Inconsistent ContentView updates from #Environment var Changes - ios

Question

I have a simple SwiftUI, CoreData application. The architecture is the basic list with
a second view for viewing the detail or editing the detail. The basic structure seems
to work with one important exception. When editing a record, the first edit after
app start is properly visible after returning to the ContentView list. The second and
further edits do not appear on the list when returning to the ContentView. The database
changes are correctly saved. Restarting the app will display the correct data. I have
also created a TabView. If I disable the return-to-main-list-after-edit code and use
just the TabView to switch, the changes are always presented.
Here's the code (I have removed most of the repetitive data fields).
In SceneDelegate:
let managedObjectContext = (UIApplication.shared.delegate as! AppDelegate).persistentContainer.viewContext
let tabby = TabBar().environment(\.managedObjectContext, managedObjectContext)
window.rootViewController = UIHostingController(rootView: tabby)
In ContentView:
#Environment(\.managedObjectContext) var managedObjectContext
#FetchRequest(fetchRequest: ToDoItem.getAllToDoItems()) var toDoItems: FetchedResults<ToDoItem>
#State private var newToDoItem = ""
#State private var gonnaShow = true
#State private var show = false
var body: some View {
NavigationView {
List {
Section(header: Text("Records")) {
ForEach(self.toDoItems) { toDoItem in
NavigationLink(destination: EditToDo(toDoItem: toDoItem)) {
ToDoItemView(
idString: toDoItem.myID.uuidString,
title: toDoItem.title!,
firstName: toDoItem.firstName!,
lastName: toDoItem.lastName!,
createdAt: self.localTimeString(date: toDoItem.createdAt!)
)
}
}//for each
.onDelete { indexSet in
let deleteItem = self.toDoItems[indexSet.first!]
self.managedObjectContext.delete(deleteItem)
do {
try self.managedObjectContext.save()
} catch {
print(error)
}
}
.onMove(perform: move)
}
}
.navigationBarTitle("Customers")
.navigationBarItems(trailing: EditButton())
}
}
Separate file EditToDo:
#Environment(\.managedObjectContext) var managedObjectContext
#Environment(\.presentationMode) var presentationMode
var toDoItem: ToDoItem
#State private var updatedTitle: String = "No Title"
#State private var updatedFirstName: String = "No First Name"
//more data fields
#State private var updatedDate: Date = Date()
#State private var updatedDateString: String = "July 2019"
var body: some View {
ScrollView {
VStack {
Image("JohnForPosting")
.resizable()
.aspectRatio(contentMode: .fill)
.frame(width: 80, height: 80)
.clipShape(Circle())
VStack(alignment: .leading) {
Text("ToDo Title:")
.padding(.leading, 5)
.font(.headline)
TextField("Enter a Title", text: $updatedTitle)
.onAppear {
self.updatedTitle = self.toDoItem.title ?? ""
}
.textFieldStyle(RoundedBorderTextFieldStyle())
}
.padding(10)
VStack(alignment: .leading) {
Text("First Name:")
.padding(.leading, 5)
.font(.headline)
TextField("Enter a First Name", text: $updatedFirstName)
.onAppear {
self.updatedFirstName = self.toDoItem.firstName ?? ""
}
.textFieldStyle(RoundedBorderTextFieldStyle())
}
.padding(10)
//more data fields
VStack {
Button(action: ({
self.toDoItem.title = self.updatedTitle
self.toDoItem.firstName = self.updatedFirstName
//more data fields
do {
try self.managedObjectContext.save()
} catch {
print(error)
}
self.updatedTitle = ""
self.updatedFirstName = ""
//more data fields
self.presentationMode.wrappedValue.dismiss()
})) {
Text("Save")
}
.padding()
}
.padding(10)
Spacer()
}
}
}
Separate file ToDoItemView:
var idString: String = ""
var title: String = ""
var firstName: String = ""
//more data fields
var body: some View {
HStack {
VStack(alignment: .leading) {
Text("\(firstName) \(lastName)")
.font(.headline)
Text("\(createdAt) and \(idString)")
.font(.caption)
}
}
}
Xcode 11 - I guess this is the real release (post GM seed 2), Catalina Beta 19A558d,
iOS13.1
I thought the #Environment changes would always cause the body of ContentView to be
redrawn. And it is the weird behavior of first edit working, others not. Any guidance
would be appreciated.

Answer 1

I have the same problem with my current project, same basic code as you as well. A list of Projects fed by a FetchRequest that navigates to a second view for editing a Project.
Like you, if I make changes in the detail view, those changes are reflected in the List, but only the first time. If I reload the List by changing to a different tab and back again, the List will update showing the updated data.
The root of the problem comes down to creating a dynamic list using the results of a #FetchRequest. FetchRequest returns a Set of NSManagedObjects (reference types). Since the List is seeded with a Set of reference types, SwiftUI would only update the view when a reference changed, not necessarily when one of the properties of the object changed.
I think #FetchRequest would be fine for things like Pickers or menu options, but for a dynamic list of TodoItems, a better solution might be to create a TodoManager.
The TodoManager would be the single source of truth for all TodoItems. It would also setup a NSManagedObjectContextObserver that would trigger a objectWillChange.send() notification when any change was made, thus signaling that SwiftUI should refresh the list.
class TodoManager: ObservableObject {
private var moc: NSManagedObjectContext
public let objectWillChange = PassthroughSubject<Void, Never>()
var todoList: [TodoItem] = []
init( context: NSManagedObjectContext ) {
moc = context
setupNSManagedObjectContextObserver( context: context )
todoList = Array( TodoItem.fetch(in: context ))
}
func setupNSManagedObjectContextObserver( context moc: NSManagedObjectContext ) {
let notificationCenter = NotificationCenter.default
notificationCenter.addObserver(self, selector: #selector(managedObjectContextObjectsDidChange), name: NSNotification.Name.NSManagedObjectContextObjectsDidChange, object: moc)
notificationCenter.addObserver(self, selector: #selector(managedObjectContextWillSave), name: NSNotification.Name.NSManagedObjectContextWillSave, object: moc)
notificationCenter.addObserver(self, selector: #selector(managedObjectContextDidSave), name: NSNotification.Name.NSManagedObjectContextDidSave, object: moc)
}
#objc func managedObjectContextObjectsDidChange(notification: NSNotification) {
self.objectWillChange.send() // Crude but works
guard let userInfo = notification.userInfo else { return }
if let inserts = userInfo[NSInsertedObjectsKey] as? Set<NSManagedObject>, inserts.count > 0 { }
if let updates = userInfo[NSUpdatedObjectsKey] as? Set<NSManagedObject>, updates.count > 0 { }
if let deletes = userInfo[NSDeletedObjectsKey] as? Set<NSManagedObject>, deletes.count > 0 { }
}
#objc func managedObjectContextWillSave(notification: NSNotification) {
guard let userInfo = notification.userInfo else { return }
if let inserts = userInfo[NSInsertedObjectsKey] as? Set<NSManagedObject>, inserts.count > 0 { }
if let updates = userInfo[NSUpdatedObjectsKey] as? Set<NSManagedObject>, updates.count > 0 { }
if let deletes = userInfo[NSDeletedObjectsKey] as? Set<NSManagedObject>, deletes.count > 0 { }
}
#objc func managedObjectContextDidSave(notification: NSNotification) {
guard let userInfo = notification.userInfo else { return }
if let inserts = userInfo[NSInsertedObjectsKey] as? Set<NSManagedObject>, inserts.count > 0 { }
if let updates = userInfo[NSUpdatedObjectsKey] as? Set<NSManagedObject>, updates.count > 0 { }
if let deletes = userInfo[NSDeletedObjectsKey] as? Set<NSManagedObject>, deletes.count > 0 { }
}
}
TodoManager is pretty dumb in that it sends an objectWillChange notification anytime any data in the ManagedObjectContext is changed.
Steve

Answer 2

Xcode 11.1 GM seed resolves this issue. For what it's worth, the Preview function for the core data fed list still does not work.