我有一个基于核心数据的应用程序，它有一个对象（列表）与许多对象（列表项）的关系。我正在设备之间同步数据，作为其中一部分，我从后台线程中的XML文件导入列表（通过NSOperation子类）。
当我更新现有列表时，我删除了所有旧列表项（来自特定于该线程的NSManagedObjectContext）并将其替换为XML文件中的新列表...删除通过枚举来处理该列表的项目：
for (ListItemCD *item in listToUpdate.listItems) {
[self.importContext deleteObject:item];
}
但是，有一段时间，我在枚举期间遇到了崩溃：
*由于未捕获的异常'NSGenericException'而终止应用程序，原因：'* 集合＆lt; _NSFaultingMutableSet：0x4fcfcb0＆gt;在被列举时被突变。
我不知道从哪里开始寻找问题的原因。在枚举发生时，我不会修改代码的任何其他部分中的列表。可以同时存在多个线程，因为导入/更新了不同的列表...将在另一个线程中保存上下文导致问题 - 因为它还通知主要上下文（如果它与枚举同时发生） ？
如果有帮助，这里是来自我的NSOperation子类的“main”函数的代码（我从Core Data中删除旧的列表项，并通过解析XML数据来更新列表）：
- (void)main {
// input the xml data into GDataXML
NSData *xmlData = [[NSMutableData alloc] initWithContentsOfFile:self.filePath];
NSError *error;
GDataXMLDocument *doc = [[GDataXMLDocument alloc] initWithData:xmlData options:0 error:&error];
// get the list name (so that I know which list to update)
NSString *listName;
NSArray *listNames = [doc.rootElement elementsForName:@"listName"];
if (listNames.count > 0) {
GDataXMLElement *listNameElement = (GDataXMLElement *) [listNames objectAtIndex:0];
listName = listNameElement.stringValue;
// NSLog(@"listName: %@", listName);
// perform a fetch to find the old list with the same name (if there is one)
NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
NSEntityDescription *entity = [NSEntityDescription entityForName:@"SubListCD" inManagedObjectContext:self.importContext];
[fetchRequest setEntity:entity];
NSPredicate *predicate = [NSPredicate predicateWithFormat:@"%K like %@", @"listName", listName];
[fetchRequest setPredicate:predicate];
NSError *error;
NSArray *fetchedObjects = [self.importContext executeFetchRequest:fetchRequest error:&error];
// NSLog(@"fetchedObjects count: %d", [fetchedObjects count]);
[fetchRequest release];
/*
// if I found the list, update its data
*/
if ([fetchedObjects count] == 1) {
SubListCD *listToUpdate = [fetchedObjects objectAtIndex:0];
// get the list icon name
NSArray *listIconNames = [doc.rootElement elementsForName:@"listIconName"];
if (listIconNames.count > 0) {
GDataXMLElement *listIconNameElement = (GDataXMLElement *) [listIconNames objectAtIndex:0];
NSString *listIconName = listIconNameElement.stringValue;
// NSLog(@"listIconName: %@", listIconName);
listToUpdate.listIconName = [NSString stringWithString:listIconName];
}
// get the isChecklist BOOL
NSArray *isChecklistBools = [doc.rootElement elementsForName:@"isChecklist"];
if (isChecklistBools.count > 0) {
GDataXMLElement *isChecklistElement = (GDataXMLElement *) [isChecklistBools objectAtIndex:0];
NSString *isChecklist = isChecklistElement.stringValue;
// NSLog(@"isChecklist: %@", isChecklist);
listToUpdate.isCheckList = [NSNumber numberWithBool:[isChecklist isEqualToString:@"YES"]];
}
// get the itemsToTop BOOL
NSArray *itemsToTopBools = [doc.rootElement elementsForName:@"itemsToTop"];
if (itemsToTopBools.count > 0) {
GDataXMLElement *itemsToTopElement = (GDataXMLElement *) [itemsToTopBools objectAtIndex:0];
NSString *itemsToTop = itemsToTopElement.stringValue;
// NSLog(@"itemsToTop: %@", itemsToTop);
listToUpdate.itemsToTop = [NSNumber numberWithBool:[itemsToTop isEqualToString:@"YES"]];
}
// get the includeInBadgeCount BOOL
NSArray *includeInBadgeCountBools = [doc.rootElement elementsForName:@"includeInBadgeCount"];
if (includeInBadgeCountBools.count > 0) {
GDataXMLElement *includeInBadgeCountElement = (GDataXMLElement *) [includeInBadgeCountBools objectAtIndex:0];
NSString *includeInBadgeCount = includeInBadgeCountElement.stringValue;
// NSLog(@"includeInBadgeCount: %@", includeInBadgeCount);
listToUpdate.includeInBadgeCount = [NSNumber numberWithBool:[includeInBadgeCount isEqualToString:@"YES"]];
}
// get the list's creation date
NSArray *listCreatedDates = [doc.rootElement elementsForName:@"listDateCreated"];
if (listCreatedDates.count > 0) {
GDataXMLElement *listDateCreatedElement = (GDataXMLElement *) [listCreatedDates objectAtIndex:0];
NSString *listDateCreated = listDateCreatedElement.stringValue;
// NSLog(@"listDateCreated: %@", listDateCreated);
listToUpdate.dateCreated = [self dateFromString:listDateCreated];
}
// get the list's modification date
NSArray *listModifiedDates = [doc.rootElement elementsForName:@"listDateModified"];
if (listModifiedDates.count > 0) {
GDataXMLElement *listDateModifiedElement = (GDataXMLElement *) [listModifiedDates objectAtIndex:0];
NSString *listDateModified = listDateModifiedElement.stringValue;
// NSLog(@"listDateModified: %@", listDateModified);
listToUpdate.dateModified = [self dateFromString:listDateModified];
}
// NOTE: it's okay to get the displayOrder from index.plist here, since these update operations aren't called until after index.plist is loaded from Dropbox
// get a reference to the documents directory
NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSString *documentsDirectory = [paths objectAtIndex:0];
// get the file path of the index.plist file
NSString *indexFilePath = [documentsDirectory stringByAppendingPathComponent:@"index.plist"];
// build an array with the names of the lists in the index
NSMutableArray *listsIndexArray = [NSMutableArray arrayWithContentsOfFile:indexFilePath];
int listIndex = [listsIndexArray indexOfObject:listName];
listToUpdate.displayOrder = [NSNumber numberWithInt:listIndex];
// remove the old list items from the listToUpdate, since I'll be adding them from scratch from the XML file
for (ListItemCD *item in listToUpdate.listItems) {
[self.importContext deleteObject:item];
}
// get an array of the list items so I can add them all
NSArray *listItems = [doc.rootElement elementsForName:@"item"];
if (listItems.count > 0) {
int counter = 0;
for (GDataXMLElement *item in listItems) {
// create the new item
ListItemCD *newItem = [NSEntityDescription insertNewObjectForEntityForName:@"ListItemCD" inManagedObjectContext:self.importContext];
// item name
NSArray *itemNames = [item elementsForName:@"itemName"];
if (itemNames.count > 0) {
GDataXMLElement *itemNameElement = (GDataXMLElement *) [itemNames objectAtIndex:0];
NSString *itemName = itemNameElement.stringValue;
// NSLog(@"itemName: %@", itemName);
newItem.itemName = [NSString stringWithString:itemName];
} else continue;
// item note
NSArray *itemNotes = [item elementsForName:@"itemNote"];
if (itemNotes.count > 0) {
GDataXMLElement *itemNoteElement = (GDataXMLElement *) [itemNotes objectAtIndex:0];
NSString *itemNote = itemNoteElement.stringValue;
// NSLog(@"itemNote: %@", itemNote);
newItem.itemNote = [NSString stringWithString:itemNote];
} else continue;
// itemReadOnly BOOL
NSArray *itemReadOnlyBools = [item elementsForName:@"itemReadOnly"];
if (itemReadOnlyBools.count > 0) {
GDataXMLElement *itemReadOnlyElement = (GDataXMLElement *) [itemReadOnlyBools objectAtIndex:0];
NSString *itemReadOnly = itemReadOnlyElement.stringValue;
// NSLog(@"itemReadOnly: %@", itemReadOnly);
newItem.itemReadOnly = [NSNumber numberWithBool:[itemReadOnly isEqualToString:@"YES"]];
} else continue;
// TODO: check my dates.. not sure if this will hold up in other locales
// item creation date
NSArray *itemCreatedDates = [item elementsForName:@"dateCreated"];
if (itemCreatedDates.count > 0) {
GDataXMLElement *dateCreatedElement = (GDataXMLElement *) [itemCreatedDates objectAtIndex:0];
NSString *dateCreated = dateCreatedElement.stringValue;
// NSLog(@"dateCreated: %@", dateCreated);
newItem.dateCreated = [self dateFromString:dateCreated];
} else continue;
// item modification date
NSArray *itemModifiedDates = [item elementsForName:@"dateModified"];
if (itemModifiedDates.count > 0) {
GDataXMLElement *dateModifiedElement = (GDataXMLElement *) [itemModifiedDates objectAtIndex:0];
NSString *dateModified = dateModifiedElement.stringValue;
// NSLog(@"dateModified: %@", dateModified);
newItem.dateModified = [self dateFromString:dateModified];
} else continue;
// item completed BOOL
NSArray *itemCompletedBools = [item elementsForName:@"itemCompleted"];
if (itemCompletedBools.count > 0) {
GDataXMLElement *itemCompletedElement = (GDataXMLElement *) [itemCompletedBools objectAtIndex:0];
NSString *itemCompleted = itemCompletedElement.stringValue;
// NSLog(@"itemCompleted: %@", itemCompleted);
newItem.itemCompleted = [NSNumber numberWithBool:[itemCompleted isEqualToString:@"YES"]];
} else continue;
// item completed date
NSArray *itemCompletedDates = [item elementsForName:@"dateCompleted"];
if (itemCompletedDates.count > 0) {
GDataXMLElement *dateCompletedElement = (GDataXMLElement *) [itemCompletedDates objectAtIndex:0];
NSString *dateCompleted = dateCompletedElement.stringValue;
// NSLog(@"dateCompleted string: %@", dateCompleted);
newItem.dateCompleted = [self dateFromString:dateCompleted];
// NSLog(@"dateCompleted: %@", newItem.dateCompleted);
} else continue;
// display order
newItem.displayOrder = [NSNumber numberWithInt:counter];
counter++;
// assign the new item to the listToUpdate
newItem.list = listToUpdate;
}
}
// the list is now imported, so set isUpdating back to NO
listToUpdate.isUpdating = [NSNumber numberWithBool:NO];
// Save the context.
NSError *saveError = nil;
if (![self.importContext save:&saveError]) {
NSLog(@"Unresolved error %@, %@", saveError, [saveError userInfo]);
abort();
}
else {
NSLog(@"saved after UPDATING a list while syncing!");
}
}
else {
NSLog(@"UpdateOperation - couldn't find an old version of the list to update!: %@", listName);
}
}
[doc release];
[xmlData release];
}
感谢您的任何建议。
答案 0 :(得分：30)
错误消息中有一些线索，您可以在其中看到列出的类NSFaultingMutableSet。实际上，您枚举的集合实际上只是可能按需加载数据的多对多关系的代理。由于在枚举期间集合中的项目被标记为已删除，因此存在一些集合在您枚举时会“更改”并且您将看到该错误的可能性。
处理此问题的常用方法是创建集合的副本并枚举副本。对此的简单方法就是：
NSSet *iterItems = [[list.items copy] autorelease];
for (ListItemCD *item in iterItems) { ... }
但是我在处理核心数据时发现，-copy实际上并没有返回副本，但通常只是另一个错误代理。所以我选择以这种方式复制集合：
NSSet *iterItems = [NSSet setWithSet:list.items];
for (ListItemCD *item in iterItems) { ... }