ios - 'NSInternalInconsistencyException'，原因 : 'Unexpected subviews' possibly in UIPageViewController (swift, iOS)

Question

过去几个小时我一直坚持这个问题，似乎无法在任何地方找到解决方案。在我的 UIPageViewController 子类显示的第一个 View Controller 上滑动后，应用程序崩溃并出现异常 'NSInternalInconsistencyException'，原因:'Unexpected subviews'。我真的不明白这意味着什么以及我应该如何修复错误。调用栈如下:

0   CoreFoundation                      0x00000001123561ab __exceptionPreprocess + 171
1   libobjc.A.dylib                     0x00000001119ebf41 objc_exception_throw + 48
2   CoreFoundation                      0x000000011235b372 +[NSException raise:format:arguments:] + 98
3   Foundation                          0x0000000111490089 -[NSAssertionHandler handleFailureInMethod:object:file:lineNumber:description:] + 193
4   UIKit                               0x000000011565c2e1 -[_UIQueuingScrollView _setWrappedViewAtIndex:withView:] + 377
5   UIKit                               0x000000011565ca09 -[_UIQueuingScrollView _replaceViews:updatingContents:adjustContentInsets:animated:] + 734
6   UIKit                               0x000000011565d00f -[_UIQueuingScrollView _viewAtIndex:loadingIfNecessary:updatingContents:animated:] + 379
7   UIKit                               0x0000000115660664 __54-[_UIQueuingScrollView _didScrollWithAnimation:force:]_block_invoke + 109
8   UIKit                               0x00000001156602e8 -[_UIQueuingScrollView _didScrollWithAnimation:force:] + 534
9   UIKit                               0x000000011565b9f3 -[_UIQueuingScrollView layoutSubviews] + 179
10  UIKit                               0x0000000114c746f5 -[UIView(CALayerDelegate) layoutSublayersOfLayer:] + 1439
11  QuartzCore                          0x0000000117f483ee -[CALayer layoutSublayers] + 153
12  QuartzCore                          0x0000000117f4c4dd _ZN2CA5Layer16layout_if_neededEPNS_11TransactionE + 401
13  QuartzCore                          0x0000000117ed4ded _ZN2CA7Context18commit_transactionEPNS_11TransactionE + 365
14  QuartzCore                          0x0000000117f00704 _ZN2CA11Transaction6commitEv + 500
15  QuartzCore                          0x0000000117f01450 _ZN2CA11Transaction17observer_callbackEP19__CFRunLoopObservermPv + 76
16  CoreFoundation                      0x00000001122f8d37 __CFRUNLOOP_IS_CALLING_OUT_TO_AN_OBSERVER_CALLBACK_FUNCTION__ + 23
17  CoreFoundation                      0x00000001122f8c8e __CFRunLoopDoObservers + 430
18  CoreFoundation                      0x00000001122dc9db CFRunLoopRunSpecific + 443
19  GraphicsServices                    0x000000011780c9c6 GSEventRunModal + 62
20  UIKit                               0x0000000114ba35e8 UIApplicationMain + 159
21  ExponentiallyMe                     0x000000010f891167 main + 55
22  libdyld.dylib                       0x0000000113b54d81 start + 1
23  ???                                 0x0000000000000002 0x0 + 2

错误是在调用 [_UIQueuingScrollView _setWrappedViewAtIndex:withView:] + 377 时引发的，我不知道为什么。下面还有来自 viewDidLoad() 的代码和 UIPageViewControllerDataSource 协议(protocol)的两个必需方法。

viewDidLoad()

override func viewDidLoad() {
    super.viewDidLoad()

    self.dataSource = self
    self.delegate = self

    self.activityIndicator("Loading Survey.")

    self.pageControl.frame = CGRect()
    self.pageControl.currentPageIndicatorTintColor = UIColor.white
    self.pageControl.pageIndicatorTintColor = UIColor.lightGray
    self.pageControl.currentPage = 0
    self.view.addSubview(self.pageControl)

    self.pageControl.translatesAutoresizingMaskIntoConstraints = false
    self.pageControl.bottomAnchor.constraint(equalTo: self.view.topAnchor, constant: -20).isActive = true
    self.pageControl.widthAnchor.constraint(equalTo: self.view.widthAnchor, constant: -20).isActive = true
    self.pageControl.heightAnchor.constraint(equalToConstant: 20).isActive = true
    self.pageControl.centerXAnchor.constraint(equalTo: self.view.centerXAnchor).isActive = true

    if self.selectedSurveyType == EMSurveyType.EMST_VISA {
        self.pageControl.numberOfPages = 12
    } else {
        self.pageControl.numberOfPages = 2
    }


    setViewControllers([self.instructionView], direction: .forward, animated: true, completion: nil)
}

UIPageViewControllerDataSource 协议(protocol)方法

// Get the previous ViewController
func pageViewController(_ pageViewController: UIPageViewController, viewControllerBefore viewController: UIViewController) -> UIViewController? {
    guard self.currentPageIndex - 1 > 0 else {
        if self.currentPageIndex - 1 == 0 {
            self.currentPageIndex = 0
            return self.instructionView
        } else {
            return nil
        }
    }
    self.currentPageIndex -= 1
    return self.questionViewControllerAtIndex(self.currentPageIndex - 1)
}

// Get the next ViewController
func pageViewController(_ pageViewController: UIPageViewController, viewControllerAfter viewController: UIViewController) -> UIViewController? {
    guard self.currentPageIndex + 1 <= self.questionCount else {
        if self.currentPageIndex == self.questionCount {
            self.currentPageIndex = self.questionCount + 1
            return completionView
        } else {
            return nil
        }
    }
    self.currentPageIndex += 1
    return self.questionViewControllerAtIndex(self.currentPageIndex - 1)
}

UIPageViewController 子类从 UITabBarController 中的 UIViewController 模态呈现也可能有帮助。此外，questionViewControllers 是在函数中创建的:

func questionViewControllerAtIndex(_ index: Int) -> UIViewController {
    let storyboard = UIStoryboard(name:"Main", bundle: nil)
    let qVC = storyboard.instantiateViewController(withIdentifier: "EMSQuestionViewController") as! EMSurveyQuestionViewController
    qVC.questionProperties(questionStatement: self.mainSurveyQuestions[index], subStatements: self.subStatementsForSurveyQuestions[index])
    return qVC
}

提前非常感谢您，我对此非常迷茫，不明白是什么导致了这些问题。非常感谢任何帮助或“给我指明正确的方向”，如果您需要任何进一步的信息/代码，请告诉我。

Answer 1

所以对于任何后来阅读这篇文章的人来说，我似乎已经解决了它。我不太确定这种方法是如何工作的，但不是前一种方法(如果有人能启发我，那就太好了)，但似乎试图跟踪当前页面索引并动态创建 View Controller 并没有工作。我重写了 viewDidLoad() 以创建一个数组 allPages，它预先保存所有页面。然后在这两个协议(protocol)方法中，我不是检查当前位置的 self.currentPageIndex，而是根据传递的 viewController 实例评估当前索引并检查 allPages 索引数组，使用 allPages.index(of: viewController)。基于该值，我检查然后通过将 index 的值增加或减少 1 来将所需的 View Controller 传回。例如对于前一个，返回基于 return allPages[index! - 1]。我希望这可以帮助将来遇到这个问题的人，如果有人可以启发我为什么这样做有效，而不是我以前的方法，那也很好。