SwiftUI CoreData master detail questions - core-data

Question

I'm trying to create a master detail relationship with CoreData. I have a settings tab that is used to select the master (it's global and not done very often by the user). There is another tab that shows the detail entries for the current master.
The master has one field, name, a string and the details array. The detail has one field, name, a string. I'm using UUID().uuidString to populate the names for the example.
The problem I'm having is that when I select the detail tab, it shows the details for the current master. If I add details (click the + button) they do not appear until I change the master (settings -> select master). If I edit the details and delete some, the list entries go away but when I finish editing, they immediately come back. I can switch masters and then go back to the edited master and the data looks correct (I have to change the activeMaster published property).
I'm thinking that the published property isn't forcing the update to the details view because swift doesn't see the master variable change. I may also not be adding or deleting the details correctly.
How is adding details to a master typically done (here master is one to many details)
How is deleting details from a master typically done?
Is the data no showing up due to the published property not "publishing" Any ideas on how to better do this?
Thanks.
Code is below.
Here's the global application data:
import Foundation
import CoreData
import SwiftUI
class ApplicationData: ObservableObject
{
let container: NSPersistentContainer
#Published var activeMaster: Master?
init(preview: Bool = false)
{
container = NSPersistentContainer(name: "MasterDetail")
if (preview)
{
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)")
}
})
}
}
Just persistence and a single optional active master. The application data is created in the application code and set as an environment object:
import SwiftUI
#main
struct MasterDetailApp: App
{
#StateObject var appData = ApplicationData()
var body: some Scene {
WindowGroup {
MainView()
.environmentObject(appData)
.environment(\.managedObjectContext, appData.container.viewContext)
}
}
}
The tab view:
import Foundation
import SwiftUI
struct MainView: View
{
#AppStorage("selectedTab") var selectedTab: Int = 0
#EnvironmentObject var appData: ApplicationData
var body: some View
{
TabView(selection: $selectedTab)
{
DetailView()
.tabItem({Label("Detail", systemImage: "house")})
.tag(0)
SettingsView()
.tabItem({Label("Settings", systemImage: "gear")})
.tag(1)
}
.environment(\.managedObjectContext, appData.container.viewContext)
}
}
The detail tab allows the user to add details and to edit the list:
import Foundation
import SwiftUI
import CoreData
struct DetailView: View
{
#Environment(\.managedObjectContext) private var viewContext
#Environment(\.dismiss) var dismiss
#EnvironmentObject var appData: ApplicationData
var body: some View
{
NavigationView
{
List
{
ForEach(appData.activeMaster?.wrappedDetail ?? [])
{
detail in Text(detail.name ?? "None")
}
.onDelete(perform: { indexes in Task(priority: .high) { await deleteDetails(indexes: indexes) } } )
}
.toolbar
{
ToolbarItem(placement: .navigationBarTrailing)
{
EditButton()
}
ToolbarItem(placement: .navigationBarTrailing)
{
Button
{
let detail = Detail(context: viewContext)
detail.name = UUID().uuidString
detail.master = appData.activeMaster
do
{
try viewContext.save()
}
catch
{
print("Error adding master")
}
} label: { Image(systemName: "plus") }
.disabled(appData.activeMaster == nil)
}
}
}
}
/*
* Delete indexes - assumes that appData.activeWeapon is set.
*/
private func deleteDetails(indexes: IndexSet) async
{
await viewContext.perform
{
for index in indexes
{
print(index)
viewContext.delete(appData.activeMaster!.wrappedDetail[index])
}
do
{
try viewContext.save()
}
catch
{
print("Error deleting dope entry")
}
}
}
}
The settings view just has a navigation link to a view to select the master and an add button to add masters:
import Foundation
import SwiftUI
struct SettingsView: View
{
#Environment(\.managedObjectContext) private var viewContext
#EnvironmentObject var appData: ApplicationData
var body: some View
{
NavigationView
{
Form
{
Section(header: Text("Masters"))
{
NavigationLink(destination: SelectMastersView(selectedMaster: $appData.activeMaster), label:
{
Text(appData.activeMaster?.name ?? "Select Master")
})
Button
{
let master = Master(context: viewContext)
master.name = UUID().uuidString
do
{
try viewContext.save()
}
catch
{
print("Error adding master")
}
} label: { Image(systemName: "plus") }
}
}
}
}
}
The view for selecting the master just has a fetch request to get all masters and assign the selected one to the global app data published property:
import Foundation
import SwiftUI
struct SelectMastersView: View
{
#Environment(\.dismiss) var dismiss
#FetchRequest(entity: Master.entity(), sortDescriptors: [], animation: .default)
var masters: FetchedResults<Master>
#Binding var selectedMaster: Master?
var body: some View
{
List
{
ForEach(masters)
{ master in
Text(master.name ?? "None")
.onTapGesture
{
selectedMaster = master
dismiss()
}
}
}
.navigationBarTitle("Masters")
}
}
Edited to add extension to Master I forgot to post.
import Foundation
extension Master
{
var wrappedDetail: [Detail]
{
detail?.allObjects as! [Detail]
}
}

Answer 1

I finally figured it out this morning. I think putting the example code together last night helped quite a bit.
I got it work by creating fetch request in the detail view and passing the master into the view in init().
Here's the updated code for the tab view:
import Foundation
import SwiftUI
struct MainView: View
{
#AppStorage("selectedTab") var selectedTab: Int = 0
#EnvironmentObject var appData: ApplicationData
var body: some View
{
TabView(selection: $selectedTab)
{
DetailView(master: appData.activeMaster)
.tabItem({Label("Detail", systemImage: "house")})
.tag(0)
SettingsView()
.tabItem({Label("Settings", systemImage: "gear")})
.tag(1)
}
.environment(\.managedObjectContext, appData.container.viewContext)
}
}
and the updated detail view:
import Foundation
import SwiftUI
import CoreData
struct DetailView: View
{
#Environment(\.managedObjectContext) private var viewContext
#Environment(\.dismiss) var dismiss
#EnvironmentObject var appData: ApplicationData
#FetchRequest(entity: Detail.entity(), sortDescriptors: [])
var details: FetchedResults<Detail>
let master: Master?
init(master: Master?)
{
self.master = master
if master != nil
{
let predicate = NSPredicate(format: "%K == %#", #keyPath(Detail.master), master ?? NSNull())
_details = FetchRequest(sortDescriptors: [], predicate: predicate)
}
}
#ViewBuilder
var body: some View
{
NavigationView
{
List
{
if master != nil
{
ForEach(details)
{
detail in Text(detail.name ?? "None")
}
.onDelete(perform: { indexes in Task(priority: .high) { await deleteDetails(indexes: indexes) } } )
}
}
.toolbar
{
ToolbarItem(placement: .navigationBarTrailing)
{
EditButton().disabled(master == nil || details.isEmpty)
}
ToolbarItem(placement: .navigationBarTrailing)
{
Button
{
let detail = Detail(context: viewContext)
detail.name = UUID().uuidString
detail.master = appData.activeMaster
do
{
try viewContext.save()
}
catch
{
print("Error adding master")
}
} label: { Image(systemName: "plus") }
.disabled(appData.activeMaster == nil)
}
}
}
}
/*
* Delete indexes - assumes that appData.activeWeapon is set.
*/
private func deleteDetails(indexes: IndexSet) async
{
await viewContext.perform
{
for index in indexes
{
print(index)
viewContext.delete(appData.activeMaster!.wrappedDetail[index])
}
do
{
try viewContext.save()
}
catch
{
print("Error deleting dope entry")
}
}
}
}
This is not as clean as I'd like. I had to move to a view build for the list. I'd like to be able to create an empty fetch request so I don't have to use a view builder.