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Day 10, I followed a tutorial on how to implement Core Data from scratch. Today, I will try to implement it into the existing app that I've been working on so far.

Things I want to accomplish

  • Persisting data on app quit

Things I accomplished

  • Adding Core Data to the app

Things I learned

Core Data is easier to add at the beginning of a project

When creating an iOS project, there is an option to add Core Data to the project. I chose no when starting this project because I did not want to overcomplicate the project. By adding it at the beginning, the AppDelegate.swift file would have the following added for me:

// 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: "TodoList")
        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
    }()

    // MARK: - Core Data Saving support

    func saveContext () {
        let context = persistentContainer.viewContext
        if context.hasChanges {
            do {
                try context.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)")
            }
        }
    }

These allow for TodoList.xcdatamodel to be used in the app and to save information in Core Data.

Since I did not add Core Data when making the app initially, I had to add the variable and function into the AppDelegate.swift file manually. To figure out what was there, I created a new application with Core Data and copied/pasted those into my current Xcode project.


If you have any questions about what I did or how I implemented anything, let me know! If you have any suggestions or other comments, let me know as well!

This post is also available on DEV.