NSDate/NSDateComponent問題

Question

假設我們是15/07/2010，我想獲得上週的第一天，即7月5日。我有以下方法，但它不起作用。似乎我的週日屬性有問題...

+ (NSDate *)getFirstDayOfPreviousWeek 
{ 
// Get current date 
NSCalendar *cal = [[NSCalendar alloc] initWithCalendarIdentifier:NSGregorianCalendar]; 
NSDate *now = [NSDate date]; 

// Get today date at midnight 
NSDateComponents *components = [cal components:(NSYearCalendarUnit | NSMonthCalendarUnit | NSDayCalendarUnit | NSHourCalendarUnit | NSMinuteCalendarUnit | NSSecondCalendarUnit | NSTimeZoneCalendarUnit) fromDate:now]; 
[components setHour:0]; 
[components setMinute:0]; 
[components setSecond:0]; 
NSInteger *dayNbr = [components weekday]; 
NSLog(@"week day:%@",dayNbr); // CRASH 
NSDate *todayMidnight = [cal dateFromComponents:components]; 

// Get first day of previous week midnight 
components = [[[NSDateComponents alloc] init] autorelease]; 
NSInteger *wd = [dayNbr intValue] * -1 + 1; 
[components setWeekDay:wd]; 
[components setWeek:-1]; 
NSDate *newDate = [cal dateByAddingComponents:components toDate:todayMidnight options:0]; 
[cal release]; 

NSLog(@"new date:%@", newDate); 

return newDate; 
} 

請問您可以幫忙嗎？

非常感謝，

呂克

Answer 1

我認爲它應該是一個容易得多

- (NSDate *)getFirstDayOfPreviousWeek 
{ 
    NSCalendar *cal = [[NSCalendar alloc] initWithCalendarIdentifier:NSGregorianCalendar]; 
    NSDate *now = [NSDate date]; 
    NSLog(@"Current date: %@", now); 

    // required components for today 
    NSDateComponents *components = [cal components:(NSYearCalendarUnit | NSMonthCalendarUnit | NSWeekCalendarUnit | NSWeekdayCalendarUnit) fromDate:now]; 

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

    // construct new date and return 
    NSDate *newDate = [cal dateFromComponents:components]; 
    NSLog(@"New date: %@", newDate); 

    return newDate; 
} 

注意此解決方案假定一週的第一天是星期一。

Answer 2

以下斯威夫特3遊樂場代碼展示瞭如何從任何日期獲得前一週的第一天：

import Foundation 

let calendar = Calendar(identifier: .gregorian) 
let intialDate = Date() 

// Prepare the new date components 
var newDateComponents = calendar.dateComponents([.year, .month, .weekOfMonth], from: intialDate) 
newDateComponents.weekOfMonth = newDateComponents.weekOfMonth! - 1 // get previous week 
newDateComponents.weekday = 2 // sunday is 1, monday is 2 

// Get the new date 
let newDate = calendar.date(from: newDateComponents) 
print(newDate ?? "Could not retrieve a date") 

---

如果您需要重複此操作，您可以重構你的代碼爲函數或方法：

import Foundation 

func firstDayOfPreviousWeek(from date: Date) -> Date? { 
    let calendar = Calendar(identifier: .gregorian) 
    var newDateComponents = calendar.dateComponents([.year, .month, .weekOfMonth], from: date) 
    newDateComponents.weekOfMonth = newDateComponents.weekOfMonth! - 1 
    newDateComponents.weekday = 2 
    return calendar.date(from: newDateComponents) 
} 

---

因此，下面的遊樂場代碼演示瞭如何獲取的第一天Ø f上週從2010年7月15日開始：

import Foundation 

func firstDayOfPreviousWeek(from date: Date) -> Date? { 
    let calendar = Calendar(identifier: .gregorian) 
    var newDateComponents = calendar.dateComponents([.year, .month, .weekOfMonth], from: date) 
    newDateComponents.weekOfMonth = newDateComponents.weekOfMonth! - 1 
    newDateComponents.weekday = 2 
    newDateComponents.timeZone = TimeZone(abbreviation: "GMT") 
    return calendar.date(from: newDateComponents) 
} 

let calendar = Calendar(identifier: .gregorian) 
var july15Components = DateComponents() 
july15Components.day = 15 
july15Components.month = 7 
july15Components.year = 2010 
july15Components.timeZone = TimeZone(abbreviation: "GMT") 
let july15 = calendar.date(from: july15Components)! 
print(july15) // prints 2010-07-15 00:00:00 +0000 

let newDate = firstDayOfPreviousWeek(from: july15) 
print(newDate ?? "Could not retrieve a date") // prints 2010-07-05 00:00:00 +0000