Question

不确定这是否是一种奇怪的方法，但在Swift 3中我想检查一个对象是否是UIViewController并且符合我的协议Transitionable。我有：

guard let toViewController = transitionContext.viewController(forKey: UITransitionContextViewControllerKey.to),
    let fromViewController = transitionContext.viewController(forKey: UITransitionContextViewControllerKey.from),
    let toTransitionable = transitionContext.viewController(forKey: UITransitionContextViewControllerKey.to) as? Transitionable,
    let fromTransitionable = transitionContext.viewController(forKey: UITransitionContextViewControllerKey.from) as? Transitionable
else {
    transitionContext.completeTransition(!transitionContext.transitionWasCancelled)
    return
}

但是我希望我可以获得和UIViewController和Transitionable的对象和对象。我尝试了let toViewController = transitionContext.viewController(forKey: UITransitionContextViewControllerKey.to) as? Transitionable as? UIViewController，但这只是UIViewController

我也尝试过：

extension Transitionable where Self: UIViewController {
    var viewController: UIViewController { return self }
}

但是当我拨打'Transitionable' is not a subtype of 'UIViewController'例如

时，我收到错误：toTransitionable.viewController

transitionContext.containerView.addSubview(toTransitionable.viewController.view)

我知道我们可以在Swift 4中做as? (UIViewController & Transitionable)但是这个项目将在Swift 3中进行

Answer 1

我不确定这可能会有所帮助，但请尝试：

if let toViewController = transitionContext.viewController(forKey: UITransitionContextViewControllerKey.to) as? UIViewController{
    if let _ = toViewController as? Transitionable{
       print("conforms to protocol")
    }
}

if let fromViewController = transitionContext.viewController(forKey: UITransitionContextViewControllerKey.from) as? UIViewController{
    if let _ = fromViewController as? Transitionable{
       print("conforms to protocol")
    }
}

或者，如果您只想在一个

的变量中使用它

您可以创建一个扩展UIViewController并实现Transitionable协议的新类。

类似的东西：

class YourNewViewControllerClass : UIViewController,Transitionable{
    //implements your  Transitionable methods
}

后：

if let viewController = transitionContext.viewController(forKey: UITransitionContextViewControllerKey.from) as? YourNewViewControllerClass{
       //success
}

检查对象是否是特定类并符合协议

1 个答案: