ios - 使用 MagicalRecord 在后台执行获取请求

Question

这是我目前所拥有的:

NSManagedObjectContext *privateContext = [NSManagedObjectContext MR_context];
[privateContext performBlock:^{
        Cat* object = [Cat MR_findFirstByAttribute:@"id" withValue:catId inContext:privateContext];
        // Convert your fetched objects into object IDs which can be pulled out of the main context
        NSString *privateObjectID = [object valueForKey:@"objectID"];

        // Return to our main thread
        dispatch_async(dispatch_get_main_queue(), ^{
            ???
        });
    }];

这是正确的做法吗？如果是这样，我如何让我的对象回到主线程？ (上面的 ??? 区域)

如果我这样做:

NSManagedObjectContext* context = [NSManagedObjectContext MR_contextForCurrentThread];
Cat* object = [Cat MR_findFirstByAttribute:@"id" withValue:catId inContext:context];

UI 被阻塞了，所以我想弄清楚如何在不阻塞主线程的情况下进行提取。

Answer 1

block 内的代码(在主线程上执行的代码)应该是:

NSManagedObjectContext* c = [NSManagedObjectContext MR_contextForCurrentThread];
Cat* o = (Cat*)[context objectWithID:object.objectID];
//access `o` so it will get faulted in by the main context
//I think you could use: [o valueForKey:nil] or [o didAccessValueForKey:nil]

重要的是在从主上下文访问它们时将 BG 获取的对象保存在(协调器)缓存中。