Problem with state management and Core Data - swiftui

Question

I'm fairly new to Swift and Core Data. I’m having a problem resolving a state issue in a new project of mine.
I have a parent view (CategoryView)that includes a context menu item to allow editing of certain category properties (EditCategoryView). When the EditCategoryView sheet is presented and an edit to a category property is made, the CategoriesView updates correctly when the sheet is dismissed. Works fine.
There is a navigation link off of CategoriesView (ItemsView) that also includes a context menu to allow editing of certain item properties (EditItemView). Unlike the prior example, when the EditItemView sheet is presented and an edit is made to an item property, the ItemsView does not update when the sheet is dismissed. The old item property still displays. If I navigate back to CategoriesView and then return to ItemsView, the updated item property displays correctly.
I’m stumped and clearly don’t understand how state is managed in a CoreData environment. My code for the 2 views seems to be similar, yet they are behaving distinctly different. I wonder if the problem relates to the difference in the structures used in the 2 ForEach lines. That is, in CategoriesView I'm looping on the results of a Fetch and in EventsView I'm looping on the results of a computed value.
Any suggestions? thanks in advance for any guidance.
I created a simple example project that demonstrates the problem. To reproduce:
tap on Load Sample Data
choose a Category
tap and hold an Item to bring up context menu
choose Edit and change the name of the item
you’ll note when sheet dismisses the updated name is not reflected
return to Category list and then select the item again to see the updated name
https://github.com/jayelevy/CoreDataState
edit to include the code for the minimal example referenced in the repo
xcdatamodeld
2 Entities
Category
Attribute: name: String
Relationships: items, destination: Item (many-to-one)
Item
Attribute: name: String
Relationships: category, destination: Category (to one)
#main
struct CoreDataStateApp: App {
#StateObject var dataController: DataController
init() {
let dataController = DataController()
_dataController = StateObject(wrappedValue: dataController)
}
var body: some Scene {
WindowGroup {
CategoriesView()
.environment(\.managedObjectContext, dataController.container.viewContext)
.environmentObject(dataController)
.onReceive(NotificationCenter.default.publisher(for: UIApplication.willResignActiveNotification), perform: save)
}
}
func save(_ note: Notification) {
dataController.save()
}
}
struct CategoriesView: View {
#EnvironmentObject var dataController: DataController
#Environment(\.managedObjectContext) var managedObjectContext
#FetchRequest(sortDescriptors: [SortDescriptor(\.name)])
var categories: FetchedResults<Category>
var body: some View {
NavigationView {
VStack {
List {
ForEach(categories) { category in
NavigationLink {
ItemsView(category: category)
} label : {
Text(category.categoryName)
}
}
}
}
.navigationTitle("My Categories")
.toolbar {
ToolbarItem(placement: .automatic) {
Button {
dataController.deleteAll()
try? dataController.createSampleData()
} label: {
Text("Load Sample Data")
}
}
}
}
}
}
problem occurs with the following view. When an item is edited in EditItemView, the updated property (name) does not display when returning to ItemsView from the sheet.
If you return to CategoryView and then return to ItemsView, the correct property name is displayed.
struct ItemsView: View {
#ObservedObject var category: Category
#State private var isEditingItem = false
var body: some View {
VStack {
List {
ForEach(category.categoryItems) { item in
NavigationLink {
//
} label: {
Text(item.itemName)
}
.contextMenu {
Button {
isEditingItem.toggle()
} label: {
Label("Edit Item", systemImage: "pencil")
}
}
.sheet(isPresented: $isEditingItem) {
EditItemView(item: item)
}
}
}
}
.navigationTitle(category.categoryName)
}
}
struct EditItemView: View {
var item: Item
#EnvironmentObject var dataController: DataController
#Environment(\.managedObjectContext) var managedObjectContext
#Environment(\.dismiss) private var dismiss
#State private var itemName: String
init(item: Item) {
// _item = ObservedObject(initialValue: item)
self.item = item
_itemName = State(initialValue: item.itemName)
}
var body: some View {
NavigationView {
VStack {
Form {
Section {
TextField("Item Name", text: $itemName)
}
}
}
.navigationTitle("Edit Item")
.toolbar {
ToolbarItem(placement: .cancellationAction) {
// add any needed cancel logic
Button("Cancel") {
dismiss()
}
}
ToolbarItem {
Button {
saveItem()
dismiss()
} label: {
Text("Update")
}
.disabled(itemName.isEmpty)
}
}
}
}
func saveItem() {
item.name = itemName
dataController.save()
}
}
extension Category {
var categoryName: String {
name ?? "New Category"
}
var categoryItems: [Item] {
items?.allObjects as? [Item] ?? []
}
extension Item {
var itemName: String {
name ?? "New Item"
}
}
extension Binding {
func onChange(_ handler: #escaping () -> Void) -> Binding<Value> {
Binding(
get: { self.wrappedValue },
set: { newValue in
self.wrappedValue = newValue
handler()
}
)
}
}
class DataController: ObservableObject {
let container: NSPersistentCloudKitContainer
init(inMemory: Bool = false) {
container = NSPersistentCloudKitContainer(name: "Model")
if inMemory {
container.persistentStoreDescriptions.first?.url = URL(fileURLWithPath: "/dev/null")
}
container.loadPersistentStores { _, error in
if let error = error {
fatalError("Fatal error loading store: \(error.localizedDescription)")
}
}
}
static var preview: DataController = {
let dataController = DataController(inMemory: true)
let viewContext = dataController.container.viewContext
do {
try dataController.createSampleData()
} catch {
fatalError("Fatal error creating preview: \(error.localizedDescription)")
}
return dataController
}()
func createSampleData() throws {
let viewContext = container.viewContext
for i in 1...4 {
let category = Category(context: viewContext)
category.name = "Category \(i)"
category.items = []
for j in 1...5 {
let item = Item(context: viewContext)
item.name = "Item \(j)"
item.category = category
}
}
try viewContext.save()
}
func save() {
if container.viewContext.hasChanges {
try? container.viewContext.save()
}
}
func delete(_ object: NSManagedObject) {
container.viewContext.delete(object)
}
func deleteAll() {
let fetchRequest1: NSFetchRequest<NSFetchRequestResult> = Item.fetchRequest()
let batchDeleteRequest1 = NSBatchDeleteRequest(fetchRequest: fetchRequest1)
_ = try? container.viewContext.execute(batchDeleteRequest1)
let fetchRequest2: NSFetchRequest<NSFetchRequestResult> = Category.fetchRequest()
let batchDeleteRequest2 = NSBatchDeleteRequest(fetchRequest: fetchRequest2)
_ = try? container.viewContext.execute(batchDeleteRequest2)
}
func count<T>(for fetchRequest: NSFetchRequest<T>) -> Int {
(try? container.viewContext.count(for: fetchRequest)) ?? 0
}
}

Answer 1

ItemsView needs its own #FetchRequest for CategoryItem with a predicate where category = %#.
Also, instead of passing your DataController object around just put your helper methods in an extension of NSManagedObjectContext. Then you can change DataController back to the struct it should be.

Answer 2

I imagine there are other opportunities to improve my code (obviously, still learning), per other posts. However, the resolution was quite simple.
Modified saveItem in EditItemView to include objectWillChange.send()
func saveItem() {
item.name = itemName
item.category = itemCategory
item.category?.objectWillChange.send()
dataController.save()
}