CODEWITHSUNDEEP
iosobjective-cclasssingleton
Luke
Luke

Reputation: 9710

Confusion over running methods on Class Method instances of objects

So I'm getting myself into a confusion over where my data's going and where it's stored in my application. It's not a specific question so hopefully someone can provide a generalised answer.

I need to pass some data around between a few UIViewController instances, and I'm currently doing that with a singleton object called my dataManager. This class has one method, a class method, called + (LCDataManager *) sharedDataManager, and that method basically checks if whether the sharedDataManager already exists, if so, return it, if not, create it and set up its variables. This means that I can refer to that class anywhere I like, access and modify its variables anywhere I like, from across multiple classes.

First question: is this the correct / best / most appropriate means of passing data around like this? I'm hoping it obeys MVC, it feels like it does, and I hope I'm right.

Second question: what if I want to put an instance method in that class, and call it from within the class method? Let's say my sharedDataManager needs to call a method to grab some objects one of its variables (an array), and put them in another array, then send that back out again. I can't do that, can I? What's the way around that? If I make an instance of that class (rather than using the shared instance), I lose the ability to use that instance across multiple viewControllers.

I'm hideously confused, and it seems like it's not the problem I'm making it. Appreciate any guidance, and preferably not that "Read the Apple documentation" stuff – they write as if you already know what you're doing, and frankly I don't yet.

Upvotes: 1

Views: 125

Answers (4)

John Topley
John Topley

Reputation: 115422

Matthijs Hollemans has an excellent three-part tutorial on his blog about the correct way to make your view controllers talk to each other:

Upvotes: 1

sergio
sergio

Reputation: 69047

First question: is this the correct / best / most appropriate means of passing data around like this? I'm hoping it obeys MVC, it feels like it does, and I hope I'm right.

Your design is perfectly MVC compliant.

Second question: what if I want to put an instance method in that class, and call it from within the class method?

you can surely define an instance method and call it like this:

[[MyModelClass sharedModel] myInstanceMethod];

indeed, [MyModelClass sharedModel] will give you an instance of MyModelClass (which should be guaranted to be unique being it a singleton).

If you want to call the instance method from the sharedModel class method, you could also do that, because sharedModel owns a reference to your singleton, so it can send messages to it.

Upvotes: 3

w-m
w-m

Reputation: 11232

is this the correct / best / most appropriate means of passing data around like this?

There's nothing wrong with only having a single instance of LCDataManager, but using the Singleton pattern has potential problems. An alternative is to just initialize one LCDataManger and to pass it around to wherever it's needed.

what if I want to put an instance method in that class, and call it from within the class method?

The accessor + (LCDataManager *) sharedDataManager should only return the instance. I guess what you want is something like

+ (LCDataManager *)preparedDataManager {
    LCDataManager *shared = [self sharedDataManager];
    [shared doSomeInstanceMagic];
    return shared;
}

- (void)doSomeInstanceMagic {
    // magic!
    // grab some objects one of its variables (an array),
    // and put them in another array
}

Upvotes: 3

tkanzakic
tkanzakic

Reputation: 5499

there is no problem with this development architecture, and it is the must used (I think) in the iOS development. In the book IOS Programming: The Big Nerd Ranch Guide they call it Model View Controller Store.

Regarding your second question, yes, you can declare instance methods and call then from your sharedDataManager. What is not usual is creating other instances of a singleton class, but it is possible.

Upvotes: 0

Related Questions