iOS / Swift: Keyboard Show/Hide Animations for Views in a UIViewController

UIHelpers.swift

/**
Gathers all the data defined in `Keyboard Notification User Info Keys` from
a keyboard will/did show/hide `NSNotification` into an easier to use tuple.

- parameter notification: A notification resulting from a keyboard appearance notification,
        e.g. `UIKeyboardWillShowNotification`

- returns: A tuple of data about the keyboard appearance extracted from the notification user info.
*/
public func keyboardInfoFromNotification(_ notification: Notification) -> (beginFrame: CGRect, endFrame: CGRect, animationCurve: UIViewAnimationOptions, animationDuration: Double) {
    let userInfo = (notification as NSNotification).userInfo!
    let beginFrameValue = userInfo[UIKeyboardFrameBeginUserInfoKey] as! NSValue
    let endFrameValue = userInfo[UIKeyboardFrameEndUserInfoKey] as! NSValue
    let animationCurve = userInfo[UIKeyboardAnimationCurveUserInfoKey] as! NSNumber
    let animationDuration = userInfo[UIKeyboardAnimationDurationUserInfoKey] as! NSNumber

    return (
        beginFrame:         beginFrameValue.cgRectValue,
        endFrame:           endFrameValue.cgRectValue,
        animationCurve:     UIViewAnimationOptions(rawValue: UInt(animationCurve.uintValue << 16)),
        animationDuration:  animationDuration.doubleValue)
}

UIViewController.swift

class ViewController: UIViewController {
    
    // MARK: - Keyboard Outlets and Properties
    
    // This should be an invisible UIView with a bottom layout constraint aligned with bottom layout Guide,
    // and a top layout constraint aligned with where the keyboard should not go above.
    // NOTE: disable UserInteraction, to allow taps through this view
    @IBOutlet weak var keyboardPlacementView: UIView!
    @IBOutlet weak var keyboardOffsetConstraint: NSLayoutConstraint!  // Y offset or Height, that moves all attached views up/down
    var keyboardInitialOffsetConstraintConstant: CGFloat = 0.0  // Set in ViewDidLoad
    let constraintDirection: CGFloat = -1 // -1 (offset up when keyboard appears) OR 1 (offsets down when keyboard appears)
    
    // MARK: - UIViewController Methods
    
    deinit {
        NotificationCenter.default.removeObserver(self)
    }

    override func viewDidLoad() {
        super.viewDidLoad()
        
        NotificationCenter.default.addObserver(self,
                                               selector: #selector(ViewController.keyboardWillShow(_:)),
                                               name: NSNotification.Name.UIKeyboardWillShow,
                                               object: nil)
        NotificationCenter.default.addObserver(self,
                                               selector: #selector(ViewController.keyboardWillHide(_:)),
                                               name: NSNotification.Name.UIKeyboardWillHide,
                                               object: nil)
        
        keyboardInitialOffsetConstraintConstant = keyboardOffsetConstraint.constant
    }
    
    // MARK: Keyboard
    
    func keyboardWillShow(_ note: Notification) {
        let keyboardData = keyboardInfoFromNotification(note)
        let offsetHeight = keyboardData.endFrame.size.height
        
        let offsetDifferenceToPlacementView = offsetHeight - keyboardPlacementView.frame.height
        if offsetDifferenceToPlacementView > 0 {
            self.view.layoutIfNeeded()
            let initialConstraintConstant = keyboardInitialOffsetConstraintConstant
            weak var constraint = keyboardOffsetConstraint
            let direction = constraintDirection
            weak var weakSelf = self
            UIView.animate(withDuration: keyboardData.animationDuration,
                           delay: 0,
                           options: keyboardData.animationCurve,
                           animations: {
                            constraint?.constant = (direction * offsetDifferenceToPlacementView) + initialConstraintConstant
                            weakSelf?.view.layoutIfNeeded()
            },
                           completion: nil)
        }
    }
    
    func keyboardWillHide(_ note: Notification) {
        let keyboardData = keyboardInfoFromNotification(note)
        
        self.view.layoutIfNeeded()
        let initialConstraintConstant = keyboardInitialOffsetConstraintConstant
        weak var constraint = keyboardOffsetConstraint
        weak var weakSelf = self
        UIView.animate(withDuration: keyboardData.animationDuration,
                       delay: 0,
                       options: keyboardData.animationCurve,
                       animations: {
                        constraint?.constant = initialConstraintConstant
                        weakSelf?.view.layoutIfNeeded()
        }, completion: nil)
    }
}