fetchRequest is null when calling second time

问题

The code is

let request: NSFetchRequest<NSFetchRequestResult> = Item.fetchRequest()
print(request)

Item is an entity of Core Data.

The first execution is correct, but when execute it again error occurs Thread 12: EXC_BAD_ACCESS (code=1, address=0x0).

The following is logs:

This is a similar question, but with Object C. It says that defining managedObjectContext in view controller directly instead of transferring it from AppDelegate can fix the bug.

In my code, the managedObjectContext is in SceneDelegate.

func scene(_ scene: UIScene, willConnectTo session: UISceneSession, options connectionOptions: UIScene.ConnectionOptions) {

    if let windowScene = scene as? UIWindowScene {
        let context = CoreData.stack.context
        let window = UIWindow(windowScene: windowScene)
        window.rootViewController = UIHostingController(rootView: ContentView()
            .environment(\.managedObjectContext, context)
            .environmentObject(UserEnvironment())
    )
        self.window = window
        window.makeKeyAndVisible()
    }
}

and

import CoreData

class CoreData: NSObject {
    
    static let stack = CoreData() 

    public var context: NSManagedObjectContext {
        
        get {
            return self.persistentContainer.viewContext
        }
    }

    private lazy var persistentContainer: NSPersistentCloudKitContainer = {
        
        let container = NSPersistentCloudKitContainer(name: "iCloud.com.xxxx")
        container.loadPersistentStores(completionHandler: { (storeDescription, error) in
            if let nserror = error as NSError? {
                fatalError("Unresolved error \(nserror), \(nserror.userInfo)")
            }
        })
        
        container.viewContext.automaticallyMergesChangesFromParent = true
        container.viewContext.mergePolicy = NSMergeByPropertyObjectTrumpMergePolicy
        
        return container
    }()
}

Then how to fix the bug in Swift? Thanks.

回答1:

I fix the bug by change

let request: NSFetchRequest<NSFetchRequestResult> = Item.fetchRequest()

to

let request: NSFetchRequest<NSFetchRequestResult> = NSFetchRequest<NSFetchRequestResult>.init(entityName: "Item")

来源：https://stackoverflow.com/questions/62936616/fetchrequest-is-null-when-calling-second-time