Question

Hello everyone — I am a beginner in iPhone programming and Core Data. I am currently trying to learn some of the theory behind Core Data, and have been using this tutorial to help me implement it in my app.

The tutorial teaches by making the main view a UITableViewController that lists the saved objects and another UITableViewController that saves objects (where you enter in the attributes).

The app that I am creating has 3 views. The main view is a plain UIViewController (it handles calculations), you are able to save your calculations by tapping a UIBarButtonItem that brings you to the second view where you enter in more specific attributes. Once you tap save, you are taken BACK to the main view, where you are able to tap a Show Saved button to access the UITableViewController containing saved objects.

I have included #imported the UITableViewController files into my main view’s interface file, but when I run the program, I get an error on this line in my prepareForSegue method:

    addShoeSizeTVC.managedObjectContext = self.managedObjectContext;

The error is “Property managedObjectContext not found on object of type ‘SSFViewController*'” I understand the meaning of this error — I don’t have any object called managedObjectContext in my SSFViewController class, but I figured that if I included my file that DOES contain managedObjectContext that it would still be recognized. I should add, that in the tutorial, the prepareForSegue method was contained in the list view for the segue to the add new object UITableViewController. I moved this method to my mainViewController.

I also get an error in my App Delegate in my ApplicationDidFinishLaunchingWithOptions method:

    controller.managedObjectContext = self.managedObjectContext;

I understand that this stems from the same problem with the other error (it gives the same error message).

I do not understand how to pass data going from my viewA (mainView), to viewB (add object), back to viewA, then to viewC (view saved objects). I have heard about delegation and am using it in my prepareForSegue method in my SSFViewController main view:

- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender {

    if ([segue.identifier isEqualToString:@"Add Object Segue"]) {

        NSLog(@"Setting ObjectsTVC as a delegate of AddObjectTVC");
        AddObjectTVC *addObjectTVC = segue.destinationViewController;
        addObjectTVC.delegate = addObjectTVC.self;
        addObjectTVC.managedObjectContext = addObjectTVC.self.managedObjectContext;
    }
}

Also on the addObjectTVC.delegate = addObjectTVC.self; line I get a warning that says “Passing ‘AddObjectTVC*’ to parameter of incompatible type ‘id'”

Do I have to set up an NSManagedContext or another delegation method in my main view? Or is it something that I must add to any of my Table views???

Thank you very much. I feel like this is a simple problem to solve, if provided with the right information. I am happy to post any other methods that I used if needed to solve the problem. I am a beginner, so it would be great if you could explain in a beginner-friendly way.

Thanks!

Answer 1

First of all, if you want data from ViewA to ViewB, insert a property in the ViewB and you can pass data from ViewA to this @property

Example

ViewB:

@property (nonatomic, strong) NSString *yourName;
(don’t forget to call @synthesize yourName )

ViewA: (in prepareForSegue method)

“ViewB-Controller” *controller = segue.destinationViewController;
controller.yourName = self.name

–> name will be passed to ViewB

Second:
I prefer a delegate which send from ViewB to ViewA “Hey please save your data”. It keeps your controller easy and smart, and you don’t have to manage the save method from all view controllers. Delegate is an important chapter in iOS and it can be very frustrated for a beginner. (I was in the same situation 9 months before ;))
Search for a delegate example and try to understand how it works (learning by doing), if you have further question about delegate, I will friendly respond to your question.