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。 helper方法从html字符串格式化NSAttributedString。当移动到后台时应用程序会崩溃，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，但是在第三个，第四个，第四个，。 ..细胞。
这是我的帮助方法和堆栈跟踪。知道为什么我在退出应用程序时崩溃了吗？
#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
答案 0 :(得分：0)
几个小时后，我也遇到了这个问题。
您只需要包装用于将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);
});
我正在使用Xamarin，所以它们是C＃代码，但我相信它们在Swift和Obj C中是相似的。
看起来像系统在页面之间进行转换（视图控制器）时，它将尝试防止在UI Thread上运行任何繁重的任务。造成此问题的原因。