Swift4.0中Runtime method_exchangeImplementations的使用和initialize()方法的替代

在swift4.0中
load（）方法已经失效
initialize（）也失效
一时间我一度不知道怎么用运行时的method_exchangeImplementations方法，后来在网上查看总结出来下面将代码贴出来

extension UIViewController {
public class func initializeMethod(){
    let originalSelector = #selector(UIViewController.viewDidAppear(_:))
    let swizzledSelector = #selector(UIViewController.myMethod(animated:))

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


    //在进行 Swizzling 的时候,需要用 class_addMethod 先进行判断一下原有类中是否有要替换方法的实现
    let didAddMethod: Bool = class_addMethod(self, originalSelector, method_getImplementation(swizzledMethod!), method_getTypeEncoding(swizzledMethod!))
    //如果 class_addMethod 返回 yes,说明当前类中没有要替换方法的实现,所以需要在父类中查找,这时候就用到 method_getImplemetation 去获取 class_getInstanceMethod 里面的方法实现,然后再进行 class_replaceMethod 来实现 Swizzing

    if didAddMethod {
        class_replaceMethod(self, swizzledSelector, method_getImplementation(originalMethod!), method_getTypeEncoding(originalMethod!))
    } else {
        method_exchangeImplementations(originalMethod!, swizzledMethod!)
    }

    }

    @objc func myMethod(animated: Bool) {
        self.myMethod(animated: animated)
        print("替换了")

    }
}

在AppDelegate的
func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions:方法中添加如下代码

    func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool {
      UIViewController.initializeMethod()
        return true
    }

下面看一下调用和打印结果