How do you handle a UIManagedDocument?

Question

First off, I should mention that this is my first post on this site. I am trying to teach myself to program iOS and in my google searches for answers I find that I'm constantly directed here. So thank you to all who have contribute here. You have help me a ton already.

I have been going through the Stanford CS193P class and LOVE it. But I'm stuck right now and not sure where to turn.

My problem has been with the UIManagedDocument.

I tired to make a simple app to test my new skills. This is what it does:

A simple accounting app that tracks individual contributions to a fundraising event.

I have a UITabBar that on each tab allows you to: 1. Track the participants (Players) - This will connect to the address book and allow you to add them or just keep them in this app. 2. Manage the events (Events) - You can add, edit or delete events that you will then add participants to and then be able to add what they brought (Bank) in on that event. 3. Settings. - I've added some buttons just to help me figure stuff out now including a reset button that clears all data and a "dummy data" button.

I have three coreData Entities. Players, Events and Bank each with relationships with the other two.

When I first tried to make this app (pre iOS5) I used the appDelegate to create my ManagedObjectContext and pass it around to my viewControllers. That worked. But now I'm supposed to use the UIManagedObjectDocument and not use the AppDelegate. I believe I understand the principle and the integration to iCloud. (I could be wrong)

Using the examples from the class and what I could find online I made a helper class that will provide the first of each of my ViewControllers within my UINavigationControllers the ManagedDocument.

+ (UIManagedDocument *)sharedManagedDocument
{
    static UIManagedDocument *sharedDocument = nil;

    NSURL *url = [[[NSFileManager defaultManager] URLsForDirectory:NSDocumentDirectory inDomains:NSUserDomainMask] lastObject];
    url = [url URLByAppendingPathComponent:@"DefaultAppDatabase"];
    // url is "<Documents Directory>/<DefaultAppDatabase>"

    // Create the shared instance lazily upon the first request.
    if (sharedDocument == nil) {
        sharedDocument = [[UIManagedDocument alloc] initWithFileURL:url];
    }

    if (sharedDocument.fileURL != url) {
        UIManagedDocument *newDocument = [[UIManagedDocument alloc] initWithFileURL:url];
        sharedDocument = newDocument;
    }

    NSLog(@"SharedDocument: %@", sharedDocument);

    return sharedDocument;
}

I then had that first ViewController open the document and perform the fetch.

From there I pass whatever NSManagedObject is selected to the next ViewController through the segue.

The problems are when I get to adding or reseting the data. (I'm assuming that if I can get it to work with the "dummy data" button I can get it to work on an individual entry) When I press the "Reset" or "Dummy" button my logs tell me that it was pushed but I don't see any change in the data until I restart the app. Then it shows up perfectly. My guess is I'm not saving the file correctly or I'm not refreshing the tableViews correctly. I made a small attempt at using NSNotification but didn't go to far into it since I couldn't get it to respond to anything. I'm happy to go back down that road if I need to.

This is my save method... pretty much just copied from the default coreData appDelegate.

- (void)saveContext
{
    NSError *error = nil;
    NSManagedObjectContext *managedObjectContext = self.appDatabase.managedObjectContext;
    if (managedObjectContext != nil)
    {
        if ([managedObjectContext hasChanges] && ![managedObjectContext save:&error])
        {
            /*
             Replace this implementation with code to handle the error appropriately.

             abort() causes the application to generate a crash log and terminate. You should not use this function in a shipping application, although it may be useful during development. 
             */
            NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
            abort();
        } 
    }

    [self.appDatabase saveToURL:self.appDatabase.fileURL
               forSaveOperation:UIDocumentSaveForOverwriting
              completionHandler:^(BOOL success){
                  if(!success) NSLog(@"failed to save document %@", self.appDatabase.localizedName);
                  if(success) NSLog(@"Success: save document %@", self.appDatabase.localizedName);
              }];

}

Paul, the instructor from CS193P, suggested in Assignment 6 to use a helper method to pass around the UIManagedDocument through a block. I get the theory behind blocks but haven't completely wrapped my head around them so I haven't ruled out that my answer may lie there as well.

Thank you so much for any help or pointing me in the right direction to do more research. Sorry this post is so long, I was trying to be as clear as I can.

caseyburden caseyburden · Accepted Answer · 2012-02-13T01:04:54

I was over thinking the whole thing. Alan asked my question perfectly in this post:

How do I create a global UIManagedDocument instance per document-on-disk shared by my whole application using blocks?

The question and the answers cleared everything up.

Thanks

How do you handle a UIManagedDocument?

1 Answers