Swift fetchResultsController：实例成员不能用于'ViewController'类型

Question

我正在研究Udacity上的CoreData项目，并且难以实现fetchedResultsController。我试图实例fetchedResultsController带有水上变种，但它提示我“实例成员背景不能在类型‘的ViewController’使用我的代码是这样的：

//AppDelegate 
class AppDelegate: UIResponder, UIApplicationDelegate { 

    var window: UIWindow? 
    let stack = CoreDataStack(modelName: "Model") 
    ... 
} 

//ViewController 
class ViewController: UIViewController, UICollectionViewDataSource, UICollectionViewDelegate, MKMapViewDelegate{ 

    lazy var context: NSManagedObjectContext = { 
     let appDelegate = UIApplication.shared.delegate as! AppDelegate 
     return appDelegate.stack!.context 
    }() 

    lazy var fetchedResultsController: NSFetchedResultsController<NSFetchRequestResult> = { 
     let fetchedRequest = NSFetchRequest<NSFetchRequestResult>(entityName: "Photo") 
     fetchedRequest.sortDescriptors = [] 

     return NSFetchedResultsController(fetchRequest: fetchedRequest, managedObjectContext: context, sectionNameKeyPath: nil, cacheName: nil) 
    }() 

这样做会给我一个错误线在“上下文“在fetchedResultsController表示：

实例成员‘？！方面的ViewController‘

有什么我做错了任何意见是非常赞赏’不能在使用类型’，感谢

Answer 1

你需要明确使用self在慵懒的属性指的是context时：

return NSFetchedResultsController(fetchRequest: fetchedRequest, managedObjectContext: self.context, sectionNameKeyPath: nil, cacheName: nil)