Swift中的类和协议继承

Question

假设我在Swift中有一个协议

protocol SearchCompletionProtocol {
    func searchSuccessful(results: [AnyObject])
    func searchCancelled()
}

现在，我们有一个类，并且要在init方法中传递单个参数。 限制是我希望此参数为UIViewController类型，并且还符合SearchCompletionProtocol协议。 我将如何去做？ 这是我尝试过的一些事例，但它们都不起作用。

class SearchDelegate: UISearchDisplayController, UISearchBarDelegate {

    let completionDelegate: SearchCompletionProtocol

    init<T: SearchCompletionProtocol where T: UIViewController>(completionDelegate: T) {
        self.completionDelegate = completionDelegate
        let _searchBar = UISearchBar()
        super.init(searchBar: _searchBar, contentsController: completionDelegate)
    }
}

我还尝试将协议的继承限制为仅UIViewController类型的类，但这也不起作用。

protocol SearchCompletionProtocol: class, UIViewController {
    func searchSuccessful(results: [AnyObject])
    func searchCancelled()
}

当然，我可以轻松地将两个参数传递给此方法，一个参数符合搜索协议，另一个参数类型为UIViewController，但这似乎不算是Swifty。

Answer 1

因此，解决方案似乎是我剥离了原始代码，认为它并不重要。 这是我的原始代码

protocol SearchCompletionProtocol {
    func searchSuccessful(results: [RTruck])
    func searchCancelled()
}

class SearchDelegate: UISearchDisplayController, UISearchBarDelegate {
    let completionDelegate: SearchCompletionProtocol

    init<T: SearchCompletionProtocol where T: UIViewController>(completionDelegate: T) {
        self.completionDelegate = completionDelegate
        let _searchBar = UISearchBar()
        super.init(searchBar: _searchBar, contentsController: completionDelegate)
        self.completionDelegate.navigationItem.rightBarButtonItem = UIBarButtonItem(barButtonSystemItem: .Search, target: self, action: "showSearchBar")
    }
}

这里的问题是我使用了self.completionDelegate.navigationItem 。 类级别的completionDelegate的类型只是SearchCompletionProtocol，它不是T类型。删除self会导致它使用传入的参数，该参数在编译器看来可以保证是UIViewController，并且一切正常。 这是工作代码

protocol SearchCompletionProtocol {
    func searchSuccessful(results: [RTruck])
    func searchCancelled()
}

class SearchDelegate: UISearchDisplayController, UISearchBarDelegate {
    let completionDelegate: SearchCompletionProtocol

    init<T: SearchCompletionProtocol where T: UIViewController>(completionDelegate: T) {
        self.completionDelegate = completionDelegate
        let _searchBar = UISearchBar()
        super.init(searchBar: _searchBar, contentsController: completionDelegate)
        completionDelegate.navigationItem.rightBarButtonItem = UIBarButtonItem(barButtonSystemItem: .Search, target: self, action: "showSearchBar")
    }
}

Answer 2

在Swift 4中，您可以使用新的＆符号实现此目的：

func foo(vc: UIViewController & SearchCompletionProtocol) {
    vc.searchCancelled()
}