Exposing an instance method to Objective-C within an extension method - xcode

Question

I've got an application that uses UIKeyboardWillShow & Hide notifications in a few different controllers. I've decided to try to consolidate the logic required to move the view with the keyboard into an extension based on a protocol.
Here's my protocol
public protocol KeyboardType : class {
func keyboardWillShow(_ sender: Notification)
func keyboardWillHide(_ sender: Notification)
}
Next, I added an extension to my new protocol so that all I need to do is implement my "KeyboardType protocol and I'll gain access to the necessary functionality to move my view with my keyboard:
Here's my extension
public extension KeyboardType where Self: UIViewController {
func addObservers() {
NotificationCenter.default.addObserver(self, selector: #selector(Self.keyboardWillShow(_:)), name:NSNotification.Name.UIKeyboardWillShow, object: self.view.window)
NotificationCenter.default.addObserver(self, selector: #selector(Self.keyboardWillHide(_:)), name:NSNotification.Name.UIKeyboardWillHide, object: self.view.window)
}
func removeObservers() {
NotificationCenter.default.removeObserver(self, name: NSNotification.Name.UIKeyboardWillShow, object: self.view.window)
NotificationCenter.default.removeObserver(self, name: NSNotification.Name.UIKeyboardWillHide, object: self.view.window)
}
func keyboardWillHide(_ sender: Notification) {
let userInfo: [AnyHashable : Any] = (sender as NSNotification).userInfo!
let keyboardSize: CGSize = (userInfo[UIKeyboardFrameBeginUserInfoKey]! as AnyObject).cgRectValue.size
self.view.frame.origin.y += keyboardSize.height
}
func keyboardWillShow(_ sender: Notification) {
let userInfo: [AnyHashable : Any] = sender.userInfo!
let keyboardSize: CGSize = (userInfo[UIKeyboardFrameBeginUserInfoKey]! as AnyObject).cgRectValue.size
let offset: CGSize = (userInfo[UIKeyboardFrameEndUserInfoKey]! as AnyObject).cgRectValue.size
if keyboardSize.height == offset.height {
if self.view.frame.origin.y == 0 {
UIView.animate(withDuration: 0.1, animations: { () -> Void in
self.view.frame.origin.y -= keyboardSize.height
})
}
} else {
UIView.animate(withDuration: 0.1, animations: { () -> Void in
self.view.frame.origin.y += keyboardSize.height - offset.height
})
}
}
}
The problem
The problem is the compiler is asking me to add #objc to my keyboardWillShow and keyboardWillHide methods. When I allow Xcode to add the keywords, the compiler immediately asks me to remove the #objc keywords.
Argument of '#selector' refers to instance method 'keyboardWillShow'
that is not exposed to Objective-C
My Question
How do I expose keyboardWillShow to Objective-C in this situation?
or
Is there a better way to accomplish the same task?

Answer 1

I would take a different approach there extending UIViewController as follow:
protocol KeyboardController {
func keyboardWillShow(_ sender: Notification)
func keyboardWillHide(_ sender: Notification)
}
extension UIViewController: KeyboardController {
func addObservers() {
NotificationCenter.default.addObserver(self,
selector: #selector(keyboardWillShow(_:)),
name:.UIKeyboardWillShow,
object: view.window)
NotificationCenter.default.addObserver(self,
selector: #selector(keyboardWillHide(_:)),
name:.UIKeyboardWillHide,
object: view.window)
}
func removeObservers() {
NotificationCenter.default.removeObserver(self, name: .UIKeyboardWillShow, object: view.window)
NotificationCenter.default.removeObserver(self, name: .UIKeyboardWillHide, object: view.window)
}
func keyboardWillHide(_ notification: Notification) {
print("---> keyboardWillHide")
guard let userInfo = notification.userInfo else { return }
let keyboardSize = (userInfo[UIKeyboardFrameBeginUserInfoKey] as? NSValue)?.cgRectValue.size
print("keyboardSize", keyboardSize)
}
func keyboardWillShow(_ notification: Notification) {
print("---> keyboardWillShow")
guard
let userInfo = notification.userInfo,
let keyboardSize = (userInfo[UIKeyboardFrameBeginUserInfoKey] as? NSValue)?.cgRectValue.size,
let offset = (userInfo[UIKeyboardFrameEndUserInfoKey] as? NSValue)?.cgRectValue.size
else { return }
if keyboardSize.height == offset.height {
if self.view.frame.origin.y == 0 {
UIView.animate(withDuration: 0.1, animations: { () -> Void in
self.view.frame.origin.y -= keyboardSize.height
})
}
} else {
UIView.animate(withDuration: 0.1, animations: { () -> Void in
self.view.frame.origin.y += keyboardSize.height - offset.height
})
}
}
}
class ViewController: UIViewController {
override func viewDidLoad() {
super.viewDidLoad()
addObservers()
// Do any additional setup after loading the view, typically from a nib.
}
override func didReceiveMemoryWarning() {
super.didReceiveMemoryWarning()
// Dispose of any resources that can be recreated.
}
}
Another option and the one I like most is to subclass UIViewController:
class KeyboardViewController: UIViewController {
override func viewWillAppear(_ animated: Bool) {
super.viewWillAppear(animated)
addObservers()
}
override func viewWillDisappear(_ animated: Bool) {
super.viewWillDisappear(animated)
removeObservers()
}
func addObservers() {
NotificationCenter.default.addObserver(self, selector: #selector(keyboardWillShow(_:)), name: .UIKeyboardWillShow, object: view.window)
NotificationCenter.default.addObserver(self, selector: #selector(keyboardWillHide(_:)), name: .UIKeyboardWillHide, object: view.window)
}
func removeObservers() {
NotificationCenter.default.removeObserver(self, name: .UIKeyboardWillShow, object: view.window)
NotificationCenter.default.removeObserver(self, name: .UIKeyboardWillHide, object: view.window)
}
func keyboardWillHide(_ notification: Notification) {
print("---> keyboardWillHide")
if let keyboardHeight = (notification.userInfo?[UIKeyboardFrameBeginUserInfoKey] as? NSValue)?.cgRectValue.size.height {
print("keyboardHeight", keyboardHeight)
view.frame.origin.y += keyboardHeight
}
}
func keyboardWillShow(_ notification: Notification) {
print("---> keyboardWillShow")
if let userInfo = notification.userInfo,
let keyboardHeight = (userInfo[UIKeyboardFrameBeginUserInfoKey] as? NSValue)?.cgRectValue.size.height,
let offsetHeight = (userInfo[UIKeyboardFrameEndUserInfoKey] as? NSValue)?.cgRectValue.size.height {
print("userInfo", userInfo)
print("keyboardHeight", keyboardHeight)
print("offsetHeight", offsetHeight)
if keyboardHeight == offsetHeight {
if self.view.frame.origin.y == 0 {
UIView.animate(withDuration: 0.1, animations: { () -> Void in
self.view.frame.origin.y -= keyboardHeight
})
}
} else {
UIView.animate(withDuration: 0.1, animations: { () -> Void in
self.view.frame.origin.y += keyboardHeight - offsetHeight
})
}
}
}
}
class ViewController: KeyboardViewController {
override func viewDidLoad() {
super.viewDidLoad()
// Do any additional setup after loading the view, typically from a nib.
}
override func didReceiveMemoryWarning() {
super.didReceiveMemoryWarning()
// Dispose of any resources that can be recreated.
}
}

Answer 2

Have you tried this?:
#objc public protocol KeyboardType {
func keyboardWillShow(_ sender: Notification)
func keyboardWillHide(_ sender: Notification)
}
You also need to import UIKit