UIPageViewController中的断言失败

Question

我在UIPageViewController中有一个断言失败.

Assertion failure in -[UIPageViewController _flushViewController:animated:], /BuildRoot/Library/Caches/com.apple.xbs/Sources/UIKit/UIKit-3512.60.12/UIPageViewController.m
Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason:
'Don't know about flushed view <UIView: 0x15a5bff30; frame = (0 0; 768 903); autoresize = W+H; layer = <CALayer: 0x15a5bfc30>>'
*** First throw call stack:
(0x181ebedb0 0x181523f80 0x181ebec80 0x182844154 0x1877a1c40 0x1877a1da8 0x18784e9c4 0x18784ebfc 0x187852318 0x18784dd98 0x1870101e4 0x1849a2994 0x18499d5d0 0x1870270a4 0x10028b620 0x100348b78 0x100379f54 0x100168878 0x18733d568 0x1870330b4 0x1870f1a00 0x18733e71c 0x1870f832c 0x18703536c 0x18700f7ac 0x18700ed40 0x18700eba8 0x1873283b4 0x18700d5e8 0x18784ebd4 0x187852318 0x18784df3c 0x1871db550 0x1871daf6c 0x101c9b768 0x1849f0234 0x1849f00e8 0x182135e54 0x181e5d030 0x181e757d4 0x181e74f0c 0x181e72c64 0x181d9cc50 0x183684088 0x18707e088 0x10033b200 0x18193a8b8)
libc++abi.dylib: terminating with uncaught exception of type NSException

我不知道为什么会出现这种错误.关于导致它的原因或如何调试它的任何线索？

Answer 1

遇到此断言的直接方法是使用循环源UIPageController定义滚动过渡样式。

当源包含两页时，每页是前一页，下一页是另一页。如果您滑动UIPageController包含两个页面，然后尝试使用 3 个页面设置源，您将获得上面提到的断言，并保证假设UIPageControllerDataSourcebefore/after 方法允许在 2 个页面的情况下循环转换。

使用UIPageController滚动过渡实现无崩溃的主要规则：

1)dataSource调用setViewControllers方法前设置

2) 使用setViewControllers没有动画的方法 ( animated: false)

3)dataSource为单页模式设置为 nil

4) 不允许循环用于 2 页模式

所有这些建议一起使UIPageController绝对稳定。

import UIKit

/// Convenient subclass of UIPageViewController
@objc class AMPageViewController: UIPageViewController {

    /// Turn on/off PageControl at the bottom
    @objc var showPageControl: Bool = true

    /// Array of all viewControllers
    @objc var source: [UIViewController]? {

        didSet {
            let count = source?.count ?? 0
            if count > 0 {
                dataSource = count > 1 ? self : nil
            }
            else {
                dataSource = nil
                delegate = nil
            }
        }
    }

    /// Index of the current viewController from source
    @objc var pageIndex: Int {

        get {
            var currentPageIndex: Int = 0
            if let vc = viewControllers?.first, let source = source, let pageIndex = source.index(of: vc) {
                currentPageIndex = pageIndex
            }

            return currentPageIndex
        }

        set {
            guard newValue >= 0, let source = source, newValue < source.count else { return }

            let vc = source[newValue]
            let direction: UIPageViewControllerNavigationDirection = newValue < pageIndex ? .reverse : .forward

            setViewController(vc, direction: direction)
        }
    }

    override weak var delegate: UIPageViewControllerDelegate? {

        get { return super.delegate }

        set {
            if source?.count ?? 0 > 0 {
                super.delegate = newValue
            }
            else {
                super.delegate = nil
            }
        }
    }

    /// Initializer in scroll-mode with interPageSpacing
    @objc init(navigationOrientation: UIPageViewControllerNavigationOrientation = .horizontal, interPageSpacing: Int = 0) {

        let options = (interPageSpacing > 0) ? [UIPageViewControllerOptionInterPageSpacingKey : 5] : nil

         super.init(transitionStyle: .scroll, navigationOrientation: navigationOrientation, options: options)
     }

    required init?(coder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }

    /// Set viewcontroller by index from source
    @objc func setPageIndex(_ index: Int, completion: ((Bool) -> Void)? = nil) {

        guard index > 0, let source = source, index < source.count else { return }

        let vc = source[index]
        let direction: UIPageViewControllerNavigationDirection = index < pageIndex ? .reverse : .forward

        setViewController(vc, direction: direction, completion: completion)
    }


    private func setViewController(_ viewController: UIViewController, direction: UIPageViewControllerNavigationDirection = .forward, completion: ((Bool) -> Void)? = nil) {

        super.setViewControllers([viewController], direction: direction, animated: false, completion: completion)
    }
}

extension FFPageViewController: UIPageViewControllerDataSource {

    func pageViewController(_ pageViewController: UIPageViewController, viewControllerBefore viewController: UIViewController) -> UIViewController? {

        guard let source = source, let index = source.index(of: viewController) else { return nil }

        let count = source.count

        if count == 2, index == 0 {
            return nil
        }

        let prevIndex = (index - 1) < 0 ? count - 1 : index - 1

        let pageContentViewController: UIViewController = source[prevIndex]

        return pageContentViewController
    }


    func pageViewController(_ pageViewController: UIPageViewController, viewControllerAfter viewController: UIViewController) -> UIViewController? {

        guard let source = source, let index = source.index(of: viewController) else { return nil }

        let count = source.count

        if count == 2, index == 1 {
            return nil
        }

        let nextIndex = (index + 1) >= count ? 0 : index + 1

        let pageContentViewController = source[nextIndex]

        return pageContentViewController
    }


    func presentationCount(for pageViewController: UIPageViewController) -> Int {

        return showPageControl ? (source?.count ?? 0) : 0
    }


    func presentationIndex(for pageViewController: UIPageViewController) -> Int {

        guard showPageControl else { return 0 }

        return pageIndex
    }
}

整体实现和使用示例可以在GitHub 项目 中找到。

Answer 2

当我在子控制器中有文本字段并且在滚动到下一个控制器时没有关闭键盘时，这种情况也发生在我身上。如果是这种情况，只需在以编程方式更改控制器的操作中添加 endEditing，或者如果您在 pageViewController 的 rollViewDidScroll 委托方法上滚动