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How to handle keyboard for UITextField in scrolling UIStackView in iOS

onmyway133 profile image Khoa Pham ・2 min read

Firstly, to make UIStackView scrollable, embed it inside UIScrollView. Read How to embed UIStackView inside UIScrollView in iOS

It's best to listen to keyboardWillChangeFrameNotification as it contains frame changes for Keyboard in different situation like custom keyboard, languages.

Posted immediately prior to a change in the keyboard’s frame.

class KeyboardHandler {
    let scrollView: UIScrollView
    let stackView: UIStackView
    var observer: AnyObject?
    var keyboardHeightConstraint: NSLayoutConstraint!

    struct Info {
        let frame: CGRect
        let duration: Double
        let animationOptions: UIView.AnimationOptions
    }

    init(scrollView: UIScrollView, stackView: UIStackView) {
        self.scrollView = scrollView
        self.stackView = stackView
    }
}

To make scrollView scroll beyond its contentSize, we can change its contentInset.bottom. Another way is to add a dummy view with certain height to UIStackView and alter its NSLayoutConstraint constant

We can't access self inside init, so it's best to have setup function

func setup() {
    let space = UIView()
    keyboardHeightConstraint = space.heightAnchor.constraint(equalToConstant: 0)
    NSLayoutConstraint.on([keyboardHeightConstraint])
    stackView.addArrangedSubview(spa
    observer = NotificationCenter.default.addObserver(
        forName: UIResponder.keyboardWillChangeFrameNotification,
        object: nil,
        queue: .main,
        using: { [weak self] notification in
            self?.handle(notification)
        }
    )
}

Convert Notification to a convenient Info struct

func convert(notification: Notification) -> Info? {
    guard
        let frameValue = notification.userInfo?[UIResponder.keyboardFrameEndUserInfoKey] NSValue,
        let durationotification.userInfo?[UIResponder.keyboardAnimationDurationUserInfoKey] as? NSNumber,
        let raw = notification.userInfo?[UIResponder.keyboardAnimationCurveUserInfoKey] NSNumber
    else {
        return nil

    return Info(
        frame: frameValue.cgRectValue,
        duration: duration.doubleValue,
        animationOptions: UIView.AnimationOptions(rawValue: raw.uintValue)
    )
}

Then we can compare with UIScreen to check if Keyboard is showing or hiding

func handle(_ notification: Notification) {
    guard let info = convert(notification: notification) else {
        return

    let isHiding = info.frame.origin.y == UIScreen.main.bounds.height
    keyboardHeightConstraint.constant = isHiding ? 0 : info.frame.hei
    UIView.animate(
        withDuration: info.duration,
        delay: 0,
        options: info.animationOptions,
        animations: {
            self.scrollView.layoutIfNeeded()
            self.moveTextFieldIfNeeded(info: info)
    }, completion: nil)
}

To move UITextField we can use scrollRectToVisible(_:animated:) but we have little control over how much we want to scroll

This method scrolls the content view so that the area defined by rect is just visible inside the scroll view. If the area is already visible, the method does nothing.

Another way is to check if keyboard overlaps UITextField. To do that we use convertRect:toView: with nil target so it uses window coordinates. Since keyboard frame is always relative to window, we have frames in same coordinate space.

Converts a rectangle from the receiver’s coordinate system to that of another view.

rect: A rectangle specified in the local coordinate system (bounds) of the receiver.
view: The view that is the target of the conversion operation. If view is nil, this method instead converts to window base coordinates. Otherwise, both view and the receiver must belong to the same UIWindow object.

func moveTextFieldIfNeeded(info: Info) {
    guard let input = stackView.arrangedSubviews
        .compactMap({ $0 as? UITextField })
        .first(where: { $0.isFirstResponder })
    else {
        return

    let inputFrame = input.convert(input.bounds, to: nil)
    if inputFrame.intersects(info.frame) {
        scrollView.setContentOffset(CGPoint(x: 0, y: inputFrame.height), animated: true)
    } else {
        scrollView.setContentOffset(.zero, animated: true)
    }
}

Original post https://github.com/onmyway133/blog/issues/329

Posted on by:

onmyway133 profile

Khoa Pham

@onmyway133

My apps https://onmyway133.com/apps/

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