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我有一些代码可以将课程下载为 JSON、解析它们并将它们放入核心数据中。然后将它们显示在 UITableView 中。目前，当用户有很多课程时，连接有时会超时。因此，我试图在课程进入时解析它们（使用 SBJson），并一次将它们添加到 tableview 中。

两者的代码基本相同，但是新的代码导致tableView的东西启动时崩溃，并报错

"Terminating app due to uncaught exception 
'NSObjectInaccessibleException', reason: 'The NSManagedObject with ID:0x5ad0570 <x-coredata://A21AC71F-175B-423D-BF7D-C67BEE094460/Lessons/p18> has been invalidated.'"

我想知道这两个可能导致此错误的代码清单之间的区别是什么。原始代码在循环中创建每个核心数据对象，但新代码在下载每个核心数据对象时创建它。listViewArray 是用于填充 UITableView 的数组。

我正在使用 SBJsonStreamParser 和 SBJsonStreamParserAdapter 来解析 Json。

我确实有一个有效的实现（未显示），它基本上每次接收到一个新对象时都会调用下面的原始代码（每次都通过接收到的对象的完整循环运行）。不过，我想知道是什么导致了错误，而不仅仅是让某些东西正常工作。

这是原始的非流式代码，在 connectionDidFinishLoading 中调用：

    NSMutableArray *tempListArray = [[NSMutableArray alloc] initWithArray:jsonStreamedData];

    if (listViewArray)
        [listViewArray release];
    listViewArray = [[NSMutableArray alloc] init];

    if(![tempListArray count]){
        UIAlertView *alertView = [[UIAlertView alloc] initWithTitle:@"Message" message:@"No active lessons " delegate:self cancelButtonTitle:@"OK" otherButtonTitles:nil, nil];
        [alertView show];
        [alertView release];
    }
    else {
        MyAppDelegate *appDelegate = (MyAppDelegate *)[[UIApplication sharedApplication] delegate];
        NSError *error = nil;
        [appDelegate.managedObjectContext reset];

        NSManagedObjectContext *managedObjectContext = appDelegate.managedObjectContext;
        for (int i = 0; i < [tempListArray count]; i++) {

            NSFetchRequest *checkRequest = [[NSFetchRequest alloc] init];
            NSEntityDescription *lessonEntity = [NSEntityDescription entityForName:@"Lessons" inManagedObjectContext:managedObjectContext];
            [checkRequest setEntity:lessonEntity];
            NSPredicate *langPredicate = [NSPredicate predicateWithFormat:@"(language = %@)", appDelegate.currentLanguage];
            NSPredicate *userPredicate = [NSPredicate predicateWithFormat:@"(username = %@)", appDelegate.userName];
            NSPredicate *idPredicate = [NSPredicate predicateWithFormat:@"(content_Id = %@)", [[tempListArray objectAtIndex:i] valueForKey:@"id"]];
            [checkRequest setPredicate:[NSCompoundPredicate andPredicateWithSubpredicates:[NSArray arrayWithObjects:langPredicate, userPredicate, idPredicate, nil]]];

            NSArray *checkResults = [managedObjectContext executeFetchRequest:checkRequest error:&error];
            [checkRequest release];

            NSMutableDictionary *tempDict = [[NSMutableDictionary alloc] init];
            if ([checkResults count]) {
                Lessons *lessonObj = [checkResults objectAtIndex:0];
                lessonObj.cards_count = [[tempListArray objectAtIndex:i] valueForKey:@"cards_count"];
                lessonObj.mTitle = [[tempListArray objectAtIndex:i] valueForKey:@"title"];
                lessonObj.sound_Url = [[tempListArray objectAtIndex:i] valueForKey:@"audio_url"];
                lessonObj.mId = [NSNumber numberWithInt:i];
                [tempDict setValue:lessonObj forKey:@"lesson"];
                [tempDict setValue: [[tempListArray objectAtIndex:i]  objectForKey:@"image_url"] forKey:@"image_url"];
                [listViewArray addObject:tempDict];

            }
            else {

                Lessons *newLesson = (Lessons *)[NSEntityDescription insertNewObjectForEntityForName:@"Lessons" inManagedObjectContext:appDelegate.managedObjectContext];
                newLesson.cards_count = [[tempListArray objectAtIndex:i] valueForKey:@"cards_count"];
                newLesson.mTitle = [[tempListArray objectAtIndex:i] valueForKey:@"title"];
                newLesson.sound_Url = [[tempListArray objectAtIndex:i] valueForKey:@"audio_url"];
                newLesson.content_Id = [[tempListArray objectAtIndex:i] valueForKey:@"id"];
                newLesson.username = appDelegate.userName;
                newLesson.language = appDelegate.currentLanguage;
                newLesson.mId = [NSNumber numberWithInt:i];
                [tempDict setValue:newLesson forKey:@"lesson"];
                [tempDict setValue: [[tempListArray objectAtIndex:i]  objectForKey:@"image_url"] forKey:@"image_url"]; 
                [listViewArray addObject:tempDict];

            }
            [tempDict release];
            tempDict = nil;
        }


        if (![appDelegate.managedObjectContext save:&error]) {
            NSLog(@"Core Data Error - %@", [error localizedDescription]);

        }   

        //      NSMutableArray *tempArray = [NSMutableArray arrayWithArray:listViewArray];
        //      [listViewArray removeAllObjects];
        //      [listViewArray addObjectsFromArray:[[tempArray reverseObjectEnumerator] allObjects]];
        //      tempArray = nil;
    }
    [tempListArray release];
}
[mListsTableView reloadData];

这是崩溃的代码，在 parser:foundObject 中调用：循环代码已被删除，因为每次下载新的 Json 对象时都会调用它。

    [jsonStreamedData addObject:dict];
    if (!listViewArray)
        listViewArray = [[NSMutableArray alloc] init];

    MyAppDelegate *appDelegate = (MyAppDelegate *)[[UIApplication sharedApplication] delegate];
    NSError *error = nil;
    [appDelegate.managedObjectContext reset];

    NSManagedObjectContext *managedObjectContext = appDelegate.managedObjectContext;

    NSFetchRequest *checkRequest = [[NSFetchRequest alloc] init];
    NSEntityDescription *lessonEntity = [NSEntityDescription entityForName:@"Lessons" inManagedObjectContext:managedObjectContext];
    [checkRequest setEntity:lessonEntity];
    NSPredicate *langPredicate = [NSPredicate predicateWithFormat:@"(language = %@)", appDelegate.currentLanguage];
    NSPredicate *userPredicate = [NSPredicate predicateWithFormat:@"(username = %@)", appDelegate.userName];
    NSPredicate *idPredicate = [NSPredicate predicateWithFormat:@"(content_Id = %@)", [dict valueForKey:@"id"]];
    [checkRequest setPredicate:[NSCompoundPredicate andPredicateWithSubpredicates:[NSArray arrayWithObjects:langPredicate, userPredicate, idPredicate, nil]]];

    NSArray *checkResults = [managedObjectContext executeFetchRequest:checkRequest error:&error];
    [checkRequest release];

    NSMutableDictionary *tempDict = [[NSMutableDictionary alloc] init];

    if ([checkResults count]) {
        Lessons *lessonObj = [checkResults objectAtIndex:0];
        lessonObj.cards_count = [dict valueForKey:@"cards_count"];
        lessonObj.mTitle = [dict  valueForKey:@"title"];
        lessonObj.sound_Url = [dict valueForKey:@"audio_url"];
        lessonObj.mId = [NSNumber numberWithInt:jsonStreamedData.count - 1]; // This should be equivalent to i from the loop in the first code
        [tempDict setValue:lessonObj forKey:@"lesson"];
        [tempDict setValue: [dict objectForKey:@"image_url"] forKey:@"image_url"];
        [listViewArray addObject:tempDict];

    }
    else {

        Lessons *newLesson = (Lessons *)[NSEntityDescription insertNewObjectForEntityForName:@"Lessons" inManagedObjectContext:appDelegate.managedObjectContext];
        newLesson.cards_count = [dict valueForKey:@"cards_count"];
        newLesson.mTitle = [dict valueForKey:@"title"];
        newLesson.sound_Url = [dict valueForKey:@"audio_url"];
        newLesson.content_Id = [dict valueForKey:@"id"];
        newLesson.username = appDelegate.userName;
        newLesson.language = appDelegate.currentLanguage;
        newLesson.mId = [NSNumber numberWithInt:jsonStreamedData.count - 1];
        [tempDict setValue:newLesson forKey:@"lesson"];
        [tempDict setValue: [dict  objectForKey:@"image_url"] forKey:@"image_url"]; 
        [listViewArray addObject:tempDict];

    }

    [tempDict release];
    tempDict = nil;

    if (![appDelegate.managedObjectContext save:&error]) {
        ALog(@"Core Data Error - %@", [error localizedDescription]);
    }   

    //  NSMutableArray *tempArray = [NSMutableArray arrayWithArray:listViewArray];
    //  [listViewArray removeAllObjects];
    //  [listViewArray addObjectsFromArray:[[tempArray reverseObjectEnumerator] allObjects]];
    //  tempArray = nil;
//[self getListsLocally];
[mListsTableView reloadData];

最后，这里是使用第二个列表时崩溃的实际部分，在 tableView:cellForRowAtIndexPath: 顺便说一下，它在 row == 1 时崩溃，而不是 row == 0。由于某种原因，第 0 行还可以......它永远不会当然，有机会加载其他行。

        titleLabel.text = [[[listViewArray objectAtIndex:indexPath.row] valueForKey:@"lesson"] valueForKey:@"mTitle"]; // CRASH!
        labelCards.text = [NSString stringWithFormat:@"%@ Cards", [[[listViewArray objectAtIndex:indexPath.row]  valueForKey:@"lesson"] valueForKey:@"cards_count"]];

        if([[listViewArray objectAtIndex:indexPath.row] objectForKey:@"userImageObj"] == nil){
            mImageView.backgroundColor = [UIColor grayColor];
            if ([[listViewArray objectAtIndex:indexPath.row] objectForKey:@"isThreadLaunched"] == nil) {
                [NSThread detachNewThreadSelector:@selector(loadImagesInBackground:) toTarget:self withObject:[NSNumber numberWithInt:indexPath.row]];
                [[listViewArray objectAtIndex:indexPath.row] setObject:@"Yes" forKey:@"isThreadLaunched"];
            }
        }else {
            mImageView.image = [[listViewArray objectAtIndex:indexPath.row] objectForKey:@"userImageObj"];
        }
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2 回答 2

3

当您reset在运行提取之前立即调用 managedObjectContext 时，最有可能发生对象失效。调用reset使内存中的对象无效，但在保存之前不会删除它们。如果一个无效的托管对象被另一个对象（例如数组）保留，那么它将在保存后以无效的形式持续存在。当您运行提取时，提取返回无效对象，当您尝试访问它们的属性之一时会导致错误

reset与撤消管理器一起使用时会被调用。它不是通用的“擦除上下文”调用。如果要删除现有对象，则需要获取它们并显式删除它们。

您的代码还有其他一些问题。即使您没有创建数组，您也release可以调用它。checkRequest这可能会导致数组随机消失。同样，这listViewArray似乎是一个类属性，但您从不使用访问器表单，例如self.listViewArray确保正确保留。

于 2011-08-29T20:31:53.957 回答
1

最可能的原因是解析器未在主线程上运行，并且您在主线程和解析器中使用相同的 ManagedObjectContext - 您不能这样做 - 保证会导致各种奇怪的行为。

您需要在解析器中创建一个新的 ManagedObjectContext 并将其与主线程的 ManagedObjectContext 的 persistentStore 相关联

CoreData 框架对此非常清楚 - 您不能跨线程边界共享 ManagedObjectContext

于 2011-08-28T22:48:12.720 回答