| Inherits from | |
| Conforms to | |
| Framework | /System/Library/Frameworks/Foundation.framework |
| Availability | Available in iPhone OS 2.0 and later. |
| Declared in | NSDate.h |
| Companion guides | |
| Related sample code |
NSDate objects represent a single point in time. NSDate is a class cluster; its single public superclass, NSDate, declares the programmatic interface for specific and relative time values. The objects you create using NSDate are referred to as date objects. They are immutable objects. Because of the nature of class clusters, objects returned by the NSDate class are instances not of that abstract class but of one of its private subclasses. Although a date object’s class is private, its interface is public, as declared by the abstract superclass NSDate. Generally, you instantiate a suitable date object by invoking one of the date... class methods.
NSDate is an abstract class that provides behavior for creating dates, comparing dates, representing dates, computing intervals, and similar functionality. NSDate presents a programmatic interface through which suitable date objects are requested and returned. Date objects returned from NSDate are lightweight and immutable since they represent an invariant point in time. This class is designed to provide the foundation for arbitrary calendrical representations.
The sole primitive method of NSDate, timeIntervalSinceReferenceDate, provides the basis for all the other methods in the NSDate interface. This method returns a time value relative to an absolute reference date—the first instant of 1 January 2001, GMT.
NSDate provides several methods to interpret and to create string representations of dates (for example, dateWithNaturalLanguageString:locale: and descriptionWithLocale:). In general, on Mac OS X v10.4 and later you should use an instance of NSDateFormatter to parse and generate strings using the methods dateFromString: and stringFromDate:—see Date Formatters for more details.
NSDate models the change from the Julian to the Gregorian calendar in October 1582, and calendrical calculations performed in conjunction with NSCalendar take this transition into account. Note, however, that some locales adopted the Gregorian calendar at other times; for example, Great Britain didn't switch over until September 1752.
NSDate is “toll-free bridged” with its Cocoa Foundation counterpart, CFDate Reference. This means that the Core Foundation type is interchangeable in function or method calls with the bridged Foundation object. Therefore, in a method where you see an NSDate * parameter, you can pass a CFDateRef, and in a function where you see a CFDateRef parameter, you can pass an NSDate instance (you cast one type to the other to suppress compiler warnings). See Interchangeable Data Types for more information on toll-free bridging.
The major reason for subclassing NSDate is to create a class with convenience methods for working with a particular calendrical system. But you could also require a custom NSDate class for other reasons, such as to get a date and time value that provides a finer temporal granularity.
If you want to subclass NSDate to obtain behavior different than that provided by the private or public subclasses, you must do these things:
Declare a suitable instance variable to hold the date and time value (relative to an absolute reference date).
Override the timeIntervalSinceReferenceDate instance method to provide the correct date and time value based on your instance variable.
Override initWithTimeIntervalSinceReferenceDate:, the designated initializer method.
If you are creating a subclass that represents a calendrical system, you must also define methods that partition past and future periods into the units of this calendar.
Because the NSDate class adopts the NSCopying and NSCoding protocols, your subclass must also implement all of the methods in these protocols.
Your subclass may use a different reference date than the absolute reference date used by NSDate (the first instance of 1 January 2001, GMT). If it does, it must still use the absolute reference date in its implementations of the methods timeIntervalSinceReferenceDate and initWithTimeIntervalSinceReferenceDate:. That is, the reference date referred to in the titles of these methods is the absolute reference date. If you do not use the absolute reference date in these methods, comparisons between NSDate objects of your subclass and NSDate objects of a private subclass will not work.
+ date
+ dateWithTimeIntervalSinceNow:
+ dateWithTimeIntervalSinceReferenceDate:
+ dateWithTimeIntervalSince1970:
– init
– initWithTimeIntervalSinceNow:
– initWithTimeInterval:sinceDate:
– initWithTimeIntervalSinceReferenceDate:
– timeIntervalSinceDate:
– timeIntervalSinceNow
+ timeIntervalSinceReferenceDate
– timeIntervalSinceReferenceDate
– timeIntervalSince1970
Creates and returns a new date set to the current date and time.
+ (id)date
A new date object set to the current date and time.
This method uses the default initializer method for the class, init.
The following code sample shows how to use date to get the current date:
NSDate *today = [NSDate date]; |
NSDate.hCreates and returns an NSDate object set to the given number of seconds from the first instant of 1 January 1970, GMT.
+ (id)dateWithTimeIntervalSince1970:(NSTimeInterval)seconds
The number of seconds from the reference date, 1 January 1970, GMT, for the new date. Use a negative argument to specify a date before this date.
An NSDate object set to seconds seconds from the reference date.
This method is useful for creating NSDate objects from time_t values returned by BSD system functions.
NSDate.hCreates and returns an NSDate object set to a given number of seconds from the current date and time.
+ (id)dateWithTimeIntervalSinceNow:(NSTimeInterval)seconds
The number of seconds from the current date and time for the new date. Use a negative value to specify a date before the current date.
An NSDate object set to seconds seconds from the current date and time.
NSDate.h
Creates and returns an NSDate object set to a given number of seconds from the first instant of 1 January 2001, GMT.
+ (id)dateWithTimeIntervalSinceReferenceDate:(NSTimeInterval)seconds
The number of seconds from the absolute reference date (the first instant of 1 January 2001, GMT) for the new date. Use a negative argument to specify a date and time before the reference date.
An NSDate object set to seconds seconds from the absolute reference date.
NSDate.h
Creates and returns an NSDate object representing a date in the distant future.
+ (id)distantFuture
An NSDate object representing a date in the distant future (in terms of centuries).
You can pass this value when an NSDate object is required to have the date argument essentially ignored. For example, the NSWindow method nextEventMatchingMask:untilDate:inMode:dequeue: returns nil if an event specified in the event mask does not happen before the specified date. You can use the object returned by distantFuture as the date argument to wait indefinitely for the event to occur.
myEvent = [myWindow nextEventMatchingMask:myEventMask |
untilDate:[NSDate distantFuture] |
inMode:NSDefaultRunLoopMode |
dequeue:YES]; |
NSDate.h
Creates and returns an NSDate object representing a date in the distant past.
+ (id)distantPast
An NSDate object representing a date in the distant past (in terms of centuries).
You can use this object as a control date, a guaranteed temporal boundary.
NSDate.hReturns the interval between the first instant of 1 January 2001, GMT and the current date and time.
+ (NSTimeInterval)timeIntervalSinceReferenceDate
The interval between the system’s absolute reference date (the first instant of 1 January 2001, GMT) and the current date and time.
This method is the primitive method for NSDate. If you subclass NSDate, you must override this method with your own implementation for it.
– timeIntervalSinceReferenceDate– timeIntervalSinceDate:– timeIntervalSince1970– timeIntervalSinceNowNSDate.hReturns a new NSDate object that is set to a given number of seconds relative to the receiver. (Deprecated. This method has been replaced by dateByAddingTimeInterval:.)
- (id)addTimeInterval:(NSTimeInterval)seconds
The number of seconds to add to the receiver. Use a negative value for seconds to have the returned object specify a date before the receiver.
A new NSDate object that is set to seconds seconds relative to the receiver. The date returned might have a representation different from the receiver’s.
NSDate.hReturns an NSComparisonResult value that indicates the temporal ordering of the receiver and another given date.
- (NSComparisonResult)compare:(NSDate *)anotherDate
The date with which to compare the receiver.
This value must not be nil. If the value is nil, the behavior is undefined and may change in future versions of Mac OS X.
If:
The receiver and anotherDate are exactly equal to each other, NSOrderedSame
The receiver is later in time than anotherDate, NSOrderedDescending
The receiver is earlier in time than anotherDate, NSOrderedAscending.
This method detects sub-second differences between dates. If you want to compare dates with a less fine granularity, use timeIntervalSinceDate: to compare the two dates.
– earlierDate:– isEqual: (NSObject protocol)– laterDate:NSDate.h
Returns a string representation of the receiver.
- (NSString *)description
A string representation of the receiver in the international format YYYY-MM-DD HH:MM:SS ±HHMM, where ±HHMM represents the time zone offset in hours and minutes from GMT (for example, “2001-03-24 10:45:32 +0600”).
NSDate.h
Returns the earlier of the receiver and another given date.
- (NSDate *)earlierDate:(NSDate *)anotherDate
The date with which to compare the receiver.
The earlier of the receiver and anotherDate, determined using timeIntervalSinceDate:. If the receiver and anotherDate represent the same date, returns the receiver.
– compare:– isEqual: (NSObject protocol)– laterDate:NSDate.hReturns an NSDate object initialized to the current date and time.
- (id)init
An NSDate object initialized to the current date and time.
This method uses the designated initializer, initWithTimeIntervalSinceReferenceDate:.
NSDate.hReturns an NSDate object initialized relative to another given date by a given number of seconds.
- (id)initWithTimeInterval:(NSTimeInterval)seconds sinceDate:(NSDate *)refDate
The number of seconds to add to refDate. A negative value means the receiver will be earlier than refDate.
The reference date.
An NSDate object initialized relative to refDate by seconds seconds.
This method uses the designated initializer, initWithTimeIntervalSinceReferenceDate:.
NSDate.hReturns an NSDate object initialized relative to the current date and time by a given number of seconds.
- (id)initWithTimeIntervalSinceNow:(NSTimeInterval)seconds
The number of seconds from relative to the current date and time to which the receiver should be initialized. A negative value means the returned object will represent a date in the past.
An NSDate object initialized relative to the current date and time by seconds seconds.
This method uses the designated initializer, initWithTimeIntervalSinceReferenceDate:.
NSDate.h
Returns an NSDate object initialized relative the first instant of 1 January 2001, GMT by a given number of seconds.
- (id)initWithTimeIntervalSinceReferenceDate:(NSTimeInterval)seconds
The number of seconds to add to the reference date (the first instant of 1 January 2001, GMT). A negative value means the receiver will be earlier than the reference date.
An NSDate object initialized relative to the absolute reference date by seconds seconds.
This method is the designated initializer for the NSDate class and is declared primarily for the use of subclasses of NSDate. When you subclass NSDate to create a concrete date class, you must override this method.
NSDate.h
Returns a Boolean value that indicates whether a given object is an NSDate object and exactly equal the receiver.
- (BOOL)isEqualToDate:(NSDate *)anotherDate
The date to compare with the receiver.
YES if the anotherDate is an NSDate object and is exactly equal to the receiver, otherwise NO.
This method detects sub-second differences between dates. If you want to compare dates with a less fine granularity, use timeIntervalSinceDate: to compare the two dates.
– compare:– earlierDate:– isEqual: (NSObject protocol)– laterDate:NSDate.h
Returns the later of the receiver and another given date.
- (NSDate *)laterDate:(NSDate *)anotherDate
The date with which to compare the receiver.
The later of the receiver and anotherDate, determined using timeIntervalSinceDate:. If the receiver and anotherDate represent the same date, returns the receiver.
– compare:– earlierDate:– isEqual: (NSObject protocol)NSDate.h
Returns the interval between the receiver and the first instant of 1 January 1970, GMT.
- (NSTimeInterval)timeIntervalSince1970
The interval between the receiver and the reference date, 1 January 1970, GMT. If the receiver is earlier than the reference date, the value is negative.
– timeIntervalSinceDate:– timeIntervalSinceNow– timeIntervalSinceReferenceDate+ timeIntervalSinceReferenceDateNSDate.h
Returns the interval between the receiver and another given date.
- (NSTimeInterval)timeIntervalSinceDate:(NSDate *)anotherDate
The date with which to compare the receiver.
The interval between the receiver and anotherDate. If the receiver is earlier than anotherDate, the return value is negative.
NSDate.h
Returns the interval between the receiver and the current date and time.
- (NSTimeInterval)timeIntervalSinceNow
The interval between the receiver and the current date and time. If the receiver is earlier than the current date and time, the return value is negative.
NSDate.hReturns the interval between the receiver and the first instant of 1 January 2001, GMT.
- (NSTimeInterval)timeIntervalSinceReferenceDate
The interval between the receiver and the system’s absolute reference date (the first instant of 1 January 2001, GMT). If the receiver is earlier than the reference date, the value is negative.
NSDate.hNSDate provides a constant that specifies the number of seconds from 1 January 1970 to the reference date, 1 January 2001.
#define NSTimeIntervalSince1970 978307200.0
NSTimeIntervalSince1970The number of seconds from 1 January 1970 to the reference date, 1 January 2001.
Available in iPhone OS 2.0 and later.
Declared in NSDate.h.
1 January 1970 is the epoch (or starting point) for Unix time.
NSDate.h
Last updated: 2009-08-17
