managedObjectContext in Swift 3

Question

I want to work through this example code in which Swift and CoreData is used to create a table. However, using Swift 3 I fail to get it to work. Most importantly, I cannot prope

Answer 1

Swift 3 in macOS

let appDelegate = NSApplication.shared().delegate as! AppDelegate
let managedContext = appDelegate.managedObjectContext

The error you provided says 'AppDelegate' has no member 'managedContext' instead of 'AppDelegate' has no member 'managedObjectContext', which would lead me to assume you just need to fix your syntax.

Swift 3 in iOS 10

Core Data needs at least 3 things to work:

1. A managed object model
2. A persistent store coordinator
3. And a managed object context

Put those three things together and you get the Core Data Stack.

When iOS 10 came out, a new object was introduced called the NSPersistentContainer which encapsulates the core data stack.

How to create the container object is answered here.

managedObjectContext is now a property called viewContext, accessed via:

let delegate = UIApplication.shared.delegate as! AppDelegate
let managedObjectContext = delegate.persistentContainer.viewContext

A helpful article is What's New in Core Data, but if that reading seems a little too heavy, this WWDC video does a great job of explaining this topic.

Answer 2

I swift 3 you can get managedContext set by this code:

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

Answer 3

For macOS and Swift 3.1

let moc: NSManagedObjectContext = (NSApplication.shared().delegate as! AppDelegate).persistentContainer.viewContext

Answer 4

AppDelegate has below members only

// MARK: - Core Data stack

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: "")
    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)")
        }
    })
    return container
}()

so use

 let managedContext = (UIApplication.shared.delegate as! appDelegate).persistentContainer.viewContext

This will work fine