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EOKeyValueCodingAdditions

(informal protocol)

Declared in:
EOControl/EOKeyValueCoding.h

Protocol Description

The EOKeyValueCodingAdditions informal protocol defines extensions to the basic EOKeyValueCoding informal protocol. One pair of methods, takeValuesFromDictionary: and valuesForKeys:, gives access to groups of properties. Another pair of methods, takeValue:forKeyPath: and valueForKeyPath: give access to properties across relationships with key paths of the form relationship.property; for example, "department.name". the Framework additions to NSObject provide default implementations of EOKeyValueCodingAdditions, which you rarely (if ever) need to override.

EONull in Collections

Because collection objects such as NSArray and NSDictionary can't contain nil as a value, nil must be represented by a special object, EONull. EONull provides a single instance that represents the NULL value for object attributes. The default implementations of takeValuesFromDictionary: and valuesForKeys: translate EONull and nil between NSDictionaries and enterprise objects so your objects don't have to explicitly test for EONull values.

Instance Methods

takeValue:forKeyPath:

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

Sets the value for the property identified by keyPath to value. A key path has the form relationship.property (with one or more relationships); for example "movieRole.roleName" or "movieRole.Talent.lastName". NSObject's implementation of this method gets the destination object for each relationship using valueForKey:, and sends the final object a takeValue:forKey:message with value and property.

takeValuesFromDictionary:

- (void)takeValuesFromDictionary:(NSDictionary *)aDictionary

Sets properties of the receiver with values from aDictionary, using its keys to identify the properties. NSObject's implementation invokes takeValue:forKey: for each key-value pair, substituting nil for EONull values in aDictionary.

valueForKeyPath:

- (id)valueForKeyPath:(NSString *)keyPath

Returns the value for the derived property identified by keyPath. A key path has the form relationship.property (with one or more relationships); for example "movieRole.roleName" or "movieRole.Talent.lastName". NSObject's implementation of this method gets the destination object for each relationship using valueForKey:, and returns the result of a valueForKey: message to the final object.

valuesForKeys:

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

Returns a dictionary containing the property values identified by each of keys. NSObject's implementation invokes valueForKey: for each key in keys, substituting EONull values in the dictionary for returned nil values.