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NSTimeZone Class Reference

Overview

NSTimeZone is an abstract class that defines the behavior of time zone objects. Time zone objects represent geopolitical regions. Consequently, these objects have names for these regions. Time zone objects also represent a temporal offset, either plus or minus, from Greenwich Mean Time (GMT) and an abbreviation (such as PST for Pacific Standard Time).

NSTimeZone provides several class methods to get time zone objects: timeZoneWithName:, timeZoneWithName:data:, timeZoneWithAbbreviation:, and timeZoneForSecondsFromGMT:. The class also permits you to set the default time zone within your application (setDefaultTimeZone:). You can access this default time zone at any time with the defaultTimeZone class method, and with the localTimeZone class method, you can get a relative time zone object that decodes itself to become the default time zone for any locale in which it finds itself.

Cocoa does not provide any API to change the time zone of the computer, or of other applications.

Some NSCalendarDate methods return date objects that are automatically bound to time zone objects. These date objects use the functionality of NSTimeZone to adjust dates for the proper locale. Unless you specify otherwise, objects returned from NSCalendarDate are bound to the default time zone for the current locale.

Note that, strictly, time zone database entries such as “America/Los_Angeles” are IDs not names. An example of a time zone name is “Pacific Daylight Time”. Although many NSTimeZone method names include the word “name”, they refer to IDs.

NSTimeZone is “toll-free bridged” with its Core Foundation counterpart, CFTimeZone 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 NSTimeZone * parameter, you can pass a CFTimeZoneRef, and in a function where you see a CFTimeZoneRef parameter, you can pass an NSTimeZone instance (you cast one type to the other to suppress compiler warnings). See Interchangeable Data Types for more information on toll-free bridging.

Adopted Protocols

• – encodeWithCoder:

• – initWithCoder:

• – copyWithZone:

Tasks

Creating and Initializing Time Zone Objects

• + timeZoneWithAbbreviation:
• + timeZoneWithName:
• + timeZoneWithName:data:
• + timeZoneForSecondsFromGMT:
• – initWithName:
• – initWithName:data:

Working with System Time Zones

• + localTimeZone
• + defaultTimeZone
• + setDefaultTimeZone:
• + resetSystemTimeZone
• + systemTimeZone

Getting Time Zone Information

• + abbreviationDictionary
• + knownTimeZoneNames

Getting Information About a Specific Time Zone

• – abbreviation
• – abbreviationForDate:
• – name
• – secondsFromGMT
• – secondsFromGMTForDate:
• – data

Comparing Time Zones

• – isEqualToTimeZone:

Describing a Time Zone

• – description
• – localizedName:locale:

Getting Information About Daylight Saving

• – isDaylightSavingTime
• – daylightSavingTimeOffset
• – isDaylightSavingTimeForDate:
• – daylightSavingTimeOffsetForDate:
• – nextDaylightSavingTimeTransition
• – nextDaylightSavingTimeTransitionAfterDate:

Class Methods

abbreviationDictionary

Returns a dictionary holding the mappings of time zone abbreviations to time zone names.

+ (NSDictionary *)abbreviationDictionary

Return Value

A dictionary holding the mappings of time zone abbreviations to time zone names.

Discussion

Note that more than one time zone may have the same abbreviation—for example, US/Pacific and Canada/Pacific both use the abbreviation “PST.” In these cases, abbreviationDictionary chooses a single name to map the abbreviation to.

Availability

• Available in Mac OS X v10.0 and later.

Declared In

NSTimeZone.h

defaultTimeZone

Returns the default time zone for the current application.

+ (NSTimeZone *)defaultTimeZone

Return Value

The default time zone for the current application. If no default time zone has been set, this method invokes systemTimeZone and returns the system time zone.

Discussion

The default time zone is the one that the application is running with, which you can change (so you can make the application run as if it were in a different time zone).

If you get the default time zone and hold onto the returned object, it does not change if a subsequent invocation of setDefaultTimeZone: changes the default time zone—you still have the specific time zone you originally got. Contrast this behavior with the object returned by localTimeZone.

Availability

• Available in Mac OS X v10.0 and later.

See Also

• + localTimeZone
• + setDefaultTimeZone:
• + systemTimeZone

Declared In

NSTimeZone.h

knownTimeZoneNames

Returns an array of strings listing the IDs of all the time zones known to the system.

+ (NSArray *)knownTimeZoneNames

Return Value

An array of strings listing the IDs of all the time zones known to the system.

Availability

• Available in Mac OS X v10.0 and later.

Declared In

NSTimeZone.h

localTimeZone

Returns an object that forwards all messages to the default time zone for the current application.

+ (NSTimeZone *)localTimeZone

Return Value

An object that forwards all messages to the default time zone for the current application.

Discussion

The local time zone represents the current state of the default time zone at all times. If you get the default time zone (using defaultTimeZone) and hold onto the returned object, it does not change if a subsequent invocation of setDefaultTimeZone: changes the default time zone—you still have the specific time zone you originally got. The local time zone adds a level of indirection, it acts as if it were the current default time zone whenever you invoke a method on it.

Availability

• Available in Mac OS X v10.0 and later.

See Also

• + defaultTimeZone
• + setDefaultTimeZone:

Declared In

NSTimeZone.h

resetSystemTimeZone

Resets the system time zone object cached by the application, if any.

+ (void)resetSystemTimeZone

Discussion

If the application has cached the system time zone, this method clears that cached object. If you subsequently invoke systemTimeZone, NSTimeZone will attempt to redetermine the system time zone and a new object will be created and cached (see systemTimeZone).

Availability

• Available in Mac OS X v10.0 and later.

See Also

• + systemTimeZone

Declared In

NSTimeZone.h

setDefaultTimeZone:

Sets the default time zone for the current application to a given time zone.

+ (void)setDefaultTimeZone:(NSTimeZone *)aTimeZone

Parameters

aTimeZone

The new default time zone for the current application.

Discussion

There can be only one default time zone, so by setting a new default time zone, you lose the previous one.

Availability

• Available in Mac OS X v10.0 and later.

See Also

• + defaultTimeZone
• + localTimeZone

Declared In

NSTimeZone.h

systemTimeZone

Returns the time zone currently used by the system.

+ (NSTimeZone *)systemTimeZone

Return Value

The time zone currently used by the system. If the current time zone cannot be determined, returns the GMT time zone.

Special Considerations

If you get the system time zone, it is cached by the application and does not change if the user subsequently changes the system time zone. The next time you invoke systemTimeZone, you get back the same time zone you originally got. You have to invoke resetSystemTimeZone to clear the cached object.

Availability

• Available in Mac OS X v10.0 and later.

See Also

• + resetSystemTimeZone

Declared In

NSTimeZone.h

timeZoneForSecondsFromGMT:

Returns a time zone object offset from Greenwich Mean Time by a given number of seconds.

+ (id)timeZoneForSecondsFromGMT:(NSInteger)seconds

Parameters

seconds

The number of seconds by which the new time zone is offset from GMT.

Return Value

A time zone object offset from Greenwich Mean Time by seconds.

Discussion

The name of the new time zone is GMT +/– the offset, in hours and minutes. Time zones created with this method never have daylight savings, and the offset is constant no matter the date.

Availability

• Available in Mac OS X v10.0 and later.

See Also

• + timeZoneWithAbbreviation:
• + timeZoneWithName:

Declared In

NSTimeZone.h

timeZoneWithAbbreviation:

Returns the time zone object identified by a given abbreviation.

+ (id)timeZoneWithAbbreviation:(NSString *)abbreviation

Parameters

abbreviation

An abbreviation for a time zone.

Return Value

The time zone object identified by abbreviation determined by resolving the abbreviation to a name using the abbreviation dictionary and then returning the time zone for that name. Returns nil if there is no match for abbreviation.

Discussion

In general, you are discouraged from using abbreviations except for unique instances such as “UTC” or “GMT”. Time Zone abbreviations are not standardized and so a given abbreviation may have multiple meanings—for example, “EST” refers to Eastern Time in both the United States and Australia

Availability

• Available in Mac OS X v10.0 and later.

See Also

• + abbreviationDictionary
• + timeZoneForSecondsFromGMT:
• + timeZoneWithName:

Declared In

NSTimeZone.h

timeZoneWithName:

Returns the time zone object identified by a given ID.

+ (id)timeZoneWithName:(NSString *)aTimeZoneName

Parameters

aName

The ID for the time zone.

Return Value

The time zone in the information directory with a name matching aName. Returns nil if there is no match for the name.

Availability

• Available in Mac OS X v10.0 and later.

See Also

• + timeZoneForSecondsFromGMT:
• + timeZoneWithAbbreviation:
• + knownTimeZoneNames

Declared In

NSTimeZone.h

timeZoneWithName:data:

Returns the time zone with a given ID whose data has been initialized using given data,

+ (id)timeZoneWithName:(NSString *)aTimeZoneName data:(NSData *)data

Parameters

aTimeZoneName

The ID for the time zone.

data

The data from the time-zone files located at /usr/share/zoneinfo.

Return Value

The time zone with the ID aTimeZoneName whose data has been initialized using the contents of data.

Discussion

You should not call this method directly—use timeZoneWithName: to get the time zone object for a given name.

Availability

• Available in Mac OS X v10.0 and later.

See Also

• + timeZoneWithName:

Declared In

NSTimeZone.h

Instance Methods

abbreviation

Returns the abbreviation for the receiver.

- (NSString *)abbreviation

Return Value

The abbreviation for the receiver, such as “EDT” (Eastern Daylight Time).

Discussion

Invokes abbreviationForDate: with the current date as the argument.

Availability

• Available in Mac OS X v10.0 and later.

Declared In

NSTimeZone.h

abbreviationForDate:

Returns the abbreviation for the receiver at a given date.

- (NSString *)abbreviationForDate:(NSDate *)aDate

Parameters

aDate

The date for which to get the abbreviation for the receiver.

Return Value

The abbreviation for the receiver at aDate.

Discussion

Note that the abbreviation may be different at different dates. For example, during daylight savings time the US/Eastern time zone has an abbreviation of “EDT.” At other times, its abbreviation is “EST.”

Availability

• Available in Mac OS X v10.0 and later.

Declared In

NSTimeZone.h

data

Returns the data that stores the information used by the receiver.

- (NSData *)data

Return Value

The data that stores the information used by the receiver.

Discussion

This data should be treated as an opaque object.

Availability

• Available in Mac OS X v10.0 and later.

Declared In

NSTimeZone.h

daylightSavingTimeOffset

Returns the current daylight saving time offset of the receiver.

- (NSTimeInterval)daylightSavingTimeOffset

Return Value

The daylight current saving time offset of the receiver.

Availability

• Available in Mac OS X v10.5 and later.

See Also

• – isDaylightSavingTime
• – isDaylightSavingTimeForDate:
• – daylightSavingTimeOffsetForDate:

Declared In

NSTimeZone.h

daylightSavingTimeOffsetForDate:

Returns the daylight saving time offset for a given date.

- (NSTimeInterval)daylightSavingTimeOffsetForDate:(NSDate *)aDate

Parameters

aDate

A date.

Return Value

The daylight saving time offset for aDate.

Availability

• Available in Mac OS X v10.5 and later.

See Also

• – isDaylightSavingTime
• – daylightSavingTimeOffset
• – isDaylightSavingTimeForDate:
• – nextDaylightSavingTimeTransitionAfterDate:

Declared In

NSTimeZone.h

description

Returns the description of the receiver.

- (NSString *)description

Return Value

The description of the receiver, including the name, abbreviation, offset from GMT, and whether or not daylight savings time is currently in effect.

Availability

• Available in Mac OS X v10.0 and later.

Declared In

NSTimeZone.h

initWithName:

Returns a time zone initialized with a given ID.

- (id)initWithName:(NSString *)aName

Parameters

aName

The ID for the time zone.

Return Value

A time zone object initialized with the ID aName.

Discussion

If aName is a known ID, this method calls initWithName:data: with the appropriate data object.

Availability

• Available in Mac OS X v10.0 and later.

Declared In

NSTimeZone.h

initWithName:data:

Initializes a time zone with a given ID and time zone data.

- (id)initWithName:(NSString *)aName data:(NSData *)data

Parameters

aName

The ID for the time zone.

data

The data from the time-zone files located at /usr/share/zoneinfo.

Discussion

You should not call this method directly—use initWithName: to get a time zone object.

Availability

• Available in Mac OS X v10.0 and later.

Declared In

NSTimeZone.h

isDaylightSavingTime

Returns a Boolean value that indicates whether the receiver is currently using daylight saving time.

- (BOOL)isDaylightSavingTime

Return Value

YES if the receiver is currently using daylight savings time, otherwise NO.

Discussion

This method invokes isDaylightSavingTimeForDate: with the current date as the argument.

Availability

• Available in Mac OS X v10.0 and later.

See Also

• – isDaylightSavingTimeForDate:
• – daylightSavingTimeOffset
• – daylightSavingTimeOffsetForDate:
• – nextDaylightSavingTimeTransition
• – nextDaylightSavingTimeTransitionAfterDate:

Declared In

NSTimeZone.h

isDaylightSavingTimeForDate:

Returns a Boolean value that indicates whether the receiver uses daylight savings time at a given date.

- (BOOL)isDaylightSavingTimeForDate:(NSDate *)aDate

Parameters

aDate

The date against which to test the receiver.

Return Value

YES if the receiver uses daylight savings time at aDate, otherwise NO.

Availability

• Available in Mac OS X v10.0 and later.

See Also

• – isDaylightSavingTime
• – daylightSavingTimeOffset
• – daylightSavingTimeOffsetForDate:
• – nextDaylightSavingTimeTransitionAfterDate:

Declared In

NSTimeZone.h

isEqualToTimeZone:

Returns a Boolean value that indicates whether the receiver has the same name and data as another given time zone.

- (BOOL)isEqualToTimeZone:(NSTimeZone *)aTimeZone

Parameters

aTimeZone

The time zone to compare with the receiver.

Return Value

YES if aTimeZone and the receiver have the same name and data, otherwise NO.

Availability

• Available in Mac OS X v10.0 and later.

Declared In

NSTimeZone.h

localizedName:locale:

Returns the name of the receiver localized for a given locale.

- (NSString *)localizedName:(NSTimeZoneNameStyle)style locale:(NSLocale *)locale

Parameters

style

The format style for the returned string.

locale

The locale for which to format the name.

Return Value

The name of the receiver localized for locale using style.

Availability

• Available in Mac OS X v10.5 and later.

Declared In

NSTimeZone.h

name

Returns the geopolitical region ID that identifies the receiver.

- (NSString *)name

Return Value

The geopolitical region ID that identifies the receiver.

Availability

• Available in Mac OS X v10.0 and later.

Declared In

NSTimeZone.h

nextDaylightSavingTimeTransition

Returns the date of the next daylight saving time transition for the receiver.

- (NSDate *)nextDaylightSavingTimeTransition

Return Value

The date of the next (after the current instant) daylight saving time transition for the receiver.

Availability

• Available in Mac OS X v10.5 and later.

See Also

• – isDaylightSavingTime
• – isDaylightSavingTimeForDate:
• – nextDaylightSavingTimeTransitionAfterDate:

Declared In

NSTimeZone.h

nextDaylightSavingTimeTransitionAfterDate:

Returns the next daylight saving time transition after a given date.

- (NSDate *)nextDaylightSavingTimeTransitionAfterDate:(NSDate *)aDate

Parameters

aDate

A date.

Return Value

The next daylight saving time transition after aDate.

Availability

• Available in Mac OS X v10.5 and later.

See Also

• – isDaylightSavingTime
• – isDaylightSavingTimeForDate:
• – nextDaylightSavingTimeTransition

Declared In

NSTimeZone.h

secondsFromGMT

Returns the current difference in seconds between the receiver and Greenwich Mean Time.

- (NSInteger)secondsFromGMT

Return Value

The current difference in seconds between the receiver and Greenwich Mean Time.

Availability

• Available in Mac OS X v10.0 and later.

Declared In

NSTimeZone.h

secondsFromGMTForDate:

Returns the difference in seconds between the receiver and Greenwich Mean Time at a given date.

- (NSInteger)secondsFromGMTForDate:(NSDate *)aDate

Parameters

aDate

The date against which to test the receiver.

Return Value

The difference in seconds between the receiver and Greenwich Mean Time at aDate.

Discussion

The difference may be different from the current difference if the time zone changes its offset from GMT at different points in the year—for example, the U.S. time zones change with daylight savings time.

Availability

• Available in Mac OS X v10.0 and later.

Declared In

NSTimeZone.h

Constants

NSTimeZoneNameStyle

Defines a type for time zone name styles.

typedef NSInteger NSTimeZoneNameStyle;

Discussion

See “Time Zone Name Styles” for possible values.

Availability

• Available in Mac OS X v10.5 and later.

Declared In

NSTimeZone.h

Time Zone Name Styles

Specify styles for presenting time zone names.

enum {
   NSTimeZoneNameStyleStandard,
   NSTimeZoneNameStyleShortStandard,
   NSTimeZoneNameStyleDaylightSaving,
   NSTimeZoneNameStyleShortDaylightSaving
};

Constants

NSTimeZoneNameStyleStandard

Specifies a standard name style.

Available in Mac OS X v10.5 and later.

Declared in NSTimeZone.h.

NSTimeZoneNameStyleShortStandard

Specifies a short name style.

Available in Mac OS X v10.5 and later.

Declared in NSTimeZone.h.

NSTimeZoneNameStyleDaylightSaving

Specifies a daylight saving name style.

Available in Mac OS X v10.5 and later.

Declared in NSTimeZone.h.

NSTimeZoneNameStyleShortDaylightSaving

Specifies a short daylight saving name style.

Available in Mac OS X v10.5 and later.

Declared in NSTimeZone.h.

Declared In

NSTimeZone.h

Notifications

NSSystemTimeZoneDidChangeNotification

Sent when the time zone changed.

Availability

• Available in Mac OS X v10.5 and later.

Declared In

NSTimeZone.h

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