更新到Xcode 10.2后出现PDFKit问题。有什么办法解决吗？

Question

当我尝试使用pdfkit显示pdf文件时，应用程序崩溃。这是简单的示例？：

import UIKit
import PDFKit

class ViewController: UIViewController {

    @IBOutlet weak var pdfView: PDFView!

    override func viewDidLoad() {
        super.viewDidLoad()
        if let path = Bundle.main.path(forResource: "file", ofType: "pdf") {
            let url = URL(fileURLWithPath: path)
            if let pdfDocument = PDFDocument(url: url) {
                pdfView.displayMode = .singlePageContinuous
                pdfView.autoScales = true
                // pdfView.displayDirection = .horizontal
                pdfView.document = pdfDocument
            }
        }
    }
}

这会因“未捕获的异常'CALayerInvalidGeometry'而崩溃，原因：'CALayer位置包含NaN：[nan nan]'”：

2019-03-26 21:09:47.837837+0400 pdfKitTest[3163:93151] libMobileGestalt MobileGestalt.c:890: MGIsDeviceOneOfType is not supported on this platform.
2019-03-26 21:09:47.927078+0400 pdfKitTest[3163:93151] *** Terminating app due to uncaught exception 'CALayerInvalidGeometry', reason: 'CALayer position contains NaN: [nan nan]'
*** First throw call stack:
(
    0   CoreFoundation                      0x000000010e2326fb __exceptionPreprocess + 331
    1   libobjc.A.dylib                     0x000000010c8daac5 objc_exception_throw + 48
    2   CoreFoundation                      0x000000010e232555 +[NSException raise:format:] + 197
    3   QuartzCore                          0x00000001112d52ae _ZN2CA5Layer12set_positionERKNS_4Vec2IdEEb + 140
    4   QuartzCore                          0x00000001112c468b -[CALayer setPosition:] + 57
    5   QuartzCore                          0x00000001112c4de3 -[CALayer setFrame:] + 560
    6   PDFKit                              0x000000010c059097 -[PDFPageLayerTile initWithFrame:forPageLayer:withRenderingTransform:tileContentsScale:generationID:] + 168
    7   PDFKit                              0x000000010c05e805 -[PDFPageLayer _updateTiles] + 3439
    8   PDFKit                              0x000000010c059d8e -[PDFPageLayer setNeedsTilesUpdate] + 87
    9   PDFKit                              0x000000010c06e97d -[PDFPageView setNeedsTilesUpdate] + 48
    10  PDFKit                              0x000000010c070816 -[PDFPageView setFrame:] + 334
    11  PDFKit                              0x000000010c06711c -[PDFDocumentView createPageViewForPageAtIndex:] + 764
    12  PDFKit                              0x000000010c068326 -[PDFDocumentView updateVisibility] + 1726
    13  PDFKit                              0x000000010c0d776f -[PDFView resizeDisplayView:] + 517
    14  PDFKit                              0x000000010c0d0cdf -[PDFView layoutDocumentView] + 464
    15  PDFKit                              0x000000010c0cc36a -[PDFView setDocument:waitDuration:] + 1246
    16  pdfKitTest                          0x000000010bd277e2 $s10pdfKitTest14ViewControllerC11viewDidLoadyyF + 1506
    17  pdfKitTest                          0x000000010bd27924 $s10pdfKitTest14ViewControllerC11viewDidLoadyyFTo + 36
    18  UIKitCore                           0x0000000112fda43b -[UIViewController loadViewIfRequired] + 1183
    19  UIKitCore                           0x0000000112fda868 -[UIViewController view] + 27
    20  UIKitCore                           0x0000000113612c33 -[UIWindow addRootViewControllerViewIfPossible] + 122
    21  UIKitCore                           0x0000000113613327 -[UIWindow _setHidden:forced:] + 289
    22  UIKitCore                           0x0000000113625f86 -[UIWindow makeKeyAndVisible] + 42
    23  UIKitCore                           0x00000001135d5f1c -[UIApplication _callInitializationDelegatesForMainScene:transitionContext:] + 4555
    24  UIKitCore                           0x00000001135db0c6 -[UIApplication _runWithMainScene:transitionContext:completion:] + 1617
    25  UIKitCore                           0x0000000112e206d6 __111-[__UICanvasLifecycleMonitor_Compatability _scheduleFirstCommitForScene:transition:firstActivation:completion:]_block_invoke + 904
    26  UIKitCore                           0x0000000112e28fce +[_UICanvas _enqueuePostSettingUpdateTransactionBlock:] + 153
    27  UIKitCore                           0x0000000112e202ec -[__UICanvasLifecycleMonitor_Compatability _scheduleFirstCommitForScene:transition:firstActivation:completion:] + 236
    28  UIKitCore                           0x0000000112e20c48 -[__UICanvasLifecycleMonitor_Compatability activateEventsOnly:withContext:completion:] + 1091
    29  UIKitCore                           0x0000000112e1efba __82-[_UIApplicationCanvas _transitionLifecycleStateWithTransitionContext:completion:]_block_invoke + 782
    30  UIKitCore                           0x0000000112e1ec71 -[_UIApplicationCanvas _transitionLifecycleStateWithTransitionContext:completion:] + 433
    31  UIKitCore                           0x0000000112e239b6 __125-[_UICanvasLifecycleSettingsDiffAction performActionsForCanvas:withUpdatedScene:settingsDiff:fromSettings:transitionContext:]_block_invoke + 576
    32  UIKitCore                           0x0000000112e24610 _performActionsWithDelayForTransitionContext + 100
    33  UIKitCore                           0x0000000112e2371d -[_UICanvasLifecycleSettingsDiffAction performActionsForCanvas:withUpdatedScene:settingsDiff:fromSettings:transitionContext:] + 223
    34  UIKitCore                           0x0000000112e286d0 -[_UICanvas scene:didUpdateWithDiff:transitionContext:completion:] + 392
    35  UIKitCore                           0x00000001135d99a8 -[UIApplication workspace:didCreateScene:withTransitionContext:completion:] + 514
    36  UIKitCore                           0x0000000113190dfa -[UIApplicationSceneClientAgent scene:didInitializeWithEvent:completion:] + 361
    37  FrontBoardServices                  0x00000001194cd125 -[FBSSceneImpl _didCreateWithTransitionContext:completion:] + 448
    38  FrontBoardServices                  0x00000001194d6ed6 __56-[FBSWorkspace client:handleCreateScene:withCompletion:]_block_invoke_2 + 283
    39  FrontBoardServices                  0x00000001194d6700 __40-[FBSWorkspace _performDelegateCallOut:]_block_invoke + 53
    40  libdispatch.dylib                   0x000000010f5c5db5 _dispatch_client_callout + 8
    41  libdispatch.dylib                   0x000000010f5c92ba _dispatch_block_invoke_direct + 300
    42  FrontBoardServices                  0x0000000119508146 __FBSSERIALQUEUE_IS_CALLING_OUT_TO_A_BLOCK__ + 30
    43  FrontBoardServices                  0x0000000119507dfe -[FBSSerialQueue _performNext] + 451
    44  FrontBoardServices                  0x0000000119508393 -[FBSSerialQueue _performNextFromRunLoopSource] + 42
    45  CoreFoundation                      0x000000010e199be1 __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE0_PERFORM_FUNCTION__ + 17
    46  CoreFoundation                      0x000000010e199463 __CFRunLoopDoSources0 + 243
    47  CoreFoundation                      0x000000010e193b1f __CFRunLoopRun + 1231
    48  CoreFoundation                      0x000000010e193302 CFRunLoopRunSpecific + 626
    49  GraphicsServices                    0x00000001166b42fe GSEventRunModal + 65
    50  UIKitCore                           0x00000001135dcba2 UIApplicationMain + 140
    51  pdfKitTest                          0x000000010bd28a7b main + 75
    52  libdyld.dylib                       0x000000010f63a541 start + 1
    53  ???                                 0x0000000000000001 0x0 + 1
)
libc++abi.dylib: terminating with uncaught exception of type NSException
(lldb) 

如果我对此行发表评论：

 pdfView.document = pdfDocument

该应用不会崩溃，但是pdf文件也不会显示。如何解决这个问题？

Answer 1

我建议（只是猜测）可能viewDidLoad为时过早。该视图尚未处于视图层次结构中，因此有些事情您无法执行。错误在于该层没有位置，这是有道理的，因为它没有上层。

要确认这是问题所在，请尝试将所有代码移至viewDidAppear。如果坠机事故消失，我们将走上正确的道路。然后，您可以根据需要尝试将其移动到更好的事件中。我建议viewDidLayoutSubviews。您需要确保代码不会多次运行（使用Bool实例属性作为标志）。