Core Data - How to check if a managed object's properties have been deallocated?

I've created a program that uses core data and it works beautifully.

I've since attempted to move all my core data methods calls and fetch routines into a class that is self contained. My main program then instantiates that class and makes some basic method calls into that class, and the class then does all the core data stuff behind the scen开发者_开发问答es. What I'm running into, is that sometimes I'll find that when I grab a managed object from the context, I'll have a valid object, but its properties have been deallocated, and I'll cause a crash. I've played with the zombies and looked for memory leaks, and what I have gathered is it seems that the run loop is probably responsible for deallocating the memory, but I'm not sure.

Is there a way to determine if that memory has been deallocated and force the core data to get it back if I need to access it? My managedObjectContext never gets deallocated, and the fetchedResultsController never does, either.

I thought maybe I needed to use the [managedObjectContext refreshObject:mergeData:] method, or the [managedObjectContext setRetainsRegisteredObjects:] method. Although, I'm under the impression that last one may not be the best bet since it will be more memory intensive (from what I understand).

These errors only popped up when I moved the core data calls into another class file, and they are random when they show up.

Any insight would be appreciated.

-Ryan

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Sounds to me like you are not retaining objects you want to keep hanging around. If you are doing something like this:

NSArray *array = [moc executeFetchRequest:request error:&error];

you do not own the returned array and it will most likely disappear when the current autorelease pool is drained. This will occur when the run loop finishes processing the current event.

All this is speculation. If you want a proper answer, you need to post your code.

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It's hard to know what the problem is based on your description, but you might want to look at the Core Data memory management guide. You shouldn't have to worry about memory management for managed objects and their entities (they're fetched and faulted automatically). When you talk about "properties," do you mean custom properties backed by ivars? If so, these should be released in didTurnIntoFault and allocd as needed (probably in the accessor).

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I was struggling with a similar issue. I'm using a managed object class and want to set its properties dependent on user input. But the sometimes the properties and sometimes the whole managed object were deallocated.

After reading the Apple documentation http://developer.apple.com/library/IOs/#documentation/Cocoa/Conceptual/CoreData/Articles/cdMemory.html the chapter "The Role of the Managed Object Context" I learned that managed objects are released each run loop completes.

And there is the golden advice to set

[myMangedObjectContext setRetainsRegisteredObjects:YES];

(I had to set it in the init method (initWithNibName for me) of my view controller.)

You should also regard to retain only the objects you need to as explained in the documentation. But read it yourself.

If I'm not right please correct me.

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I also made a class that handles all my CoreData fetching and stuff. I ran into a couple of gotcha's, so here are some tips. (If I am making any memory management errors in these examples, please let me know.)

Two things:

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1) Made a "fetchFiredObject" method in the CoreData handler class. So when I want to get a managedObject that has all its variables and is a "fully feathered bird" so to speak, instead of doing:

aManagedObject *myManagedObject = [myCoreDataHandler.managedObjectStorageArray objectAtIndex:1];
int x = myManagedObject.someVariable.intValue;

instead I do:

aManagedObject *myManagedObject = [myCoreDataHandler fetchFiredObjectAtIndex:1];
int x = myManagedObject.someVariable.intValue;

And in myCoreDataHandler's fetchFiredObjectAtIndex:i method, we're going into the array, finding the object key at index i, then doing a fetchRequest for that object key, and returning the freshly-fetched managedObject so that it won't have been faulted or deallocated, etc. :D

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2) When I create a new child viewController, I populate its "myCoreDataHandler" value from the parent upon creation. However, this happens on a subsequent line of code after the line of code that creates the new viewController. Therefore, any code in the child's viewDidLoad that tries to use myCoreDataHandler's methods will return empty objects because viewDidLoad completes before the parent's next line of code where it sets the values of globals in the child object. So make sure you are not accessing your "Core Data handling object" from within viewDidLoad or anything local methods called by viewDidLoad! Instead call them from the parent after creating the new viewController.