How to solve this async/await error (CoreData)? - swiftui

Question

I am new to Core Data and I'm trying to create a notes app.My project builds but when I try to add a note it crashes. I'm a newbie to using async/await, and there's not many explanations online, so I don't understand the compiler error I have.
It says "No 'async' operations occur within 'await' expression".
import SwiftUI
struct ContentView: View {
#Environment(\.managedObjectContext) private var viewContext
#FetchRequest(sortDescriptors: [NSSortDescriptor(keyPath: \Note.name, ascending: true)])
var notes: FetchedResults<Note>
#State private var NoteIds: Set<Note.ID> = []
var body: some View {
List(notes, selection: $NoteId){ note in
Text(note.name)
}
.toolbar{
ToolbarItem(placement: .primaryAction){
Button(action: newNote){
Label("New Note", systemImage: "square.and.pencil")
}
}
}
}
private func newNote(){
Task{ await newNote(name: "New Note", text:"")}
}
private func newNote(name: String, text: String) async {
await viewContext.perform { //where error is
let note = Note(context: viewContext)
note.id = UUID()
note.name = name
note.text = text
}
try? PersistenceController.shared.saveContext()
}
}
struct ContentView_Previews: PreviewProvider {
static var previews: some View {
ContentView()
}
}
PersistanceController:
final class PersistenceController{
static let shared = PersistenceController()
lazy var container: NSPersistentContainer = {
let container = NSPersistentContainer(name: "Notes")
container.loadPersistentStores {description, error in
if let error = error {
fatalError("Unable to load persistent stores: \(error)")
}
}
return container
}()
private init() {}
public func saveContext(backgroundContext: NSManagedObjectContext? = nil) throws {
let context = backgroundContext ?? container.viewContext
guard context.hasChanges else {return}
try context.save()
}
}

Answer 1

Make sure your projects only supports
iOS 15.0+
iPadOS 15.0+
macOS 12.0+
Mac Catalyst 15.0+
tvOS 15.0+
watchOS 8.0+
Xcode 13.0+
I want to emphasize the versions async/await is Swift and is supported by more platform versions than the Core Data method.
With a basic project provided by Xcode this works in the ContentView
private func addItem() async{
do {
try await viewContext.perform {
let newItem = Item(context: viewContext)
newItem.timestamp = Date()
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)")
}
}
https://developer.apple.com/documentation/coredata/nsmanagedobjectcontext/3802018-perform
From WWDC Bring Core Data Concurrency to Swift and SwiftUI

Answer 2

The view context is on the main thread you don't need async/await. Here is the sample addItem from Xcode's Core Data app template:
private func addItem() {
withAnimation {
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)")
}
}
}