Is there a way to use Core Data/CloudKit to store and move data with Swift UI in Xcode 12?

Question

Created Jun ’20

Replies 5

Boosts 0

Views 4.3k

Participants 6

It seems that AppDelegate and SceneDelegate are no longer needed in Swift UI in Xcode 12. I'm having trouble figuring out how to build an iCloud/Core Data enabled application with Swift UI. Is there a video/tutorial/guide on implementing Core Data or Cloudkit with the new Swift UI frameworks yet?

Answered by Volker88 in 614060022

You can create your custom PersistentCloudKitContainer Class.

One thing I was still struggling with was to apply the Merge Policies. I couldn't figure out how this works. Thats why they are commented out in my code below.

Code Block import SwiftUI
import CoreData
@main
struct TestApp: App {
    let context = PersistentCloudKitContainer.persistentContainer.viewContext
    //context.automaticallyMergesChangesFromParent = true
    //context.mergePolicy = NSMergeByPropertyObjectTrumpMergePolicy
    var body: some Scene {
        WindowGroup {
            ContentView().environment(\.managedObjectContext, context)
        }
    }
}

And my Custom Class

Code Block import CoreData
public class PersistentCloudKitContainer {
    // MARK: - Define Constants / Variables
    public static var context: NSManagedObjectContext {
        return persistentContainer.viewContext
    }
    // MARK: - Initializer
    private init() {}
    // MARK: - Core Data stack
    public static var persistentContainer: NSPersistentContainer = {
        let container = NSPersistentContainer(name: "Model")
        container.loadPersistentStores(completionHandler: { (storeDescription, error) in
            if let error = error as NSError? {
                fatalError("Unresolved error \(error), \(error.userInfo)")
            }
        })
        return container
    }()
    // MARK: - Core Data Saving support
    public static func saveContext () {
        let context = persistentContainer.viewContext
        if context.hasChanges {
            do {
                try context.save()
            } catch {
                let nserror = error as NSError
                fatalError("Unresolved error \(nserror), \(nserror.userInfo)")
            }
        }
    }
}

Boost

Answer 1

Volker88 OP

Jun ’20

Accepted Answer

You can create your custom PersistentCloudKitContainer Class.

One thing I was still struggling with was to apply the Merge Policies. I couldn't figure out how this works. Thats why they are commented out in my code below.

Code Block import SwiftUI
import CoreData
@main
struct TestApp: App {
    let context = PersistentCloudKitContainer.persistentContainer.viewContext
    //context.automaticallyMergesChangesFromParent = true
    //context.mergePolicy = NSMergeByPropertyObjectTrumpMergePolicy
    var body: some Scene {
        WindowGroup {
            ContentView().environment(\.managedObjectContext, context)
        }
    }
}

And my Custom Class

Code Block import CoreData
public class PersistentCloudKitContainer {
    // MARK: - Define Constants / Variables
    public static var context: NSManagedObjectContext {
        return persistentContainer.viewContext
    }
    // MARK: - Initializer
    private init() {}
    // MARK: - Core Data stack
    public static var persistentContainer: NSPersistentContainer = {
        let container = NSPersistentContainer(name: "Model")
        container.loadPersistentStores(completionHandler: { (storeDescription, error) in
            if let error = error as NSError? {
                fatalError("Unresolved error \(error), \(error.userInfo)")
            }
        })
        return container
    }()
    // MARK: - Core Data Saving support
    public static func saveContext () {
        let context = persistentContainer.viewContext
        if context.hasChanges {
            do {
                try context.save()
            } catch {
                let nserror = error as NSError
                fatalError("Unresolved error \(nserror), \(nserror.userInfo)")
            }
        }
    }
}

12

Answer 2

OP

Apple

Jun ’20

You can set the merge policy when creating the container; between line 20 and 21 in your example:

Code Block swiftcontainer.viewContext.automaticallyMergesChangesFromParent = true
container.viewContext.mergePolicy = NSMergeByPropertyObjectTrumpMergePolicy

8

Answer 3

Adamhumbug OP

Jun ’20

When following this, i keep getting the error, cannot find type "MyHumidor" in scope.

My App.swift and the CoreData.swift files below (created the coredata.swift to hold the public class)

Code Block import SwiftUI
@main
struct My_HumidorApp: App {
		let context = PersistentCloudKitContainer.persistentContainer.viewContext
		var body: some Scene {
				WindowGroup {
						ContentView().environment(\.managedObjectContext, context)
				}
		}
}

Code Block //
//	CoreData.swift
//	My Humidor
//
//	Created by Adam Hewitt on 28/06/2020.
//
import Foundation
import CoreData
public class PersistentCloudKitContainer {
		// MARK: - Define Constants / Variables
		public static var context: NSManagedObjectContext {
				return persistentContainer.viewContext
		}
		// MARK: - Initializer
		private init() {}
		// MARK: - Core Data stack
		public static var persistentContainer: NSPersistentContainer = {
				let container = NSPersistentContainer(name: "My_Humidor")
				container.loadPersistentStores(completionHandler: { (storeDescription, error) in
						if let error = error as NSError? {
								fatalError("Unresolved error \(error), \(error.userInfo)")
						}
				})
				container.viewContext.automaticallyMergesChangesFromParent = true
				container.viewContext.mergePolicy = NSMergeByPropertyObjectTrumpMergePolicy
				return container
		}()
		// MARK: - Core Data Saving support
		public static func saveContext () {
				let context = persistentContainer.viewContext
				if context.hasChanges {
						do {
								try context.save()
						} catch {
								let nserror = error as NSError
								fatalError("Unresolved error \(nserror), \(nserror.userInfo)")
						}
				}
		}
}

This is the start of my content view:

Code Block 		import SwiftUI
struct ContentView: View {
		@Environment(\.managedObjectContext) var moc
		@FetchRequest(entitiy: MyHumidors.entity(), sortDescriptors:[]) var humidor: FetchRequest<MyHumidors>

Any ideas what is causing this from a code perspective?

0

Answer 4

dev_agg OP

Jul ’20

An important warning, sometimes Xcode 12 doesn't recognize the entity, to solve this, close and reopen the Xcode and everything will work normally.

0

Answer 5

ryanbdevilled OP

Jul ’20

There's a longer thread about that here. There you'll find a few posts with possibly helpful examples.

0