"Extensions must not contain stored properties" preventing me from refactoring code

Question

I have a 13 lines func that is repeated in my app in every ViewController, which sums to a total of 690 lines of code across the entire project!

/// Adds Menu Button
func addMenuButton() {
    let menuButton = UIButton(frame: CGRect(x: 0, y: 0, width: 30, height: 30))
    let menuImage = UIImage(named: "MenuWhite")
    menuButton.setImage(menuImage, for: .normal)

    menuButton.addTarget(self, action: #selector(menuTappedAction), for: .touchDown)
    self.navigationItem.rightBarButtonItem = UIBarButtonItem(customView: menuButton)
}
/// Launches the MenuViewController
@objc func menuTappedAction() {
    coordinator?.openMenu()
}

for menuTappedAction function to work, I have to declare a weak var like this:

extension UIViewController {

weak var coordinator: MainCoordinator?

But by doing this I get error Extensions must not contain stored properties What I tried so far:

1) Removing the weak keyword will cause conflicts in all my app. 2) Declaring this way:

weak var coordinator: MainCoordinator?
extension UIViewController {

Will silence the error but the coordinator will not perform any action. Any suggestion how to solve this problem?

Answer 1

You can move your addMenuButton() function to a protocol with a protocol extension. For example:

@objc protocol Coordinated: class {
    var coordinator: MainCoordinator? { get set }
    @objc func menuTappedAction()
}

extension Coordinated where Self: UIViewController {
    func addMenuButton() {
        let menuButton = UIButton(frame: CGRect(x: 0, y: 0, width: 30, height: 30))
        let menuImage = UIImage(named: "MenuWhite")
        menuButton.setImage(menuImage, for: .normal)

        menuButton.addTarget(self, action: #selector(menuTappedAction), for: .touchDown)
        self.navigationItem.rightBarButtonItem = UIBarButtonItem(customView: menuButton)
    }
}

Unfortunately, you can't add @objc methods to class extensions (see: this stackoverflow question), so you'll still have to setup your view controllers like this:

class SomeViewController: UIViewController, Coordinated {
    weak var coordinator: MainCoordinator?
    /// Launches the MenuViewController
    @objc func menuTappedAction() {
        coordinator?.openMenu()
    }
}

It'll save you some code, and it will allow you to refactor the bigger function addMenuButton(). Hope this helps!

Answer 2

For it to work in an extension you have to make it computed property like so : -

extension ViewController {

   // Make it computed property
    weak var coordinator: MainCoordinator? {
        return MainCoordinator()
    }

}