swift : AppDelegate 和 NSManagedObjectContext 为 nil

Question

我尝试用 CoreData 和 CoreLocation 创建一个 APP。

CoreLocation 运行良好，但 CoreData 总是给我一个致命错误：在每次加载 AppDelegate 时展开 Option 值时发现 nil。

我打印 appDelegate 和 NSManagedObjectContext 并为两者返回 nil

这是我在 ViewController 中的代码

import UIKit
import CoreLocation
import CoreData

class ViewController: UIViewController, CLLocationManagerDelegate  {

let locationManager = CLLocationManager()

var appDelegate :AppDelegate?
var context :NSManagedObjectContext?

var entitylUtenti :NSEntityDescription?

func loadCoreData() {
    let appDelegate = (UIApplication.sharedApplication().delegate as! AppDelegate)
    let context : NSManagedObjectContext = appDelegate.managedObjectContext!

    let entityUtenti = NSEntityDescription.entityForName("Utenti", inManagedObjectContext: context)
    if(entitylUtenti == nil) {
        println("vuoto")
    }
}
override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view, typically from a nib.

    loadCoreData()
    locationManager.desiredAccuracy = kCLLocationAccuracyBest
    locationManager.delegate = self
    locationManager.requestWhenInUseAuthorization()
    locationManager.startUpdatingLocation()
}
}

在我的 AppDelegate.swift 中插入

lazy var applicationDocumentsDirectory: NSURL = {
    // The directory the application uses to store the Core Data store file. This code uses a directory named "xCodingIT.DiarioScolastico" in the application's documents Application Support directory.
    let urls = NSFileManager.defaultManager().URLsForDirectory(.DocumentDirectory, inDomains: .UserDomainMask)
    return urls[urls.count-1] as! NSURL
    }()

lazy var managedObjectModel: NSManagedObjectModel = {
    // The managed object model for the application. This property is not optional. It is a fatal error for the application not to be able to find and load its model.
    let modelURL = NSBundle.mainBundle().URLForResource("staffandstock", withExtension: "momd")!
    return NSManagedObjectModel(contentsOfURL: modelURL)!
    }()

lazy var persistentStoreCoordinator: NSPersistentStoreCoordinator? = {
    // The persistent store coordinator for the application. This implementation creates and return a coordinator, having added the store for the application to it. This property is optional since there are legitimate error conditions that could cause the creation of the store to fail.
    // Create the coordinator and store
    var coordinator: NSPersistentStoreCoordinator? = NSPersistentStoreCoordinator(managedObjectModel: self.managedObjectModel)
    let url = self.applicationDocumentsDirectory.URLByAppendingPathComponent("staffandstock.sqlite")
    var error: NSError? = nil
    var failureReason = "There was an error creating or loading the application's saved data."
    if coordinator!.addPersistentStoreWithType(NSSQLiteStoreType, configuration: nil, URL: url, options: nil, error: &error) == nil {
        coordinator = nil
        // Report any error we got.
        let dict = NSMutableDictionary()
        dict[NSLocalizedDescriptionKey] = "Failed to initialize the application's saved data"
        dict[NSLocalizedFailureReasonErrorKey] = failureReason
        dict[NSUnderlyingErrorKey] = error
        error = NSError(domain: "YOUR_ERROR_DOMAIN", code: 9999, userInfo: dict as [NSObject : AnyObject])
        // Replace this with code to handle the error appropriately.
        // abort() causes the application to generate a crash log and terminate. You should not use this function in a shipping application, although it may be useful during development.
        NSLog("Unresolved error \(error), \(error!.userInfo)")
        abort()
    }

    return coordinator
    }()

lazy var managedObjectContext: NSManagedObjectContext? = {
    // Returns the managed object context for the application (which is already bound to the persistent store coordinator for the application.) This property is optional since there are legitimate error conditions that could cause the creation of the context to fail.
    let coordinator = self.persistentStoreCoordinator
    if coordinator == nil {
        return nil
    }
    var managedObjectContext = NSManagedObjectContext()
    managedObjectContext.persistentStoreCoordinator = coordinator
    return managedObjectContext
    }()

// MARK: - Core Data Saving support

func saveContext () {
    if let moc = self.managedObjectContext {
        var error: NSError? = nil
        if moc.hasChanges && !moc.save(&error) {
            // Replace this implementation with code to handle the error appropriately.
            // abort() causes the application to generate a crash log and terminate. You should not use this function in a shipping application, although it may be useful during development.
            NSLog("Unresolved error \(error), \(error!.userInfo)")
            abort()
        }
    }
}

有人有解决办法吗？

Answer 1

通过在函数中重新定义 appDelegate 和 context，您实际上是在“隐藏”实例变量：

func loadCoreData() {
    // these two lines
    let appDelegate = (UIApplication.sharedApplication().delegate as! AppDelegate)
    let context : NSManagedObjectContext = appDelegate.managedObjectContext!

删除let 关键字并重试。

Answer 2

我解决了！！！

我删除了我的函数 loadCoreData 并在没有 let 的情况下将我的 appdelegate 和我的上下文插入到 func viewDidLoad 中。

我不知道为什么如果我从 loadCoreData 中删除 let 没有任何改变......但现在它可以工作了！！！