SwiftUI CoreData not saving / not detecting changes - swift

Question

I have an entity called Cart, but it seems I can't get it to save a new data from my viewmodel.
Persistence.swift
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()
}
for _ in 0..<10 {
let newCart = Cart(context: viewContext)
newCart.menuName = "name"
newCart.menuImg = "img"
newCart.menuCode = "code"
}
do {
try viewContext.save()
} catch {
let nsError = error as NSError
fatalError("Unresolved error \(nsError), \(nsError.userInfo)")
}
return result
}()
let container: NSPersistentContainer
init(inMemory: Bool = false) {
container = NSPersistentContainer(name: "Project")
if inMemory {
container.persistentStoreDescriptions.first!.url = URL(fileURLWithPath: "/dev/null")
}
container.loadPersistentStores(completionHandler: { (storeDescription, error) in
if let error = error as NSError? {
fatalError("Unresolved error \(error), \(error.userInfo)")
}
})
}
func save() {
let context = container.viewContext
if context.hasChanges {
print("Found Changes")
do {
try context.save()
} catch {
print("ERROR")
let nserror = error as NSError
fatalError("Unresolved error \(nserror), \(nserror.userInfo)")
}
} else {
print("NO Changes")
}
}
}
MenuViewModel.swift
class MenuViewModel.swift: ObservableObject, MenuDetailService {
#Environment(\.managedObjectContext) var managedObjectContext
func addToCart() {
let newCart = Cart(context: managedObjectContext)
newCart.menuCode = menuCode
newCart.menuName = menuName
newCart.menuImg = menuImg
PersistenceController.shared.save()
}
}
ProjectApp.swift
#main
struct ProjectApp: App {
#Environment(\.scenePhase) var scenePhase
let persistenceController = PersistenceController.shared
var body: some Scene {
WindowGroup {
ContentView()
.environment(\.managedObjectContext, persistenceController.container.viewContext)
}.onChange(of: scenePhase) { _ in
persistenceController.save()
}
}
}
The persistence controller func save() always print no changes, seems like I use different context? and I don't know how to use the context in the persistence controller to save the new data. How do I do this? Thank you very much.

Answer 1

//Remove the `.swift`
class MenuViewModel: ObservableObject, MenuDetailService {
//#Environment does not work well outside of a struct :View . Updates are unreliable
var managedObjectContext = PersistenceController.shared.container.viewContext
// You need to pass the variables somehow to the new object when you call the method from the `View`
func addToCart(menuCode: String, menuName: String, menuImg: UIImage) {
let newCart = Cart(context: managedObjectContext)
newCart.menuCode = menuCode
newCart.menuName = menuName
newCart.menuImg = menuImg
PersistenceController.shared.save()
}
}

Answer 2

I am not sure about that tutorial, I have not looked into it, but as I have used CoreData with SwiftUI, this was nothing I have seen:
let newCart = Cart(context: managedObjectContext)
newCart.menuCode = menuCode
newCart.menuName = menuName
newCart.menuImg = menuImg
PersistenceController.shared.save()
Rather what I would expect is that you replace the last line there with this:
do {
try managedObjectContext.save()
} catch {
print(error.localizedDescription)
}