iPhone app launch times and Core Data migration

Question

I have a Core Data application which I plan to update with a new schema. The lightweight migration seems to work, but it takes time proportional to the amount of data in the dat

Answer 1

Here is an outline of an approach similar to what ohhorob describes. The difference is that I just display an animated "Upgrading..." HUD rather than a more informative progress bar.

The key point is that nothing tries to access Core Data until the migration has had a chance to do its thing. Therefore, I move all the remaining launch code (including the setting of the rootViewController) that could potentially touch Core Data into a separate method. I then call this method after the migration has completed, or immediately if no migration is required. That looks like this:

-(BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
    self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
    [self.window makeKeyAndVisible];

    if ([MyManagedObject doesRequireMigration]) { // -doesRequireMigration is a method in my RHManagedObject Core Data framework
        [SVProgressHUD showWithStatus:NSLocalizedString(@"Upgrading...", nil) maskType:SVProgressHUDMaskTypeGradient];

        dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0), ^{

            // do your migration here

            dispatch_async(dispatch_get_main_queue(), ^{
                [SVProgressHUD showSuccessWithStatus:NSLocalizedString(@"Success!",nil)];
                [self postApplication:application didFinishLaunchingWithOptions:launchOptions];
            });
        });

    } else {
        [self postApplication:application didFinishLaunchingWithOptions:launchOptions];
    }

    return YES;
}

-(void)postApplication:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
    self.window.rootViewController = ....

    // anything else you want to run at launch
}

This approach should play nice with the watchdog that monitors startup times since the migration will take place off the main thread.