Frederick Squid Frederick Squid - 1 month ago 6
Swift Question

Two singletons referencing each other prevent the initialization from ending

I have a situation where I want to have two singleton objects that hold references to each other.

ManagerA:

import Foundation

class ManagerA: NSObject {

static let sharedInstance = ManagerA()

let managerB = ManagerB.sharedInstance

private override init() {
super.init()
}
}


ManagerB (in this example symmetric to ManagerA):

import Foundation

class ManagerB: NSObject {

static let sharedInstance = ManagerB()

let managerA = ManagerA.sharedInstance

private override init() {
super.init()
}
}


Manager A is being created in the AppDelegate.
Unfortunately this leads to the ViewController not being shown anymore, so I assume the initialization process is endless.

How can I solve the initialization?

I'd like to stay with the pattern. Both managers are used throughout the app from various places and the singleton pattern seems fit. Yet it'd be useful if they could also directly access each other.

Answer

Yes, this is infinite recursion.

You can fix that in several ways.

Here I am making one of the 2 properties a computed property, look

final class ManagerA {
    static let sharedInstance = ManagerA()
    var managerB = { return ManagerB.sharedInstance }
    private init() { }
}

final class ManagerB {
    static let sharedInstance = ManagerB()
    let managerA = ManagerA.sharedInstance
    private init() { }
}

More

However do you really need a property to reference a singleton? The beauty of a singleton is that you can retrieve the only allowed instance of a class from everywhere simply writing ClassName.sharedInstance.

So you could easily remove both the managerA and managerB properties.

Some changes I made

  • I removed the NSObject stuff since you don't really need that don't you?
  • I made your classes final, otherwise someone could subclass them, add an init and break the singletons paradigm
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