How can I share collection between view controllers without passing it back and forth?

Question

In my app I have 3 view controllers, each of them working on the same collection of elements. Is there a way to share that collection other than passing it back and forth while performing segues? Can I somehow make collection accessible by all 3? What would be the right way to go about it?

What about use core data? Or maybe use a parent viewcontorller and treat the others as child? — Alejandro L.Rocha, Mar 12 '20 at 16:30
Are there a lot of elements or only a few? In the last case, you could maybe use `UserDefaults`. — koen, Mar 12 '20 at 16:31
Well he had mention a collection, thats why I ignoer `UserDefailts` but yeah, could be another option — Alejandro L.Rocha, Mar 12 '20 at 16:32
Make a super class for the view controllers with a static variable for the collection. — john elemans, Mar 12 '20 at 16:34
Thank you all for your answers. I think I will go with Singleton for now. — Stormwaker, Mar 12 '20 at 17:01
By the way, what's wrong with passing data from one view controller to the next? — koen, Mar 12 '20 at 20:07
Does this answer your question? [Pass data between view controllers constantly without a segue? USING SWIFT](https://stackoverflow.com/questions/29144857/pass-data-between-view-controllers-constantly-without-a-segue-using-swift) — Magnas, Mar 12 '20 at 20:21

score 2 · Accepted Answer · answered Mar 12 '20 at 16:37

You could make a singleton containing the collection of elements. Singletons however are often considered bad as they can cause more problems than they solve, so perhaps using Core Data would be a better option.

class Singleton {

    static let shared = Singleton()

    private init(){}

    private let internalQueue = DispatchQueue(label: "com.singletoninternal.queue",
                                              qos: .default,
                                              attributes: .concurrent)

    private var _elementCollection: Set<T>

    var elementCollection: String {
        get {
            return internalQueue.sync {
               _elementCollection
            }
        }
        set (newState) {
            internalQueue.async(flags: .barrier) {
                self._elementCollection = newState
            }
        }
    }

    func setup(collection: Set<T>) {
        _elementCollection = collection
    }
}

I'll look into Core Data and see if it's something I was looking for. — Stormwaker, Mar 12 '20 at 16:48
It will be a lot more hassle to set it up, and if all you're passing around is a simple set or array, the solution I provided will be suffice. — Thijs van der Heijden, Mar 12 '20 at 16:49

score 0 · Answer 2 · edited Mar 13 '20 at 14:29

0

You can use singleton classes like below example

class YourClassName {
    static let shared = YourClassName()
    var test : String = "String"
    private init(){}
}

and then call your variables using

YourClassName.shared.test

edited Mar 13 '20 at 14:29

koen

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answered Mar 13 '20 at 01:09

How can I share collection between view controllers without passing it back and forth?

2 Answers2