Saving NSManagedObjectContext on Stackmob -- uploads to server, but crashes app

Question

I have been running into an issue in using StackMob as the backend of my iOS application (though I'm not sure if this is an issue in wrongly using StackMob's methods or an iOS issue).

I am allowing a user to create a post object that is just a subclassed NSManagedObject, and uploading that to the server to be used in other parts of the application. The issue that arises occurs in the method:

[NSManagedObjectContext saveOnSuccess:<^(void)successBlock> onFailure:<^(NSError *error)failureBlock>];

Here, I am using a StackMob method for asynchronously saving the MOC found in the NSManagedObjectContext(Concurrency) Category Reference.

The view before this one performs a fetch on recent posts, and in the case where the fetch is not performed posting works fine, but if a fetch was performed then in saving the MOC in order to upload the new post I receive the following output as an error message:

2013-09-11 17:08:09.284 imageTagging[1824:1843] -[__NSDictionaryI bytes]: unrecognized
selector sent to instance 0x1e3123d0

2013-09-11 17:08:09.291 imageTagging[1824:1843] *** Terminating app due to uncaught
exception 'NSInvalidArgumentException', reason: '-[__NSDictionaryI bytes]: unrecognized
selector sent to instance 0x1e3123d0'

*** First throw call stack:
(0x318cb3e7 0x395c6963 0x318cef31 0x318cd64d 0x31825208 0x321631cf 0x3216b991 0x15ea99
 0x318c8757 0x15e109 0x15dabf 0x10d1c3 0x318d05b7 0x10cd4d 0x10c829 0x10923b 0x1076d9
 0x3166c431 0x316c44d1 0x1685c3 0x316c7e5d 0x399e3b3b 0x399e167d 0x399e4613 0x399e47d9
 0x39a087f1 0x39a08684)

libc++abi.dylib: terminate called throwing an exception
(lldb) 

The data is still uploading to the StackMob server, and can be called upon when the app is run later -- but the app crashes in trying to save it. All of this is performed in the view controller. I've tried to enforce all MOC saves to be performed on the main thread, but the error still occurs. I've also tried dispatching a "save queue" and updating the UI after save completes. This method seemed to work for a bit, but then the errors came up again (may have just been a fluke). I also tried to do this with the synchronous save calls in the documentation

The same error occurs when trying to perform other saves as well (such as after creating a new user or when updating a user's information), and all come down to the same function call causing the problems. It may also be worthwhile to note that the error is always the same (specifically that a type __NSDictionaryI is trying to access its unrecognized selector bytes.

Here is the full method call with the input parameters filled out:

//save context
[[[[SMClient defaultClient] coreDataStore] contextForCurrentThread] saveOnSuccess:^{
    NSLog(@"You created a new Post object!");
    [[[[SMClient defaultClient] coreDataStore] contextForCurrentThread] refreshObject:newPost mergeChanges:YES];
    NSLog(@"refreshed");
} onFailure:^(NSError *error) {
    NSLog(@"There was an error! %@", error);
}];

UPDATE: I have narrowed down the problem to a mishandling of information returned from a fetch performed by the previous view controller. Specifically, it occurs after the results are fetched in trying to use the data to update.

As a result of this new insight, the question I am really facing is how to properly save a managed object in the context after a fetch. I believe StackMob takes care of creating the managed objects after the fetch (i.e. server query). I've tried creating a new object from the results array (each "obj" is an NSManagedObject) with:

[results enumerateObjectsUsingBlock:^(id obj, NSUInteger idx, BOOL *stop) {
    NSManagedObject *newObj = obj;
}];

I've also tried referencing the fetched results by object id (each "obj" is an objectID) with:

[results enumerateObjectsUsingBlock:^(id obj, NSUInteger idx, BOOL *stop) {
    NSManagedObject *newObj = [self.managedObjectContext objectWithID:obj];
}];

Any insight on how to properly do this would be greatly appreciated!

UPDATE 2: It looks like the error is actually occurring in trying to use and save geolocation data. In order to use the queried objects' geolocation data, it must be unarchived -- but to save it, it must be archived. I'm looking into how to do this now, and if I come across a good solution, I'll update again.

FINAL UPDATE: Got it figured out! It turns out that the issue I was having was that I was unarchiving the geolocation data to update the UI and do some calculations, and while I was archiving it again to be stored properly, I created an annotation on a map that referenced the unarchived data. As a result, the MOC maintained the data that could not be saved via the StackMob methods. By only saving the archived data, I can save as often as I'd like and just unarchive the geodata when it needs to be used. Problem solved!

Please feel free to comment if anyone comes across a similar problem and needs some insight or references!

Answer 1

I am just going to put my final update in here as an answer, since it explains how I solved the issue.

FINAL UPDATE: Got it figured out! It turns out that the issue I was having was that I was unarchiving the geolocation data to update the UI and do some calculations, and while I was archiving it again to be stored properly, I created an annotation on a map that referenced the unarchived data. As a result, the MOC maintained the data that could not be saved via the StackMob methods. By only saving the archived data, I can save as often as I'd like and just unarchive the geodata when it needs to be used. Problem solved!

Please feel free to comment if anyone comes across a similar problem and needs some insight or references!

Moral of the story, if you are running into issues similar to this, make sure you are not (even if you don't mean to be) storing references to the unarchived SMGeoPoint data in any of your managed objects. It is trying to store those that causes the problem.