SwiftUI dismiss after list reorder - swift

Question

I'm trying to reorder my CoreData items, but when I try reorder items and drop cell my list view is being dismissed. All changes are saved and displayed correctly in other views and in the list that is modified.
Here's my code
import SwiftUI
struct DaysOrderView: View {
#Environment(\.managedObjectContext) var moc
#FetchRequest(entity: Days.entity(), sortDescriptors:[NSSortDescriptor(key: "id", ascending: true)]) var days : FetchedResults<Days>
var body: some View {
List {
ForEach(days, id: \.self ) { day in
HStack {
Image(systemName: day.isDisplayed.boolValue ? "checkmark.circle.fill" : "checkmark.circle").foregroundColor(.yellow)
Text(day.name)
}
}
.onMove(perform: onMove)
}
.toolbar {
EditButton()
}
}
private func onMove(source: IndexSet, destination: Int) {
var revisedItems: [ Days ] = days.map{ $0 }
revisedItems.move(fromOffsets: source, toOffset: destination )
for reverseIndex in stride( from: revisedItems.count - 1,
through: 0,
by: -1 )
{
revisedItems[ reverseIndex ].id = Int16( reverseIndex )
}
}
}

Answer 1

An id is not arbitrary, and changing id's to change the sort order can have consequences. If you want a changeable order, I would recommend keeping track of it with an attribute dedicated to the sort order and change that.
I put together a quick app using both a sortOrder attribute and an id attribute. When I used 'idas anInt16` and sorted and changed on that, I got the following error:
ForEach<FetchedResults, Int16, NavigationLink<Text, Text>>: the
ID 2 occurs multiple times within the collection, this will give
undefined results!
Swapping it out for a sortOrder attribute gave no errors. Since you didn't, understandably with Core Data, post the entire code, I can't be 100% sure, but I am betting your problem comes down to this issue. Also, you should make your id a UUID() that is what it exists for, and do not change the id. It is like the parents with multiple kids swapping the kids' names on a daily basis. It might work, but most likely it is chaos.
FWIW the code used to test:
struct ContentView: View {
#Environment(\.managedObjectContext) private var viewContext
#FetchRequest(
sortDescriptors: [NSSortDescriptor(keyPath: \Item.sortOrder, ascending: true)],
animation: .default)
private var items: FetchedResults<Item>
var body: some View {
NavigationView {
List {
ForEach(items) { item in
NavigationLink {
Text("Item \(item.sortOrder) at \(item.timestamp!, formatter: itemFormatter)")
} label: {
Text(item.timestamp!, formatter: itemFormatter)
}
}
.onDelete(perform: deleteItems)
.onMove(perform: onMove)
}
.toolbar {
ToolbarItem(placement: .navigationBarTrailing) {
EditButton()
}
ToolbarItem {
Button(action: addItem) {
Label("Add Item", systemImage: "plus")
}
}
}
Text("Select an item")
}
}
private func addItem() {
withAnimation {
let newItem = Item(context: viewContext)
newItem.timestamp = Date()
newItem.id = UUID()
newItem.sortOrder = Int16(items.count)
do {
try viewContext.save()
} catch {
// Replace this implementation with code to handle the error appropriately.
// fatalError() causes the application to generate a crash log and terminate. You should not use this function in a shipping application, although it may be useful during development.
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 implementation with code to handle the error appropriately.
// fatalError() causes the application to generate a crash log and terminate. You should not use this function in a shipping application, although it may be useful during development.
let nsError = error as NSError
fatalError("Unresolved error \(nsError), \(nsError.userInfo)")
}
}
}
private func onMove(source: IndexSet, destination: Int) {
var revisedItems: [ Item ] = items.map{ $0 }
revisedItems.move(fromOffsets: source, toOffset: destination )
for reverseIndex in stride( from: revisedItems.count - 1,
through: 0,
by: -1 )
{
revisedItems[ reverseIndex ].sortOrder = Int16( reverseIndex )
}
}
}
It is the base "Use Core Data" code that I added the attributes to.