问题描述
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我有一个基于核心数据的应用程序，该应用程序具有一个对象（列表）与许多对象（列表项）的关系。我正在努力在设备之间同步数据，并且作为其中一部分，我从后台线程中的XML文件中导入列表（通过NSOperation子类）。
当我更新现有列表时，我删除了所有旧列表项（从特定于该线程的NSManagedobjectContext中），并用XML文件中的新列表项替换了它们。删除操作通过枚举以下项来处理：该列表：
for (ListItemCD *item in listToUpdate.listItems) {
[self.importContext deleteObject:item];
}
- (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];
}
解决方法
错误消息中有一些线索，您可以在其中看到列出的类“ 2”。确实，您要枚举的集合实际上只是一对多关系的代理，这将潜在地按需加载数据。由于在枚举过程中集合中的项目被标记为已删除，因此在枚举集合时某些集合可能会“更改”，并且您会看到该错误。
解决此问题的常用方法是创建集合的副本并枚举副本。天真的方法是：
NSSet *iterItems = [[list.items copy] autorelease];
for (ListItemCD *item in iterItems) { ... }
NSSet *iterItems = [NSSet setWithSet:list.items];
for (ListItemCD *item in iterItems) { ... }