最佳答案
“集合在枚举时发生了变异”
我被一个问题困住了好几个小时，在阅读了关于 stackoverflow 的所有相关内容(并应用了所有找到的建议)之后，我现在正式需要帮助了。; o)
背景是这样的:
在我的 iPhone 项目中，我需要在后台导入数据并将其插入到托管对象上下文中。根据这里发现的建议，以下是我正在做的:
- 保存主机
- Instantiate a background moc with the persistent store coordinator used by the main moc
- 将我的控制器注册为后台 moc 的 NSManagedObjectContextDidSaveNotification 通知的观察者
- Call the import method on a background thread
- 每次接收到数据时，将其插入到后台 moc 中
- 导入所有数据后，保存后台 moc
- Merge the changes into the main moc, on the main thread
- 将我的控制器注销为通知的观察者
- Reset and release the background moc
有时候(随机) ，例外..。
*** Terminating app due to uncaught exception 'NSGenericException', reason: '*** Collection <__NSCFSet: 0x5e0b930> was mutated while being enumerated...
... 在后台 moc 上调用 ExecuteFetchRequest 时引发，以检查导入的数据是否已经存在于数据库中。我想知道是什么在变异集合，因为在 import 方法之外没有运行任何东西。
我已经包含了我的控制器和测试实体的全部代码(我的项目由这两个类和应用程序委托组成，它们没有被修改) :
//
// RootViewController.h
// FK1
//
// Created by Eric on 09/08/10.
// Copyright (c) 2010 __MyCompanyName__. All rights reserved.
//
#import <CoreData/CoreData.h>
@interface RootViewController : UITableViewController <NSFetchedResultsControllerDelegate> {
NSManagedObjectContext *managedObjectContext;
NSManagedObjectContext *backgroundMOC;
}
@property (nonatomic, retain) NSManagedObjectContext *managedObjectContext;
@property (nonatomic, retain) NSManagedObjectContext *backgroundMOC;
@end
//
// RootViewController.m
// FK1
//
// Created by Eric on 09/08/10.
// Copyright (c) 2010 __MyCompanyName__. All rights reserved.
//
#import "RootViewController.h"
#import "FK1Message.h"
@implementation RootViewController
@synthesize managedObjectContext;
@synthesize backgroundMOC;
- (void)viewDidLoad {
[super viewDidLoad];
self.navigationController.toolbarHidden = NO;
UIBarButtonItem *refreshButton = [[UIBarButtonItem alloc] initWithBarButtonSystemItem:UIBarButtonSystemItemRefresh target:self action:@selector(refreshAction:)];
self.toolbarItems = [NSArray arrayWithObject:refreshButton];
}
#pragma mark -
#pragma mark ACTIONS
- (void)refreshAction:(id)sender {
// If there already is an import running, we do nothing
if (self.backgroundMOC != nil) {
return;
}
// We save the main moc
NSError *error = nil;
if (![self.managedObjectContext save:&error]) {
NSLog(@"error = %@", error);
abort();
}
// We instantiate the background moc
self.backgroundMOC = [[[NSManagedObjectContext alloc] init] autorelease];
[self.backgroundMOC setPersistentStoreCoordinator:[self.managedObjectContext persistentStoreCoordinator]];
// We call the fetch method in the background thread
[self performSelectorInBackground:@selector(_importData) withObject:nil];
}
- (void)_importData {
NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(backgroundMOCDidSave:) name:NSManagedObjectContextDidSaveNotification object:self.backgroundMOC];
FK1Message *message = nil;
NSFetchRequest *fetchRequest = nil;
NSEntityDescription *entity = [NSEntityDescription entityForName:@"FK1Message" inManagedObjectContext:self.backgroundMOC];
NSPredicate *predicate = nil;
NSArray *results = nil;
// fake import to keep this sample simple
for (NSInteger index = 0; index < 20; index++) {
predicate = [NSPredicate predicateWithFormat:@"msgId == %@", [NSString stringWithFormat:@"%d", index]];
fetchRequest = [[[NSFetchRequest alloc] init] autorelease];
[fetchRequest setEntity:entity];
[fetchRequest setPredicate:predicate];
// The following line sometimes randomly throw the exception :
// *** Terminating app due to uncaught exception 'NSGenericException', reason: '*** Collection <__NSCFSet: 0x5b71a00> was mutated while being enumerated.
results = [self.backgroundMOC executeFetchRequest:fetchRequest error:NULL];
// If the message already exist, we retrieve it from the database
// If it doesn't, we insert a new message in the database
if ([results count] > 0) {
message = [results objectAtIndex:0];
}
else {
message = [NSEntityDescription insertNewObjectForEntityForName:@"FK1Message" inManagedObjectContext:self.backgroundMOC];
message.msgId = [NSString stringWithFormat:@"%d", index];
}
// We update the message
message.updateDate = [NSDate date];
}
// We save the background moc which trigger the backgroundMOCDidSave: method
[self.backgroundMOC save:NULL];
[[NSNotificationCenter defaultCenter] removeObserver:self name:NSManagedObjectContextDidSaveNotification object:self.backgroundMOC];
[self.backgroundMOC reset]; self.backgroundMOC = nil;
[pool drain];
}
- (void)backgroundMOCDidSave:(NSNotification*)notification {
if (![NSThread isMainThread]) {
[self performSelectorOnMainThread:@selector(backgroundMOCDidSave:) withObject:notification waitUntilDone:YES];
return;
}
// We merge the background moc changes in the main moc
[self.managedObjectContext mergeChangesFromContextDidSaveNotification:notification];
}
@end
//
// FK1Message.h
// FK1
//
// Created by Eric on 09/08/10.
// Copyright 2010 __MyCompanyName__. All rights reserved.
//
#import <CoreData/CoreData.h>
@interface FK1Message : NSManagedObject
{
}
@property (nonatomic, retain) NSString * msgId;
@property (nonatomic, retain) NSDate * updateDate;
@end
//
// FK1Message.m
// FK1
//
// Created by Eric on 09/08/10.
// Copyright 2010 __MyCompanyName__. All rights reserved.
//
#import "FK1Message.h"
@implementation FK1Message
#pragma mark -
#pragma mark PROPERTIES
@dynamic msgId;
@dynamic updateDate;
@end
这就是全部！整个项目都在这里。没有表视图，没有 NSFetcheResultsController，只有一个在后台 moc 上导入数据的后台线程。
在这种情况下，什么会使集合发生突变？
我很确定我错过了一些显而易见的事情，这让我很抓狂。
EDIT:
下面是完整的堆栈跟踪:
2010-08-10 10:29:11.258 FK1[51419:1b6b] *** Terminating app due to uncaught exception 'NSGenericException', reason: '*** Collection <__NSCFSet: 0x5d075b0> was mutated while being enumerated.<CFBasicHash 0x5d075b0 [0x25c6380]>{type = mutable set, count = 0,
entries =>
}
'
*** Call stack at first throw:
(
0 CoreFoundation 0x0255d919 __exceptionPreprocess + 185
1 libobjc.A.dylib 0x026ab5de objc_exception_throw + 47
2 CoreFoundation 0x0255d3d9 __NSFastEnumerationMutationHandler + 377
3 CoreData 0x02287702 -[NSManagedObjectContext executeFetchRequest:error:] + 4706
4 FK1 0x00002b1b -[RootViewController _fetchData] + 593
5 Foundation 0x01d662a8 -[NSThread main] + 81
6 Foundation 0x01d66234 __NSThread__main__ + 1387
7 libSystem.B.dylib 0x9587681d _pthread_start + 345
8 libSystem.B.dylib 0x958766a2 thread_start + 34
)
terminate called after throwing an instance of 'NSException'
