Swift fetchResultsController：實例成員不能用於'ViewController'類型

Question

我正在研究Udacity上的CoreData項目，並且難以實現fetchedResultsController。我試圖實例fetchedResultsController帶有水上變種，但它提示我「實例成員背景不能在類型‘的ViewController’使用我的代碼是這樣的：

//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) 
    }() 

這樣做會給我一個錯誤線在「上下文「在fetchedResultsController表示：

實例成員‘？！方面的ViewController‘

有什麼我做錯了任何意見是非常讚賞’不能在使用類型’，感謝

Answer 1

你需要明確使用self在慵懶的屬性指的是context時：

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