使用NSDateComponents获得一周的第一天：更改年份

Question

您好，我在设置firstWeekDay时遇到问题，这是我的工作：

NSCalendar *gregorian = [[NSCalendar alloc] initWithCalendarIdentifier:NSGregorianCalendar]; 
comp = [gregorian components:(NSYearCalendarUnit | NSMonthCalendarUnit | NSWeekCalendarUnit | NSWeekdayCalendarUnit) fromDate:targetDate];
[comp setWeekday:2];

NSDate *firstWeekDay = [gregorian dateFromComponents:comp];

如果2011年1月1日星期六是targetDate，则我日历中的firstWeekDay似乎是2011年12月26日星期一，但实际上应该是2010年12月26日星期一。 我该怎么做？

Answer 1

若要解决此问题， 请在NSDateComponents中添加NSYearForWeekOfYearCalendarUnit 。

例如：

NSCalendar* calendar = [NSCalendar currentCalendar];
NSDateComponents* comps = [calendar components:NSYearForWeekOfYearCalendarUnit |NSYearCalendarUnit|NSMonthCalendarUnit|NSWeekCalendarUnit|NSWeekdayCalendarUnit fromDate:curDate];

[comps setWeekday:2]; // 2: monday
firstDayOfTheWeek = [calendar dateFromComponents:comps];
[comps setWeekday:7]; // 7: saturday
lastDayOfTheWeek = [calendar dateFromComponents:comps];

Answer 2

下面还介绍了边缘情况，

- (NSDate *)getFirstDayOfTheWeekFromDate:(NSDate *)givenDate
{
    NSCalendar *calendar = [NSCalendar currentCalendar];


   NSDateComponents *components = [calendar components:NSYearCalendarUnit|NSMonthCalendarUnit|NSWeekCalendarUnit|NSWeekdayCalendarUnit fromDate:givenDate];
    [components setWeekday:2]; // 1 == Sunday, 7 == Saturday
    if([[calendar dateFromComponents:components] compare: curDate] == NSOrderedDescending) // if start is later in time than end
    {
        [components setWeek:[components week]-1];
    }

    return [calendar dateFromComponents:components];
}

Answer 3

Swift解决方案（感谢@YvesJusot）：

let calendar = NSCalendar.currentCalendar()
let comps = calendar.components(NSCalendarUnit.WeekOfYearCalendarUnit|NSCalendarUnit.YearCalendarUnit|NSCalendarUnit.MonthCalendarUnit|NSCalendarUnit.WeekCalendarUnit|NSCalendarUnit.WeekdayCalendarUnit, fromDate: NSDate()) as NSDateComponents

comps.setValue(2, forComponent: NSCalendarUnit.WeekdayCalendarUnit)
let monday = calendar.dateFromComponents(comps)!

println("\(monday)")

Answer 4

您假设使用动态值，而不是像星期一那样对2进行硬编码！

NSCalendar* calendar = [NSCalendar currentCalendar];
NSDateComponents* comps = [calendar components:NSYearForWeekOfYearCalendarUnit|NSYearCalendarUnit|NSMonthCalendarUnit|NSWeekCalendarUnit|NSWeekdayCalendarUnit fromDate:[NSDate date]];

comps.weekday = calendar.firstWeekday;
firstDayOfTheWeek = [calendar dateFromComponents:comps];
comps.weekday = calendar.firstWeekday - 1;
lastDayOfTheWeek = [calendar dateFromComponents:comps];

Answer 5

尝试这个

// adjust them for first day of previous week (Monday)
[comp setWeekday:2];
[comp setWeek:([comp week] - 1)];

请注意，此解决方案假定一周的第一天为星期一。

Answer 6

我在@JasonGarrett答案中做了一些更改，它对我有用。

let calendar = NSCalendar.currentCalendar()
let flags : NSCalendarUnit = NSCalendarUnit.CalendarUnitDay | NSCalendarUnit.CalendarUnitMonth | NSCalendarUnit.CalendarUnitYear
let comps = calendar.components(flags, fromDate: NSDate()) as NSDateComponents
                comps.setValue(2, forComponent: NSCalendarUnit.CalendarUnitWeekday)
let monday = calendar.dateFromComponents(comps)!

Answer 7

// Make these two methods as categories to NSDate
// Use This to get First date of the week (Monday)

- (NSDate *) getFirstDayOfWeek {

    NSCalendar *calendar = [[NSCalendar alloc] initWithCalendarIdentifier:NSCalendarIdentifierGregorian];

    NSDateComponents *compOfDate = [calendar components:(NSCalendarUnitYear | NSCalendarUnitMonth | NSCalendarUnitDay | NSCalendarUnitWeekday) fromDate:self];

    NSInteger numOfDaysToAdd = compOfDate.weekday == 1 ? -6 : (2 - compOfDate.weekday);

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

    compToAdd.day = numOfDaysToAdd;

    return [calendar dateByAddingComponents:compToAdd toDate:self options:0];
}

// Use This to get last date of the week (Sunday)

- (NSDate *)getLastDayOfWeek {

    NSCalendar *calendar = [[NSCalendar alloc] initWithCalendarIdentifier:NSCalendarIdentifierGregorian];

    NSDateComponents *compOfDate = [calendar components:(NSCalendarUnitYear | NSCalendarUnitMonth | NSCalendarUnitDay | NSCalendarUnitWeekday) fromDate:self];

    NSInteger numOfDaysToAdd = compOfDate.weekday == 1 ? 0 : (8 - compOfDate.weekday);

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

    compToAdd.day = numOfDaysToAdd;

    return [calendar dateByAddingComponents:compToAdd toDate:self options:0];
}