On 2009 Mar 11, at 18:39, Dave Fernandes wrote:
It helped me figure out what was changing by overriding
willChangeValueForKey in my NSManagedObject subclass...
Dave, I just used your idea and was able to track down two of these
phantom changes this afternoon.
At first, I was getting information overload, but then I modified your
code so that it would only print when I was undoing. Details are
explained in the code comments below. This is a great trick!
#define DEBUG_MANAGED_OBJECT_CHANGES
#ifdef DEBUG_MANAGED_OBJECT_CHANGES
#warning overrode willChangeValueForKey. Do not ship this.
/*!
@brief In a Core Data document-based application, you
often have the problem of the close button getting a dirty
dot immediately after a new document is created or an old
one loaded. To find out what is changing, paste this
code into the NSManagedObject subclass that you suspect
might be changing, or even better, if you have a
NSManagedObject parent class for all your subclasses
paste it in there. Define the constant above, compile,
and run your app so that the dot gets dirty. Then click
Undo until the dot becomes clean as you watch the console.
To your great delight, the answer will be magically printed.
@details Thanks to Dave Fernandes for this great idea!
*/
- (void)willChangeValueForKey:(NSString*)key
{
if ([[[self managedObjectContext] undoManager] isUndoing]) {
NSLog(@"%@ undid changed value for key: %@",
[[self entity] name],
key) ;
}
[super willChangeValueForKey:key];
}
#endif
One of problems I tracked down was that I was setting a managed object
value in response to a notification, so this occurred after I invoked -
clearChanges at the end of my document's initializer:
- (void)clearAllChanges {
[self.managedObjectContext processPendingChanges] ;
[self.managedObjectContext.undoManager removeAllActions] ;
[self updateChangeCount:NSChangeCleared] ;
}
The solution, which I had worked out a couple weeks ago, is to invoke
this with performSelector:afterDelay:0.0. It's maybe a little
kludgey, but now since I know why it's needed I don't feel so bad
about it.
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