Keyboard handling

.swift

//MARK: - Observers
extension UIViewController {
  
  func addObserverForNotification(_ notificationName: Notification.Name, actionBlock: @escaping (Notification) -> Void) {
    NotificationCenter.default.addObserver(forName: notificationName, object: nil, queue: OperationQueue.main, using: actionBlock)
  }
  
  func removeObserver(_ observer: AnyObject, notificationName: Notification.Name) {
    NotificationCenter.default.removeObserver(observer, name: notificationName, object: nil)
  }
}

//MARK: - Keyboard handling
extension UIViewController {
  
  typealias KeyboardHeightClosure = (CGFloat) -> ()
  
  func addKeyboardChangeFrameObserver(willShow willShowClosure: KeyboardHeightClosure?,
                                      willHide willHideClosure: KeyboardHeightClosure?) {
    NotificationCenter.default.addObserver(forName: NSNotification.Name.UIKeyboardWillChangeFrame,
                                           object: nil, queue: OperationQueue.main, using: { [weak self](notification) in
                                            if let userInfo = notification.userInfo,
                                              let frame = (userInfo[UIKeyboardFrameEndUserInfoKey] as? NSValue)?.cgRectValue,
                                              let duration = userInfo[UIKeyboardAnimationDurationUserInfoKey] as? Double,
                                              let c = userInfo[UIKeyboardAnimationCurveUserInfoKey] as? UInt,
                                              let kFrame = self?.view.convert(frame, from: nil),
                                              let kBounds = self?.view.bounds {
                                              
                                              let animationType = UIViewAnimationOptions(rawValue: c)
                                              let kHeight = kFrame.size.height
                                              UIView.animate(withDuration: duration, delay: 0, options: animationType, animations: {
                                                if kBounds.intersects(kFrame) { // keyboard will be shown
                                                  willShowClosure?(kHeight)
                                                } else { // keyboard will be hidden
                                                  willHideClosure?(kHeight)
                                                }
                                              }, completion: nil)
                                            } else {
                                              print("Invalid conditions for UIKeyboardWillChangeFrameNotification")
                                            }
    })
  }
  
  func removeKeyboardObserver() {
    removeObserver(self, notificationName: NSNotification.Name.UIKeyboardWillChangeFrame)
  }
}