Unmodified SwiftUI / Core Data default app code does not run in simulator? - xcode

Question

When I create and run a new, unmodified, Core Data / SwiftUI app project in Xcode (12.3), the simulator shows a blank screen. Code below.
Upon creation of the new app project, SwiftUI code is generated that includes a List along with Add and Edit buttons. The UI displays correctly in Xcode's preview but not in the simulator.
This is the default code in the ContentView.swift file:
import SwiftUI
import CoreData
struct ContentView: View {
#Environment(\.managedObjectContext) private var viewContext
#FetchRequest(
sortDescriptors: [NSSortDescriptor(keyPath: \Item.timestamp, ascending: true)],
animation: .default)
private var items: FetchedResults<Item>
var body: some View {
List {
ForEach(items) { item in
Text("Item at \(item.timestamp!, formatter: itemFormatter)")
}
.onDelete(perform: deleteItems)
}
.toolbar {
#if os(iOS)
EditButton()
#endif
Button(action: addItem) {
Label("Add Item", systemImage: "plus")
}
}
}
private func addItem() {
withAnimation {
let newItem = Item(context: viewContext)
newItem.timestamp = Date()
do {
try viewContext.save()
} catch {
// Replace this...
let nsError = error as NSError
fatalError("Unresolved error \(nsError), \(nsError.userInfo)")
}
}
}
private func deleteItems(offsets: IndexSet) {
withAnimation {
offsets.map { items[$0] }.forEach(viewContext.delete)
do {
try viewContext.save()
} catch {
// Replace this...
let nsError = error as NSError
fatalError("Unresolved error \(nsError), \(nsError.userInfo)")
}
}
}
}
private let itemFormatter: DateFormatter = {
let formatter = DateFormatter()
formatter.dateStyle = .short
formatter.timeStyle = .medium
return formatter
}()
struct ContentView_Previews: PreviewProvider {
static var previews: some View {
ContentView().environment(\.managedObjectContext, PersistenceController.preview.container.viewContext)
}
}
You can reproduce this simply by creating a new iOS App project with SwiftUI and Core Data enabled:
Trying to wrap my head around this stuff. Getting stuck on the default code is not promising!

Answer 1

IMHO Yes this seems like a bug with the example, might be worth submitting with a feedback
Problem:
Since the view is not inside the navigation view the navigation buttons are not visible
The tool bar modifier requires to use the ToolbarItem which is missing.
Overview:
Please wrap the view contents inside a NavigationView
Wrap the tool bar buttons inside ToolbarItem
Solution:
Replace the body computed property as follows:
var body: some View {
NavigationView {
List {
ForEach(items) { item in
Text("Item at \(item.timestamp!, formatter: itemFormatter)")
}
.onDelete(perform: deleteItems)
}
.toolbar {
#if os(iOS)
ToolbarItem(placement: .navigationBarTrailing) {
EditButton()
}
#endif
ToolbarItem(placement: .navigationBarLeading) {
Button(action: addItem) {
Label("Add Item", systemImage: "plus")
}
}
}
}
}