ios - 为什么顶部布局指南会在我的iMessage扩展中移动

我有一个iMessage扩展名，并且顶部布局指南存在一些问题。我有一个MSMessagesAppViewController，用于处理表示样式之间的更改。在我的扩展程序中，我有一个按钮。单击它时，我过渡到扩展的表示样式，然后以模态形式显示 View Controller 。这是问题所在:第二个VC中的UI隐藏在顶部导航栏的后面。当我将约束设置在顶部布局指南上时，我认为这很奇怪。因此，我仔细研究了代码，然后开始调试顶级布局指南。我注意到，在过渡到扩展的表示样式后，topLayoutGuide.length =86。这应该是这样。但是，当我以模态形式显示第二个 View Controller 时，顶部布局指南会重置为0。为什么它不是应该的86？这是我的代码:

在我的主viewController中:

@IBAction func addStickerButtonPressed(_ sender: AnyObject) {
    shouldPerformCreateSegue = true
    theSender = sender
    requestPresentationStyle(.expanded)

}
override func didTransition(to presentationStyle: MSMessagesAppPresentationStyle) {
    if presentationStyle == .expanded {
        if shouldPerformCreateSegue == true {
            shouldPerformCreateSegue = false
            performSegue(withIdentifier: "CreateStickerSegue", sender: theSender)//here is where I present the new viewController
        } else {
            searchBar.becomeFirstResponder()
            searchBar.placeholder = nil
            searchBar.showsCancelButton = true
            searchBar.tintColor = UIColor.white
        }
    } else {
        searchBar.showsCancelButton = false
    }
    print(topLayoutGuide.length) //This prints out 86
}

在另一个以模态表示的 View Controller 中:

override func viewWillAppear(_ animated: Bool) {
    super.viewWillAppear(animated)
    self.view.addConstraint(navBar.topAnchor.constraint(equalTo: topLayoutGuide.bottomAnchor))
    print(topLayoutGuide.length) //This prints out 0
}

最佳答案

作为解决方法，我使用UIPresentationController，它将topLayoutGuide.length点移动模态视图 Controller :

class MyViewController: MSMessagesAppViewController {

    private func presentModalViewController() {
        let imagePicker = UIImagePickerController()
        imagePicker.delegate = self
        imagePicker.sourceType = .savedPhotosAlbum

        imagePicker.modalPresentationStyle = .custom
        imagePicker.transitioningDelegate = self

        present(imagePicker, animated: true, completion: nil)
    }
}
// MARK: - UIViewControllerTransitioningDelegate
extension MyViewController: UIViewControllerTransitioningDelegate {

    func presentationController(forPresented presented: UIViewController, presenting: UIViewController?, source: UIViewController) -> UIPresentationController? {
        let vc = PresentationController(presentedViewController: presented, presenting: presenting)
        // I really don't want to hardcode the value of topLayoutGuideLength here, but when the extension is in compact mode, topLayoutGuide.length returns 172.0.
        vc.topLayoutGuideLength = topLayoutGuide.length > 100 ? 86.0 : topLayoutGuide.length
        return vc
    }
}


class PresentationController: UIPresentationController {

    var topLayoutGuideLength: CGFloat = 0.0

    override var frameOfPresentedViewInContainerView: CGRect {
        guard let containerView = containerView else {
            return super.frameOfPresentedViewInContainerView
        }
        return CGRect(x: 0, y: topLayoutGuideLength, width: containerView.bounds.width, height: containerView.bounds.height - topLayoutGuideLength)
    }
}

唯一的问题是，从紧凑模式调用presentModalViewController时，出于未知原因，topLayoutGuide.length是172.0。所以我不得不为这种情况硬编码一个值。