Swift4转Swift5报错：ViewController无keyboardDidShow(notification:)成员

Hey there! Let's fix this Swift 5 migration error step by step. That error pops up because the compiler can't locate your keyboardDidShow(notification:) method when registering the notification observer, and there are a few common culprits in Swift 5:

1. Ensure Your Method Has the Right Access & Decorator #

Swift 5 is stricter about exposing methods to Objective-C (since NotificationCenter relies on Objective-C runtime for selectors). Make sure your keyboardDidShow method is marked with @objc and has an accessible scope (default internal works, avoid private unless necessary):

@objc func keyboardDidShow(notification: NSNotification) {
    // Your keyboard handling logic here
}

Pro tip: If you prefer using Swift's native Notification type instead of NSNotification, that's fine too—just keep the selector and method signature matched:

@objc func keyboardDidShow(notification: Notification) {
    // Same logic applies
}

2. Check for Extension Scope Issues #

If you've defined keyboardDidShow inside an extension of ViewController, you need to explicitly mark the method (or the entire extension) with @objc so the Objective-C runtime can find it:

extension ViewController {
    @objc func keyboardDidShow(notification: NSNotification) {
        // Your code here
    }
}

3. Verify Selector & Method Name Match #

Double-check for typos! Even a tiny mismatch (like keyboardDidShowNotification instead of keyboardDidShow) will trigger this error. Ensure the name inside #selector() exactly matches your method's name and parameter label.

4. Try the Safer Closure-Based Notification Syntax (Swift 5+) #

To avoid selector-related headaches entirely, use Swift 5's preferred closure-based NotificationCenter API. No @objc needed, and it eliminates signature mismatch risks:

override func viewDidLoad() {
    super.viewDidLoad()
    
    NotificationCenter.default.addObserver(forName: UIResponder.keyboardDidShowNotification, object: nil, queue: .main) { [weak self] notification in
        guard let self = self else { return }
        if let keyboardFrame = notification.userInfo?[UIResponder.keyboardFrameEndUserInfoKey] as? CGRect {
            print("Keyboard height: \(keyboardFrame.height)")
            // Adjust your layout here
        }
    }
}

Here's a complete snippet to reference:

class ViewController: UIViewController {
    override func viewDidLoad() {
        super.viewDidLoad()
        // Register the notification observer
        NotificationCenter.default.addObserver(self, selector: #selector(keyboardDidShow(notification:)), name: UIResponder.keyboardDidShowNotification, object: nil)
    }
    
    @objc func keyboardDidShow(notification: NSNotification) {
        if let keyboardFrame = notification.userInfo?[UIResponder.keyboardFrameEndUserInfoKey] as? CGRect {
            // Update your UI to account for the keyboard
            print("Keyboard appeared with height: \(keyboardFrame.height)")
        }
    }
    
    // Clean up observer (optional for iOS 9+, but good practice)
    deinit {
        NotificationCenter.default.removeObserver(self)
    }
}

内容的提问来源于stack exchange，提问作者user11721027