How to create managedObjectContext using Swift 3 in Xcode 8?

55,258

Solution 1

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

Solution 2

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 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()
            }
        }
    }
}

Solution 3

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.

Solution 4

NSPersistentContainer has a viewContext property that is an NSManagedObjectContext type.

As a side note, if you create a Master-Detail application in Xcode 8, Apple's sample code puts the managedObjectContext property in the MasterViewController.swift file and sets it by using said viewContext property in AppDelegate.

Solution 5

First, get AppDelegate object:-

let appDelegateObject = UIApplication.shared.delegate as! AppDelegate

And now, we can get managed object as:

let managedObject = appDelegateObject.persistentContainer.viewContext
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Adelmaer
Author by

Adelmaer

Indie iOS Developer, Currently exploring iOSLand

Updated on January 18, 2020

Comments

  • Adelmaer
    Adelmaer almost 4 years

    Facing issue "Value of type 'AppDelegate' has no member 'managedObjectContext' In new Xcode 8 (using Swift 3, iOS 10) when trying to create new context in View Controller

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

    In Xcode 8 there is no code for managedObjectContext inside AppDelegate.swift file. Core Data stack code inside AppDelegate.swift 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 ?

  • andrewcbancroft
    andrewcbancroft over 7 years
    I think it's important to note that NSPersistentContainer is an iOS 10 API and is not particularly tied to Swift 3. If you plan to support iOS 9.x, you won't be able to use NSPersistentContainer, and will need to set up your Core Data stack as you would have prior to using Xcode 8.
  • DaPhil
    DaPhil about 7 years
    Hi. Is there a similarly easy way to do this for a Mac App? Since NSPersitentContainer is iOS, the first line approach does not work.
  • mic
    mic about 7 years
    The documentation states macOS 10.12 as a supported SDK.
  • sbbs
    sbbs about 7 years
    I'm using Swift 3.0 with Xcode 8.0. UIApplication.shared() produces an error message like "Cannot call value of non-function type UIApplication". However, UIApplication.shared works fine.
  • legel
    legel about 7 years
    This is a solid start, but to address the incompatibility of this approach with iOS 9 and below, please see my answer below.
  • Nicolas Miari
    Nicolas Miari about 7 years
    @user1913623 I think the API changed and shared is now an actual property, not a getter method.
  • SleepsOnNewspapers
    SleepsOnNewspapers about 7 years
    make sure to add the persistentContainer var to the AppDelegate.swift
  • Garrett Cox
    Garrett Cox almost 7 years
    I think this is exactly what I am looking for. If this class is simply shared with both the app and an extension in the same group (targeted to both apps) will this allow the data to be accessible by both? I am running into this issue with a keyboard extension where they are both using the same "persistent container" and the same data model, but the data is not shared. Any thoughts?
  • anoop4real
    anoop4real almost 7 years
    Hello, I am not actually sure on this, I just created this :)... no extensive testing done. May be you can try the framework approach andrewcbancroft.com/2015/08/25/…
  • Garrett Cox
    Garrett Cox almost 7 years
    I ended up getting it. You add an NSPersistentStoreDescription pointing to the app group when creating the container in the ios 10 version.
  • anoop4real
    anoop4real almost 7 years
    Great to know...enjoy and do share the tips
  • mirt
    mirt almost 7 years
    @Garrett Cox could you shed a light on this "add an NSPersistentStoreDescription pointing to the app group when creating the container"
  • Garrett Cox
    Garrett Cox almost 7 years
    @mirt yeah, if you post a new question. I can answer/post my code on there regarding whatever questions you still have unanswered. I know I had a hard time finding relevant answers.
  • mirt
    mirt almost 7 years
  • Alex Cio
    Alex Cio almost 7 years
    It's strange to see apple changing something essential like this as CoreData is a very elemental feature and might be used by many out there!
  • javimuu
    javimuu over 6 years
    Thanks, it help me very much!
  • Sasho
    Sasho over 6 years
    Best Solution for me