Question

我希望协议能够从Apple协议UIViewControllerTransitioningDelegate 继承，添加其他协议要求并为该协议中的某些方法提供默认实现。当我这样做时，方法不会被调用。当我在类本身中实现方法时，方法 do 被调用。

这就是我所说的：

class FirstViewController: UIViewController, SlideDismissor {
    let transition: PercentDrivenInteractiveTransitionWithState? = PercentDrivenInteractiveTransitionWithState()
}

protocol SlideDismissor: UIViewControllerTransitioningDelegate {
    var transition: PercentDrivenInteractiveTransitionWithState? { get }
}

extension SlideDismissor {
    func animationControllerForDismissedController(dismissed: UIViewController) -> UIViewControllerAnimatedTransitioning? {
        return nil // I do return something here, but for this example it isn't necessary
    }

    func interactionControllerForDismissal(animator: UIViewControllerAnimatedTransitioning) -> UIViewControllerInteractiveTransitioning? {
        return transition
    }
}

如果我添加以下代码，则会调用函数。

extension FirstViewController: UIViewControllerTransitioningDelegate {

    func animationControllerForDismissedController(dismissed: UIViewController) -> UIViewControllerAnimatedTransitioning? {
        return nil // I do return something here, but for this example it isn't necessary
    }

    func interactionControllerForDismissal(animator: UIViewControllerAnimatedTransitioning) -> UIViewControllerInteractiveTransitioning? {
        return transition
    }

}

我试图提供默认实现的这些方法是可选方法。

Answer 1

针对这些问题的更好解决方案是使用组合而不是继承。而不是符合SlideDismissor，委托给一个。

（我还没有对这段代码进行测试，甚至确保编译，但这是我要探索的基本方法。）

class FirstViewController: UIViewController {

    // Rather than handle your own transitioning, delegate it to another, reusable, object.    
    override func viewDidLoad() {
        // Your original protocol suggested that the view controller wanted
        // to control what kind of transition was used, so we pass it as a paramater.
        transitioningDelegate = SlideDismissor(transition: PercentDrivenInteractiveTransitionWithState())
    }
}

// In that object, implement all the delegate methods
class SlideDismissor: NSObject, UIViewControllerTransitioningDelegate {
    let transition: PercentDrivenInteractiveTransitionWithState?

    init(transition: PercentDrivenInteractiveTransitionWithState?) {
        self.transition = transition
    }

    func animationControllerForDismissedController(dismissed: UIViewController) -> UIViewControllerAnimatedTransitioning? {
        return nil // I do return something here, but for this example it isn't necessary
    }

    func interactionControllerForDismissal(animator: UIViewControllerAnimatedTransitioning) -> UIViewControllerInteractiveTransitioning? {
        return transition
    }
}

Answer 2

我有同样的问题试图做类似的事情。显然，协议扩展的当前限制似乎是我们无法提供Objective-C协议的默认实现。因此，在UIKit中声明的任何协议都属于这一类。对于面向协议的编程，还提出了以下建议的article。这个有效期截至2016年9月。我觉得你的痛苦=（但我想现在这种更清洁的扩展方法暂时不可行

协议扩展现有Apple API协议时，不会调用协议扩展方法

2 个答案: