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EOAssociation


Inherits from:
EODelayedObserver (EOControl) : NSObject
Conforms to:
NSCoding
EOObserving (EODelayedObserver)
NSObject (NSObject)
Declared in:
EOInterface/EOAssociation.h



Class at a Glance


An EOAssociation maintains a two-way binding between the properties of a display object, such as a text field or combo box, and the properties of one or more enterprise objects contained in one or more EODisplayGroups. You typically create and configure associations in Interface Builder, using the programmatic interface only when you write your own EOAssociation subclasses.

Principal Attributes



Class Description


EOAssociation defines the mechanism that transfers values between EODisplayGroups and the user interface of an application. An EOAssociation instance is tied to a single display object, a user interface object or other kind of object that manages values intended for display. The EOAssociation takes over certain outlets of the display object and sets its value according to the selection in the EODisplayGroup. An EOAssociation also has various aspects, which define the different parameters of the display object that it controls, such as the value or values displayed and whether the display object is enabled or editable. Each aspect can be bound to an EODisplayGroup with a key denoting a property of the enterprise objects in the EODisplayGroup. The value or values of this property determine the value for the EOAssociation's aspect.

EOAssociation is an abstract class, defining only the general mechanism for binding display objects to EODisplayGroups. You always create instances of its various subclasses, which define behavior specific to different kinds of display objects. For information on the different EOAssociation subclasses you can use, see the following subclass specifications:


EOActionAssociation EOActionCellAssociation
EOActionInsertionAssociation EOColumnAssociation
EOComboBoxAssociation EOControlAssociation
EODetailSelectionAssociation EOGenericControlAssociation
EOMasterCopyAssociation EOMasterDetailAssociation
EOMasterPeerAssociation EOMatrixAssociation
EOPickTextAssociation EOPopUpAssociation
EORadioMatrixAssociation EORecursiveBrowserAssociation
EOTableViewAssociation EOTextAssociation

You normally set up EOAssociations using Interface Builder; each of the class specifications for EOAssociation's subclasses provide an example using Interface Builder to set them up. EOAssociation's programmatic interface is more important when defining custom EOAssociation subclasses. For more information on EOAssociations, see the sections:




Adopted Protocols


NSCoding
- encodeWithCoder:
- initWithCoder:


Method Types


Declaring capabilities
+ aspects
+ aspectSignatures
+ objectKeysTaken (Yellow Box)
+ isUsableWithObject:
+ associationClassesSuperseded
+ displayName
+ primaryAspect
- canBindAspect:displayGroup:key:
Getting all possible EOAssociations for a display object
+ associationClassesForObject:
Creating and configuring instances
- initWithObject:
- bindAspect:displayGroup:key:
- establishConnection
- breakConnection
- copyMatchingBindingsFromAssociation:
Getting the display object
- object
Examining bindings
- displayGroupForAspect:
- displayGroupKeyForAspect:
Updating values
- subjectChanged
- endEditing
Accessing enterprise object values
- setValue:forAspect:
- setValue:forAspect:atIndex:
- valueForAspect:
- valueForAspect:atIndex:
Handling validation errors
- shouldEndEditingForAspect:invalidInput:errorDescription:
- shouldEndEditingForAspect:invalidInput:errorDescription:index:


Constructors




Class Methods



aspects

+ (NSArray *)aspects

Overridden by subclasses to return the names of the receiving class's aspects as an array of string objects. Subclasses should include their superclass's aspects and add their own when overriding this method.



aspectSignatures

+ (NSArray *)aspectSignatures

Overridden by subclasses to return the signatures of the receiver's aspects, an array of string objects matching its aspects array index for index. Each signature string can contain the following characters:
Signature Character Meaning
A The aspect can be bound to attributes.
1 (one) The aspect can be bound to to-one relationships.
M The aspect can be bound to to-many relationships.

An aspect signature string of "A1", for example, means the corresponding aspect can be bound to either attributes or to-one relationships. An empty signature indicates that the corresponding aspect can be bound to an EODisplayGroup without a key (that is, the key is irrelevant). Interface Builder uses aspect signatures to enable and disable keys in its Connections inspectors.

EOAssociation's implementation of this method returns an array of "A1M" of the length of its aspects array.



associationClassesForObject:

+ (NSArray *)associationClassesForObject:(id)aDisplayObject

Returns the subclasses of EOAssociation usable with aDisplayObject. Sends isUsableWithObject: to every loaded subclass of EOAssociation, adding those that respond YES to the array. Subclasses shouldn't override this method; override isUsableWithObject: instead.



associationClassesSuperseded

+ (NSArray *)associationClassesSuperseded

Overridden by subclasses to return the other EOAssociation classes that the receiver supplants. This allows a subclass to mask its superclasses from the Connection Inspector's pop-up list in Interface Builder, since the subclass always includes the aspects and functionality of its superclasses. For example, EOPopUpAssociation supersedes EOControlAssociation, because EOPopUpAssociation is always more appropriate to use with pop-up buttons.



displayName

+ (NSString *)displayName

Returns the name used by Interface Builder in the Connection Inspector's pop-up list. EOAssociation's implementation simply returns the name of the receiving class.



isUsableWithObject:

+ (BOOL)isUsableWithObject:(id)aDisplayObject

Overridden by subclasses to return YES if instances of the receiving class are usable with aDisplayObject, NO if they aren't. The receiving class can examine any relevant characteristic of aDisplayObject-its class, configuration (such as whether an NSMatrix operates in radio mode), and so on.



objectKeysTaken

+ (NSArray *)objectKeysTaken

Overridden by subclasses to return the names of display object outlets that instances assume control of, such as "target" and "delegate". Interface Builder uses this information to disable connections from these outlets in its Connections Inspector.



primaryAspect

+ (NSString *)primaryAspect

Overridden by subclasses to return the default aspect, usually one denoting the displayed value, which by convention is named "value". EOAssociation's implementation returns nil.




Instance Methods



bindAspect:displayGroup:key:

- (void)bindAspect:(NSString *)aspectName displayGroup:(EODisplayGroup *)aDisplayGroup key:(NSString *)key

Defines the receiver's link between its display object and aDisplayGroup. aspectName is the name of the aspect it observer in its display object, and key is the name of the property it observes in aDisplayGroup. Invoke establishConnection after this method to finish setting up the binding. See "Setting up an EOAssociation Programmatically" in the class description for more information.

See Also: - initWithObject:, - establishConnection



breakConnection

- (void)breakConnection

Removes the receiver from its EODisplayGroup and display object. This causes it to be released, so be sure to retain the EOAssociation before invoking this method if you want to keep it for another use. Subclasses should override this method to remove the receiver from any outlets of the display object, such as target or delegate, and invoke super's implementation at the end.

See Also: - establishConnection



canBindAspect:displayGroup:key:

- (BOOL)canBindAspect:(NSString *)aspectName displayGroup:(EODisplayGroup *)aDisplayGroup key:(NSString *)key

Overridden by subclasses to return YES if the receiver can tie an aspect named aspectName from its display object to the property identified by key in aDisplayGroup, NO if it can't. aspectName should name an aspect supported by the receiver's class.

Interface Builder uses this information to disable aspects in its Connections Inspector. Subclasses can override this method to base their answers on other binds already made, or on characteristics of the receiver's display object or of aDisplayGroup. EOAssociation's implementation always returns YES.

See Also: - localKeys (EODisplayGroup), - attributeKeys (EOClassDescription), - toOneRelationshipKeys (EOClassDescription), - toManyRelationshipKeys (EOClassDescription)



copyMatchingBindingsFromAssociation:

- (void)copyMatchingBindingsFromAssociation:(EOAssociation *)anAssociation

Duplicates the bindings of anAssociation in the receiver. For each aspect of anAssociation that has an EODisplayGroup, invokes bindAspect:displayGroup:key: with the EODisplayGroup and key for that aspect.

displayGroupForAspect:

- (EODisplayGroup *)displayGroupForAspect:(NSString *)aspectName

Returns the EODisplayGroup bound to the receiver for aspectName, or nil if there's no such object.

See Also: - displayGroupKeyForAspect:



displayGroupKeyForAspect:

- (NSString *)displayGroupKeyForAspect:(NSString *)aspectName

Returns the EODisplayGroup key bound to the receiver for aspectName, or nil if there's no EODisplayGroup.

See Also: - displayGroupForAspect:



endEditing

- (BOOL)endEditing

Overridden by subclasses to pass the value of the receiver's display object to the EODisplayGroup, by invoking setValue:forAspect: with the display object's value and the appropriate aspect (typically "value"). Returns YES if successful, NO if not-specifically if setValue:forAspect: returns NO. The receiver should also send an associationDidEndEditing: message to its EODisplayGroup.

Subclasses whose display objects immediately pass their changes back to the EOAssociation-such as a button or pop-up list-need not override this method. It's only needed when the display object's value is edited rather than simply set.

EOAssociation's implementation does nothing but return YES.



establishConnection

- (void)establishConnection

Overridden by subclasses to attach the receiver to the outlets of its display object, and to otherwise configure the display object (such as by setting its action method). EOAssociation's implementation subscribes the receiver as an observer of its EODisplayGroups and causes the display object to retain the receiver. Subclasses should invoke super's implementation after establishing their own connections.

See "Setting up an EOAssociation Programmatically" in the class description for more information.

See Also: - breakConnection



initWithObject:

- (id)initWithObject:(id)aDisplayObject

Initializes the receiver to monitor and update the value in aDisplayObject, which is typically a user-interface object or an EODisplayGroup. This is the designated initializer for the EOAssociation class. Returns self.
Because of the way that EOAssociations are set up, this method doesn't retain aDisplayObject. See "Setting up an EOAssociation Programmatically" in the class description for more information.

See Also: - bindAspect:displayGroup:key:, - establishConnection



object

- (id)object

Returns the receiver's display object.

See Also: - initWithObject:



setValue:forAspect:

- (BOOL)setValue:(id)value forAspect:(NSString *)aspectName

Sets a value of the selected enterprise object in the EODisplayGroup bound to aspectName. Retrieves the display group and key bound to aspectName, and sends the display group a setSelectedObjectValue:forKey: message with value and the key as arguments. Returns YES if successful, or if there's no display group bound to aspectName. Returns NO if there's an display group and it doesn't accept the new value.

See Also: - valueForAspect:



setValue:forAspect:atIndex:

- (BOOL)setValue:(id)value forAspect:(NSString *)aspectName atIndex:(unsigned int)index

Sets a value of the enterprise object at index in the EODisplayGroup bound to aspectName. Retrieves the display group and key bound to aspectName, and sends the display group a setValue:forObjectAtIndex:key: message with value, index, and the key as arguments. Returns YES if successful, or if there's no display group bound to aspectName. Returns NO if there's a display group and it doesn't accept the new value.

See Also: - valueForAspect:atIndex:



shouldEndEditingForAspect:invalidInput:errorDescription:

- (BOOL)shouldEndEditingForAspect:(NSString *)aspectName invalidInput:(NSString *)inputString errorDescription:(NSString *)errorDescription

Invoked by subclasses when the display object fails to validate its input, this method informs the EODisplayGroup bound to aspectName with an association:failedToValidateValue:forKey:object:errorDescription: message, using the display group's selected object. Returns the result of that message, or YES if there's no display group.

For example, an association bound to an NSControl object (Application Kit) receives a control:didFailToFormatString:errorDescription: delegate message when the control's formatter fails to format the input string. Its implementation of that method invokes shouldEndEditingForAspect:invalidInput:errorDescription:.

See Also: - shouldEndEditingForAspect:invalidInput:errorDescription:index:



shouldEndEditingForAspect:invalidInput:errorDescription:index:

- (BOOL)shouldEndEditingForAspect:(NSString *)aspectName invalidInput:(NSString *)inputString errorDescription:(NSString *)errorDescription index:(unsigned int)index

Works in the same manner as shouldEndEditingForAspect:invalidInput:errorDescription:, but allows you to specify a particular object by index rather than implicitly specifying the selected object.

subjectChanged

- (void)subjectChanged

Overridden by subclasses to update state based when an EODisplayGroup's selection or contents changes. This method is invoked automatically anytime a display group that's bound to the receiver changes. The receiver can query its display group with selectionChanged and contentsChanged messages to determine how it needs to update.

valueForAspect:

- (id)valueForAspect:(NSString *)aspectName

Returns a value of the selected enterprise object in the EODisplayGroup bound to aspectName. Retrieves the display group and key bound to aspectName, and sends the display group a selectedObjectValueForKey: message with the key. Returns nil if there's no display group or key bound to aspectName.

See Also: - setValue:forAspect:



valueForAspect:atIndex:

- (id)valueForAspect:(NSString *)aspectName atIndex:(unsigned int)index

Returns a value of the enterprise object at index in the EODisplayGroup bound to aspectName. Retrieves the display group and key bound to aspectName, and sends the display group a valueForObjectAtIndex:key: message with index and the key. Returns nil if there's no display group or key bound to aspectName.

See Also: - setValue:forAspect:atIndex:




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