协议扩展中的快速关闭

Question

I want to Decorate UIViewController with the ability to adjust it's interface when setInteractionEnabled method is called from another class (ex. Network State Manager). All changes (if any) should be provided in the concrete controller by overriding onInteractionChanged . Here is my code:

import Foundation

typealias InteractionClosure = ((enabled: Bool) -> Void)

protocol Interaction: class {

    var onInteractionChanged: InteractionClosure? { get set }

    func setInteractionEnabled(enabled: Bool)

}

extension Interaction where Self: UIViewController {

    // Default: Do nothing
    // Throws: - Extensions may not contain stored properties
    var onInteractionChanged: InteractionClosure? = nil

    func setInteractionEnabled(enabled: Bool) {
        onInteractionChanged?(enabled: enabled)
    }

}

extension UIViewController : Interaction {}

How to add default implementation for onInteractionChanged ?

Answer 1

Answering my own question is something usually I don't do, but here is my solution:

typealias InteractionClosure = (enabled: Bool) -> Void

protocol Interaction: class {

    func addOnInteractionChanged(closure: InteractionClosure)
    func setInteractionEnabled(enabled: Bool)

}

extension Interaction where Self: UIViewController {

    func addOnInteractionChanged(closure: InteractionClosure) {
        onInteractionChanged = closure
    }

    func setInteractionEnabled(enabled: Bool) {
        onInteractionChanged?(enabled: enabled)
    }

    // MARK: - Private

    private var onInteractionChanged: InteractionClosure? {
        get {
            let wrapper =
                objc_getAssociatedObject(self, &icAssociationKey) as? ClosureWrapper
            return wrapper?.closure
        }
        set(newValue) {
            objc_setAssociatedObject(self,
                                     &icAssociationKey,
                                     ClosureWrapper(newValue),
                                     .OBJC_ASSOCIATION_RETAIN)
        }
    }

}

extension UIViewController : Interaction {}

// Helpers

private var icAssociationKey: UInt8 = 0

private class ClosureWrapper {
    var closure: InteractionClosure?

    init(_ closure: InteractionClosure?) {
        self.closure = closure
    }
}

Client class:

class LoginViewController: UIViewController {

    // MARK: - Lifecycle

    override func viewDidLoad() {
        super.viewDidLoad()
        self.setup()
    }

    // MARK: - Private

    private func setup() {
        // ...

        addOnInteractionChanged { [unowned self] (enabled) in            
            self.signInButton.enabled = enabled
            self.activityIndicatorView.hidden = !enabled
        }
    }

}

In manager class:

visibleViewController?.setInteractionEnabled(true)

Answer 2

If you would like property to have only { get } ability, you can use:

protocol TestProtocol {
    var testClosure: ((_ parameter: Bool) -> Void)? { get }
}

extension TestProtocol {
    var testClosure: ((_ parameter: Bool) -> Void)? {
        return { parameter in
            print(parameter)
        }
    }
}