小编lou*_*nsa的帖子

我的应用程序使用CoreData,一个叫模型:mupo-ios.xcdatamodel.此模型是原始模型的第二个版本:Model.xcdatamodeld.我正在使用managedObjectContext通过文件:

        NSURL *url = [[[NSFileManager defaultManager] URLsForDirectory:NSLibraryDirectory inDomains:NSUserDomainMask] lastObject];
        url = [url URLByAppendingPathComponent:@"MyDocument"];

        self.document = [[UIManagedDocument alloc] initWithFileURL:url];

        // Set our document up for automatic migrations
        NSDictionary *options = [NSDictionary dictionaryWithObjectsAndKeys:
                                 [NSNumber numberWithBool:YES], NSMigratePersistentStoresAutomaticallyOption,
                                 [NSNumber numberWithBool:YES], NSInferMappingModelAutomaticallyOption, nil];            
        self.document.persistentStoreOptions = options;
    }

后来,我访问managedObjectContext:

    self.managedObjectContext = self.document.managedObjectContext;

现在,我想直接访问主要上下文,这里是代码:

- (NSManagedObjectContext *)mainContext {
    if (!_mainContext) {
        _mainContext = [[NSManagedObjectContext alloc] initWithConcurrencyType:NSMainQueueConcurrencyType];
        _mainContext.persistentStoreCoordinator = self.persistentStoreCoordinator;
    }
    return _mainContext;
}

问题是当我尝试指定managedObjectModel:

- (NSManagedObjectModel *)managedObjectModel …