No Method declared with Objective-C Selector for N

问题:

After the recent update of Xcode, this code that used to work no longer works. Most of the Selector(":") has an auto correction with the exception for this code:

override func viewDidLoad() {
    super.viewDidLoad()

    NSNotificationCenter.defaultCenter().addObserver(self, selector: Selector("keyboardWillShow:"), name:UIKeyboardWillShowNotification, object: nil);
    NSNotificationCenter.defaultCenter().addObserver(self, selector: Selector("keyboardWillHide:"), name:UIKeyboardWillHideNotification, object: nil);
}

which flags an error:

No method declared with Objective C selector 'keyboardWillSHow:'

This image show different attempts which have all failed.

What is the new syntax for this code?

回答1:

Assign the Selector as below:

NSNotificationCenter.defaultCenter().addObserver(self, selector: #selector(YourClassName.keyboardWillShow(_:)), name:UIKeyboardWillShowNotification, object: nil);

And the method to update what you want:

func keyboardWillShow(notification: NSNotification) {

     //Update UI or Do Something

}

Same way you can do for UIKeyboardWillHideNotification.

回答2:

Swift 3 example:

NotificationCenter.default.addObserver(self, selector: #selector(YourClass.keyboardWillShow(notification:)), name:NSNotification.Name.UIKeyboardWillShow, object: nil);
NotificationCenter.default.addObserver(self, selector: #selector(YourClass.keyboardWillHide(notification:)), name:NSNotification.Name.UIKeyboardWillHide, object: nil);

// MARK: - Actions

@objc private func keyboardWillShow(notification: Notification) {
    print("keyboardWillShow called")
}

@objc private func keyboardWillHide(notification: Notification) {
    print("keyboardWillHide called")
}

回答3:

The swift syntax changed. Try this:

NSNotificationCenter.defaultCenter().addObserver(self, selector: #Selector(ClassThatHasTheSelector.keyboardWillShow), name:UIKeyboardWillShowNotification, object: nil);

回答4:

I have had same issues and also find out that the class you refer on must also be subclassed from NSObject (which is not necc. the case in Swift) Otherwise you get the message

error: argument of '#selector' refers to instance method 'yourMethod(notification:)' that is not exposed to Objective-C"

回答5:

Swift 3 syntax (just like Sohil's above):

    func someMethod(sender: Any?) {
      ...
    }

    func someBlockCallingWithSelector() {
      someObject.addTarget(self, action: #selector(someMethod), for: .valueChanged) 
    }