Swift 中 UITextView 和 UITextField 的单一扩展

我想创建一个扩大对彼此而言UITextField and UITextView并向其中添加以下方法：

    func addDoneButtonOnKeyboardWith(selector : Selector)
    {
        let keyBoardToolBar = UIToolbar(frame: CGRect(x: 0, y: 0, width: 320, height: 30))
        let barButtonItem = UIBarButtonItem(barButtonSystemItem: .done, target: nil, action: selector)
        let flexibleSpace = UIBarButtonItem(barButtonSystemItem: .flexibleSpace, target: nil, action: nil)
        keyBoardToolBar.items = [flexibleSpace, barButtonItem]
        keyBoardToolBar.barStyle = .default
        self.inputAccessoryView = keyBoardToolBar
        self.reloadInputViews()
    }

我希望扩展方法仅适用于UITextField and UITextView.

我有一个想法，可以利用协议的默认实现来做你想做的事情。从技术上来说您仍然需要两个扩展，但它们都完全是空的。考虑以下：

为您的方法创建一个协议，并提供默认实现：

protocol DoneButtonBearer {
    func addDoneButtonOnKeyboardWith(selector: Selector)
}

extension DoneButtonBearer {
    func addDoneButtonOnKeyboardWith(selector: Selector) {
        var view: UIView?
        defer  {
            if view != nil {
                let keyBoardToolBar = UIToolbar(frame: CGRect(x: 0, y: 0, width: 320, height: 30))
                let barButtonItem = UIBarButtonItem(barButtonSystemItem: .done, target: nil, action: selector)
                let flexibleSpace = UIBarButtonItem(barButtonSystemItem: .flexibleSpace, target: nil, action: nil)
                keyBoardToolBar.items = [flexibleSpace, barButtonItem]
                keyBoardToolBar.barStyle = .default
                view!.inputAccessoryView = keyBoardToolBar
                view!.reloadInputViews()
            }
        }
        if let textField = self as? UITextField {
            view = textField
            return
        }
        if let textView = self as? UITextView {
            view = textView
            return
        }
    }
}

然后只需扩展UITextField and UITextView具有此功能：

extension UITextField: DoneButtonBearer { }

extension UITextView: DoneButtonBearer { }