ObjC协议的协议扩展

Question

我有一个objects协议，主要由objects对象和一两个Swift对象使用。

我想在Swift中扩展该协议，并添加2个函数。一个注册通知，另一个处理通知。

如果我加上这些

func registerForPresetLoadedNotification() {
    NSNotificationCenter.defaultCenter().addObserver(self as AnyObject,
                                                     selector: #selector(presetLoaded(_:)),
                                                     name: kPresetLoadedNotificationName,
                                                     object: nil)
}

func presetLoaded(notification: NSNotification) {
    
}

我在#选择器上有一个错误，上面写着：

“选择器”的参数是指不暴露于目标C的方法。

如果我将presetLoaded标记为@objc，则会得到一个错误，即：

@objc只能用于类、@objc协议和类的具体扩展的成员。

我也不能将协议扩展标记为@objc。

当我以Swift协议的形式创建Objective协议时，我也会遇到同样的错误。

是否有一种方法可以实现这个目标-C和Swift类使用该协议？

Answer 1

实际上，不能将协议扩展的函数标记为@objc (或者dynamic，顺便说一下，这是等价的)。对象-C运行时只允许分派类的方法。

在您的特殊情况下，如果您真的想通过协议扩展来实现它，我可以提出以下解决方案(假设您的原始协议名为ObjcProtocol). )

让我们为我们的通知处理程序做一个包装：

final class InternalNotificationHandler {
    private let source: ObjcProtocol

    init(source: ObjcProtocol) {
        // We require source object in case we need access some properties etc.
        self.source = source
    }

    @objc func presetLoaded(notification: NSNotification) {
        // Your notification logic here
    }
}

现在我们需要扩展ObjcProtocol来引入所需的逻辑。

import Foundation
import ObjectiveC

internal var NotificationAssociatedObjectHandle: UInt8 = 0

extension ObjcProtocol {
    // This stored variable represent a "singleton" concept
    // But since protocol extension can only have stored properties we save it via Objective-C runtime
    private var notificationHandler: InternalNotificationHandler {
        // Try to an get associated instance of our handler
        guard let associatedObj = objc_getAssociatedObject(self, &NotificationAssociatedObjectHandle)
            as? InternalNotificationHandler else {
            // If we do not have any associated create and store it
            let newAssociatedObj = InternalNotificationHandler(source: self)
            objc_setAssociatedObject(self,
                                     &NotificationAssociatedObjectHandle,
                                     newAssociatedObj,
                                     objc_AssociationPolicy.OBJC_ASSOCIATION_RETAIN_NONATOMIC)
            return newAssociatedObj
        }

        return associatedObj
    }

    func registerForPresetLoadedNotification() {
        NSNotificationCenter.defaultCenter().addObserver(self,
                                                         selector: #selector(notificationHandler.presetLoaded(_:)),
                                                         name: kPresetLoadedNotificationName,
                                                         object: self)
    }

    func unregisterForPresetLoadedNotification() {
        // Clear notification observer and associated objects
        NSNotificationCenter.defaultCenter().removeObserver(self,
                                                            name: kPresetLoadedNotificationName,
                                                            object: self)
        objc_removeAssociatedObjects(self)
    }
}

我知道这看起来可能不那么优雅，所以我真的会考虑改变一个核心方法。

一个注意事项:您可能需要限制协议扩展的

extension ObjcProtocol where Self: SomeProtocolOrClass

Answer 2

我找到了一种方法:)只要避免@objc在一起:D

//Adjusts UITableView content height when keyboard show/hide
public protocol KeyboardObservable: NSObjectProtocol {
    func registerForKeyboardEvents()
    func unregisterForKeyboardEvents()
}

extension KeyboardObservable where Self: UITableView {

    public func registerForKeyboardEvents() {
        let defaultCenter = NotificationCenter.default

        var tokenShow: NSObjectProtocol!
        tokenShow = defaultCenter.addObserver(forName: .UIKeyboardDidShow, object: nil, queue: nil) { [weak self] (notification) in
            guard self != nil else {
                defaultCenter.removeObserver(tokenShow)
                return
            }
            self!.keyboardWilShow(notification as NSNotification)
        }

        var tokenHide: NSObjectProtocol!
        tokenHide = defaultCenter.addObserver(forName: .UIKeyboardWillHide, object: nil, queue: nil) { [weak self] (notification) in
            guard self != nil else {
                defaultCenter.removeObserver(tokenHide)
                return
            }
            self!.keyboardWilHide(notification as NSNotification)
        }
    }

    private func keyboardDidShow(_ notification: Notification) {
        let rect = ((notification as NSNotification).userInfo![UIKeyboardFrameBeginUserInfoKey] as! NSValue).cgRectValue
        let height = rect.height
        var insets = UIEdgeInsetsMake(0, 0, height, 0)
        insets.top = contentInset.top
        contentInset = insets
        scrollIndicatorInsets = insets
    }

    private func keyboardWillHide(_ notification: Notification) {
        var insets = UIEdgeInsetsMake(0, 0, 0, 0)
        insets.top = contentInset.top
        UIView.animate(withDuration: 0.3) { 
            self.contentInset = insets
            self.scrollIndicatorInsets = insets
        }
    }

    public func unregisterForKeyboardEvents() {
        NotificationCenter.default.removeObserver(self)
    }

}

示例

class CreateStudentTableView: UITableView, KeyboardObservable {

  init(frame: CGRect, style: UITableViewStyle) {
    super.init(frame: frame, style: style)
    registerForKeyboardEvents()
  }

  required init?(coder aDecoder: NSCoder) {
    fatalError("init(coder:) has not been implemented")
  }
}