iOS Swift - Reference between Objects

Question

I have a shared handler class in which I 'manage' objects.

In this shared class, there is a 'main object (mainObject)' and a 'single object (singleData)'.

If I now assign the singleData with the reference to mainObject.data[index] in viewA and then change mainObject.data[index] in viewB, then the singleData object also changes. How can I avoid this strong-reference here?

==> In short: I want to change the mainObject without changing the singleObject. <==


struct kOBJECT {
    let name: String
    let data: [Int]
}

class HandlerClass {
    
    let shared = HandlerClass()
    
    var mainObject = kOBJECT(name: "AnyName", data: [1,2,3,4,5])
    var singleData: Int?
    
}


class viewA: UIViewController {
    
    .....
    
    func didSelectRow(at indexPath: IndexPath) {
        HandlerClass.shared.singleData = HandlerClass.shared.mainObject.data[indexPath.row] // Create Reference
        viewB.indexPath = indexPath
        pushToViewController(viewB)
    }
    
}


class viewB: UIViewController {
    
    .....

    public var indexPath: IndexPath!
    
    func someFunction() {
        HandlerClass.shared.mainObject.data[indexPath.row] = 10000 // <- Does this also change the `singleData` Reference? In my case it does......
    }
    
}

I tried the following in 'didSelectRow'

let tempValue = HandlerClass.shared.mainObject.data[indexPath.row]
HandlerClass.shared.singleObject = tempValue

The whole point of having a shared(singleton) object is to share data, if you don't want this then each view controller should have its own instance of HandlerClass — Joakim Danielson
– Joakim Danielson, Commented Feb 10, 2023 at 15:12

Oleg · Accepted Answer · 2023-02-10 15:12:56Z

1

You misunderstand reference meaning. Reference works only of instances - that's a part of memory reserved for specific objects. Structs are also objects, but it works as Type (similar to Int, String, Double, Float, etc), so when you modify a struct as a result you will have a new object, but for class instance, you will still modify the same object as you copied only reference to that object.

Here example below:

class Apple {
    init(name: String) {
        self.name = name
    }
    var name: String
}

struct Pear {
    var name: String
}

var apple = Apple(name: "Apple 1")
var pear = Pear(name: "Pear 1")

var apple2 = apple // here we copy only reference
apple2.name = "Apple 2"
print(apple.name) // 1st object
print(apple2.name) // the same object

var pear2 = pear // here we create new object
pear2.name = "Pear 2"
print(pear.name) // 1st object
print(pear2.name) // 2nd object

Also a result (run on Playground)

answered Feb 10, 2023 at 15:12

Oleg

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2 Comments

INFINITE Over a year ago

Thanks for your reply, that opened my eyes. The struct was just an example here, in my app I actually use a class as an object. "var apple2 = apple" How can I prevent this from creating a reference?

Oleg Over a year ago

If you need to create new object instead of copy reference, just initiate a new instance: var apple2 = Apple(name: apple.name).

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