如何使用Cocoa查找任何给定日期的星期几

Question

I'm trying to figure out what day (ie Monday, Friday...) of any given date (ie Jun 27th, 2009)

Thank you.

Answer 1

I've been doing:

NSDateFormatter* theDateFormatter = [[[NSDateFormatter alloc] init] autorelease];
[theDateFormatter setFormatterBehavior:NSDateFormatterBehavior10_4];
[theDateFormatter setDateFormat:@"EEEE"];
NSString *weekDay =  [theDateFormatter stringFromDate:[NSDate date]];

This has the added bonus of letting you choose how you'd like the weekday to be returned (by changing the date format string in the setDateFormat: call

Lots more information at:

http://developer.apple.com/documentation/Cocoa/Conceptual/DataFormatting/Articles/dfDateFormatting10_4.html#//apple_ref/doc/uid/TP40002369

Answer 2

You may have a look to the NSDate and NSCalendar classes. For example, here and here

They provide the following code:

NSDate *today = [NSDate date];
NSCalendar *gregorian = [[NSCalendar alloc]
                         initWithCalendarIdentifier:NSGregorianCalendar];
NSDateComponents *weekdayComponents =
                [gregorian components:(NSDayCalendarUnit | NSWeekdayCalendarUnit) fromDate:today];
NSInteger day = [weekdayComponents day];
NSInteger weekday = [weekdayComponents weekday];

Answer 3

Use NSCalendar and NSDateComponents. As shown in the NSDateComponents documentation:

NSCalendar *gregorian = [[NSCalendar alloc]
initWithCalendarIdentifier:NSGregorianCalendar];
NSDate *date = [gregorian dateFromComponents:comps];
NSDateComponents *weekdayComponents = [gregorian components:NSWeekdayCalendarUnit fromDate:date];
int weekday = [weekdayComponents weekday];

Answer 4

Here's what I wound up with, which works exactly as intended. It takes a date, alters the date to be the first of the month, and gets the day of that date:

    NSDateComponents *components = [[NSCalendar currentCalendar] components:NSCalendarUnitDay | NSCalendarUnitMonth | NSCalendarUnitYear fromDate:date];
NSDateComponents *monthDateComponents = [[NSCalendar currentCalendar] components: NSCalendarUnitDay | NSCalendarUnitMonth | NSCalendarUnitYear |
                                         NSCalendarUnitHour | NSCalendarUnitMinute | NSCalendarUnitSecond fromDate: date];

//  build date as start of month
monthDateComponents.year = components.year;
monthDateComponents.month = components.month;
monthDateComponents.day = 1;

NSCalendar *gregorian = [[NSCalendar alloc] initWithCalendarIdentifier:NSCalendarIdentifierGregorian];
//    [gregorian setFirstWeekday:1];

NSDate *builtDate =[gregorian dateFromComponents: monthDateComponents];
//    NSDateComponents *weekdayComponents =[gregorian components: NSCalendarUnitWeekday fromDate: builtDate];

NSDateFormatter *df = [NSDateFormatter new];
[df setDateFormat:@"E"];

NSString *firstDay = [df stringFromDate:builtDate];
if([firstDay isEqual:@"Sun"])  //  do for the other 6 days as appropriate
    return 7;