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Re: Observing Undo in a Core Data App

Subject: Re: Observing Undo in a Core Data App
From: Ron Lue-Sang <email@hidden>
Date: Fri, 24 Feb 2006 16:08:18 -0800
Delivered-to: email@hidden
Delivered-to: email@hidden

Yeah, what Joshua is suggesting is a much simpler and perfectly reasonable solution. You could go out of your way to do all the work yourself. Assuming your array is called "things"

- (void)objectsChangedInContext:(NSNotification *)info { NSUndoManager *undoManager = [[self managedObjectContext] undoManager]; BOOL work = [undoManager isUndoing] | [undoManager isRedoing];

// only need this stuff in the case your undoing/redoing. You might also need this logic if something other than the array controller will change things in the context if (work == YES) {

NSSet *deleted = nil; if ((deleted = [[info userInfo] objectForKey:NSDeletedObjectsKey]) != nil) { // lazy, we'll skip computing the indexes that will be deleted, but it's a good idea to do [self willChangeValueForKey:@"things"]; [things removeObjectsInArray:[deleted allObjects]]; [self didChangeValueForKey:@"things"]; } NSSet *inserted = nil; if ((inserted = [[info userInfo] objectForKey:NSInsertedObjectsKey]) != nil) { int baseIndex = [things count]; int endIndex = [inserted count]-1;

NSIndexSet *indexes = [NSIndexSet indexSetWithIndexesInRange:NSMakeRange(baseIndex,endIndex)];

// it's easy to compute the indexes here, so we should [self willChange:NSKeyValueChangeInsertion valuesAtIndexes:indexes forKey:@"things"]; [things addObjectsFromArray:[inserted allObjects]]; [self didChange:NSKeyValueChangeInsertion valuesAtIndexes:indexes forKey:@"things"]; } } }

- (void)applicationDidFinishLaunching:(NSNotification *)notification {

// register for a notification when objects are changed in the MOC [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(objectsChangedInContext:) name:NSManagedObjectContextObjectsDidChangeNotification object:[self managedObjectContext]];

// fetch and stuff NSFetchRequest *request = [[[NSFetchRequest alloc] init] autorelease]; [request setEntity:[NSEntityDescription entityForName:@"Entity" inManagedObjectContext:[self managedObjectContext]]]; [self willChangeValueForKey:@"things"]; things = [[[self managedObjectContext] executeFetchRequest:request error:nil] mutableCopy]; [self didChangeValueForKey:@"things"];

Make sense?

-----------------------------
Ronzilla
Core Bindings/Cocoa Builder/Interface Data

On Feb 24, 2006, at 11:43 AM, email@hidden wrote:

Message: 12
Date: Fri, 24 Feb 2006 11:19:53 -0600
From: Joshua Scott Emmons <email@hidden>
Subject: Re: Observing Undo in a Core Data App
To: Michael Clark <email@hidden>
Cc: Cocoa List <email@hidden>
Message-ID: <email@hidden>
Content-Type: text/plain; charset=US-ASCII; delsp=yes; format=flowed

What do I observe to see if an item has been placed back into the
NSManagedObject context via Undo. Undo works: the most recently
deleted object is put back into the context - it's there when I
restart the application and reload the array. I just need to know
when an object is put back into the context so that I can update my
UI on the fly. Any suggestions on how to do this?


My solution to this was to crate a base managed object, "Office".
Office has a to-many relationship called "employees". My array
controller adds and deletes Employee managed objects from this to-
many relationship. Then, to recognize undo/redos, I just KVO Office's
"employees" relationship.

This was a quick fix when I did it. I didn't look for a better way,
and there very well might be one. But this worked well enough for me.

Oh, one more note. When proceessing the KVO with -
observeValueForKeyPath:ofObject:change:context:,
NSKeyValueChangeKindKey is NSKeyValueChangeRemoval on deletions and
NSKeyValueChangeInsertion on insertions. But as I recall it's NEITHER
on undos and redos. Just a heads up.


Cheers,
-Joshua Emmons


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