Saving favorites to UserDefaults using struct id - swiftui

Question

I'm trying to save the users favorite cities in UserDefaults. Found this solution saving the struct ID - builds and runs but does not appear to be saving: On app relaunch, the previously tapped Button is reset.
I'm pretty sure I'm missing something…
Here's my data struct and class:
struct City: Codable {
var id = UUID().uuidString
var name: String
}
class Favorites: ObservableObject {
private var cities: Set<String>
let defaults = UserDefaults.standard
var items: [City] = [
City(name: "London"),
City(name: "Paris"),
City(name: "Berlin")
]
init() {
let decoder = PropertyListDecoder()
if let data = defaults.data(forKey: "Favorites") {
let cityData = try? decoder.decode(Set<String>.self, from: data)
self.cities = cityData ?? []
return
} else {
self.cities = []
}
}
func getTaskIds() -> Set<String> {
return self.cities
}
func contains(_ city: City) -> Bool {
cities.contains(city.id)
}
func add(_ city: City) {
objectWillChange.send()
cities.contains(city.id)
save()
}
func remove(_ city: City) {
objectWillChange.send()
cities.remove(city.id)
save()
}
func save() {
let encoder = PropertyListEncoder()
if let encoded = try? encoder.encode(tasks) {
defaults.setValue(encoded, forKey: "Favorites")
}
}
}
and here's the TestDataView
struct TestData: View {
#StateObject var favorites = Favorites()
var body: some View {
ForEach(self.favorites.items, id: \.id) { item in
VStack {
Text(item.title)
Button(action: {
if self.favorites.contains(item) {
self.favorites.remove(item)
} else {
self.favorites.add(item)
}
}) {
HStack {
Image(systemName: self.favorites.contains(item) ? "heart.fill" : "heart")
.foregroundColor(self.favorites.contains(item) ? .red : .white)
}
}
}
}
}
}

Answer 1

There were a few issues, which I'll address below. Here's the working code:
struct ContentView: View {
#StateObject var favorites = Favorites()
var body: some View {
VStack(spacing: 10) {
ForEach(Array(self.favorites.cities), id: \.id) { item in
VStack {
Text(item.name)
Button(action: {
if self.favorites.contains(item) {
self.favorites.remove(item)
} else {
self.favorites.add(item)
}
}) {
HStack {
Image(systemName: self.favorites.contains(item) ? "heart.fill" : "heart")
.foregroundColor(self.favorites.contains(item) ? .red : .black)
}
}
}
}
}
}
}
struct City: Codable, Hashable {
var id = UUID().uuidString
var name: String
}
class Favorites: ObservableObject {
#Published var cities: Set<City> = []
#Published var favorites: Set<String> = []
let defaults = UserDefaults.standard
var initialItems: [City] = [
City(name: "London"),
City(name: "Paris"),
City(name: "Berlin")
]
init() {
let decoder = PropertyListDecoder()
if let data = defaults.data(forKey: "Cities") {
cities = (try? decoder.decode(Set<City>.self, from: data)) ?? Set(initialItems)
} else {
cities = Set(initialItems)
}
self.favorites = Set(defaults.array(forKey: "Favorites") as? [String] ?? [])
}
func getTaskIds() -> Set<String> {
return self.favorites
}
func contains(_ city: City) -> Bool {
favorites.contains(city.id)
}
func add(_ city: City) {
favorites.insert(city.id)
save()
}
func remove(_ city: City) {
favorites.remove(city.id)
save()
}
func save() {
let encoder = PropertyListEncoder()
if let encoded = try? encoder.encode(self.cities) {
self.defaults.set(encoded, forKey: "Cities")
}
self.defaults.set(Array(self.favorites), forKey: "Favorites")
defaults.synchronize()
}
}
Issues with the original:
The biggest issue was that items was getting recreated on each new launch and City has an id that is assigned a UUID on creation. This guaranteed that every new launch, each batch of cities would have different UUIDs, so a saving situation would never work.
There were some general typos and references to properties that didn't actually exist.
What I did:
Made cities and favorites both #Published properties so that you don't have to call objectWillChange.send by hand
On init, load both the cities and the favorites. That way, the cities, once initially created, will always have the same UUIDs, since they're getting loaded from a saved state
On save, I save both Sets -- the favorites and the cities
In the original ForEach, I iterate through all of the cities and then only mark the ones that are part of favorites
Important note: While testing this, I discovered that at least on Xcode 12.3 / iOS 14.3, syncing to UserDefaults is slow, even when using the now-unrecommended synchronize method. I kept wondering why my changes weren't reflected when I killed and then re-opened the app. Eventually figured out that everything works if I give it about 10-15 seconds to sync to UserDefaults before killing the app and then opening it again.