iOS 11 UIStackView按比例填充分布会导致奇怪的视图加载动画

我想我找到了一个固定电话 self.view.layoutIfNeeded() 在 animations 块

import UIKit

class ViewController: UIViewController {

    var showB = true

    weak var viewB: UIView!

    override func viewDidLoad() {
        super.viewDidLoad()

        let viewA = UIView()
        viewA.backgroundColor = UIColor.green

        let toggleViewBButtonAnimated = UIButton(frame: CGRect(x: 50, y: 150, width: 200, height: 40))
        toggleViewBButtonAnimated.backgroundColor = UIColor.cyan
        toggleViewBButtonAnimated.setTitle("Toggle B (animated)", for: .normal)
        viewA.addSubview(toggleViewBButtonAnimated)
        toggleViewBButtonAnimated.addTarget(self, action: #selector(toggleBButtonTappedAnimated), for: .touchUpInside)


        let viewB = UIView()
        viewB.backgroundColor = UIColor.orange
        let viewBHeightConstraint = viewB.heightAnchor.constraint(equalToConstant: 200)
        viewBHeightConstraint.priority = 999
        viewBHeightConstraint.isActive = true
        self.viewB = viewB


        let stackView = UIStackView(arrangedSubviews: [viewA, viewB])
        stackView.axis = .vertical
        stackView.alignment = .fill
        stackView.distribution = .fill
        stackView.translatesAutoresizingMaskIntoConstraints = false

        self.view.addSubview(stackView)

        stackView.topAnchor.constraint(equalTo: self.view.topAnchor).isActive = true
        stackView.bottomAnchor.constraint(equalTo: self.view.bottomAnchor).isActive = true
        stackView.leadingAnchor.constraint(equalTo: self.view.leadingAnchor).isActive = true
        stackView.trailingAnchor.constraint(equalTo: self.view.trailingAnchor).isActive = true
    }

    @IBAction func toggleBButtonTappedAnimated() {
        self.showB = !self.showB
        UIView.animate(withDuration: 0.3,
                       animations: { self.viewB.isHidden = !self.showB; self.view.layoutIfNeeded() }
        )
    }
}

该控制器设置 UIStackView 它有两个垂直视图,一个绿色的(a)和一个橙色的(B)。点击按钮隐藏/取消隐藏视图B。

不 有 动画 然后,当显示视图B时,它会从屏幕顶部飞入。(当视图B被隐藏时,它会正常隐藏-从屏幕底部向下移动。)

到 块,视图B按预期显示-它从屏幕底部出现。

感谢@g3rv4的回答,为我指明了这个方向!

对我来说,问题是iOS 11中引入的行为回归,与UIStackView分布类型无关。我尝试了两种基于代码的解决方案,但都没有成功:首先,在容器层次结构上调用layoutifneed;其次,(如另一个类似问题的答案所示)调整视图的内容模式。

今天早上,我在使用转基因种子时遇到了同样的问题。我最终使用了 UIView.performWithoutAnimation { 阻止执行任何操作 UIStackView