ios - 为什么我的应用程序在使用 [NSAttributedString initWithData] 时在后台崩溃

Question

我有一个管理 UICollectionView 的 viewController。我有一个从 cellForItemAtIndexPath 调用的辅助方法，它为单元格中的标签提供 NSAttributedString 。辅助方法从 html 字符串格式化 NSAttributedString。当移动到后台时，应用程序将会崩溃，但前提是 indexPath.item 大于 1。换句话说，我可以退出应用程序，而不会从第一个或第二个单元格崩溃，但会在第三个、第四个单元格上持续崩溃。 ..细胞。

这是我的辅助方法和堆栈跟踪。知道为什么我退出应用程序时崩溃吗？

#pragma mark - === Utility Methods === -

- (NSAttributedString *)stepDescriptionStringForIndexPath:(NSIndexPath *)indexPath {

    NSString *headerString;
    NSString *htmlString;
    NSString *categoryString = [NSString stringWithFormat:@"Category: %@", self.knot.category.categoryName];
    NSString *abokString = [NSString stringWithFormat:@"ABOK #: %@", self.knot.abokNumber];
    NSMutableString *activitiesString = [NSMutableString stringWithCapacity:10];
    [activitiesString appendString:@"Activities: "];

    // build a string of activities to append to the description html
    NSArray *activities = [self.knot.activities allObjects];
    if ([activities count] > 0) {
        int counter = 1;
        for (Activity *activity in activities) {
            [activitiesString appendString:activity.activityName];
            if (counter < [activities count]) {
                [activitiesString appendString:@", "];
            }
            counter ++;
        }
    }

    // build an HTML string by concatinating the activities to the step description
    // and add the header string
    if(indexPath.item > 0){
        Step *step = (Step *)self.steps[indexPath.item - 1];
        headerString = [NSString stringWithFormat:@"Step %ld of %lu", (long)indexPath.item, (unsigned long)[self.steps count]];
        htmlString =[NSString stringWithFormat:@"<p>%@</p>%@", headerString, step.stepDescription];
    } else {
        headerString = @"Overview";
        htmlString = [NSString stringWithFormat:@"<p>%@</p>%@<p>%@</br>%@</br>%@</p>", headerString, self.knot.knotDescription, categoryString, abokString, activitiesString];

    }

    // convert the html string to an attributed string
    NSMutableAttributedString *attrStringFromHTML = [[NSMutableAttributedString alloc] initWithData:[htmlString dataUsingEncoding:NSUTF8StringEncoding]
                                                                                            options:@{NSDocumentTypeDocumentAttribute: NSHTMLTextDocumentType,
                                                                                                      NSCharacterEncodingDocumentAttribute: [NSNumber numberWithInt:NSUTF8StringEncoding]}
                                                                                 documentAttributes:nil
                                                                                              error:nil];

    // set the font for the body
    NSRange totalRange;
    totalRange.location = 0;
    totalRange.length = attrStringFromHTML.length;
    [attrStringFromHTML addAttribute:NSFontAttributeName value:[UIFont systemFontOfSize:16] range:totalRange];

    // set the font for the header
    NSString *temp = [attrStringFromHTML string];

    NSRange headerRange = [temp rangeOfString:headerString];
    NSRange categoryRange = [temp rangeOfString:categoryString];
    NSRange abokRange = [temp rangeOfString:abokString];
    NSRange activitiesRange = [temp rangeOfString:activitiesString];

    [attrStringFromHTML addAttribute:NSFontAttributeName value:[UIFont boldSystemFontOfSize:18] range:headerRange];
    //set the font for the activities paragraph
    if(indexPath.item == 1){

        [attrStringFromHTML addAttribute:NSFontAttributeName value:[UIFont systemFontOfSize:12] range:categoryRange];
        [attrStringFromHTML addAttribute:NSFontAttributeName value:[UIFont systemFontOfSize:12] range:abokRange];
        [attrStringFromHTML addAttribute:NSFontAttributeName value:[UIFont systemFontOfSize:12] range:activitiesRange];


    }
    return attrStringFromHTML;
}

*** Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: 'unexpected start state'*** First throw call stack:(    0   CoreFoundation                      0x00000001131aad85 __exceptionPreprocess + 165    1   libobjc.A.dylib                     0x0000000112c1edeb objc_exception_throw + 48    2   CoreFoundation                      0x00000001131aabea +[NSException raise:format:arguments:] + 106    3   Foundation                          0x0000000110b96e1e -[NSAssertionHandler handleFailureInFunction:file:lineNumber:description:] + 169    4   UIKit                               0x00000001113a7d4e _prepareForCAFlush + 256    5   UIKit                               0x00000001113b40b4 _beforeCACommitHandler + 12    6   CoreFoundation                      0x00000001130cfc37 __CFRUNLOOP_IS_CALLING_OUT_TO_AN_OBSERVER_CALLBACK_FUNCTION__ + 23    7   CoreFoundation                      0x00000001130cfba7 __CFRunLoopDoObservers + 391    8   CoreFoundation                      0x00000001130c511c CFRunLoopRunSpecific + 524    9   UIFoundation                        0x000000011a697a7a -[NSHTMLReader _loadUsingWebKit] + 2093    10  UIFoundation                        0x000000011a698e74 -[NSHTMLReader attributedString] + 22    11  UIFoundation                        0x000000011a6323c0 _NSReadAttributedStringFromURLOrData + 5623    12  UIFoundation                        0x000000011a630d34 -[NSAttributedString(NSAttributedStringUIFoundationAdditions) initWithData:options:documentAttributes:error:] + 115    13  WhatKnotToDo                        0x000000010e84d3ac -[CSC_iPad_KnotDetailViewController stepDescriptionStringForIndexPath:] + 2476    14  WhatKnotToDo                        0x000000010e84c31d -[CSC_iPad_KnotDetailViewController collectionView:cellForItemAtIndexPath:] + 477    15  UIKit                               0x0000000111bff08f -[UICollectionView _createPreparedCellForItemAtIndexPath:withLayoutAttributes:applyAttributes:isFocused:] + 483    16  UIKit                               0x0000000111c02d96 -[UICollectionView _updateVisibleCellsNow:] + 4988    17  UIKit                               0x0000000111c07575 -[UICollectionView layoutSubviews] + 258    18  UIKit                               0x0000000111442980 -[UIView(CALayerDelegate) layoutSublayersOfLayer:] + 703    19  QuartzCore                          0x0000000112af6c00 -[CALayer layoutSublayers] + 146    20  QuartzCore                          0x0000000112aeb08e _ZN2CA5Layer16layout_if_neededEPNS_11TransactionE + 366    21  QuartzCore                          0x0000000112aeaf0c _ZN2CA5Layer28layout_and_display_if_neededEPNS_11TransactionE + 24    22  QuartzCore                          0x0000000112adf3c9 _ZN2CA7Context18commit_transactionEPNS_11TransactionE + 277    23  QuartzCore                          0x0000000112b0d086 _ZN2CA11Transaction6commitEv + 486    24  UIKit                               0x0000000111394a0b __65-[UIApplication _beginSnapshotSessionForScene:withSnapshotBlock:]_block_invoke2222 + 601    25  UIKit                               0x0000000111395201 __65-[UIApplication _performSnapshotsWithAction:forScene:completion:]_block_invoke2243 + 131    26  FrontBoardServices                  0x00000001153e3039 -[FBSSceneSnapshotAction _finishAllRequests] + 65    27  FrontBoardServices                  0x00000001153e2de3 -[FBSSceneSnapshotAction executeRequestsWithHandler:completionHandler:expirationHandler:] + 218    28  UIKit                               0x0000000111395024 __65-[UIApplication _performSnapshotsWithAction:forScene:completion:]_block_invoke + 305    29  UIKit                               0x0000000111394592 -[UIApplication _beginSnapshotSessionForScene:withSnapshotBlock:] + 1138    30  UIKit                               0x0000000111394eb2 -[UIApplication _performSnapshotsWithAction:forScene:completion:] + 629    31  UIKit                               0x0000000111394bbc -[UIApplication _handleSnapshotAction:forScene:completion:] + 153    32  UIKit                               0x0000000111390a8f __102-[UIApplication _handleApplicationDeactivationWithScene:shouldForceExit:transitionContext:completion:]_block_invoke1993 + 290    33  UIKit                               0x0000000111390657 __102-[UIApplication _handleApplicationDeactivationWithScene:shouldForceExit:transitionContext:completion:]_block_invoke1979 + 1258    34  UIKit                               0x0000000111393f62 _runAfterCACommitDeferredBlocks + 317    35  UIKit                               0x00000001113a7e4c _cleanUpAfterCAFlushAndRunDeferredBlocks + 95    36  UIKit                               0x00000001113b4147 _afterCACommitHandler + 90    37  CoreFoundation                      0x00000001130cfc37 __CFRUNLOOP_IS_CALLING_OUT_TO_AN_OBSERVER_CALLBACK_FUNCTION__ + 23    38  CoreFoundation                      0x00000001130cfba7 __CFRunLoopDoObservers + 391    39  CoreFoundation                      0x00000001130c57fb __CFRunLoopRun + 1147    40  CoreFoundation                      0x00000001130c50f8 CFRunLoopRunSpecific + 488    41  GraphicsServices                    0x0000000115203ad2 GSEventRunModal + 161    42  UIKit                               0x0000000111387f09 UIApplicationMain + 171    43  WhatKnotToDo                        0x000000010e820b7f main + 111    44  libdyld.dylib                       0x000000011396592d start + 1    45  ???                                 0x0000000000000001 0x0 + 1)libc++abi.dylib: terminating with uncaught exception of type NSException

Answer 1

我也遇到过这个问题，几个小时后，我找到了解决方案。

您只需要包装将 NSAttributedString 转换为dispatch_async 的代码即可。

例如:

   DispatchQueue.MainQueue.DispatchAsync(() =>
        {
            var encodingData = ((NSString)html).Encode(NSStringEncoding.Unicode, true);
            NSAttributedString data = new NSAttributedString(
            encodingData,
            new NSAttributedStringDocumentAttributes()
            {
                DocumentType = NSDocumentType.HTML,

            }, ref error);
        });

我使用的是 Xamarin，因此这些是 C# 代码，但我相信它们在 Swift 和 Obj C 中是相似的。

看起来当系统在页面( View Controller )之间进行转换时，它会尝试阻止任何繁重的任务在 UI 线程上运行。这导致了这个问题。