在我删除它并重新启动我的应用程序后，核心数据是持久的

Question

早上好，

我第一次在 Swift 2.2 中使用 CoreData。目前，我可以将对象添加到我的实体“项目”中，并且在按下“删除所有内容”按钮后我可以删除所有项目。这是正确的，但是当我删除所有对象然后重新启动我的应用程序时，在“删除所有内容”操作之前我仍然拥有相同的核心数据。

这就是我删除核心数据对象的方式：

@IBAction func removeWishlist(sender: AnyObject) {
    deleteAllData("ItemsWishlist")
    getWishlist()
    self.tableView.reloadData()
}

func deleteAllData(entity: String) {

    let appDelegate = UIApplication.sharedApplication().delegate as! AppDelegate
    let managedContext = appDelegate.managedObjectContext
    let fetchRequest = NSFetchRequest(entityName: entity)
    fetchRequest.returnsObjectsAsFaults = false

    do
    {
        let results = try managedContext.executeFetchRequest(fetchRequest)
        for managedObject in results
        {
            let managedObjectData:NSManagedObject = managedObject as! NSManagedObject
            managedContext.deleteObject(managedObjectData)
            print("Deleted")
        }

    } catch let error as NSError {
        print(error)
    }
}

它正在工作，因为当我按下按钮时，列表是空的，但是当我重新启动应用程序时，它再次显示与我按下“清除”按钮之前相同的项目。

这是我的AppDelegate与核心数据部分：

// MARK: - Core Data stack

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

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("wishlist", withExtension: "momd")!
    return NSManagedObjectModel(contentsOfURL: modelURL)!
}()

lazy var persistentStoreCoordinator: NSPersistentStoreCoordinator = {
    // The persistent store coordinator for the application. This implementation creates and returns 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
    let coordinator = NSPersistentStoreCoordinator(managedObjectModel: self.managedObjectModel)
    let url = self.applicationDocumentsDirectory.URLByAppendingPathComponent("SingleViewCoreData.sqlite")
    var failureReason = "There was an error creating or loading the application's saved data."
    do {
        try coordinator.addPersistentStoreWithType(NSSQLiteStoreType, configuration: nil, URL: url, options: nil)
    } catch {
        // Report any error we got.
        var dict = [String: AnyObject]()
        dict[NSLocalizedDescriptionKey] = "Failed to initialize the application's saved data"
        dict[NSLocalizedFailureReasonErrorKey] = failureReason

        dict[NSUnderlyingErrorKey] = error as NSError
        let wrappedError = NSError(domain: "YOUR_ERROR_DOMAIN", code: 9999, userInfo: dict)
        // 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 \(wrappedError), \(wrappedError.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
    var managedObjectContext = NSManagedObjectContext(concurrencyType: .MainQueueConcurrencyType)
    managedObjectContext.persistentStoreCoordinator = coordinator
    return managedObjectContext
}()

// MARK: - Core Data Saving support

func saveContext () {
    if managedObjectContext.hasChanges {
        do {
            try managedObjectContext.save()
        } catch {
            // 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.
            let nserror = error as NSError
            NSLog("Unresolved error \(nserror), \(nserror.userInfo)")
            abort()
        }
    }
}

我对核心数据做错了什么？我该如何解决这个问题？

非常感激，

问候。

Answer 1

您在重新启动应用程序后取回这些对象的原因是，您在执行所有删除操作后没有保存 NSManagedObjectContext，以便可以将这些更改保留到您正在使用的持久性存储中。

上下文就像一个虚拟板。将上下文中的托管对象视为放在桌子上玩的玩具。您可以移动它们，打破它们，将它们移出桌子，并带入新玩具。该桌子是您的托管对象上下文，您可以在准备好时保存其状态。当您保存托管对象上下文的状态时，此保存操作将传达给上下文所连接的持久存储协调器。然后持久存储协调器将信息存储到持久存储，然后存储到磁盘。

func deleteAllData(entity: String) {

let appDelegate = UIApplication.sharedApplication().delegate as! AppDelegate
let managedContext = appDelegate.managedObjectContext
let fetchRequest = NSFetchRequest(entityName: entity)
fetchRequest.returnsObjectsAsFaults = false

do
  {
    let results = try managedContext.executeFetchRequest(fetchRequest)
    for managedObject in results
    {
        let managedObjectData:NSManagedObject = managedObject as! NSManagedObject
        managedContext.deleteObject(managedObjectData)
        print("Deleted")
    }

  } catch let error as NSError {
    print(error)
  }
  appDelegate.saveContext()
}

为了性能优势，您应该查看 NSBatchDeleteRequest。