textview shakes when resizing view

Question

I'm resizing the view that a textview belongs to and the text shakes when the view either gets bigger or gets smaller.

Declaration of said text view:

lazy var textview: UITextView = {
        let textView = UITextView()
        textView.text = ""
        textView.font = .systemFont(ofSize: 12, weight: UIFontWeightMedium)
        textView.isScrollEnabled = false
        textView.isEditable = false
        textView.isSelectable = true
        textView.isUserInteractionEnabled = true
        textView.translatesAutoresizingMaskIntoConstraints = false
        textView.textAlignment = .center
        textView.textColor = .lightGray
        textView.dataDetectorTypes = .link
        return textView
    }()

I'm resizing the view that it's in to fit the full screen like this

if let window = UIApplication.shared.keyWindow  {
    let statusBarHeight = UIApplication.shared.statusBarFrame.size.height

    UIView.animate(withDuration: 0.5, delay: 0, usingSpringWithDamping: 1, initialSpringVelocity: 1, options: .curveLinear, animations: {

        self.frame = CGRect(x: 0, y: statusBarHeight, width: window.frame.width, height: window.frame.height - statusBarHeight)

        self.layer.cornerRadius = 0

        self.layoutIfNeeded()

    }, completion: nil)
}

Upon doing so, the view expands perfectly but the textviews text does a bounce effect that makes the animation look extremely unprofessional... any advice?

Edit: It seems like when I remove the center text alignment option it works fine. How do I make it work with the text center aligned?

Answer 1

edit: I took another look at this and attempted to use the technique based in UIScrollView animation of height and contentOffset "jumps" content from bottom.

Here's a minimal working example with text view with centered text alignment which is working for me!

I'd recommend managing animations either to be all constraint based, or all frame based. I attempted a version where the animation is driven by updating the container view frame but it was starting to take too long to left it at this constraint based approach.

Hope this points you in the right direction :)

import UIKit

class ViewController: UIViewController {

    lazy var textView: UITextView = {
        let textView = UITextView()
        textView.text = "testing text view"
        textView.textAlignment = .center
        textView.translatesAutoresizingMaskIntoConstraints = false
        return textView
    }()

    lazy var containerView: UIView = {
        let view = UIView()
        view.translatesAutoresizingMaskIntoConstraints = false
        return view
    }()

    var widthConstraint: NSLayoutConstraint!
    var topAnchor: NSLayoutConstraint!

    override func viewDidLoad() {

        view.backgroundColor = .groupTableViewBackground

        // add container view and constraints
        view.addSubview(containerView)
        containerView.frame = view.bounds.insetBy(dx: 100, dy: 200)
        containerView.centerXAnchor.constraint(equalTo: view.centerXAnchor).isActive = true
        containerView.heightAnchor.constraint(equalToConstant: 100).isActive = true

        // keep reference to topAnchor and width as properties to animate
        topAnchor = containerView.topAnchor.constraint(lessThanOrEqualTo: view.topAnchor, constant: 100)
        widthConstraint = containerView.widthAnchor.constraint(equalToConstant: 300)
        topAnchor.isActive = true
        widthConstraint.isActive = true

        // add text view to container view and set constraints
        containerView.addSubview(textView)
        textView.leftAnchor.constraint(equalTo: containerView.leftAnchor).isActive = true
        textView.rightAnchor.constraint(equalTo: containerView.rightAnchor).isActive = true
        textView.topAnchor.constraint(equalTo: containerView.topAnchor).isActive = true
        textView.bottomAnchor.constraint(equalTo: containerView.bottomAnchor).isActive = true
    }

    @IBAction func toggleResize(_ sender: UIButton) {

        sender.isSelected = !sender.isSelected

        view.layoutIfNeeded()
        widthConstraint.constant = sender.isSelected ? view.bounds.width : 300
        topAnchor.constant = sender.isSelected ? 20 : 100

        // caculate the textView content offset for starting position based on
        // expected end position at end of the animation
        let xOffset = (textView.bounds.width - widthConstraint.constant) / 2
        textView.contentOffset = CGPoint(x: -xOffset, y: textView.contentOffset.y)

        UIView.animate(withDuration: 1) {
            self.view.layoutIfNeeded()
        }
    }
}