如何在Xcode 8中使用Swift 3创buildmanagedObjectContext？
面临的问题“types'AppDelegate'的值没有成员'managedObjectContext'在新的Xcode 8（使用Swift 3，iOS 10），当试图在View Controller中创build新的上下文
let context = (UIApplication.shared().delegate as! AppDelegate).managedObjectContext 在Xcode 8中，在AppDelegate.swift文件中没有managedObjectContext的代码。 AppDelegate.swift中的核心数据堆栈代码仅提供：lazy var persistentContainer：NSPersistentContainer属性和func saveContext（）。 没有managedObjectContext属性。
如何在Xcode 8中使用Swift 3创buildmanagedObjectContext）或者也许不需要使用Swift 3来完成？
在Swift3中，可以通过viewContext as访问managedObjectContext
let context = (UIApplication.shared.delegate as! AppDelegate).persistentContainer.viewContext
如果在创build项目时启用了核心数据，则此选项可用。 但是，对于想要包含核心数据的现有项目，请通过添加核心数据的正常stream程并添加以下代码，以便获取
lazy var persistentContainer: NSPersistentContainer = { let container = NSPersistentContainer(name: "you_model_file_name") container.loadPersistentStores(completionHandler: { (storeDescription, error) in if let error = error { fatalError("Unresolved error \(error), \(error.userInfo)") } }) return container }()
您将需要导入CoreData。
注意：对于Swift3，ManagedObject子类是自动生成的。 从WWDC 2016了解更多信息
将所有核心数据堆栈代码移至单个文件，并添加iOS 10和iOS10以下。 下面是我的尝试（不知道它完全达标）
import Foundation import CoreData class CoreDataManager { // MARK: - Core Data stack static let sharedInstance = CoreDataManager() private lazy var applicationDocumentsDirectory: URL = { // The directory the application uses to store the Core Data store file. This code uses a directory named in the application's documents Application Support directory. let urls = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask) return urls[urls.count-1] }() private 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 = Bundle.main.url(forResource: "CoreDataSwift", withExtension: "momd")! return NSManagedObjectModel(contentsOf: modelURL)! }() private 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.appendingPathComponent("CoreDataSwift.sqlite") var failureReason = "There was an error creating or loading the application's saved data." do { // Configure automatic migration. let options = [ NSMigratePersistentStoresAutomaticallyOption : true, NSInferMappingModelAutomaticallyOption : true ] try coordinator.addPersistentStore(ofType: NSSQLiteStoreType, configurationName: nil, at: url, options: options) } catch { // Report any error we got. var dict = [String: AnyObject]() dict[NSLocalizedDescriptionKey] = "Failed to initialize the application's saved data" as AnyObject? dict[NSLocalizedFailureReasonErrorKey] = failureReason as AnyObject? 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 = { var managedObjectContext: NSManagedObjectContext? if #available(iOS 10.0, *){ managedObjectContext = self.persistentContainer.viewContext } else{ // 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 managedObjectContext = NSManagedObjectContext(concurrencyType: .mainQueueConcurrencyType) managedObjectContext?.persistentStoreCoordinator = coordinator } return managedObjectContext! }() // iOS-10 @available(iOS 10.0, *) lazy var persistentContainer: NSPersistentContainer = { /* The persistent container for the application. This implementation creates and returns a container, having loaded 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. */ let container = NSPersistentContainer(name: "CoreDataSwift") container.loadPersistentStores(completionHandler: { (storeDescription, error) in if let error = error as NSError? { // Replace this implementation with code to handle the error appropriately. // fatalError() 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. /* Typical reasons for an error here include: * The parent directory does not exist, cannot be created, or disallows writing. * The persistent store is not accessible, due to permissions or data protection when the device is locked. * The device is out of space. * The store could not be migrated to the current model version. Check the error message to determine what the actual problem was. */ fatalError("Unresolved error \(error), \(error.userInfo)") } }) print("\(self.applicationDocumentsDirectory)") return container }() // 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() } } } }
James Amo的解决scheme为您带来了iOS 10.0的大部分解决scheme，但是并未解决iOS 9.0及更低版本的问题，无法访问该方法，需要手动构buildNSManagedObjectModel 。 这是为我工作的解决scheme：
var context: NSManagedObjectContext? if #available(iOS 10.0, *) { context = (UIApplication.shared.delegate as! AppDelegate).persistentContainer.viewContext } else { // iOS 9.0 and below - however you were previously handling it guard let modelURL = Bundle.main.url(forResource: "Model", withExtension:"momd") else { fatalError("Error loading model from bundle") } guard let mom = NSManagedObjectModel(contentsOf: modelURL) else { fatalError("Error initializing mom from: \(modelURL)") } let psc = NSPersistentStoreCoordinator(managedObjectModel: mom) context = NSManagedObjectContext(concurrencyType: .mainQueueConcurrencyType) let urls = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask) let docURL = urls[urls.endIndex-1] let storeURL = docURL.appendingPathComponent("Model.sqlite") do { try psc.addPersistentStore(ofType: NSSQLiteStoreType, configurationName: nil, at: storeURL, options: nil) } catch { fatalError("Error migrating store: \(error)") } }
很显然，10.0的变化使得CoreData变得更加简单，但不幸的是现有的开发人员为了跳跃而痛苦不堪。
为了实现上述，请确保将persistentContainer放入您的AppDelegate.swift中，在James Amo的答案中定义。
NSPersistentContainer具有一个NSManagedObjectContexttypes的viewContext属性。
另外，如果你在Xcode 8中创build一个Master-Detail应用程序，Apple的示例代码将managedObjectContext属性放在MasterViewController.swift文件中，并使用AppDelegate中的viewContext属性进行设置。
