How to share Core Data with Widget?

Question

I want to share Core Data with the Widget. I guess I'll need to create App Group (I know how to do this). But how do I then share the Core Data database with the Widget?

If I wanna use Core Data in my app, I always just simply create a new Xcode project and check "Use Core Data", and I get this code (Persistence.swift - below), which hooks me up to a database.

How can I modify it, so that this Core Data database is shared with the Widget?

Persistence.swift

import CoreData

struct PersistenceController {
    static let shared = PersistenceController()

    static var preview: PersistenceController = {
        let result = PersistenceController(inMemory: true)
        let viewContext = result.container.viewContext
        for _ in 0..<10 {
            let newItem = Item(context: viewContext)
            newItem.timestamp = Date()
        }
        do {
            try viewContext.save()
        } catch {
            // 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.
            let nsError = error as NSError
            fatalError("Unresolved error \(nsError), \(nsError.userInfo)")
        }
        return result
    }()

    let container: NSPersistentContainer

    init(inMemory: Bool = false) {
        container = NSPersistentContainer(name: "MyAppName")
        if inMemory {
            container.persistentStoreDescriptions.first!.url = URL(fileURLWithPath: "/dev/null")
        }
        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)")
            }
        })
        container.viewContext.automaticallyMergesChangesFromParent = true
    }
}

Answer 1

In the PersistenceController class first add a property to get the URL of the App Group

var containerURL: URL {
   return FileManager.default.containerURL(forSecurityApplicationGroupIdentifier: "group.com.myappname")!
}

then set the URL in the store descriptions of the persistent container

init(inMemory: Bool = false) {
    container = NSPersistentContainer(name: "MyAppName")
    if inMemory {
        container.persistentStoreDescriptions.first!.url = URL(fileURLWithPath: "/dev/null")
    } else {
        let storeURL = containerURL.appendingPathComponent("MyAppName.sqlite")
        container.persistentStoreDescriptions.first!.url = storeURL
    }
    container.loadPersistentStores(completionHandler: { (storeDescription, error) in ...

Replace the string literals with your actual data.