swift - 调整 View 大小时，textview 会抖动

Question

我正在调整 TextView 所属的 View 的大小，当 View 变大或变小时，文本会晃动。

所述 TextView 的声明:

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
    }()

我正在调整它所在的 View 大小以适合全屏，如下所示

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)
}

这样做后， View 完美展开，但 textviews 文本会产生反弹效果，使动画看起来非常不专业......有什么建议吗？

编辑:看起来当我删除中心文本对齐选项时它工作正常。如何使其在文本居中对齐的情况下工作？

Answer 1

编辑:我又看了一遍，并尝试使用基于 UIScrollView animation of height and contentOffset "jumps" content from bottom 的技术。 .

这是一个最小的工作示例，其中 TextView 具有居中文本对齐方式，这对我有用!

我建议管理动画要么全部基于约束，要么全部基于帧。我尝试了一个通过更新容器 View 框架来驱动动画的版本，但开始需要很长时间才能将其保留在这种基于约束的方法中。

希望这能为您指明正确的方向:)

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()
        }
    }
}