Question

在子vc上引用transitionCoordinator时，它曾经在iOS7中的自定义容器类上调用transitionCoordinator，但在iOS8中，情况并非如此。现在它返回零，我不知道应该改变什么来使这项工作。

我猜它是关于在iOS8中引入的UIPresentationController，但无法找到自定义容器视图控制器的正确实现。

Answer 1

如马特在之前的SO question中所说：

因此，由于您甚至无法在特定情况下获得过渡协调员您可以在其中为内置的父视图控制器，很明显您获得的机会一种在您尝试做自己的父视图的情况下控制器为零

但是，根据transitionCoordinator，允许对其进行覆盖：

容器视图控制器可以覆盖此方法，但在大多数情况下应该不需要。如果您确实要重写此方法，请先调用super 看看是否有合适的过渡协调员返回，然后，如果有的话，将其退回。

因此，我将尝试为自己的VC容器创建自己的协调器。如果您使用UIViewPropertyAnimator来操作VC容器的子级，则几乎是很简单的。

这里是一个例子：

class PropertyAnimatorTransitionCoordinator: NSObject, UIViewControllerTransitionCoordinator, UIViewControllerTransitionCoordinatorContext {

    private let parentView: UIView
    private let fromViewController: UIViewController?
    private let toViewController: UIViewController
    private let animator: UIViewPropertyAnimator

    // MARK: - Life Cycle

    init(parentView: UIView,
         fromViewController: UIViewController?,
         toViewController: UIViewController,
         animator: UIViewPropertyAnimator) {
        self.parentView = parentView
        self.fromViewController = fromViewController
        self.toViewController = toViewController
        self.animator = animator
    }

    // MARK: - UIViewControllerTransitionCoordinator

    func animate(alongsideTransition animation: ((UIViewControllerTransitionCoordinatorContext) -> Void)?,
                 completion: ((UIViewControllerTransitionCoordinatorContext) -> Void)? = nil) -> Bool {
        var isSuccessful = false
        if let animation = animation {
            animator.addCompletion { [weak self] _ in
                guard let context = self else { return }
                animation(context)
            }
            isSuccessful = true
        }
        if let completion = completion {
            animator.addCompletion { [weak self] _ in
                guard let context = self else { return }
                completion(context)
            }
            isSuccessful = true
        }
        return isSuccessful
    }

    func animateAlongsideTransition(in view: UIView?, animation: ((UIViewControllerTransitionCoordinatorContext) -> Void)?, completion: ((UIViewControllerTransitionCoordinatorContext) -> Void)? = nil) -> Bool {
        return animate(alongsideTransition: animation, completion: completion)
    }

    func notifyWhenInteractionEnds(_ handler: @escaping (UIViewControllerTransitionCoordinatorContext) -> Void) {
        animator.addCompletion { [weak self] _ in
            guard let context = self else { return }
            handler(context)
        }
    }

    func notifyWhenInteractionChanges(_ handler: @escaping (UIViewControllerTransitionCoordinatorContext) -> Void) {
        animator.addCompletion { [weak self] _ in
            guard let context = self else { return }
            handler(context)
        }
    }

    // MARK: - UIViewControllerTransitionCoordinatorContext

    var isAnimated: Bool {
        return true
    }

    var presentationStyle: UIModalPresentationStyle {
        return .none
    }

    var initiallyInteractive: Bool {
        return false
    }

    var isInterruptible: Bool {
        return animator.isInterruptible
    }

    var isInteractive: Bool {
        return animator.isUserInteractionEnabled
    }

    var isCancelled: Bool {
        return !animator.isRunning
    }

    var transitionDuration: TimeInterval {
        return animator.duration
    }

    var percentComplete: CGFloat {
        return animator.fractionComplete
    }

    var completionVelocity: CGFloat {
        return 0
    }

    var completionCurve: UIView.AnimationCurve {
        return animator.timingParameters?.cubicTimingParameters?.animationCurve ?? .linear
    }

    var targetTransform: CGAffineTransform {
        return .identity
    }

    var containerView: UIView {
        return parentView
    }

    func viewController(forKey key: UITransitionContextViewControllerKey) -> UIViewController? {
        switch key {
        case .from:
            return fromViewController
        case .to:
            return toViewController
        default:
            return nil
        }
    }

    func view(forKey key: UITransitionContextViewKey) -> UIView? {
        switch key {
        case .from:
            return fromViewController?.view
        case .to:
            return toViewController.view
        default:
            return nil
        }
    }
}

在我的自定义容器中，我将像这样使用它：

class CustomContainerViewController: UIViewController {

    private var customTransitionCoordinator: UIViewControllerTransitionCoordinator?

    override var transitionCoordinator: UIViewControllerTransitionCoordinator? {
        if let coordinator = super.transitionCoordinator {
            return coordinator
        }
        return customTransitionCoordinator
    }

    override var shouldAutomaticallyForwardAppearanceMethods: Bool {
        return false
    }

    func insertNewChild(_ viewController: UIViewController) {
        let animator = UIViewPropertyAnimator(duration: 0.3, curve: .easeInOut)
        customTransitionCoordinator = PropertyAnimatorTransitionCoordinator(
            parentView: view,
            fromViewController: nil,
            toViewController: viewController,
            animator: animator
        )
        animator.addCompletion { [weak self] _ in
            guard let parent = self else { return }
            viewController.didMove(toParent: parent)
            self?.customTransitionCoordinator = nil
        }
        addChild(viewController)
        viewController.beginAppearanceTransition(true, animated: true)
        view.addSubview(viewController.view)
        let target = view.bounds
        viewController.view.frame = target
        viewController.view.frame.origin.x = -target.width
        view.layoutIfNeeded()
        animator.addAnimations {
            viewController.view.frame = target
        }
        animator.addCompletion { [weak self] _ in
            guard let parent = self else { return }
            viewController.endAppearanceTransition()
            viewController.didMove(toParent: parent)
            self?.customTransitionCoordinator = nil
        }
        animator.startAnimation()
    }
}

当然，某些边缘情况没有处理。这是一个非常基本的例子。

transitionCoordinator在iOS8中为自定义容器视图控制器返回nil

1 个答案: