Ios MagicalRecords通过图像获取在后台线程中持久化？

我有以下代码：

dispatch_async(dispatch_get_main_queue(), ^{
    NSManagedObjectContext *localContext = [NSManagedObjectContext contextForCurrentThread];

    Item *newItem = [Item createInContext:localContext];
    newItem.title = NULL_TO_NIL([itemJson valueForKey:@"title"]);
    newItem.image_url = NULL_TO_NIL([itemJson valueForKey:@"image_url"]);
    newItem.order_id = @([[self largestOrderId] intValue] + 1);

    NSURL *url = [NSURL URLWithString:newItem.image_url];
    NSData *data = [[NSData alloc] initWithContentsOfURL: url];
    if (data == nil) {
        NSLog(@"Image data is nil from %@", url);
    } else {
        NSLog(@"Image fetched in saveItemFromJson for cid:%@ order_id:%@", newItem.cid, newItem.order_id);
        newItem.image = [UIImage imageWithData:data];
    }

    if (![localContext hasChanges]) {
        NSLog(@"No local change detected. Quitting");
        return;
    }

    [localContext saveToPersistentStoreWithCompletion:^(BOOL success, NSError *error) {
        if (!success)
            NSLog(@"Error: %@", [error localizedDescription]);
        else
            NSLog(@"Item persisted for cid:%@ order_id:%@", newItem.cid, newItem.order_id);
    }];
});

我似乎得到了以下很多信息：

2013-02-13 18:55:47.404 Giordano.iPhone[13956:c07] -[NSManagedObjectContext(MagicalSaves) MR_saveWithOptions:completion:](0x8386a90) → Saving <NSManagedObjectContext (0x8386a90): *** DEFAULT ***> on *** MAIN THREAD ***
2013-02-13 18:55:47.404 Giordano.iPhone[13956:c07] -[NSManagedObjectContext(MagicalSaves) MR_saveWithOptions:completion:](0x8386a90) → Save Parents? 1
2013-02-13 18:55:47.404 Giordano.iPhone[13956:c07] -[NSManagedObjectContext(MagicalSaves) MR_saveWithOptions:completion:](0x8386a90) → Save Synchronously? 0
2013-02-13 18:55:47.497 Giordano.iPhone[13956:c07] Image fetched in saveItemFromJson for cid:7218 order_id:10
2013-02-13 18:55:47.497 Giordano.iPhone[13956:c07] -[NSManagedObjectContext(MagicalSaves) MR_saveWithOptions:completion:](0x8386a90) → Saving <NSManagedObjectContext (0x8386a90): *** DEFAULT ***> on *** MAIN THREAD ***
2013-02-13 18:55:47.498 Giordano.iPhone[13956:c07] -[NSManagedObjectContext(MagicalSaves) MR_saveWithOptions:completion:](0x8386a90) → Save Parents? 1
2013-02-13 18:55:47.498 Giordano.iPhone[13956:c07] -[NSManagedObjectContext(MagicalSaves) MR_saveWithOptions:completion:](0x8386a90) → Save Synchronously? 0
2013-02-13 18:55:47.499 Giordano.iPhone[13956:c07] -[NSManagedObjectContext(MagicalRecord) MR_contextWillSave:](0x8386a90) Context DEFAULT is about to save. Obtaining permanent IDs for new 10 inserted objects
2013-02-13 18:55:47.501 Giordano.iPhone[13956:c07] -[NSManagedObjectContext(MagicalSaves) MR_saveWithOptions:completion:](0x8385aa0) → Saving <NSManagedObjectContext (0x8385aa0): *** BACKGROUND SAVING (ROOT) ***> on *** MAIN THREAD ***
2013-02-13 18:55:47.502 Giordano.iPhone[13956:c07] -[NSManagedObjectContext(MagicalSaves) MR_saveWithOptions:completion:](0x8385aa0) → Save Parents? 0
2013-02-13 18:55:47.502 Giordano.iPhone[13956:c07] -[NSManagedObjectContext(MagicalSaves) MR_saveWithOptions:completion:](0x8385aa0) → Save Synchronously? 1
2013-02-13 18:55:47.502 Giordano.iPhone[13956:c07] -[NSManagedObjectContext(MagicalRecord) MR_contextWillSave:](0x8385aa0) Context BACKGROUND SAVING (ROOT) is about to save. Obtaining permanent IDs for new 10 inserted objects
2013-02-13 18:55:47.505 Giordano.iPhone[13956:c07] __70-[NSManagedObjectContext(MagicalSaves) MR_saveWithOptions:completion:]_block_invoke21(0x8385aa0) → Finished saving: <NSManagedObjectContext (0x8385aa0): *** BACKGROUND SAVING (ROOT) ***> on *** MAIN THREAD ***
2013-02-13 18:55:47.505 Giordano.iPhone[13956:c07] -[NSManagedObjectContext(MagicalSaves) MR_saveWithOptions:completion:](0x8385aa0) NO CHANGES IN ** BACKGROUND SAVING (ROOT) ** CONTEXT - NOT SAVING

我避免使用

saveinbackgroundithblock

，因为它已被弃用（文档需要更新？）

我的代码有什么问题吗

更新

---

我的团队认为MagicalRecord目前还太过时了。我们已经将代码从MR完全迁移回CoreData。谢谢你的关注

您是否尝试过

先生只保存自己并完成：

？

我也遇到过同样的问题！只有在没有MR

以下是我的解决方案：

NSManagedObject+MyCategory.h

+ (void)saveDataInBackgroundWithBlock:(void(^)(NSManagedObjectContext *localContext))saveBlock
                           completion:(void(^)(void))completion;

+ (NSManagedObjectContext *)newMergableBackgroundThreadContext;

- (void)saveWithCompletion:(void(^)(void))completion;

m

下面是使用示例：

[NSManagedObjectContext saveDataInBackgroundWithBlock:^(NSManagedObjectContext *localContext){
// do your stuff with local context
} completion:^{
// handle completion, update UI or something
}];

---

几周前，我在使用MR时遇到了类似的问题。最后，我决定放弃它，自己做一切。这不是你问题的真正解决办法，但我放弃它的理由是合理的。您可能需要去查看MR.的实际来源。大部分文档是不正确的，相当一部分库只能通过阅读来源来学习。最有可能的问题是试图与MR

如果您的代码是针对iOS6+，那么您应该只使用上下文设置。使用dispatch\u async可能也是一个问题。通过使用[NSManagedContext performBlock:]方法让核心数据管理线程可能更安全

如果您使用的是iOS5或更低版本，则子上下文和performBlock:代码不起作用。最简单的解决方案是不让核心数据进入线程。在进入新线程/块之前，从核心数据中提取所需信息。将该数据传递到块中并执行任何必要的处理。然后将其返回到字典/某种类型的对象中的主线程，并在那里执行核心数据保存

还有一个附带说明，我遇到这个问题是因为我下载了图像并将其保存到核心数据中，您可能想看看我在过去几周提出/解决的与此相关的问题。也许可以节省你以后拔头发的时间：

这最终导致我使用自己的存储机制而不是文件的核心数据，并最终导致我遇到以下问题/解决方案：

---

你的主要目标是什么？谢谢。我也把MR

+ (NSManagedObjectContext *)newMergableBackgroundThreadContext {
    NSManagedObjectContext *context = [[NSManagedObjectContext alloc] initWithConcurrencyType:NSPrivateQueueConcurrencyType];
    context.parentContext = [self mainThreadContext];
    [context.userInfo setObject:[NSNumber numberWithInteger:VKCoreDataManagedObjectContextIDTempBackground]
                         forKey:@"contextID"];
    [context.userInfo setObject:kVKCoreDataManagedObjectContextBackgroundTemp
                         forKey:@"contextDebugName"];
    VKDLog(@"* New mergable backround context created! *");
    return context;
}

+ (void)saveDataInBackgroundWithBlock:(void (^)(NSManagedObjectContext *))saveBlock completion:(void (^)(void))completion {
    NSManagedObjectContext *tempContext = [self newMergableBackgroundThreadContext];
    [tempContext performBlock:^{

        if (saveBlock) {
            saveBlock(tempContext);
        }

        if ([tempContext hasChanges]) {
            [tempContext saveWithCompletion:completion];
        } else {
            dispatch_async(dispatch_get_main_queue(), ^{
                if (completion) {
                    completion();
                }
            });
        }
    }];
}

- (void)saveWithCompletion:(void(^)(void))completion {
    [self performBlock:^{
        NSError *error = nil;
        if ([self save:&error]) {
            NSNumber *contextID = [self.userInfo objectForKey:@"contextID"];
            if (contextID.integerValue == VKCoreDataManagedObjectContextIDMainThread) {
                dispatch_async(dispatch_get_main_queue(), ^{
                    if (completion) {
                        completion();
                    }
                });
            }
            [[self class] logContextSaved:self];
            if (self.parentContext) {
                [self.parentContext saveWithCompletion:completion];
            }
        } else {
            [VKCoreData handleError:error];
            dispatch_async(dispatch_get_main_queue(), ^{
                if (completion) {
                    completion();
                }
            });
        }
    }];
}

[NSManagedObjectContext saveDataInBackgroundWithBlock:^(NSManagedObjectContext *localContext){
// do your stuff with local context
} completion:^{
// handle completion, update UI or something
}];