CODEWITHSUNDEEP
iosobjective-cerror-handlingexceptionmigration
Eddie
Eddie

Reputation: 1942

How to avoid "Terminating app due to uncaught exception"

There are times when you face exception and crash the app. In my case, here:

+ (void)saveContext:(NSManagedObjectContext *)context
{
    if ([context hasChanges]) {
        [context performBlockAndWait:^{
            NSError *error = nil;
            BOOL saved = [context save:&error];
            if (!saved) {
                // do some real error handling
                NSLog(@"Could not save master context due to %@", error);
            }
            else {
                if ([context parentContext]) {
                    [self saveContext:[context parentContext]];
                }
            }
        }];
    }
}

It terminated due to save context while migrating Coredata. I don't understand why that piece of code doesn't escape the exception. Shouldn't it log "Could not save master context due to $error"?

Question is, is the NSError has any meaning? How to escape the exception and crash? Should I use @try-catch instead of NSError?

EDIT 1

So, thanks to Mr. TheEye below, I understand that NSError doesn't escape this uncaught exception, and to avoid the crash, I better use @try-catch instead.

But, "it would be better to correct the cause of the exception, as it should not happen.", so I thought it should be better to update the question as below:

How should I make the context wait until migration done and perform save? In the case of migration failed, I will remove all context and persistent store, so the save process (in case migration failed) should be nullified. Else (migration successful), save normally.

Edit 2

So, to "correct the cause of the exception", I ended up fixed save context like this:

if (context.hasChanges && context.persistentStoreCoordinator.persistentStores.count) {
...
}

And that concluded my issue. Thanks for spending your time here.

Upvotes: 1

Views: 876

Answers (1)

TheEye
TheEye

Reputation: 9346

The error object only is for expected errors - if something unforeseen happens (eg some threading issue), an exception will be thrown. You can catch it with a try/catch, but it would be better to correct the cause of the exception, as it should not happen.

Upvotes: 1

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