How to create managedObjectContext using Swift 3 in Xcode 8?

Question

The facing of the question “AppDelegate type value” does not have the “managedObjectContext” control in the new Xcode 8 (using Swift 3, iOS 10) when trying to create a new context in the view controller

let context = (UIApplication.shared().delegate as! AppDelegate).managedObjectContext 

In Xcode 8, there is no code for the managed ObjectContext inside the AppDelegate.swift file. The Core Data stack code inside AppDelegate.swift is presented only with: lazy var persistentContainer: NSPersistentContainer property and func saveContext (). There is no managedObjectContext property.

How to create managedObjectContext using Swift 3 in Xcode 8), or maybe there is no need to do it using Swift 3?

Answer 1

In Swift3, you can access managedObjectContext through viewContext as

 let context = (UIApplication.shared.delegate as! AppDelegate).persistentContainer.viewContext 

This option is available if the master data was included when creating the project. However, for an existing project that you want to include master data, go through the normal process of adding master data and add the following code that will allow you to get

 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 }() 

You will need to import CoreData.

Note. For Swift3, a subclass of ManagedObject is created automatically. See WWDC 2016 for more details.

Answer 2

Moved the entire master data stack code to a single file and added iOS 10 and below iOS10. below is my attempt (not sure if it fully matches the sign)

 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 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 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 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() } } } } 

Answer 3

James Amo's solution gives you the most features for iOS 10.0, but does not apply to iOS 9.0 and below, which cannot access this method and you need to manually create NSManagedObjectModel . Here is the solution that worked for me:

  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)") } } 

Clearly, changing to 10.0 makes CoreData much easier, but unfortunately, it hurts so much for existing developers to make the jump ...

To implement the above, just make sure you select persistentContainer in your AppDelegate.swift specified in James Amo .

Answer 4

NSPersistentContainer has a viewContext property, which is an NSManagedObjectContext type.

As a side note, if you are creating a Master-Detail application in Xcode 8, the Apple code example places the managedObjectContext property in the MasterViewController.swift file and sets it using the specified viewContext property in AppDelegate.

Answer 5

First get the AppDelegate object: -

 let appDelegateObject = UIApplication.shared.delegate as! AppDelegate 

And now we can get the managed entity as:

 let managedObject = appDelegateObject.persistentContainer.viewContext