ios - UIProgressView 约束问题

Question

我有一个以编程方式添加到 Storyboard View 的 UIProgressView 以及将其放置在导航栏底部的约束。有一个菜单，打开时会暂时隐藏导航栏，关闭时会再次取消隐藏。打开和关闭此菜单后，UIProgressView 上的约束将其放置在窗口的最顶部，因此它会被导航栏隐藏。因此，在隐藏导航栏时，布局和约束似乎正在重新计算和应用。如何在取消隐藏导航栏后强制应用约束？我试过 layoutIfNeeded 无济于事。此外，了解 View 层次结构有点困难，因为 View 是嵌入在导航 Controller 中的 Storyboard放置 View ，但此 View 的自定义 View Controller 从 xib 加载自己的 View 。关于如何强制应用约束和破译 View 层次结构的任何想法？

Answer 1

没有看到您的代码是很难回答的。顺便说一句，这是可行的:

override func viewDidLoad() {
    super.viewDidLoad()

    // if VC is pushed in a navigation controller I add a progress bar
    if let navigationVC = self.navigationController {

        // create progress bar with .bar style and add it as subview
        let progressBar = UIProgressView(progressViewStyle: .Bar)
        navigationVC.navigationBar.addSubview(progressBar)

        // create constraints
        // NOTE: bottom constraint has 1 as constant value instead of 0; this way the progress bar will look like the one in Safari
        let bottomConstraint = NSLayoutConstraint(item: navigationVC.navigationBar, attribute: .Bottom, relatedBy: .Equal, toItem: progressBar, attribute: .Bottom, multiplier: 1, constant: 1)
        let leftConstraint = NSLayoutConstraint(item: navigationVC.navigationBar, attribute: .Leading, relatedBy: .Equal, toItem: progressBar, attribute: .Leading, multiplier: 1, constant: 0)
        let rightConstraint = NSLayoutConstraint(item: navigationVC.navigationBar, attribute: .Trailing, relatedBy: .Equal, toItem: progressBar, attribute: .Trailing, multiplier: 1, constant: 0)

        // add constraints
        progressBar.translatesAutoresizingMaskIntoConstraints = false
        navigationVC.view.addConstraints([bottomConstraint, leftConstraint, rightConstraint])
    }
}