PATH  Documentation > Mac OS X > Foundation Reference: Objective-C



Table of Contents

NSDateFormatter


Inherits from:
NSFormatter : NSObject
Conforms to:
NSObject
(NSObject)
NSCoding (NSObject)
NSCopying (NSObject)
Declared in:
Foundation/NSDateFormatter.h




Class Description


Instances of NSDateFormatter format the textual representation of cells that contain NSDates (including NSCalendarDates), and convert textual representations of dates and times into NSDates. You can express the representation of dates and times very flexibly: "Thu 22 Dec 1994" is just as acceptable as "12/22/94". With natural-language processing for dates enabled, users can also express dates colloquially, such as "today," "day after tomorrow," and "a month from today."

To use an NSDateFormatter, allocate an instance of it and initialize it with initWithDateFormat:allowNaturalLanguage:. In the first argument use strftime-style conversion specifiers to compose the format string for textual representation. (For more information on these specifiers, see the see the description of NSCalendarDate's dateWithString:calendarFormat:locale: method.) Then use NSCell's setFormatter: method to associate the NSDateFormatter object with a cell. The value of a cell (NSCell) is represented by an object, typically an NSDate object in this case. When this value needs to be displayed or edited, the cell passes its object to the NSDateFormatter instance, which returns the formatted string. When the user enters a string, or when one is programmatically written in a cell (using setStringValue:), the cell obtains the equivalent NSDate object from the NSDateFormatter.

NSControl provides delegation methods that permit you to validate cell contents and to handle errors in formatting. See the specification of the NSFormatter class for details.

When a cell with a NSDateFormatter is copied, the new cell retains the NSDateFormatter object instead of copying it. You remove an NSDateFormatter from a cell by specifying nil as the argument of setFormatter:.

Instances of NSDateFormatter are immutable.


The Calendar Format


You must specify a format whenever you create a NSDateFormatter. This format is a string that contains specifiers that are very similar to those used in the standard C library function strftime(). When NSDateFormatter converts a date to a string, it uses this format.

Some NSCalendarDate methods, including setCalendarFormat: and many initialization methods, also expect format strings made from these specifiers.

The date conversion specifiers cover a range of date conventions:


Specifier Description
%% a '%' character
%a abbreviated weekday name
%A full weekday name
%b abbreviated month name
%B full month name
%c shorthand for "%X %x", the locale format for date and time
%d day of the month as a decimal number (01-31)
%e same as %d but does not print the leading 0 for days 1 through 9
%F milliseconds as a decimal number (000-999)
%H hour based on a 24-hour clock as a decimal number (00-23)
%I hour based on a 12-hour clock as a decimal number (01-12)
%j day of the year as a decimal number (001-366)
%m month as a decimal number (01-12)
%M minute as a decimal number (00-59)
%p AM/PM designation for the locale
%S second as a decimal number (00-59)
%w weekday as a decimal number (0-6), where Sunday is 0
%x date using the date representation for the locale
%X time using the time representation for the locale
%y year without century (00-99)
%Y year with century (such as 1990)
%Z time zone name (such as Pacific Daylight Time)
%z time zone offset in hours and minutes from GMT (HHMM)




Method Types


Initializing an NSDateFormatter
- initWithDateFormat:allowNaturalLanguage:
Determining attributes
- allowsNaturalLanguage
- dateFormat


Instance Methods



allowsNaturalLanguage

- (BOOL)allowsNaturalLanguage

Returns YES if the NSDateFormatter attempts to process dates entered as a vernacular string ("today," "day before yesterday," and so on). Returns NO if the NSDateFormatter does not do any natural-language processing of these date expressions.



dateFormat

- (NSString *)dateFormat

Returns the date format string used by an NSDateFormatter object. See "The Calendar Format" for a list of the conversion specifiers permitted in date format strings.



initWithDateFormat:allowNaturalLanguage:

- (id)initWithDateFormat:(NSString *)format allowNaturalLanguage:(BOOL)flag

Initializes and returns an NSDateFormatter instance that uses the date format in its conversions. See the description of NSCalendarDate's dateWithString:calendarFormat:locale: for a list of conversion specifiers permitted in date format strings. Set flag to YES if you want the NSDateFormatter to process dates entered as expressions in the vernacular (for example, "tomorrow"); NSDateFormatter attempts natural-language processing only after it fails to interpret an entered string according to format. The following example creates a date formatter with the format string (as example) "Mar 15 1994" and then associates the formatter with the cells of a form (contactsForm).

NSDateFormatter *dateFormat = [[NSDateFormatter alloc]
    initWithDateFormat:@"%b %d %Y" allowNaturalLanguage:NO];
[[contactsForm cells] makeObjectsPerform:@selector(setFormatter:)
     withObject:dateFormat]




Table of Contents