Detect keyboard height while UIScrollView is scrolled down and the keypad is being interactively dragged

Question

I have a UIScrollView and a UITextView, just like in any messaging / chat app, whenUIScrollView is scrolled down, the keypad interactively being dragged too.

I need to detect keyboard height while UIScrollView is scrolled, I tried UIKeyboardWillChangeFrame observer, but this event is called after scroll tap is released.

Without knowing keyboard height, I am unable to update the UITextView bottom constraint, and I get a gap between the keypad and bottom view @screenshot.

Also attaching screenshot from Viber, that does align the bottom bar when keyboard being dragged from scroll bar, also can be seen in WhatsApp too.

Answer 1

As of iOS 10, Apple doesn't provide a NSNotification observer to detect the frame change while the keypad is dragged interactively by UIScrollView, UIKeyboardWillChangeFrame and UIKeyboardDidChangeFrame are observed only once releasing tap.

Anyways, after looking around DAKeyboardControl library, I had the idea to attach UIScrollView.UIPanGestureRecognizer in the UIViewController, so any gesture events that are produced will be handled in UIViewController as well. After screwing around several hours, I got it to work, here is all the code that is necessary for this:

class ViewController: UIViewController, UIGestureRecognizerDelegate {

    fileprivate let collectionView = UICollectionView(frame: .zero)
    private let bottomView = UIView()
    fileprivate var bottomInset: NSLayoutConstraint!

    // This holds height of keypad
    private var maxKeypadHeight: CGFloat = 0 {
        didSet {
            self.updateCollectionViewInsets(maxKeypadHeight + self.bottomView.frame.height)
            self.bottomInset.constant = -maxKeypadHeight
        }
    }

    private var isListeningKeypadChange = false

    override func viewWillAppear(_ animated: Bool) {
        super.viewWillAppear(animated)

        NotificationCenter.default.addObserver(self, selector: #selector(keypadWillChange(_:)), name: .UIKeyboardWillChangeFrame, object: nil)
        NotificationCenter.default.addObserver(self, selector: #selector(keypadWillShow(_:)), name: .UIKeyboardWillShow, object: nil)
        NotificationCenter.default.addObserver(self, selector: #selector(keypadWillHide(_:)), name: .UIKeyboardWillHide, object: nil)
        NotificationCenter.default.addObserver(self, selector: #selector(keypadDidHide), name: .UIKeyboardDidHide, object: nil)
    }

    override func viewWillDisappear(_ animated: Bool) {
        super.viewWillDisappear(animated)

        NotificationCenter.default.removeObserver(self)
    }

    func keypadWillShow(_ notification: Notification) {
        guard !self.isListeningKeypadChange, let userInfo = notification.userInfo as? [String : Any],
            let animationDuration = userInfo[UIKeyboardAnimationDurationUserInfoKey] as? TimeInterval,
            let animationCurve = userInfo[UIKeyboardAnimationCurveUserInfoKey] as? UInt,
            let value = userInfo[UIKeyboardFrameEndUserInfoKey] as? NSValue
            else {
                return
        }

        self.maxKeypadHeight = value.cgRectValue.height

        let options = UIViewAnimationOptions.beginFromCurrentState.union(UIViewAnimationOptions(rawValue: animationCurve))
        UIView.animate(withDuration: animationDuration, delay: 0, options: options, animations: { [weak self] in
            self?.view.layoutIfNeeded()
            }, completion: { finished in
                guard finished else { return }

                // Some delay of about 500MS, before ready to listen other keypad events
                DispatchQueue.main.asyncAfter(deadline: .now() + 0.5) { [weak self] in
                    self?.beginListeningKeypadChange()
                }
        })
    }

    func handlePanGestureRecognizer(_ pan: UIPanGestureRecognizer) {
        guard self.isListeningKeypadChange, let windowHeight = self.view.window?.frame.height else { return }

        let barHeight = self.bottomView.frame.height
        let keypadHeight = abs(self.bottomInset.constant)
        let usedHeight = keypadHeight + barHeight

        let dragY = windowHeight - pan.location(in: self.view.window).y
        let newValue = min(dragY < usedHeight ? max(dragY, 0) : dragY, self.maxKeypadHeight)

        print("Old: \(keypadHeight)        New: \(newValue)        Drag: \(dragY)        Used: \(usedHeight)")
        guard keypadHeight != newValue else { return }
        self.updateCollectionViewInsets(newValue + barHeight)
        self.bottomInset.constant = -newValue
    }

    func keypadWillChange(_ notification: Notification) {
        if self.isListeningKeypadChange, let value = notification.userInfo?[UIKeyboardFrameEndUserInfoKey] as? NSValue {
            self.maxKeypadHeight = value.cgRectValue.height
        }
    }

    func keypadWillHide(_ notification: Notification) {
        guard let userInfo = notification.userInfo as? [String : Any] else { return }

        self.maxKeypadHeight = 0

        var options = UIViewAnimationOptions.beginFromCurrentState
        if let animationCurve = userInfo[UIKeyboardAnimationCurveUserInfoKey] as? UInt {
            options = options.union(UIViewAnimationOptions(rawValue: animationCurve))
        }

        let duration = userInfo[UIKeyboardAnimationDurationUserInfoKey] as? TimeInterval
        UIView.animate(withDuration: duration ?? 0, delay: 0, options: options, animations: {
            self.view.layoutIfNeeded()
        }, completion: nil)
    }

    func keypadDidHide() {
        self.collectionView.panGestureRecognizer.removeTarget(self, action: nil)
        self.isListeningKeypadChange = false
        if (self.maxKeypadHeight != 0 || self.bottomInset.constant != 0) {
            self.maxKeypadHeight = 0
        }
    }

    private func beginListeningKeypadChange() {
        self.isListeningKeypadChange = true
        self.collectionView.panGestureRecognizer.addTarget(self, action: #selector(self.handlePanGestureRecognizer(_:)))
    }

    fileprivate func updateCollectionViewInsets(_ value: CGFloat) {
        let insets = UIEdgeInsets(top: 0, left: 0, bottom: value + 8, right: 0)
        self.collectionView.contentInset = insets
        self.collectionView.scrollIndicatorInsets = insets
    }        
}