How to handle keyboard for UITextField in scrolling UIStackView in iOS

Issue #329

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)
    }
}

Move up the entire view

For simplicity, we can move up the entire view

func move(info: Info) {
    let isHiding = info.frame.origin.y == UIScreen.main.bounds.height
    let moveUp = CGAffineTransform(translationX: 0, y: -info.frame.height)

    switch (view.transform, isHiding) {
    case (.identity, false):
        view.transform = moveUp
    case (moveUp, true):
        view.transform = .identity
     default:
        break
     }
}

Prefer willShow and willHide

There ‘s an edge case with the above switch on view.transform and isHiding with one time verification sms code, which make it into the correct case handling. It’s safe to just set view.transform depending on show with willHide and willShow

import UIKit

class KeyboardHandler {
    let view: UIView
    var observerForWillShow: AnyObject?
    var observerForWillHide: AnyObject?
    var keyboardHeightConstraint: NSLayoutConstraint!

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

	init(view: UIView) {
        self.view = view
    }

    func setup() {
        observerForWillShow = NotificationCenter.default.addObserver(
            forName: UIResponder.keyboardWillShowNotification,
            object: nil,
            queue: .main,
            using: { [weak self] notification in
                self?.handle(notification, show: true)
            }
        )

        observerForWillHide = NotificationCenter.default.addObserver(
            forName: UIResponder.keyboardWillHideNotification,
            object: nil,
            queue: .main,
            using: { [weak self] notification in
                self?.handle(notification, show: false)
            }
        )
    }

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

        UIView.animate(
            withDuration: info.duration,
            delay: 0,
            options: info.animationOptions,
            animations: {
				self.move(info: info, show: show)
        }, completion: nil)
    }

    func move(info: Info, show: Bool) {
        let moveUp = CGAffineTransform(translationX: 0, y: -info.frame.height)
        if show {
            view.transform = moveUp
        } else {
            view.transform = .identity
        }
    }

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

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

Read more

• Managing the Keyboard

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Updated at 2020-07-06 07:09:07