Keyboard Height Change Observer Swift

Keyboard height change observer

If you search on UIKeyboardWillShowNotification in the Xcode docs you get to the section on UIWindow, which has a table of notifications at the end.

I suggest trying the UIKeyboardWillChangeFrameNotification.

Time to find the answer: About 30 seconds.

How to get height of Keyboard?

Swift

You can get the keyboard height by subscribing to the UIKeyboardWillShowNotification notification. (Assuming you want to know what the height will be before it's shown).

Swift 4

NotificationCenter.default.addObserver(
    self,
    selector: #selector(keyboardWillShow),
    name: UIResponder.keyboardWillShowNotification,
    object: nil
)

@objc func keyboardWillShow(_ notification: Notification) {
    if let keyboardFrame: NSValue = notification.userInfo?[UIResponder.keyboardFrameEndUserInfoKey] as? NSValue {
        let keyboardRectangle = keyboardFrame.cgRectValue
        let keyboardHeight = keyboardRectangle.height
    }
}

Swift 3

NotificationCenter.default.addObserver(
    self,
    selector: #selector(keyboardWillShow),
    name: NSNotification.Name.UIKeyboardWillShow,
    object: nil
)

@objc func keyboardWillShow(_ notification: Notification) {
    if let keyboardFrame: NSValue = notification.userInfo?[UIKeyboardFrameEndUserInfoKey] as? NSValue {
        let keyboardRectangle = keyboardFrame.cgRectValue
        let keyboardHeight = keyboardRectangle.height
    }
}

Swift 2

NSNotificationCenter.defaultCenter().addObserver(self, selector: "keyboardWillShow:", name: UIKeyboardWillShowNotification, object: nil)

func keyboardWillShow(notification: NSNotification) {
        let userInfo: NSDictionary = notification.userInfo!
        let keyboardFrame: NSValue = userInfo.valueForKey(UIKeyboardFrameEndUserInfoKey) as! NSValue
        let keyboardRectangle = keyboardFrame.CGRectValue()
        let keyboardHeight = keyboardRectangle.height
    }

UITableView adds height of keyboard to contentSize when the keyboard appears on iOS11

Workaround

This is not specifically answering the original question, but might be a solution for those who don't have a translucent keyboard and input view.

I could get around this problem by changing the constraints and not setting the bottom insets. Initially the bottom constraint of the table view was set to the bottom of the super view (bottom of the screen, basically). So when the keyboard appeared, I didn't change the table view's frame, but the bottom inset. This apparently didn't work properly.

Now I've set the bottom constraint of the table view to the top of the input view (black bar) and the bottom inset to zero. Since the input view moves up when the keyboard appears, it changes the frame of the table view and the bottom inset remains zero. I still set the content offset, because I need specific behavior in different situations, but that's it.

This only works in my situation, because I neither have a translucent input bar nor keyboard and don't need to show blurry content behind it.

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

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
    }        
}

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