Swift access control with target selectors

问题

Have a look at this example code:

class ViewController: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()

        let letterButton = UIButton.buttonWithType(.Custom) as UIButton
        self.view.addSubview(letterButton)
        letterButton.addTarget(self, action:Selector("buttonDidTap:"), forControlEvents: .TouchUpInside)

    }

    func buttonDidTap(button: UIButton!) {
        print(button.char)
    }

}

The target action for the UIButton works fine as long as Selector is public or internal, but if it's private, it crashes due to unrecognized selector sent to instance

Is there any way I can achieve this ? I don't want to make tap function public or internal.

回答1:

you need @objc to expose a private method to objc runtime

@objc private func buttonDidTap(button:UIButton!) {
    println(button.char)
}

From Xcode6 beta4 release notes

Declarations marked private are not exposed to the Objective-C runtime if not otherwise annotated. IB outlets, IB actions, and Core Data managed properties remain exposed to Objective-C whatever their access level. If you need a private method or property to be callable from Objective-C (such as for an older API that uses a selector-based callback), add the @objc attribute to the declaration explicitly.! !

来源：https://stackoverflow.com/questions/25056278/swift-access-control-with-target-selectors