如何实现swift swift 3.0的方法？

Question

如何在Swift 3.0中实现方法调配？

我已经阅读了关于它的nshipster文章,但是在这个代码的块中

struct Static {
    static var token: dispatch_once_t = 0
}

编译器给我一个错误

dispatch_once_t在Swift中不可用:改为使用延迟初始化的全局变量

Answer 1

首先dispatch_once_t在Swift 3.0中不可用.您可以选择两种选择:

1. 全局变量

2. 静态属性struct,enum或class

有关更多详细信息,请参阅Swift 3中的dispatch_once

出于不同的目的,您必须使用不同的混合实现

• Swizzling CocoaTouch类,例如UIViewController;
• Swizzling自定义Swift类;

Swizzling CocoaTouch类

例如混写viewWillAppear(_:)的UIViewController使用全局变量

private let swizzling: (UIViewController.Type) -> () = { viewController in

    let originalSelector = #selector(viewController.viewWillAppear(_:))
    let swizzledSelector = #selector(viewController.proj_viewWillAppear(animated:))

    let originalMethod = class_getInstanceMethod(viewController, originalSelector)
    let swizzledMethod = class_getInstanceMethod(viewController, swizzledSelector)

    method_exchangeImplementations(originalMethod, swizzledMethod) }

extension UIViewController {

    open override class func initialize() {
        // make sure this isn't a subclass
        guard self === UIViewController.self else { return }
        swizzling(self)
    }

    // MARK: - Method Swizzling

    func proj_viewWillAppear(animated: Bool) {
        self.proj_viewWillAppear(animated: animated)

        let viewControllerName = NSStringFromClass(type(of: self))
        print("viewWillAppear: \(viewControllerName)")
    } 
 }

Swizzling自定义Swift类

要使用Swift类的方法调用,必须遵守两个要求(更多详细信息):

• 包含要调整的方法的类必须扩展 NSObject
• 您想要调配的方法必须具有该dynamic属性

和自定义Swift基类的示例混合方法 Person

class Person: NSObject {
    var name = "Person"
    dynamic func foo(_ bar: Bool) {
        print("Person.foo")
    }
}

class Programmer: Person {
    override func foo(_ bar: Bool) {
        super.foo(bar)
        print("Programmer.foo")
    }
}

private let swizzling: (Person.Type) -> () = { person in

    let originalSelector = #selector(person.foo(_:))
    let swizzledSelector = #selector(person.proj_foo(_:))

    let originalMethod = class_getInstanceMethod(person, originalSelector)
    let swizzledMethod = class_getInstanceMethod(person, swizzledSelector)

    method_exchangeImplementations(originalMethod, swizzledMethod)
}

extension Person {

    open override class func initialize() {
        // make sure this isn't a subclass
        guard self === Person.self else { return }
        swizzling(self)
    }

    // MARK: - Method Swizzling

    func proj_foo(_ bar: Bool) {
        self.proj_foo(bar)

        let className = NSStringFromClass(type(of: self))
        print("class: \(className)")
    }
}

Answer 2

@TikhonovAlexander:很好的答案

我修改了swizzler以获取两个选择器并使其更通用.

斯威夫特3

private let swizzling: (AnyClass, Selector, Selector) -> () = { forClass, originalSelector, swizzledSelector in
    let originalMethod = class_getInstanceMethod(forClass, originalSelector)
    let swizzledMethod = class_getInstanceMethod(forClass, swizzledSelector)
    method_exchangeImplementations(originalMethod, swizzledMethod)
}

// perform swizzling in initialize()

extension UIView {

    open override class func initialize() {
        // make sure this isn't a subclass
        guard self === UIView.self else { return }

        let originalSelector = #selector(layoutSubviews)
        let swizzledSelector = #selector(swizzled_layoutSubviews)
        swizzling(self, originalSelector, swizzledSelector)
    }

    func swizzled_layoutSubviews() {
        swizzled_layoutSubviews()
        print("swizzled_layoutSubviews")
    }

}

斯威夫特4

private let swizzling: (AnyClass, Selector, Selector) -> () = { forClass, originalSelector, swizzledSelector in
    guard
        let originalMethod = class_getInstanceMethod(forClass, originalSelector),
        let swizzledMethod = class_getInstanceMethod(forClass, swizzledSelector)
    else { return }
    method_exchangeImplementations(originalMethod, swizzledMethod)
}

extension UIView {

    static let classInit: Void = {            
        let originalSelector = #selector(layoutSubviews)
        let swizzledSelector = #selector(swizzled_layoutSubviews)
        swizzling(UIView.self, originalSelector, swizzledSelector)
    }()

    @objc func swizzled_layoutSubviews() {
        swizzled_layoutSubviews()
        print("swizzled_layoutSubviews")
    }

}

// perform swizzling in AppDelegate.init()

@UIApplicationMain
class AppDelegate: UIResponder, UIApplicationDelegate {

    override init() {
        super.init()
        UIView.classInit
    }

}

Answer 3

在 Playground Swift 5 中混搭

import Foundation
class TestSwizzling : NSObject {
    @objc dynamic func methodOne()->Int{
        return 1
    }
}

extension TestSwizzling {
    @objc func methodTwo()->Int{
        // It will not be a recursive call anymore after the swizzling
        return 2
    }
    //In Objective-C you'd perform the swizzling in load(),
    //but this method is not permitted in Swift
    func swizzle(){
        let i: () -> () = {
            let originalSelector = #selector(TestSwizzling.methodOne)
            let swizzledSelector = #selector(TestSwizzling.methodTwo)
            let originalMethod = class_getInstanceMethod(TestSwizzling.self, originalSelector);
            let swizzledMethod = class_getInstanceMethod(TestSwizzling.self, swizzledSelector)
            method_exchangeImplementations(originalMethod!, swizzledMethod!)
            print("swizzled!")
        }
        i()
    }
}

var c = TestSwizzling()
print([c.methodOne(), c.methodTwo()])  // [1, 2]
c.swizzle()                            // swizzled!
print([c.methodOne(), c.methodTwo()])  // [2, 1]