# NSUserDefaults class reference

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rfm@gnu.org
Generated at 2025-12-02 21:52:00 +0000
1995-2016 Free Software Foundation, Inc.
Software documentation for the NSUserDefaults class
Foundation/NSUserDefaults.h

NSUserDefaults provides an interface to the defaults system, which allows an application access to global and/or application specific defaults set by the user. A particular instance of NSUserDefaults, standardUserDefaults, is provided as a convenience. Most of the information described below pertains to the standardUserDefaults. It is unlikely that you would want to instantiate your own userDefaults object, since it would not be set up in the same way as the standardUserDefaults.

Defaults are managed based on domains. Certain domains, such as `NSGlobalDomain`, are persistent. These domains have defaults that are stored externally. Other domains are volatile. The defaults in these domains remain in effect only during the existence of the application and may in fact be different for applications running at the same time. When asking for a default value from standardUserDefaults, NSUserDefaults looks through the various domains in a particular order.

`GSPrimaryDomain`... volatile
Contains values set at runtime and intended to supercede any values set in other domains. This should be used with great care since it overrides values which may have been set explicitly by the user.
`NSArgumentDomain`... volatile
Contains defaults read from the arguments provided to the application at startup.
Pairs of arguments are used for this, with the first argument in each pair being the name of a default (with a hyphen prepended) and the second argument of the pair being the value of the default.
NB. In GNUstep special arguments of the form `--GNU-Debug=...` are used to enable debugging. Despite beginning with a hyphen, these are not treated as default keys.
Application (name of the current process)... persistent
Contains application specific defaults, such as window positions. This is the domain used by the -setObject:forKey: method and is the domain normally used when setting preferences for an application.
`NSGlobalDomain`... persistent
Global defaults applicable to all applications.
Language (name based on users's language)... volatile
Constants that help with localization to the users's language.
`GSConfigDomain`... volatile
Information retrieved from the GNUstep configuration system. Usually the system wide and user specific GNUstep.conf files, or from information compiled in when the base library was built.
In addition to this standard configuration information, this domain contains all values from property lists store in the GlobalDefaults subdirectory or from the GlobalDefaults.plist file stored in the same directory as the system wide GNUstep.conf file.
`NSRegistrationDomain`... volatile
Temporary defaults set up by the application.

The NSLanguages default value is used to set up the constants for localization. GNUstep will also look for the `LANGUAGES` environment variable if it is not set in the defaults system. If it exists, it consists of an array of languages that the user prefers. At least one of the languages should have a corresponding localization file (typically located in the Languages directory of the GNUstep resources).

As a special extension, on systems that support locales (e.g. GNU/Linux and Solaris), GNUstep will use information from the user specified locale, if the NSLanguages default value is not found. Typically the locale is specified in the environment with the `LANG` environment variable.

The first change to a persistent domain after a -synchronize will cause an NSUserDefaultsDidChangeNotification to be posted (as will any change caused by reading new values from disk), so your application can keep track of changes made to the defaults by other software.

NB. The GNUstep implementation differs from the Apple one in that it is thread-safe while Apple's (as of MacOS-X 10.1) is not.

resetStandardUserDefaults
Resets the shared user defaults object to reflect the current user ID. Needed by setuid processes which change the user they are running as.
In GNUstep you should call GSSetUserName() when changing your effective user ID, and that function will call this function for you.
setUserLanguages:
languages
Sets the array of user languages preferences. Places the specified array in the NSLanguages user default.
standardUserDefaults
Returns the shared defaults object. If it doesn't exist yet, it's created. The defaults are initialized for the current user. The search list is guaranteed to be standard only the first time this method is invoked. The shared instance is provided as a convenience; other instances may also be created.
userLanguages
Returns the array of user languages preferences. Uses the NSLanguages user default if available, otherwise tries to infer setup from operating system information etc (in particular, uses the LANGUAGES environment variable).
addSuiteNamed:
aName
Adds the domain names aName to the search list of the receiver.
The domain is added after the application domain.
Suites may be removed using the -removeSuiteNamed: method.
arrayForKey:
defaultName
Looks up a value for a specified default using -objectForKey: and checks that it is an NSArray object. Returns `nil` if it is not.
boolForKey:
defaultName
Looks up a value for a specified default using -objectForKey: and returns its boolean representation.
Returns `NO` if it is not a boolean.
The text 'yes' or 'true' or any non zero numeric value is considered to be a boolean `YES`. Other string values are `NO`.
NB. This differs slightly from the documented behavior for MacOS-X (August 2002) in that the GNUstep version accepts the string 'TRUE' as equivalent to 'YES'.
dataForKey:
defaultName
Looks up a value for a specified default using -objectForKey: and checks that it is an NSData object. Returns `nil` if it is not.
dictionaryForKey:
defaultName
Looks up a value for a specified default using -objectForKey: and checks that it is an NSDictionary object. Returns `nil` if it is not.
dictionaryRepresentation
Returns a dictionary representing the current state of the defaults system... this is a merged version of all the domains in the search list.
doubleForKey:
defaultName
Looks up a value for a specified default using -objectForKey: and checks that it is a double. Returns 0.0 if it is not.
floatForKey:
defaultName
Looks up a value for a specified default using -objectForKey: and checks that it is a float. Returns 0.0 if it is not.
init
Initializes defaults for current user calling initWithUser:
initWithUser:
userName
Initializes defaults for the specified user.
Returns an object with an empty search list.
integerForKey:
defaultName
Looks up a value for a specified default using -objectForKey: and returns its integer value or 0 if it is not representable as an integer.
objectForKey:
defaultName
Looks up a value for a specified default using. The lookup is performed by accessing the domains in the order given in the search list.
Returns `nil` if defaultName cannot be found.
persistentDomainForName:
domainName
Returns the persistent domain specified by domainName.
persistentDomainNames
Returns an array listing the name of all the persistent domains.
registerDefaults:
newVals
Merges the contents of the dictionary newVals into the registration domain. Registration defaults may be added to or replaced using this method, but may never be removed. Thus, setting registration defaults at any point in your program guarantees that the defaults will be available thereafter.
removeObjectForKey:
defaultName
Removes the default with the specified name from the application domain.
removePersistentDomainForName:
domainName
Removes the persistent domain specified by domainName from the user defaults.
Causes a NSUserDefaultsDidChangeNotification to be posted if this is the first change to a persistent-domain since the last -synchronize .
removeSuiteNamed:
aName
Removes the named domain from the search list of the receiver.
Suites may be added using the -addSuiteNamed: method.
removeVolatileDomainForName:
domainName
Removes the volatile domain specified by domainName from the user defaults.
searchList
Returns an array listing the domains searched in order to look up a value in the defaults system. The order of the names in the array is the order in which the domains are searched.
setBool:
value
forKey:
defaultName
Sets a boolean value for defaultName in the application domain.
Calls -setObject:forKey: to make the change by storing a string containing either the word `YES` or `NO`.
setDouble:
value
forKey:
defaultName
Sets a double value for defaultName in the application domain.
Calls -setObject:forKey: to make the change by storing a double NSNumber instance.
setFloat:
value
forKey:
defaultName
Sets a float value for defaultName in the application domain.
Calls -setObject:forKey: to make the change by storing a float NSNumber instance.
setInteger:
value
forKey:
defaultName
Sets an integer value for defaultName in the application domain.
Calls -setObject:forKey: to make the change by storing an intege NSNumber instance.
setObject:
value
forKey:
defaultName
Sets a copy of an object value for defaultName in the application domain.
The defaultName must be a non-empty string.
The value to be copied into the domain must be an instance of one of the [NSString -propertyList] classes.

Causes a NSUserDefaultsDidChangeNotification to be posted if this is the first change to a persistent-domain since the last -synchronize .

If value is `nil`, this is equivalent to the -removeObjectForKey: method.
setPersistentDomain:
domain
forName:
domainName
Replaces the persistent-domain specified by domainName with domain... a dictionary containing keys and defaults values.
Raises an NSInvalidArgumentException if domainName already exists as a volatile-domain.
Causes a NSUserDefaultsDidChangeNotification to be posted if this is the first change to a persistent-domain since the last -synchronize .
setSearchList:
newList
Sets the list of the domains searched in order to look up a value in the defaults system. The order of the names in the array is the order in which the domains are searched.
On lookup, the first match is used.
setVolatileDomain:
domain
forName:
domainName
Sets the volatile-domain specified by domainName to domain... a dictionary containing keys and defaults values.
Raises an NSInvalidArgumentException if domainName already exists as either a volatile-domain or a persistent-domain.
stringArrayForKey:
defaultName
Calls -arrayForKey: to get an array value for defaultName and checks that the array contents are string objects... if not, returns `nil`.
stringForKey:
defaultName
Looks up a value for a specified default using -objectForKey: and checks that it is an NSString. Returns `nil` if it is not.
synchronize
Ensures that the in-memory and on-disk representations of the defaults are in sync. You may call this yourself, but probably don't need to since it is invoked at intervals whenever a runloop is running.
If any persistent domain is changed by reading new values from disk, an NSUserDefaultsDidChangeNotification is posted.
volatileDomainForName:
domainName
Returns the volatile domain specified by domainName.
volatileDomainNames
Returns an array listing the name of all the volatile domains.