How to create managedObjectContext using Swift 3 in Xcode 8?

In Swift3, you can access the managedObjectContext via the viewContext as

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

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

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 the CoreData.

Note: For Swift3, the ManagedObject Subclass are generated automatically. See more from WWDC 2016

Moved all the core data stack code to a single file and added iOS 10 and below iOS10. below is my try (not sure its fully up to the mark)

import Foundationimport CoreDataclass 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()            }        }    }}

The solution by James Amo gets you most of the way there for iOS 10.0, but doesn't address iOS 9.0 and below, which can't access that method and needs to manually build the 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)")        }    }

It's clear that the change to 10.0 makes CoreData significantly simpler, but it's unfortunate that it's so painful for existing developers to make the jump...

To implement the above, just make sure to throw the persistentContainer into your AppDelegate.swift, defined in James Amo's answer.