快速向下转换和协议变量 [英] Swift downcasting and protocol variables

问题描述

我有一个包含一个属性的swift协议：

I have a swift protocol that contains one property:

protocol WireframeProtocol: class
{
    var rootViewController: UIViewController  { get }
}

然后我有一个实现此协议的类因此：

I then have a class that implements this protocol as such:

class MenuWireframe : WireframeProtocol
{
    let rootViewController: UIViewController

    init()
    {
        self.rootViewController = MenuViewController(nibName: "MenuViewController", bundle: nil)
        (self.rootViewController as! MenuViewController).presenter = MenuPresenter(interactor: MenuInteractor())
    }
}

在我的Wireframe类中，变量实际上是类型为MenuViewController但必须声明为UIViewController以确认协议。我必须使用（self.rootViewController as！MenuViewController）将它向下转换为我想要的正确类，以便能够访问其属性。在我上面的简单例子中它很好但是不是很易读，特别是在更复杂的情况下。有没有更好的方法来声明协议变量？

In my Wireframe class the variable is actually of type MenuViewController but has to instead be declared as UIViewController to confirm to the protocol. I have to use (self.rootViewController as! MenuViewController) to downcast it to the correct class I want so as to be able to access its properties. It is fine in my simple example above but is not very readable, especially in more complex situations. Is there a better way to declare the protocol variable?

非常感谢！

推荐答案

是的，通过使用通用协议，有更好的方法。要实现这一点，你必须声明你的协议类似于：

Yes there is a better way and thats by using generic protocols. To implement that you must declare your protocol similar like this :

protocol WireframeProtocol{

    typealias RootViewController : UIViewController
    var rootViewController: RootViewController  { get }

}

然后在你的采用类中将rootViewController类型设置为MenuViewController

then in your adoption class set rootViewController type as MenuViewController

class MenuWireframe : WireframeProtocol{

let rootViewController: MenuViewController

    init(){
        self.rootViewController = MenuViewController(nibName: "MenuViewController", bundle: nil)
        self.rootViewController.presenter = MenuPresenter(interactor: MenuInteractor())
    }
}

这篇关于快速向下转换和协议变量的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！