComponents alloc] init];
        [componentsToAdd setDay: 1];
        [componentsToAdd setHour: 1];
        endDate = [calender dateByAddingComponents:componentsToAdd
                                             toDate:endDate options:0];

        return endDate;
    }
}

【讨论】：

非常感谢马丁。如果我理解正确，您的这种方法适用于每个地区，无论星期一还是星期日是一周的第一天，无论什么时区等？你能告诉我你是如何用这种方法得到一个时期的开始日期的吗？
@MichiZH：开始日期已经用那个代码计算出来了。它在 startDate:&startOfPeriod 参数中有点“隐藏”。是的，这应该会根据您的语言环境和时区给出正确的结果。
再次感谢您。现在将在我的应用程序中尝试 :-) 总是很高兴学到一些东西 :-)
还有一个问题：半年期间你会使用什么单位和lengthOfPeriod？
@MichiZH：半年没有日历单位。对于这种情况，您必须使用 NSDateComponents 计算它。