如何将 ViewController 堆栈解除到某个 Route ViewController？

Question

一些RootViewController 提供ParentViewController，而不是提供ChildViewController。

如何在不再次显示ParentViewController 的情况下将ChildViewController 动画 直接发送到RootViewController？

---

详细说明

• 假设 some 提供了 ParentViewController，它允许用户输入一些凭据以登录到某个用户帐户。
• 建立连接后，ParentViewController 会显示ChildViewController，向用户显示连接/帐户详细信息
• 当用户关闭ChildViewController 时，它应该被动画（向下滑动等）关闭。但与其返回ParentViewController，不如直接返回RootViewController

当然，ParentViewController 本身并不存在ChildViewController，但（不知何故）告诉RootViewController 这也是可能的。这样从ChildViewController直接返回到RootViewController就没有问题了。然而，这不是我正在寻找的，因为RootViewController 不应该知道ChildViewController 甚至不在乎ParentViewController 是否代表其他 VC。

我正在寻找一种解决方案，其中ParentViewController 控制是否在其呈现的 VC 或其父级（= 根 VC）被解散后显示自身。

代码：

typealias CompletionBlock = () -> Void

class RootViewController: UIViewController {
    @IBAction func showParentVC(_ sender: Any) {
        let parentVC = ParentViewController()
        parentVC.completion = {
            self.dismiss(animated: true, completion: nil)
        }

        present(parentVC, animated: true)
    }
}

class ParentViewController: UIViewController {
    var completion: CompletionBlock?

    @IBAction func showChild(_ sender: Any) {
        let childVC = ChildViewController()
        childVC.completion = {
            self.completion?()
        }

        present(childVC, animated: true)
    }
}

class ChildViewController: UIViewController {
    var completion: CompletionBlock?

    @IBAction func close(_ sender: Any) {
        completion?()
    }
}

使用此代码不会解决所描述的问题。如果在ChildViewController 上调用close，则RootViewController 调用self.dismiss(animated: true, completion: nil)。这样ChildViewController 动画消失，ParentViewController 变得可见。然后ParentViewController 动画消失，RootViewController 变得可见。

如何跳过ParentViewController，在动画掉ChildViewController后直接显示RootViewController？

Answer 1

我的建议是将您的 RootViewController 嵌入到 NavigationController 中（如果您还没有的话）并为父母双方提供一个孩子

navigationController?.present(viewController, animated: true, completion: nil)
//instead of viewController.present(...)

然后你可以在你的 childViewController 中使用这个方法

navigationController?.popToRootViewController(animated: true)

Answer 2

一种方法是当您将另一个 VC 呈现到呈现的 VC 的“堆栈”上时，将视图的 alpha 设置为零。

因此，正常显示“根”VC 中的第一个模态 VC。对于呈现另一个 VC 的每个“孩子”，请使用：

present(vc, animated: true, completion: {
    self.view.alpha = 0.0
})

现在，当您回调“根”VC 以关闭所有 VC 时，您将看不到中间 VC / VC 的部分 / flash。

这是一个完整的测试示例。没有 @IBOutlets 或 @IBActions ... 只需从黑色视图控制器开始并将其自定义类分配给 MultiPresentDismissViewController：

import UIKit

class MultiPresentDismissViewController: UIViewController {

    let theLabel: UILabel = {
        let v = UILabel()
        v.textAlignment = .center
        v.font = UIFont.boldSystemFont(ofSize: 40)
        v.backgroundColor = .yellow
        v.text = "\"Root\" VC"
        return v
    }()

    let showAnotherButton: UIButton = {
        let v = UIButton()
        v.backgroundColor = UIColor(white: 0.9, alpha: 1.0)
        v.setTitle("Present a VC", for: .normal)
        v.setTitleColor(.blue, for: .normal)
        v.setTitleColor(.cyan, for: .highlighted)
        return v
    }()

    let theStackView: UIStackView = {
        let v = UIStackView()
        v.axis = .vertical
        v.alignment = .fill
        v.distribution = .fill
        v.spacing = 32
        return v
    }()

    override func viewDidLoad() {
        super.viewDidLoad()

        view.backgroundColor = .white

        [theLabel, showAnotherButton].forEach {
            theStackView.addArrangedSubview($0)
            $0.layer.borderWidth = 1.0
        }

        theStackView.translatesAutoresizingMaskIntoConstraints = false

        view.addSubview(theStackView)

        NSLayoutConstraint.activate([
            theStackView.centerXAnchor.constraint(equalTo: view.centerXAnchor),
            theStackView.topAnchor.constraint(equalTo: view.topAnchor, constant: 100.0),
            theStackView.widthAnchor.constraint(equalTo: view.widthAnchor, multiplier: 0.8),
            ])

        showAnotherButton.addTarget(self, action: #selector(presentAnotherVC), for: .touchUpInside)

    }

    @objc func presentAnotherVC() -> Void {
        let vc = AnotherViewController()
        vc.myID = 1
        present(vc, animated: true, completion: nil)
    }

}

class AnotherViewController: UIViewController {

    let theLabel: UILabel = {
        let v = UILabel()
        v.textAlignment = .center
        v.font = UIFont.boldSystemFont(ofSize: 100)
        v.backgroundColor = .yellow
        return v
    }()

    let showAnotherButton: UIButton = {
        let v = UIButton()
        v.backgroundColor = UIColor(white: 0.9, alpha: 1.0)
        v.setTitle("Present Another VC", for: .normal)
        v.setTitleColor(.blue, for: .normal)
        v.setTitleColor(.cyan, for: .highlighted)
        return v
    }()

    let defaultDismissButton: UIButton = {
        let v = UIButton()
        v.backgroundColor = UIColor(white: 0.9, alpha: 1.0)
        v.setTitle("Default Dismiss All", for: .normal)
        v.setTitleColor(.blue, for: .normal)
        v.setTitleColor(.cyan, for: .highlighted)
        return v
    }()

    let theStackView: UIStackView = {
        let v = UIStackView()
        v.axis = .vertical
        v.alignment = .fill
        v.distribution = .fill
        v.spacing = 20
        return v
    }()

    var myID: Int = 0

    override func viewDidLoad() {
        super.viewDidLoad()

        view.backgroundColor = .random()

        [theLabel, showAnotherButton, defaultDismissButton].forEach {
            theStackView.addArrangedSubview($0)
            $0.layer.borderWidth = 1.0
        }

        theStackView.translatesAutoresizingMaskIntoConstraints = false

        view.addSubview(theStackView)

        NSLayoutConstraint.activate([
            theStackView.centerXAnchor.constraint(equalTo: view.centerXAnchor),
            theStackView.topAnchor.constraint(equalTo: view.topAnchor, constant: 100.0),
            theStackView.widthAnchor.constraint(equalTo: view.widthAnchor, multiplier: 0.8),
            ])

        theLabel.text = "\(myID)"

        showAnotherButton.addTarget(self, action: #selector(presentAnotherVC), for: .touchUpInside)
        defaultDismissButton.addTarget(self, action: #selector(defaultDismissAll), for: .touchUpInside)

    }

    @objc func presentAnotherVC() -> Void {
        let vc = AnotherViewController()
        vc.myID = myID + 1
        present(vc, animated: true, completion: {
            self.view.alpha = 0.0
        })
    }

    @objc func defaultDismissAll() -> Void {
        // walk up the "presenting" hierarchy to find the "root" VC
        var vc = self.presentingViewController
        while vc?.presentingViewController != nil {
            vc = vc?.presentingViewController
        }
        vc?.dismiss(animated: true, completion: nil)
    }

}

extension CGFloat {
    static func random() -> CGFloat {
        return CGFloat(arc4random()) / CGFloat(UInt32.max)
    }
}

extension UIColor {
    static func random() -> UIColor {
        return UIColor(red:   .random(),
                       green: .random(),
                       blue:  .random(),
                       alpha: 1.0)
    }
}