Swift class_getInstanceMethod返回nil

我在斯威夫特杂志上读到了关于方法swizzle的文章。试图理解class_getInstanceMethod方法，但它不起作用

class Abc {

func testing() {
    print("testin...")
}

   func check() {
    print("check")
    let originalSelector = Selector.init(("testing"))
    let originalMethod = class_getInstanceMethod(Abc.self , originalSelector)
    print("\(String(describing: originalMethod))")
  }
}  

 let a = Abc()
  a.check()

---

您只需要更改选择器。还必须在测试中添加@objc标记。这起作用了。我做了测试

class Abc {

    @objc func testing() {
        print("testin...")
    }

    func check() {
        print("check")
        let originalMethod = class_getInstanceMethod(Abc.self , #selector(self.testing))
        print("\(originalMethod))")
    }
}