使用Selector时遇类型转换错误，求Swift4（Xcode9.0）解决方案

Hey there, I’ve run into this exact issue back when Swift 4 launched—let’s break down what’s going on and how to fix it quickly.

Why this error happens #

The error is telling you that you’re trying to pass a closure (() -> ()) where a Selector is required. In Swift 4, Selector is tied to Objective-C-exposed methods, and you can’t directly use a closure in place of one. A common mistake here is trying to pass inline closure code instead of referencing a proper method.

Step-by-step fixes #

• Mark your target method with @objc
  Swift 4 stopped automatically exposing Swift methods to Objective-C by default. So if you’re using a custom method, you need to add the @objc modifier to make it accessible for Selector:

  @objc func handleButtonTap() {
      // Your button action logic here
  }
  

  If your class inherits from NSObject (like UIViewController or UIView), this is all you need for the method to be visible to Objective-C. If it’s a pure Swift class, you’ll also need to make it inherit from NSObject or use @objcMembers on the class to expose all methods.

• Use #selector() to reference your method
  Replace that closure with the #selector() syntax that points to your method. For example, when adding a target to a button:

  myButton.addTarget(self, action: #selector(handleButtonTap), for: .touchUpInside)
  

  If your method takes parameters (like a sender), make sure to include the parameter label in the selector:

  @objc func handleButtonTap(_ sender: UIButton) {
      // Logic with sender
  }
  
  // Then reference it as:
  #selector(handleButtonTap(_:))
  

• Avoid passing closures directly
  The wrong code that triggers this error usually looks like this:

  // ❌ This will throw the error you're seeing
  myButton.addTarget(self, action: { self.handleButtonTap() }, for: .touchUpInside)
  

  Ditch the closure and use the #selector approach instead.

内容的提问来源于stack exchange，提问作者Kion