ios - 在自定义 UIViewController 容器中管理子项和在子项之间导航的正确方法？

Question

我一直使用标准的 UIKit UIViewController 容器，比如 UIPageViewController 来满足我的容器需求，但我想尝试创建自定义容器。但有一些具体的事情我不确定。如果没有 Storyboard，这将完全是程序化的(因此，没有 segue)。

1. 我希望容器容纳(为了这个示例)4 个 UIViewController，它们将成为 UI 的 4 个主要部分。在每个部分中，将有一个 UINavigationController 来处理其部分中的堆栈。因此，这 4 个 UIViewController 应该作为子项永久添加到容器中(永远不要删除)，对吗？推理:以便用户在离开和返回该部分时不会丢失他/她在导航堆栈中的位置。

2. 我想在这 4 个 View Controller 之间实现自定义动画转换，这些 View Controller 将使用平移手势将它们拖入和拖出 View 。例如，在过去，使用 UINavigationController 时，自定义动画对象会有效地覆盖 pushViewController()，但我会在这里有效地覆盖什么？

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如果我错了请纠正我，但根据 Apple 的说法，据我所知， View Controller 可以被推送或“呈现”。我说“presented”是因为“presented”包括“present”(我认为这是令人困惑的地方)，它以模态方式引入 UIViewController，而“show”也包含在“presented”下"umbrella，不会以模态方式引入 UIViewController，它的工作方式类似于 push()，只是它不在导航堆栈中。

Answer 1

你问:

Therefore, these 4 UIViewController's should be permanently added as children to the container (and never removed), correct?

作为一个小的改进，您可以以即时方式加载它们，仅在您真正需要它们时加载它们。这避免了由于加载许多可能还不可见(如果有的话)的 View Controller 而导致的任何潜在延迟。但是，可以肯定的是，一旦加载，您可以将它们保存在内存中。这是 Apple 自己的容器 View Controller 所采用的模式。

... show ... does not bring in a UIViewController modally, it works in some way like push() except that it's not in a navigation stack.

show 方法将导航 View Controller 层次结构，确定它在哪个上下文中找到自己并相应地进行转换。如果您在导航 Controller 或 Split View Controller 中，它将执行适当的转换。但是，如果您不在其中一个 Controller 中，它将执行模式演示。查看show documentation .

I want to implement custom animation transitions between these 4 view controllers that will use pan gestures to drag them in and out of view...

我建议引用 Custom Container View Controller Transitions ，其中概述了他们如何使用 custom transition结合自己的图案view controller containment .

如果这变得太笨重，您可能只是“守旧派”，只是使用手势为包含的 View Controller 进出动画 View ，执行所有适当的 View Controller 包含相关调用。它没有那么优雅，但我怀疑这可能更容易。

---

如果您手动执行此操作(更容易)，唯一的技巧是确保执行适当的外观和 View Controller 包含调用。因此，在下面的示例中，我们从添加为容器 View Controller 的 subview Controller 的四个 subview Controller 之一开始，这显示了如何使用手势将那个 subview Controller 替换为另一个 subview Controller 。这使 View Controller 层次结构与 View 层次结构保持同步，并确保子级获得适当的外观方法调用:

import UIKit
import UIKit.UIGestureRecognizerSubclass
import os.log

class ViewController: UIViewController {

    lazy private var swipeFromRight: UIScreenEdgePanGestureRecognizer = {
        let swipe = UIScreenEdgePanGestureRecognizer(target: self, action: #selector(handleSwipeFromRight(_:)))
        swipe.edges = .right
        return swipe
    }()

    private var nextChildController: UIViewController?
    private var currentChildController: UIViewController?

    override func viewDidLoad() {
        super.viewDidLoad()

        view.addGestureRecognizer(swipeFromRight)
    }

    @objc func handleSwipeFromRight(_ gesture: UIScreenEdgePanGestureRecognizer) {
        let percent = -gesture.translation(in: gesture.view).x / gesture.view!.bounds.width

        if gesture.state == .began {
            os_log("starting gesture", type: .debug)

            guard let next = nextViewController() else {
                gesture.state = .cancelled
                return
            }

            currentChildController = childViewControllers.first!
            nextChildController = next
            startAppearance(next, replacing: currentChildController!, in: currentChildController!.view.superview)

            // prepare for gesture driven animation

            next.view.frame = currentChildController!.view.frame
            next.view.transform = .init(translationX: next.view.frame.width, y: 0)
        } else if gesture.state == .changed {
            // update animation based upon progress percent

            nextChildController!.view.transform = .init(translationX: nextChildController!.view.frame.width * (1 - percent), y: 0)
        } else if gesture.state == .ended {
            // figure out whether we should finish the animation (if not, we'll reverse it)

            let velocity = gesture.velocity(in: gesture.view).x
            let shouldFinish = velocity < 0 || (velocity == 0 && percent > 0.5)

            os_log("finishing gesture: shouldFinish=%@", type: .debug, shouldFinish ? "true" : "false")

            let next = nextChildController!
            let previous = self.currentChildController!

            if shouldFinish {
                UIView.animate(withDuration: 0.25, delay: 0, options: .curveEaseOut, animations: {
                    next.view.transform = .identity
                }, completion: { finished in
                    self.endAppearance(next, replacing: previous)
                })
            } else {
                beginCancelAppearance(next, replacing: previous)

                UIView.animate(withDuration: 0.25, delay: 0, options: .curveEaseOut, animations: {
                    next.view.transform = .init(translationX: next.view.frame.width, y: 0)
                }, completion: { finished in
                    self.endCancelAppearance(next, replacing: previous)

                    next.view.transform = .identity
                })
            }
        }
    }

    // MARK: Child appearance/containment helpers

    private func startAppearance(_ appearingController: UIViewController, replacing disappearingController: UIViewController, in view: UIView? = nil) {
        appearingController.beginAppearanceTransition(true, animated: true)

        addChildViewController(appearingController)
        view?.addSubview(appearingController.view)

        disappearingController.willMove(toParentViewController: nil)
        disappearingController.beginAppearanceTransition(false, animated: true)
    }

    private func beginCancelAppearance(_ appearingController: UIViewController, replacing disappearingController: UIViewController) {
        appearingController.willMove(toParentViewController: nil)
        appearingController.beginAppearanceTransition(false, animated: true)

        disappearingController.willMove(toParentViewController: self)
        disappearingController.beginAppearanceTransition(true, animated: true)
    }

    private func endCancelAppearance(_ appearingController: UIViewController, replacing disappearingController: UIViewController) {
        appearingController.view.removeFromSuperview()
        appearingController.removeFromParentViewController()
        appearingController.endAppearanceTransition()

        disappearingController.endAppearanceTransition()
    }

    private func endAppearance(_ appearingController: UIViewController, replacing disappearingController: UIViewController) {
        appearingController.endAppearanceTransition()
        appearingController.didMove(toParentViewController: self)

        disappearingController.view.removeFromSuperview()
        disappearingController.removeFromParentViewController()
        disappearingController.endAppearanceTransition()
    }

    // MARK: Next/Previous child helpers

    private func nextViewController() -> UIViewController? { ... }

    private func previousViewController() -> UIViewController? { ... }

}

显然，用您想要的任何动画替换动画。而且，很明显，出售适合您的应用程序的 View Controller 。但它说明了需要完成的手势、外观和遏制调用的性质。