On Jun 27, 2010, at 4:08 , Jerry Krinock wrote:
>
> On 2010 Jun 26, at 16:01, Guillaume Laurent wrote:
>
>> I'm having difficulties with the undo/redo mechanism and my Core Data
>> objects.
>
> Uh-huh.
>
>> The problem is that I create a CoreData object (say a rectangle), then set
>> some of its attributes according to some controls values (the position and
>> size of a CALayer the user has just created in a view). This set of actions
>> is a single one from the user's point of view. I know I can make it appear
>> so with NSUndoManager:beginUndoGrouping/endUndoGrouping. But when I undo
>> this in the app, each of the steps of the object's creation are undone
>> seperately, including the setting of each of the attributes. ....
>
>> Bottom line : is there a way to make it so that the CoreData object's
>> instantiation and its setup are registered as a single action in the
>> undo/redo stack ?
>
> I presume that you are setting these attributes in -awakeFromInsert. One
> solution I've seen used for this particular problem is to disable undo
> registration when the attributes are set. Something like this:
>
> - (void)awakeFromInsert {
> [super awakeFromInsert] ;
>
> // Close the curtain so the wizard can do some magic
> [[self managedObjectContext] processPendingChanges] ;
> [[[self managedObjectContext] undoManager] disableUndoRegistration] ;
>
> // Do some magic
> [self setFoo:whatever] ;
> [self setBar:whateverElse] ;
>
> // Re-open the curtain
> [[self managedObjectContext] processPendingChanges] ;
> [[[self managedObjectContext] undoManager] enableUndoRegistration] ;
> }
>
> So the setting of foo and bar aren't even on the undo stack. But when you
> Undo, it removes the object, so no one cares.
Yes, that's what I did, but a friend gave me a better one, which was to
dissociate element creation and insertion :
NSEntityDescription* segmentEntity = [NSEntityDescription
entityForName:@"Segment" inManagedObjectContext:managedObjectContext];
NSManagedObject<Segment>* newSegment = [[NSManagedObject alloc]
initWithEntity:segmentEntity insertIntoManagedObjectContext:nil];
// do some init stuff on newSegment
[managedObjectContext insertObject:newSegment];
That does exactly what I need.
--
Guillaume
http://telegraph-road.org
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