如何实现方法 swizzling swift 3.0? [英] How to implement method swizzling swift 3.0?

问题描述

如何在 Swift 3.0 中实现方法 swizzling?

How can I implement method swizzling in Swift 3.0 ?

我已经阅读了关于它的 nshipster 文章，但是在这段代码中

I've read nshipster article about it, but in this code's chunk

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:使用延迟初始化改为全局变量

dispatch_once_t is unavailable in Swift: Use lazily initialized globals instead

推荐答案

首先 dispatch_once_t 在 Swift 3.0 中不可用.您可以从两个选项中进行选择:

First of all dispatch_once_t is unavailable in Swift 3.0. You can choose from two alternatives:

1. 全局变量

1. Global variable

struct、enum 或 class

有关更多详细信息，请参阅 Swift 3 中的 dispatch_once

For more details, see that Whither dispatch_once in Swift 3

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

混合 CocoaTouch 类

示例 swizzling viewWillAppear(_:) 的 UIViewController 使用全局变量

Swizzling CocoaTouch class

example swizzling viewWillAppear(_:) of UIViewController using global variable

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

要在 Swift 类中使用方法 swizzling，您必须遵守两个要求 (了解更多详情):

• 包含要调配的方法的类必须扩展NSObject
• 你想要 swizzle 的方法必须有 dynamic 属性

以及自定义 Swift 基类的示例 swizzling 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)")
    }
}

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