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Foundation Framework Reference NSKeyValueCoding Protocol Reference

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NSKeyValueCoding

The NSKeyValueCoding informal protocol defines a mechanism by which you can access the properties of an object indirectly by name (or key), rather than directly through invocation of an accessor method or as instance variables. Thus, all of an object’s properties can be accessed in a consistent manner. More...

Inheritance


Not Applicable

Conforms To


Not Applicable

Import Statement


Swift

import Foundation

Objective-C

@import Foundation;

Availability


Available in iOS 2.0 and later.
  • Returns the value for the property identified by a given key.

    Declaration

    Swift

    func valueForKey(_ key: String) -> AnyObject?

    Objective-C

    - (id)valueForKey:(NSString *)key

    Parameters

    key

    The name of one of the receiver's properties.

    Return Value

    The value for the property identified by key.

    Discussion

    The search pattern that valueForKey: uses to find the correct value to return is described in Accessor Search Implementation Details in Key-Value Coding Programming Guide.

    Import Statement

    Swift

    import Foundation

    Availability

    Available in iOS 2.0 and later.

  • Returns the value for the derived property identified by a given key path.

    Declaration

    Swift

    func valueForKeyPath(_ keyPath: String) -> AnyObject?

    Objective-C

    - (id)valueForKeyPath:(NSString *)keyPath

    Parameters

    keyPath

    A key path of the form relationship.property (with one or more relationships); for example “department.name” or “department.manager.lastName”.

    Return Value

    The value for the derived property identified by keyPath.

    Discussion

    The default implementation gets the destination object for each relationship using valueForKey: and returns the result of a valueForKey: message to the final object.

    Import Statement

    Swift

    import Foundation

    Availability

    Available in iOS 2.0 and later.

  • Returns a dictionary containing the property values identified by each of the keys in a given array.

    Declaration

    Swift

    func dictionaryWithValuesForKeys(_ keys: [AnyObject]) -> [NSObject : AnyObject]

    Objective-C

    - (NSDictionary *)dictionaryWithValuesForKeys:(NSArray *)keys

    Parameters

    keys

    An array containing NSString objects that identify properties of the receiver.

    Return Value

    A dictionary containing as keys the property names in keys, with corresponding values being the corresponding property values.

    Discussion

    The default implementation invokes valueForKey: for each key in keys and substitutes NSNull values in the dictionary for returned nil values.

    Import Statement

    Swift

    import Foundation

    Availability

    Available in iOS 2.0 and later.

  • Invoked by valueForKey: when it finds no property corresponding to a given key.

    Declaration

    Swift

    func valueForUndefinedKey(_ key: String) -> AnyObject?

    Objective-C

    - (id)valueForUndefinedKey:(NSString *)key

    Parameters

    key

    A string that is not equal to the name of any of the receiver's properties.

    Discussion

    Subclasses can override this method to return an alternate value for undefined keys. The default implementation raises an NSUndefinedKeyException.

    Import Statement

    Swift

    import Foundation

    Availability

    Available in iOS 2.0 and later.

  • Returns a mutable array proxy that provides read-write access to an ordered to-many relationship specified by a given key.

    Declaration

    Swift

    func mutableArrayValueForKey(_ key: String) -> NSMutableArray

    Objective-C

    - (NSMutableArray *)mutableArrayValueForKey:(NSString *)key

    Parameters

    key

    The name of an ordered to-many relationship.

    Return Value

    A mutable array proxy that provides read-write access to the ordered to-many relationship specified by key.

    Discussion

    Objects added to the mutable array become related to the receiver, and objects removed from the mutable array become unrelated. The default implementation recognizes the same simple accessor methods and array accessor methods as valueForKey:, and follows the same direct instance variable access policies, but always returns a mutable collection proxy object instead of the immutable collection that valueForKey: would return.

    The search pattern that mutableArrayValueForKey: uses is described in Accessor Search Implementation Details in Key-Value Coding Programming Guide.

    Import Statement

    Swift

    import Foundation

    Availability

    Available in iOS 2.0 and later.

  • Returns a mutable array that provides read-write access to the ordered to-many relationship specified by a given key path.

    Declaration

    Swift

    func mutableArrayValueForKeyPath(_ keyPath: String) -> NSMutableArray

    Objective-C

    - (NSMutableArray *)mutableArrayValueForKeyPath:(NSString *)keyPath

    Parameters

    keyPath

    A key path, relative to the receiver, to an ordered to-many relationship.

    Return Value

    A mutable array that provides read-write access to the ordered to-many relationship specified by keyPath.

    Discussion

    See mutableArrayValueForKey: for additional details.

    Import Statement

    Swift

    import Foundation

    Availability

    Available in iOS 2.0 and later.

  • Returns a mutable set proxy that provides read-write access to the unordered to-many relationship specified by a given key.

    Declaration

    Swift

    func mutableSetValueForKey(_ key: String) -> NSMutableSet

    Objective-C

    - (NSMutableSet *)mutableSetValueForKey:(NSString *)key

    Parameters

    key

    The name of an unordered to-many relationship.

    Return Value

    A mutable set that provides read-write access to the unordered to-many relationship specified by key.

    Discussion

    Objects added to the mutable set proxy become related to the receiver, and objects removed from the mutable set become unrelated. The default implementation recognizes the same simple accessor methods and set accessor methods as valueForKey:, and follows the same direct instance variable access policies, but always returns a mutable collection proxy object instead of the immutable collection that valueForKey: would return.

    The search pattern that mutableSetValueForKey: uses is described in Accessor Search Implementation Details in Key-Value Coding Programming Guide.

    Import Statement

    Swift

    import Foundation

    Availability

    Available in iOS 2.0 and later.

  • Returns a mutable set that provides read-write access to the unordered to-many relationship specified by a given key path.

    Declaration

    Swift

    func mutableSetValueForKeyPath(_ keyPath: String) -> NSMutableSet

    Objective-C

    - (NSMutableSet *)mutableSetValueForKeyPath:(NSString *)keyPath

    Parameters

    keyPath

    A key path, relative to the receiver, to an unordered to-many relationship.

    Return Value

    A mutable set that provides read-write access to the unordered to-many relationship specified by keyPath.

    Discussion

    See mutableSetValueForKey: for additional details.

    Import Statement

    Swift

    import Foundation

    Availability

    Available in iOS 2.0 and later.

  • Returns a mutable ordered set that provides read-write access to the uniquing ordered to-many relationship specified by a given key.

    Declaration

    Swift

    func mutableOrderedSetValueForKey(_ key: String) -> NSMutableOrderedSet

    Objective-C

    - (NSMutableOrderedSet *)mutableOrderedSetValueForKey:(NSString *)key

    Parameters

    key

    The name of a uniquing ordered to-many relationship.

    Return Value

    A mutable ordered set that provides read-write access to the uniquing to-many relationship specified by key.

    Discussion

    Objects added to the mutable set proxy become related to the receiver, and objects removed from the mutable set become unrelated. The default implementation recognizes the same simple accessor methods and set accessor methods as valueForKey:, and follows the same direct instance variable access policies, but always returns a mutable collection proxy object instead of the immutable collection that valueForKey: would return.

    The search pattern that mutableOrderedSetValueForKey: uses is described in Accessor Search Implementation Details in Key-Value Coding Programming Guide.

    Import Statement

    Swift

    import Foundation

    Availability

    Available in iOS 5.0 and later.

  • Returns a mutable ordered set that provides read-write access to the uniquing ordered to-many relationship specified by a given key path.

    Declaration

    Swift

    func mutableOrderedSetValueForKeyPath(_ keyPath: String) -> NSMutableOrderedSet

    Objective-C

    - (NSMutableOrderedSet *)mutableOrderedSetValueForKeyPath:(NSString *)keyPath

    Parameters

    keyPath

    A key path, relative to the receiver, to a uniquing ordered to-many relationship represented by a set.

    Return Value

    A mutable ordered set that provides read-write access to the uniquing to-many relationship specified by keyPath.

    Discussion

    See mutableOrderedSetValueForKey: for additional details.

    Import Statement

    Swift

    import Foundation

    Availability

    Available in iOS 5.0 and later.

  • Sets the value for the property identified by a given key path to a given value.

    Declaration

    Swift

    func setValue(_ value: AnyObject?, forKeyPath keyPath: String)

    Objective-C

    - (void)setValue:(id)value forKeyPath:(NSString *)keyPath

    Parameters

    value

    The value for the property identified by keyPath.

    keyPath

    A key path of the form relationship.property (with one or more relationships): for example “department.name” or “department.manager.lastName.”

    Discussion

    The default implementation of this method gets the destination object for each relationship using valueForKey:, and sends the final object a setValue:forKey: message.

    Special Considerations

    When using this method, and the destination object does not implement an accessor for the value, the default behavior is for that object to retain value rather than copy or assign value.

    Import Statement

    Swift

    import Foundation

    Availability

    Available in iOS 2.0 and later.

  • Sets properties of the receiver with values from a given dictionary, using its keys to identify the properties.

    Declaration

    Swift

    func setValuesForKeysWithDictionary(_ keyedValues: [NSObject : AnyObject])

    Objective-C

    - (void)setValuesForKeysWithDictionary:(NSDictionary *)keyedValues

    Parameters

    keyedValues

    A dictionary whose keys identify properties in the receiver. The values of the properties in the receiver are set to the corresponding values in the dictionary.

    Discussion

    The default implementation invokes setValue:forKey: for each key-value pair, substituting nil for NSNull values in keyedValues.

    Import Statement

    Swift

    import Foundation

    Availability

    Available in iOS 2.0 and later.

  • Invoked by setValue:forKey: when it’s given a nil value for a scalar value (such as an int or float).

    Declaration

    Swift

    func setNilValueForKey(_ key: String)

    Objective-C

    - (void)setNilValueForKey:(NSString *)key

    Parameters

    key

    The name of one of the receiver's properties.

    Discussion

    Subclasses can override this method to handle the request in some other way, such as by substituting 0 or a sentinel value for nil and invoking setValue:forKey: again or setting the variable directly. The default implementation raises an NSInvalidArgumentException.

    Import Statement

    Swift

    import Foundation

    Availability

    Available in iOS 2.0 and later.

  • Sets the property of the receiver specified by a given key to a given value.

    Declaration

    Swift

    func setValue(_ value: AnyObject?, forKey key: String)

    Objective-C

    - (void)setValue:(id)value forKey:(NSString *)key

    Parameters

    value

    The value for the property identified by key.

    key

    The name of one of the receiver's properties.

    Discussion

    If key identifies a to-one relationship, relate the object specified by value to the receiver, unrelating the previously related object if there was one. Given a collection object and a key that identifies a to-many relationship, relate the objects contained in the collection to the receiver, unrelating previously related objects if there were any.

    The search pattern that setValue:forKey: uses is described in Accessor Search Implementation Details in Key-Value Coding Programming Guide.

    In a reference-counted environment, if the instance variable is accessed directly, value is retained.

    Import Statement

    Swift

    import Foundation

    Availability

    Available in iOS 2.0 and later.

  • Invoked by setValue:forKey: when it finds no property for a given key.

    Declaration

    Swift

    func setValue(_ value: AnyObject?, forUndefinedKey key: String)

    Objective-C

    - (void)setValue:(id)value forUndefinedKey:(NSString *)key

    Parameters

    value

    The value for the key identified by key.

    key

    A string that is not equal to the name of any of the receiver's properties.

    Discussion

    Subclasses can override this method to handle the request in some other way. The default implementation raises an NSUndefinedKeyException.

    Import Statement

    Swift

    import Foundation

    Availability

    Available in iOS 2.0 and later.

  • Returns a Boolean value that indicates whether the key-value coding methods should access the corresponding instance variable directly on finding no accessor method for a property.

    Declaration

    Swift

    class func accessInstanceVariablesDirectly() -> Bool

    Objective-C

    + (BOOL)accessInstanceVariablesDirectly

    Return Value

    YEStrue if the key-value coding methods should access the corresponding instance variable directly on finding no accessor method for a property, otherwise NOfalse.

    Discussion

    The default returns YEStrue. Subclasses can override it to return NOfalse, in which case the key-value coding methods won’t access instance variables.

    Import Statement

    Swift

    import Foundation

    Availability

    Available in iOS 2.0 and later.

  • Returns a Boolean value that indicates whether the value specified by a given pointer is valid for the property identified by a given key.

    Declaration

    Swift

    func validateValue(_ ioValue: AutoreleasingUnsafeMutablePointer<AnyObject?>, forKey key: String, error outError: NSErrorPointer) -> Bool

    Objective-C

    - (BOOL)validateValue:(inout id *)ioValue forKey:(NSString *)key error:(out NSError **)outError

    Parameters

    ioValue

    A pointer to a new value for the property identified by key. This method may modify or replace the value in order to make it valid.

    key

    The name of one of the receiver's properties. The key must specify an attribute or a to-one relationship.

    outError

    If validation is necessary and ioValue is not transformed into a valid value, upon return contains an NSError object that describes the reason that ioValue is not a valid value.

    Return Value

    YES if *ioValue is a valid value for the property identified by key, or if the method is able to modify the value to *ioValue to make it valid; otherwise NOfalse.

    Discussion

    The default implementation of this method searches the class of the receiver for a validation method whose name matches the pattern validate<Key>:error:. If such a method is found it is invoked and the result is returned. If no such method is found, YEStrue is returned.

    The sender of the message is never given responsibility for releasing ioValue or outError.

    See Key-Value Validation in Key-Value Coding Programming Guide for more information.

    Import Statement

    Swift

    import Foundation

    Availability

    Available in iOS 2.0 and later.

  • Returns a Boolean value that indicates whether the value specified by a given pointer is valid for a given key path relative to the receiver.

    Declaration

    Swift

    func validateValue(_ ioValue: AutoreleasingUnsafeMutablePointer<AnyObject?>, forKeyPath key: String, error outError: NSErrorPointer) -> Bool

    Objective-C

    - (BOOL)validateValue:(inout id *)ioValue forKeyPath:(NSString *)key error:(out NSError **)outError

    Parameters

    ioValue

    A pointer to a new value for the property identified by keyPath. This method may modify or replace the value in order to make it valid.

    key

    The name of one of the receiver's properties. The key path must specify an attribute or a to-one relationship. The key path has the form relationship.property (with one or more relationships); for example “department.name” or “department.manager.lastName”.

    outError

    If validation is necessary and ioValue is not transformed into a valid value, upon return contains an NSError object that describes the reason that ioValue is not a valid value.

    Discussion

    The default implementation gets the destination object for each relationship using valueForKey: and returns the result of a validateValue:forKey:error: message to the final object.

    Import Statement

    Swift

    import Foundation

    Availability

    Available in iOS 2.0 and later.

  • This constant defines the name of an exception raised when a key value coding operation fails.

    Declaration

    Swift

    let NSUndefinedKeyException: String

    Objective-C

    extern NSString *NSUndefinedKeyException;

    Constants

    • NSUndefinedKeyException

      NSUndefinedKeyException

      Raised when a key value coding operation fails. userInfo keys are described in NSUndefinedKeyException userInfo Keys

      Available in iOS 2.0 and later.

  • These constants are keys into an NSUndefinedKeyException userInfo dictionary

    Declaration

    Objective-C

    extern NSString *NSTargetObjectUserInfoKey; extern NSString *NSUnknownUserInfoKey;

    Constants

    • NSTargetObjectUserInfoKey

      NSTargetObjectUserInfoKey

      The object on which the key value coding operation failed.

    • NSUnknownUserInfoKey

      NSUnknownUserInfoKey

      The key for which the key value coding operation failed.

    Discussion

    For additional information see Key Value Coding Exception Names.

  • These constants define the available array operators. See Set and Array Operators in Key-Value Coding Programming Guide for more information.

    Declaration

    Swift

    let NSAverageKeyValueOperator: String let NSCountKeyValueOperator: String let NSDistinctUnionOfArraysKeyValueOperator: String let NSDistinctUnionOfObjectsKeyValueOperator: String let NSDistinctUnionOfSetsKeyValueOperator: String let NSMaximumKeyValueOperator: String let NSMinimumKeyValueOperator: String let NSSumKeyValueOperator: String let NSUnionOfArraysKeyValueOperator: String let NSUnionOfObjectsKeyValueOperator: String let NSUnionOfSetsKeyValueOperator: String

    Objective-C

    NSString *const NSAverageKeyValueOperator; NSString *const NSCountKeyValueOperator; NSString *const NSDistinctUnionOfArraysKeyValueOperator; NSString *const NSDistinctUnionOfObjectsKeyValueOperator; NSString *const NSDistinctUnionOfSetsKeyValueOperator; NSString *const NSMaximumKeyValueOperator; NSString *const NSMinimumKeyValueOperator; NSString *const NSSumKeyValueOperator; NSString *const NSUnionOfArraysKeyValueOperator; NSString *const NSUnionOfObjectsKeyValueOperator; NSString *const NSUnionOfSetsKeyValueOperator;

    Constants

    • NSAverageKeyValueOperator

      NSAverageKeyValueOperator

      The @avg array operator.

      Available in iOS 2.0 and later.

    • NSCountKeyValueOperator

      NSCountKeyValueOperator

      The @count array operator.

      Available in iOS 2.0 and later.

    • NSDistinctUnionOfArraysKeyValueOperator

      NSDistinctUnionOfArraysKeyValueOperator

      The @distinctUnionOfArrays array operator.

      Available in iOS 2.0 and later.

    • NSDistinctUnionOfObjectsKeyValueOperator

      NSDistinctUnionOfObjectsKeyValueOperator

      The @distinctUnionOfObjects array operator.

      Available in iOS 2.0 and later.

    • NSDistinctUnionOfSetsKeyValueOperator

      NSDistinctUnionOfSetsKeyValueOperator

      The @distinctUnionOfSets array operator.

      Available in iOS 2.0 and later.

    • NSMaximumKeyValueOperator

      NSMaximumKeyValueOperator

      The @max array operator.

      Available in iOS 2.0 and later.

    • NSMinimumKeyValueOperator

      NSMinimumKeyValueOperator

      The @min array operator.

      Available in iOS 2.0 and later.

    • NSSumKeyValueOperator

      NSSumKeyValueOperator

      The @sum array operator.

      Available in iOS 2.0 and later.

    • NSUnionOfArraysKeyValueOperator

      NSUnionOfArraysKeyValueOperator

      The @unionOfArrays array operator.

      Available in iOS 2.0 and later.

    • NSUnionOfObjectsKeyValueOperator

      NSUnionOfObjectsKeyValueOperator

      The @unionOfObjects array operator.

      Available in iOS 2.0 and later.

    • NSUnionOfSetsKeyValueOperator

      NSUnionOfSetsKeyValueOperator

      The @unionOfSets array operator.

      Available in iOS 2.0 and later.