我正在使用Swift构建一个iPad应用程序，但我无法弄清楚如何在前台和后台切换时保留我的实体。 如果我关闭应用程序（从任务管理器中），所有实体都会再次出现。 我正在使用Apple提供的标准Core Data堆栈。 如果我使用iCloud，这种情况就不会发生。
有任何想法吗？ 我爬过StackOverflow，但找不到任何东西。 谢谢。
编辑：
App Delegate
// 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 "it.b3lab.ProjectIceCream" 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("ProjectIceCream", 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)
//Add support to ligtweight migrations, and iCloud persistent storage
var options = [
NSMigratePersistentStoresAutomaticallyOption: true,
NSInferMappingModelAutomaticallyOption: true,
NSPersistentStoreUbiquitousContentNameKey: "ProjectIceCreamCloudStore"
]
//enabled iCloud notiiccation subscription
var notification = NSNotificationCenter.defaultCenter()
notification.addObserver(self, selector: "storeDidChangeNotification:",
name: NSPersistentStoreCoordinatorStoresDidChangeNotification,
object:nil)
notification.addObserver(self, selector: "storeWillChangeNotification:",
name: NSPersistentStoreCoordinatorStoresWillChangeNotification,
object:nil)
notification.addObserver(self, selector: "storeDidImportUbiquitousContent:",
name: NSPersistentStoreDidImportUbiquitousContentChangesNotification,
object:nil)
let url = self.applicationDocumentsDirectory.URLByAppendingPathComponent("ProjectIceCream.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:options, 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)
// 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(concurrencyType: .MainQueueConcurrencyType)
managedObjectContext.persistentStoreCoordinator = coordinator
return managedObjectContext
}()
//MARK: iCloud notification methods
func storeDidChangeNotification(notification: NSNotification) {
println("Core Data successfully created and configured an iCloud-enabled persistent store")
//TODO: controllare che i dati in ingresso siano validi
//TODO: Implement Refresh your User Interface.
}
func storeWillChangeNotification(notification: NSNotification) {
println("Called storeWillChangeNotification")
var moc: NSManagedObjectContext = self.managedObjectContext!
moc.performBlock { () -> Void in
if moc.hasChanges {
var saveError: NSError?
if moc.save(&saveError) {
print("iCloud save error \(saveError)")
}
}else{
moc.reset()
}
}
//TODO: Implement Refresh your User Interface.
}
func storeDidImportUbiquitousContent(notification: NSNotification) {
println("Called storeDidImportUbiquitousContent")
var moc: NSManagedObjectContext = self.managedObjectContext!
moc.performBlock { () -> Void in
moc.mergeChangesFromContextDidSaveNotification(notification)
}
}
// 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()
}
}
}
获取请求的示例
class func getReceipesFormCoreData() -> [Recipes] {
let managedContext = getManagedObjectContext()
let request: NSFetchRequest = NSFetchRequest()
let entity: NSEntityDescription = NSEntityDescription.entityForName("Recipes",
inManagedObjectContext: managedContext)!
request.entity = entity
var error: NSError?
var results: [Recipes] = managedContext.executeFetchRequest(request, error: &error)
as [Recipes]
if (error != nil) {
println("ERROR: Could not load \(error), \(error?.userInfo)")
}
return results
}