为什么持久化容器返回nil？

Question

我已经在我的应用程序中设置了 CoreData 堆栈，但对 NSPersistentContainer 的引用在 PassWordTableVC 中返回 nil。

应用程序委托

var window: UIWindow?

func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {
    print("AppDelegate: Application didFinishLaunching")

    // Override point for customization after application launch.
    if let rootVC = window?.rootViewController as? PassWordTableVC{
            rootVC.container = persistentContainer
    }

    return true
}



lazy var persistentContainer: NSPersistentContainer = {
    let container = NSPersistentContainer(name: "PasswordModel")
    container.loadPersistentStores { description, error in
        if let error = error {
            
            fatalError("Unable to load persistent stores: \(error)")
        }
    }
    return container
}()

PassWordTableVC

var container: NSPersistentContainer!

override func viewDidLoad() {
    super.viewDidLoad()
    // Do any additional setup after loading the view.

    guard container != nil else{
        fatalError("This view needs a persistent container")
    }
    
}

Answer 1

PassWordTableVC viewDidLoad

可能会在

didFinishLaunchingWithOptions

中的代码之前调用。一个简单的解决方案是向您的

didSet

属性添加一个

container

观察者：

var container: NSPersistentContainer! {
    didSet {
        // do what you currently have in viewDidLoad that needs the container
    }
}