Create a dynamic list of editable objects in swiftUI, store in the mobile itself - swift

Question

I tried to create a list of editable objects in SwiftUI. Here is my idea.
First of all, the editable item is as follows:
struct Item: Identifiable {
var id: UUID
var ItemNum: Int
var notes: String = ""
}
final class ItemStore: ObservableObject {
#Published var items: [Item] = [
.init(id: .init(), ItemNum: 55),
.init(id: .init(), ItemNum: 57),
.init(id: .init(), ItemNum: 87)
]
}
After that I created a list that get data from the ItemStore:
struct ItemView: View {
#State private var editMode = EditMode.inactive
#ObservedObject var store: ItemStore
var body: some View {
NavigationView {
List {
ForEach(store.items.indexed(), id:\.1.id) {index, item in
NavigationLink(destination: ItemEditingView(item: self.$store.items[index])) {
VStack(alignment: .leading) {
Text("Item Num: \(item.itemNum)")
}
}
}
}
//.onAppear(perform: store.fetch) // want to fetch the data from the store whenever the list appear, however, no idea to perform the function?!
.navigationBarTitle("Items")
.navigationBarItems( trailing: addButton)
.environment(\.editMode, $editMode)
}
}
private var addButton: some View {
switch editMode {
case .inactive:
return AnyView(Button(action: onAdd) { Image(systemName: "plus") })
default:
return AnyView(EmptyView())
}
}
private func onAdd() {
store.items.append(Item(id: UUID(), itemNum: 10))
}
}
The editView:
struct ItemEditingView: View {
#Environment(\.presentationMode) var presentation
#Binding var item: Item
var body: some View {
Form {
Section(header: Text("Item")) {
Text(Text("Item Num: \(item.itemNum)"))
TextField("Type something...", text: $item.notes)
}
Section {
Button("Save") {
self.presentation.wrappedValue.dismiss()
}
}
}.navigationTitle(Text("Item Num: \(item.itemNum)"))
}
}
My question here:
I would like to fetch the data from 'store' onAppear. but it fails.
After I quit the app, all the previous data gone. How can I make them to keep inside my app, even the app is kill?

Answer 1

Your second question first: In terms of storing (persisting your data), you have many options. The easiest would be to store it in UserDefaults, which I'll show in my example. You could also choose to use CoreData, which would be more of a process to set up, but would give you a more robust solution later on. Many more options like Realm, Firebase, SQLite, etc. exist as well.
struct Item: Identifiable, Codable {
var id: UUID = UUID()
var itemNum: Int
var notes: String = ""
}
final class ItemStore: ObservableObject {
#Published var items: [Item] = [] {
didSet {
let encoder = JSONEncoder()
if let encoded = try? encoder.encode(items) {
UserDefaults.standard.set(encoded, forKey: "savedItems")
}
}
}
let defaultValues : [Item] = [
.init(itemNum: 55),
.init(itemNum: 57),
.init(itemNum: 87)
]
func fetch() {
let decoder = JSONDecoder()
if let savedItems = UserDefaults.standard.object(forKey: "savedItems") as? Data,
let loadedItems = try? decoder.decode([Item].self, from: savedItems) {
items = loadedItems
} else {
items = defaultValues
}
}
}
struct ContentView : View {
#State private var editMode = EditMode.inactive
#ObservedObject var store: ItemStore = ItemStore()
var body: some View {
NavigationView {
List {
ForEach(Array(store.items.enumerated()), id:\.1.id) { (index,item) in
NavigationLink(destination: ItemEditingView(item: self.$store.items[index])) {
VStack(alignment: .leading) {
Text("Item Num: \(item.itemNum)")
}
}
}
}
.onAppear(perform: store.fetch)
.navigationBarTitle("Items")
.navigationBarItems( trailing: addButton)
.environment(\.editMode, $editMode)
}
}
private var addButton: some View {
switch editMode {
case .inactive:
return AnyView(Button(action: onAdd) { Image(systemName: "plus") })
default:
return AnyView(EmptyView())
}
}
private func onAdd() {
store.items.append(Item(id: UUID(), itemNum: 10))
}
}
struct ItemEditingView: View {
#Environment(\.presentationMode) var presentation
#Binding var item: Item
var body: some View {
Form {
Section(header: Text("Item")) {
Text("Item Num: \(item.itemNum)")
TextField("Type something...", text: $item.notes)
}
Section {
Button("Save") {
self.presentation.wrappedValue.dismiss()
}
}
}.navigationTitle(Text("Item Num: \(item.itemNum)"))
}
}
Regarding your first question, the reason that fetch failed is you had no fetch method. Plus, there was nothing to fetch, since the array of items just got populated upon creation of the ItemStore each time.
Notes:
Item now conforms to Codable -- this is what allows it to get transformed into a value that can be saved/loaded from UserDefaults
fetch is now called on onAppear.
Every time the data is changed, didSet is called, saving the new data to UserDefaults
There were a number of typos and things that just plain wouldn't compile in the original code, so make sure that the changes are reflected. Some of those include: enumerated instead of indexed in the ForEach, not calling Text(Text( with nested values, using the same capitalization of itemNum throughout, etc
Important: when testing this, make sure to give the simulator a few seconds after a change to save the data into UserDefaults before killing the app and opening it again.