ChangeManager.rtf

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ChangeManager

INHERITS FROM Responder : Object

DECLARED IN ChangeManager.h

CLASS DESCRIPTION

The ChangeManager class is the part of the undo mechanism that collects change objects and manipulates the undo and redo menu items. This class works with the Change class to provide a simple way to implement multi-level undo. Change managers communicate with change objects through the responder chain. By deriving window delegates from ChangeManager you can easily implement document-level undo. By installing a change manager as an application delegate you can also implement application wide undo.

INSTANCE VARIABLES

Inherited from Object Class isa;

Inherited from Responder id nextResponder;

Declared in ChangeManager List *_changesList;
Change *_lastChange;
Change *_nextChange;
Change *_changeInProgress;
int _numberOfDoneChanges;
int _numberOfUndoneChanges;
int _numberOfDoneChangesAtLastClean;
BOOL _someChangesForgotten;
int _changesDisabled;

_changesList A list of changes that have been made.

_lastChange The id of the change that can be undone.

_nextChange The id of the change that can be redone.

_changeInProgress The id of the change which is currently underway.

_numberOfDoneChanges The number of changes made.

_numberOfUndoneChanges The number of changes that have been undone.

_numberofDoneChangesAtLastClean A count of changes made when clean was last called.

_someChangesForgotten YES if some changes have been thrown away

_changesDisabled The number of nested calls to disableChanges:.

METHOD TYPES

Initializing and freeing - init
� free

Disabling undo � disableChanges:
� enableChanges:

Examining state � canUndo
� canRedo
� isDirty

Setting state � dirty:
� clean:
� reset:

Validating Menu Commands � validateCommand:

Undoing and Redoing � undoOrRedoChange:
� undoChange:
� redoChange:

Tracking change progress � changeInProgress:
� changeComplete:

Subclass notification � changeWasDone
� changeWasUndone
� changeWasRedone

INSTANCE METHODS

canRedo
- (BOOL)canRedo

Returns YES if there is a Change that can be redone. The name of this Change will be visible in the redo or undo/redo menu item. You should not need to override this method.

See also: � validateCommand:

changeComplete:
- changeComplete:change

Called by Change objects to signify that change is done. The receiving ChangeManager will then ask change to save the new state information via saveAfterChange. Just before returning, the changeComplete: method sends a changeWasDone message to self, which provides subclasses of ChangeManager with an opportunity to react to the change. You should never call changeComplete: directly, nor should you override it.

See also: � changeInProgress:, � changeWasDone, � saveAfterChange (Change)

changeInProgress:
- changeInProgress:change

Called by Change objects to signify that a change is about to be made. If changes have been disabled using disableChanges: then changeInProgress: will send a disable message to change and immediately return. If changes have not been disabled, the receiving ChangeManager tries to find a home for change. If another Change is already in progress that Change is sent an incorporateChange: message with change as the argument. If the Change in progress returns YES then change is sent a saveBeforeChange message, otherwise it is sent a disable message. If there is no Change already in progress, but there is a previous completed Change then the previous Change is sent a subsumeChange: message with change as the argument. If the previous Change returns YES then change is sent a disable message. If the previous Change returns NO, or if there is no previous Change, change is sent a saveBeforeChange message and set to be the current Change in progress, and the previous Change, if there is one, is sent a finishChange message. You should never need to call changeInProgress: directly, nor should you need to override it.

See also: � changeComplete:, � saveBeforeChange (Change), � incorporateChange: (Change), � subsumeChange: (Change), � finishChange (Change)

changeWasDone
- changeWasDone

Override this method if your subclass needs to know when a change has been made. For example, this hook can be used to update the close box on a document window to reflect the dirty state of the ChangeManager. You should not call this method directly.

See also: � changeWasRedone, � changeWasUndone, � isDirty

changeWasRedone
- changeWasRedone

Override this method if your subclass needs to know when a change has been redone. For example, this hook can be used to update the close box on a document window to reflect the dirty state of the ChangeManager. You should not call this method directly.

See also: � changeWasDone, � changeWasUndone, � isDirty

changeWasUndone
- changeWasUndone

Override this method if your subclass needs to know when a change has been undone. For example, this hook can be used to update the close box on a document window to reflect the dirty state of the ChangeManager. You should not call this method directly.

See also: � changeWasDone, � changeWasRedone, � isDirty

clean:
- clean:sender

Tells the receiving ChangeManager to consider its current state to be clean. Calls to isDirty will return NO until further change activity occurs. In ChangeManagers that correspond to documents, you should call clean: each time the document is saved. By doing this, the isDirty method can be used to tell whether the saved representation of the document matches the internal memory representation. When overriding this method you should begin your method with �[super clean:sender]�.

See also: � dirty:, � reset:, � isDirty

dirty:
- dirty:sender

Forces the receiving ChangeManager to appear dirty. Call this method when your code as made a change that wasn't recorded with a Change object. After a dirty message is received the isDirty method will return YES until a clean: or reset: message is received. When overriding this method you should begin your method with �[super dirty:sender]�.

See also: � clean:, � reset:, � isDirty

disableChanges:
- disableChanges:sender

This method increments the receiver's changesDisabled instance variable. As long as changesDisabled is non-zero, new change objects will be disabled. You should not need to override this method.

See also: � enableChanges, � disable (Change)

enableChanges:
- enableChanges:sender

Decrements the receiver's changesDisabled instance variable. You should not need to override this method.