如何通过自定义转换在当前上下文中呈现视图控制器？

Question

我遇到了视图控制器包含问题,并希望使用自定义演示文稿/动画呈现视图控制器"当前上下文".

我有一个根视图控制器,它有两个子视图控制器,可以作为子项添加到根目录中.当这些子视图控制器呈现视图控制器时,我希望该呈现是在当前上下文中,以便当从视图中移除所呈现的子项时,所述呈现的模式也将被移除.此外,如果子A呈现视图控制器,我会期望子B的'presentViewController'属性在"当前上下文"演示中为零,即使A仍然呈现.

当我将modalPresentationStyle我呈现的视图控制器设置为overCurrentContext,并且子视图控制器definesPresentationContext设置为true 时,一切都按预期工作.

如果我已经modalPresentationStyle设置custom并覆盖shouldPresentInFullscreen在我的自定义演示控制器中返回false,那么当我期望它时,这不起作用.

这是一个说明问题的示例:

import UIKit

final class ProgressController: UIViewController {
    private lazy var activityIndicatorView = UIActivityIndicatorView(activityIndicatorStyle: .white)
    private lazy var progressTransitioningDelegate = ProgressTransitioningDelegate()

    // MARK: Lifecycle

    override init(nibName nibNameOrNil: String?, bundle nibBundleOrNil: Bundle?) {
        super.init(nibName: nibNameOrNil, bundle: nibBundleOrNil)

        setup()
    }

    required public init?(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)

        setup()
    }

    override public func viewDidLoad() {
        super.viewDidLoad()

        view.backgroundColor = UIColor(white: 0, alpha: 0)

        view.addSubview(activityIndicatorView)
        activityIndicatorView.startAnimating()
    }

    override func viewDidAppear(_ animated: Bool) {
        super.viewDidAppear(animated)
    }

    override public func viewDidLayoutSubviews() {
        super.viewDidLayoutSubviews()

        activityIndicatorView.center = CGPoint(x: view.bounds.width/2, y: view.bounds.height/2)
    }

    // MARK: Private

    private func setup() {
        modalPresentationStyle = .custom
        modalTransitionStyle = .crossDissolve
        transitioningDelegate = progressTransitioningDelegate
    }
}

final class ProgressTransitioningDelegate: NSObject, UIViewControllerTransitioningDelegate {
    func presentationController(forPresented presented: UIViewController, presenting: UIViewController?, source: UIViewController) -> UIPresentationController? {
        return DimBackgroundPresentationController(presentedViewController: presented, presenting: source)
    }
}

final class DimBackgroundPresentationController: UIPresentationController {
    lazy var overlayView: UIView = {
        let v = UIView()
        v.backgroundColor = UIColor(white: 0, alpha: 0.5)
        return v
    }()

    override var shouldPresentInFullscreen: Bool {
        return false
    }

    override func presentationTransitionWillBegin() {
        super.presentationTransitionWillBegin()

        overlayView.alpha = 0
        containerView!.addSubview(overlayView)
        containerView!.addSubview(presentedView!)

        if let coordinator = presentedViewController.transitionCoordinator {
            coordinator.animate(alongsideTransition: { _ in
                self.overlayView.alpha = 1
            }, completion: nil)
        }
    }

    override func containerViewDidLayoutSubviews() {
        super.containerViewDidLayoutSubviews()

        overlayView.frame = presentingViewController.view.bounds
    }

    override func dismissalTransitionWillBegin() {
        super.dismissalTransitionWillBegin()

        let coordinator = presentedViewController.transitionCoordinator
        coordinator?.animate(alongsideTransition: { _ in
            self.overlayView.alpha = 0
        }, completion: nil)
    }
}

class ViewControllerA: UIViewController {
    override func viewDidAppear(_ animated: Bool) {
        super.viewDidAppear(animated)

        definesPresentationContext = true

        let vc = ProgressController()
        self.present(vc, animated: true) {
        }
    }
}

class ViewController: UIViewController {

    let container = UIScrollView()

    override func viewDidLoad() {
        super.viewDidLoad()

        container.frame = view.bounds
        view.addSubview(container)

        let lhs = ViewControllerA()
        lhs.view.backgroundColor = .red

        let rhs = UIViewController()
        rhs.view.backgroundColor = .blue

        addChildViewController(lhs)
        lhs.view.frame = CGRect(x: 0, y: 0, width: view.bounds.width, height: view.bounds.height)
        container.addSubview(lhs.view)
        lhs.didMove(toParentViewController: self)

        addChildViewController(rhs)
        rhs.view.frame = CGRect(x: view.bounds.width, y: 0, width: view.bounds.width, height: view.bounds.height)
        container.addSubview(rhs.view)
        rhs.didMove(toParentViewController: self)


        container.contentSize = CGSize(width: view.bounds.width * 2, height: view.bounds.height)
    }

    override func viewDidAppear(_ animated: Bool) {
        super.viewDidAppear(animated)
//        let rect = CGRect(x: floor(view.bounds.width/2.0), y: 0, width: view.bounds.width, height: view.bounds.height)
//        container.scrollRectToVisible(rect, animated: true)
    }
}

1. 这将显示一个ViewController,其滚动视图包含两个子视图控制器
2. 左侧的红色视图控制器将显示应呈现当前上下文的进度视图控制器.
3. 如果视图控制器被正确呈现为"当前上下文",那么您将能够滚动滚动视图,如果您检查了蓝色右侧视图控制器的"presentViewController"属性,则它应该为零.这些都不是真的.

如果您将setup()功能更改ProgressController为:

private func setup() {
    modalPresentationStyle = .overCurrentContext
    modalTransitionStyle = .crossDissolve
    transitioningDelegate = progressTransitioningDelegate
}

演示文稿/视图层次结构将按预期运行,但不会使用自定义演示文稿.

Apple的文档shouldPresentInFullscreen似乎表明这应该有效:

此方法的默认实现返回true,表示演示文稿覆盖整个屏幕.您可以覆盖此方法并返回false以强制演示文稿仅在当前上下文中显示.

如果重写此方法,请不要调用super.

我在iOS 10的Xcode 8和iOS 11的Xcode 9上进行了测试,上述代码在任何一种情况下都无法正常工作.

Answer 1

我猜你已经发现了一个错误。文档说shouldPresentInFullscreen可以将其变成currentContext演示文稿，但它没有任何作用。（除了你的测试和我的测试之外，我还发现了一些网上对此的抱怨，让我认为情况确实如此。）

结论是，如果您使用 的表示样式，则无法获得默认currentContext行为（运行时查阅源视图控制器并向上查找层次结构） 。definesPresentationContext.custom

我建议向 Apple 提交错误。