只能在使用队列创建的NSManagedObjectContext上使用-performBlock :.

Question

我想对Core Data使用多线程.我在NSManageObjects中解析xml文件.我使用下面的代码,我得到运行时错误Can only use -performBlock: on an NSManagedObjectContext that was created with a queue.怎么了？

//xmlParser

- (void)main
{
    dispatch_queue_t queueB = dispatch_queue_create("Create Books", NULL);
    dispatch_async(queueB, ^{
        // Opening xml
        // ...
        NSManagedObjectContext* context = [[NSManagedObjectContext alloc] init];
        [context setPersistentStoreCoordinator:mainContext].persistentStoreCoordinator];
        [context performBlock:^{
             // ...
             [self _parseNode:container_node appendTo:books inContext:context];
             // ...
             NSError* error = nil;
             [context save:&error];
             [mainContext performBlock:^{
                 NSError* parentError = nil;
                 [mainContext save:&parentError];
             }];
         }];
         [context release];
     });
     dispatch_release(queueB);
}

- (int)_parseNode:(axlNode*)inode appendTo:(NSMutableArray*)ioarray inContext:(NSManagedObjectContext*)context
{
    // ...
    [context executeFetchRequest:request error:&error];
    //...
}

Answer 1

performBlock只能用的被管理对象的上下文(MOC)中使用NSMainQueueConcurrencyType或 NSPrivateQueueConcurrencyType.在您的情况下,您应该创建上下文

NSManagedObjectContext *context = [[NSManagedObjectContext alloc]
                     initWithConcurrencyType:NSPrivateQueueConcurrencyType];

并且无需创建调度队列或使用dispatch_async().MOC创建并管理自己的队列,并performBlock确保在MOC队列上执行该块.