Dependency injection – UIViewController in Storyboard (iOS 13)

Finally Apple (iOS 13 +) has added constructor dependency injection to Storyboards!

No excuses anymore for not using DI properly on UIViewControllers.

Let’s see a quick example.

We have an app with a simple Storyboard with two UIViewControllers.

The code for the second UIViewController is as follows:

final class AnotherViewController: UIViewController {
    
    private let aDependency: String
    @IBOutlet weak var showDependencyLabel: UILabel!
    
    init?(coder: NSCoder, aDependency: String) {
        self.aDependency = aDependency
        super.init(coder: coder)
    }
    
    required init?(coder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
    
    @IBAction func didTapButton(_ sender: Any) {
        showDependencyLabel.text = aDependency
    }
}

final class AnotherViewController: UIViewController {

private let aDependency: String

@IBOutlet weak var showDependencyLabel: UILabel!

init?(coder: NSCoder, aDependency: String) {

self.aDependency = aDependency

super.init(coder: coder)

}

required init?(coder: NSCoder) {

fatalError("init(coder:) has not been implemented")

}

@IBAction func didTapButton(_ sender: Any) {

showDependencyLabel.text = aDependency

}

In order to pass the dependency we have to use the failable init method.

The code for the UIViewController that shows the AnotherViewController is:

import UIKit

final class ViewController: UIViewController {
    
    @IBAction func didTapButton(_ sender: Any) {
        guard let anotherViewController = storyboard?.instantiateViewController(identifier: "AnotherViewController", creator: { coder in
            return AnotherViewController(coder: coder, aDependency: "something")
        }) else { fatalError("AnotherViewController failed to be initialized")}
        
        present(anotherViewController, animated: true, completion: nil)
    }
}