Is there a better way to make sure a variable is initialized when using blocks?

Question

I have a method to provide an NSManagedObjectContext using UIManagedDocument. I need to ensure that the context did initialize before I return, so I added an infinite while loop at the end of the method. But I think that was very stupid and is not acceptable.

- (NSManagedObjectContext *)context {
    NSURL *url = [[[NSFileManager defaultManager] URLsForDirectory:NSDocumentDirectory inDomains:NSUserDomainMask] lastObject];
    url = [url URLByAppendingPathComponent:@"Test"];
    UIManagedDocument *document = [[UIManagedDocument alloc] initWithFileURL:url];

    if (![[NSFileManager defaultManager] fileExistsAtPath:[url path]]) {
        [document saveToURL:url forSaveOperation:UIDocumentSaveForCreating completionHandler:^(BOOL success) {
            if (success) {
                self.managedObjectContext = document.managedObjectContext;
            }
            else {
                NSLog(@"[%@ %@] FATAL Error CANNOT create DB", NSStringFromClass([self class]), NSStringFromSelector(_cmd));
                exit(1);
            }
        }];
    }
    else if (document.documentState == UIDocumentStateClosed) {
        [document openWithCompletionHandler:^(BOOL success) {
            if (success) {
                self.managedObjectContext = document.managedObjectContext;
            }
            else {
                NSLog(@"[%@ %@] FATAL Error CANNOT open DB", NSStringFromClass([self class]), NSStringFromSelector(_cmd));
                exit(1);
            }
        }];
    }
    else {
        self.managedObjectContext = document.managedObjectContext;
    }

    while (!self.managedObjectContext) {
        // Is there any way better?
        NSDate *futureTime = [NSDate dateWithTimeIntervalSinceNow:1];
        [[NSRunLoop currentRunLoop] runMode:NSDefaultRunLoopMode beforeDate:futureTime];
    }

    return self.managedObjectContext;
}

Any suggestion will be appreciated.

Answer 1

Create and run operation using

NSOperation *op = [NSBlockOperation ... your block...];
[[NSOperationQueue new] addOperation: op];

and instead of using a runloop, wait for the result:

[op waitUntilFinished];