I am making an app that has information about different woods, herbs and spices, and a few other things. I am including the ability to save their favorite item to a favorites list, so I have a heart button that the user can press to add it to the favorites. Pressing the button toggles the isFavorite property of the item and then leaving the page calls a method that encodes the data to save it to the user's device. The problem that I am running into is that it is not encoding the updated value of the isFavorite property. It is still encoding the value as false, so the favorites list is not persisting after closing and reopening the app.
Here is my Wood.swift code, this file sets up the structure for Wood items. I also included the test data that I was using to make sure that it displayed properly in the Wood extension:
import Foundation
struct Wood: Identifiable, Codable {
var id = UUID()
var mainInformation: WoodMainInformation
var preparation: [Preparation]
var isFavorite = false
init(mainInformation: WoodMainInformation, preparation: [Preparation]) {
self.mainInformation = mainInformation
self.preparation = preparation
}
}
struct WoodMainInformation: Codable {
var category: WoodCategory
var description: String
var medicinalUses: [String]
var magicalUses: [String]
var growZone: [String]
var lightLevel: String
var moistureLevel: String
var isPerennial: Bool
var isEdible: Bool
}
enum WoodCategory: String, CaseIterable, Codable {
case oak = "Oak"
case pine = "Pine"
case cedar = "Cedar"
case ash = "Ash"
case rowan = "Rowan"
case willow = "Willow"
case birch = "Birch"
}
enum Preparation: String, Codable {
case talisman = "Talisman"
case satchet = "Satchet"
case tincture = "Tincture"
case salve = "Salve"
case tea = "Tea"
case ointment = "Ointment"
case incense = "Incense"
}
extension Wood {
static let woodTypes: [Wood] = [
Wood(mainInformation: WoodMainInformation(category: .oak,
description: "A type of wood",
medicinalUses: ["Healthy", "Killer"],
magicalUses: ["Spells", "Other Witchy Stuff"],
growZone: ["6A", "5B"],
lightLevel: "Full Sun",
moistureLevel: "Once a day",
isPerennial: false,
isEdible: true),
preparation: [Preparation.incense, Preparation.satchet]),
Wood(mainInformation: WoodMainInformation(category: .pine,
description: "Another type of wood",
medicinalUses: ["Healthy"],
magicalUses: ["Spells"],
growZone: ["11G", "14F"],
lightLevel: "Full Moon",
moistureLevel: "Twice an hour",
isPerennial: true,
isEdible: true),
preparation: [Preparation.incense, Preparation.satchet])
]
}
Here is my WoodData.swift file, this file contains methods that allow the app to display the correct wood in the list of woods, as well as encode, and decode the woods:
import Foundation
class WoodData: ObservableObject {
#Published var woods = Wood.woodTypes
var favoriteWoods: [Wood] {
woods.filter { $0.isFavorite }
}
func woods(for category: WoodCategory) -> [Wood] {
var filteredWoods = [Wood]()
for wood in woods {
if wood.mainInformation.category == category {
filteredWoods.append(wood)
}
}
return filteredWoods
}
func woods(for category: [WoodCategory]) -> [Wood] {
var filteredWoods = [Wood]()
filteredWoods = woods
return filteredWoods
}
func index(of wood: Wood) -> Int? {
for i in woods.indices {
if woods[i].id == wood.id {
return i
}
}
return nil
}
private var dataFileURL: URL {
do {
let documentsDirectory = try FileManager.default.url(for: .documentDirectory, in: .userDomainMask, appropriateFor: nil, create: true)
return documentsDirectory.appendingPathComponent("evergreenData")
}
catch {
fatalError("An error occurred while getting the url: \(error)")
}
}
func saveWoods() {
if let encodedData = try? JSONEncoder().encode(woods) {
do {
try encodedData.write(to: dataFileURL)
let string = String(data: encodedData, encoding: .utf8)
print(string)
}
catch {
fatalError("An error occurred while saving woods: \(error)")
}
}
}
func loadWoods() {
guard let data = try? Data(contentsOf: dataFileURL) else { return }
do {
let savedWoods = try JSONDecoder().decode([Wood].self, from: data)
woods = savedWoods
}
catch {
fatalError("An error occurred while loading woods: \(error)")
}
}
}
Finally, this is my WoodsDetailView.swift file, this file displays the information for the wood that was selected, as well as calls the method that encodes the wood data:
import SwiftUI
struct WoodsDetailView: View {
#Binding var wood: Wood
#State private var woodsData = WoodData()
var body: some View {
VStack {
List {
Section(header: Text("Description")) {
Text(wood.mainInformation.description)
}
Section(header: Text("Preparation Techniques")) {
ForEach(wood.preparation, id: \.self) { technique in
Text(technique.rawValue)
}
}
Section(header: Text("Edible?")) {
if wood.mainInformation.isEdible {
Text("Edible")
}
else {
Text("Not Edible")
}
}
Section(header: Text("Medicinal Uses")) {
ForEach(wood.mainInformation.medicinalUses.indices, id: \.self) { index in
let medicinalUse = wood.mainInformation.medicinalUses[index]
Text(medicinalUse)
}
}
Section(header: Text("Magical Uses")) {
ForEach(wood.mainInformation.magicalUses.indices, id: \.self) { index in
let magicalUse = wood.mainInformation.magicalUses[index]
Text(magicalUse)
}
}
Section(header: Text("Grow Zone")) {
ForEach(wood.mainInformation.growZone.indices, id: \.self) { index in
let zone = wood.mainInformation.growZone[index]
Text(zone)
}
}
Section(header: Text("Grow It Yourself")) {
Text("Water: \(wood.mainInformation.moistureLevel)")
Text("Needs: \(wood.mainInformation.lightLevel)")
if wood.mainInformation.isPerennial {
Text("Perennial")
}
else {
Text("Annual")
}
}
}
}
.navigationTitle(wood.mainInformation.category.rawValue)
.onDisappear {
woodsData.saveWoods()
}
.toolbar {
ToolbarItem {
HStack {
Button(action: {
wood.isFavorite.toggle()
}) {
Image(systemName: wood.isFavorite ? "heart.fill" : "heart")
}
}
}
}
}
}
struct WoodsDetailView_Previews: PreviewProvider {
#State static var wood = Wood.woodTypes[0]
static var previews: some View {
WoodsDetailView(wood: $wood)
}
}
This is my MainTabView.swift file:
import SwiftUI
struct MainTabView: View {
#StateObject var woodData = WoodData()
var body: some View {
TabView {
NavigationView {
List {
WoodsListView(viewStyle: .allCategories(WoodCategory.allCases))
}
}
.tabItem { Label("Main", systemImage: "list.dash")}
NavigationView {
List {
WoodsListView(viewStyle: .favorites)
}
.navigationTitle("Favorites")
}.tabItem { Label("Favorites", systemImage: "heart.fill")}
}
.environmentObject(woodData)
.onAppear {
woodData.loadWoods()
}
.preferredColorScheme(.dark)
}
}
struct MainTabView_Previews: PreviewProvider {
static var previews: some View {
MainTabView()
}
}
This is my WoodListView.swift file:
import SwiftUI
struct WoodsListView: View {
#EnvironmentObject private var woodData: WoodData
let viewStyle: ViewStyle
var body: some View {
ForEach(woods) { wood in
NavigationLink(wood.mainInformation.category.rawValue, destination: WoodsDetailView(wood: binding(for: wood)))
}
}
}
extension WoodsListView {
enum ViewStyle {
case favorites
case singleCategory(WoodCategory)
case allCategories([WoodCategory])
}
private var woods: [Wood] {
switch viewStyle {
case let .singleCategory(category):
return woodData.woods(for: category)
case let .allCategories(category):
return woodData.woods(for: category)
case .favorites:
return woodData.favoriteWoods
}
}
func binding(for wood: Wood) -> Binding<Wood> {
guard let index = woodData.index(of: wood) else {
fatalError("Wood not found")
}
return $woodData.woods[index]
}
}
struct WoodsListView_Previews: PreviewProvider {
static var previews: some View {
WoodsListView(viewStyle: .singleCategory(.ash))
.environmentObject(WoodData())
}
}
Any assistance into why it is not encoding the toggled isFavorite property will be greatly appreciated.
Your problem is that structs are value types in Swift. Essentially this means that the instance of Wood that you have in WoodsDetailView is not the same instance that is in your array in your model (WoodData); It is a copy (Technically, the copy is made as soon as you modify the isFavourite property).
In SwiftUI it is important to maintain separation of responsibilities between the view and the model.
Changing the favourite status of a Wood is something the view should ask the model to do.
This is where you have a second issue; In your detail view you are creating a separate instance of your model; You need to refer to a single instance.
You have a good start; you have put your model instance in the environment where views can access it.
First, change the detail view to remove the binding, refer to the model from the environment and ask the model to do the work:
struct WoodsDetailView: View {
var wood: Wood
#EnvironmentObject private var woodsData: WoodData
var body: some View {
VStack {
List {
Section(header: Text("Description")) {
Text(wood.mainInformation.description)
}
Section(header: Text("Preparation Techniques")) {
ForEach(wood.preparation, id: \.self) { technique in
Text(technique.rawValue)
}
}
Section(header: Text("Edible?")) {
if wood.mainInformation.isEdible {
Text("Edible")
}
else {
Text("Not Edible")
}
}
Section(header: Text("Medicinal Uses")) {
ForEach(wood.mainInformation.medicinalUses, id: \.self) { medicinalUse in
Text(medicinalUse)
}
}
Section(header: Text("Magical Uses")) {
ForEach(wood.mainInformation.magicalUses, id: \.self) { magicalUse in
Text(magicalUse)
}
}
Section(header: Text("Grow Zone")) {
ForEach(wood.mainInformation.growZone, id: \.self) { zone in
Text(zone)
}
}
Section(header: Text("Grow It Yourself")) {
Text("Water: \(wood.mainInformation.moistureLevel)")
Text("Needs: \(wood.mainInformation.lightLevel)")
if wood.mainInformation.isPerennial {
Text("Perennial")
}
else {
Text("Annual")
}
}
}
}
.navigationTitle(wood.mainInformation.category.rawValue)
.onDisappear {
woodsData.saveWoods()
}
.toolbar {
ToolbarItem {
HStack {
Button(action: {
self.woodsData.toggleFavorite(for: wood)
}) {
Image(systemName: wood.isFavorite ? "heart.fill" : "heart")
}
}
}
}
}
}
struct WoodsDetailView_Previews: PreviewProvider {
static var wood = Wood.woodTypes[0]
static var previews: some View {
WoodsDetailView(wood: wood)
}
}
I also got rid of the unnecessary use of indices when listing the properties.
Now, add a toggleFavorite function to your WoodData object:
func toggleFavorite(for wood: Wood) {
guard let index = self.woods.firstIndex(where:{ $0.id == wood.id }) else {
return
}
self.woods[index].isFavorite.toggle()
}
You can also remove the index(of wood:Wood) function (which was really just duplicating Array's firstIndex(where:) function) and the binding(for wood:Wood) function.
Now, not only does your code do what you want, but you have hidden the mechanics of toggling a favorite from the view; It simply asks for the favorite status to be toggled and doesn't need to know what this actually involves.
I've adapted an example from blog post which lets me share data associated with the selected element in a ForEach with another view on the screen. It sets up the FocusedValueKey conformance:
struct FocusedNoteValue: FocusedValueKey {
typealias Value = String
}
extension FocusedValues {
var noteValue: FocusedNoteValue.Value? {
get { self[FocusedNoteValue.self] }
set { self[FocusedNoteValue.self] = newValue }
}
}
Then it has a ForEach view with Buttons, where the focused Button uses the .focusedValue modifier to set is value to the NotePreview:
struct ContentView: View {
var body: some View {
Group {
NoteEditor()
NotePreview()
}
}
}
struct NoteEditor: View {
var body: some View {
VStack {
ForEach((0...5), id: \.self) { num in
let numString = "\(num)"
Button(action: {}, label: {
(Text(numString))
})
.focusedValue(\.noteValue, numString)
}
}
}
}
struct NotePreview: View {
#FocusedValue(\.noteValue) var note
var body: some View {
Text(note ?? "Note is not focused")
}
}
This works fine with the ForEach, but fails to work when the ForEach is replaced with List. How could I get this to work with List, and why is it unable to do so out of the box?
I'm trying to show some placeholder data when the array is empty. This works in iOS 13.7 but something has changed in iOS 14.3 so when the last item is deleted you get this crash:
Fatal error: Index out of range: file Swift/ContiguousArrayBuffer.swift, line 444
If I comment out testStore.data.isEmpty and just return the Form I get no crash.
How can I show placeholder when array is empty in iOS 14.3?
struct Test: Identifiable {
var text: String
var id: String { text }
}
extension Test {
final class Store: ObservableObject {
#Published var data = [Test(text: "Hi"), Test(text: "Bye")]
}
}
struct TestList: View {
#EnvironmentObject var testStore: Test.Store
var body: some View {
Group {
if testStore.data.isEmpty {
Text("Empty")
} else {
Form {
ForEach(testStore.data.indices, id: \.self) { index in
TestRow(test: $testStore.data[index], deleteHandler: { testStore.data.remove(at: index) })
}
}
}
}
}
}
struct TestRow: View {
#Binding var test: Test
let deleteHandler: (() -> ())
var body: some View {
HStack {
Text(test.text)
.font(.headline)
Spacer()
Button(action: deleteHandler, label: Image(systemName: "trash"))
}
}
}
You can use the extension proposed here:
struct Safe<T: RandomAccessCollection & MutableCollection, C: View>: View {
typealias BoundElement = Binding<T.Element>
private let binding: BoundElement
private let content: (BoundElement) -> C
init(_ binding: Binding<T>, index: T.Index, #ViewBuilder content: #escaping (BoundElement) -> C) {
self.content = content
self.binding = .init(get: { binding.wrappedValue[index] },
set: { binding.wrappedValue[index] = $0 })
}
var body: some View {
content(binding)
}
}
Then, if you also want to keep ForEach instead of List you can do:
struct TestList: View {
#EnvironmentObject var testStore: Test.Store
var body: some View {
Group {
if testStore.data.isEmpty {
Text("Empty")
} else {
Form {
ForEach(testStore.data.indices, id: \.self) { index in
Safe($testStore.data, index: index) { binding in
TestRow(test: binding, deleteHandler: { testStore.data.remove(at: index) })
}
}
}
}
}
}
}
I have a model like this:
protocol PurchasableProduct {
var randomId: String { get }
}
class Cart: Identifiable {
var items: [PurchasableProduct]
init(items: [PurchasableProduct]) {
self.items = items
}
}
class Product: Identifiable, PurchasableProduct {
var randomId = UUID().uuidString
var notes: String = ""
}
class DigitalGood: Identifiable, PurchasableProduct {
var randomId = UUID().uuidString
}
where items conform to protocol PurchasableProduct.
I want to build a View that shows cart like this:
struct CartView: View {
#State var cart: Cart
var body: some View {
List {
ForEach(cart.items.indices) { index in
CartItemView(item: self.$cart.items[index])
}
}
}
}
where CartItemView is:
struct CartItemView: View {
#Binding var item: PurchasableProduct
var body: some View {
VStack {
if self.item is Product {
Text("Product")
} else {
Text("Digital Good")
}
}
}
}
That's working and give me result as
This (screenshot)
But I want to extend this a but more that my items element can be passed as a binding variable lets say as:
struct CartItemView: View {
#Binding var item: PurchasableProduct
var body: some View {
VStack {
if self.item is Product {
VStack {
TextField("add notes", text: (self.$item as! Product).notes) // ❌ Cannot convert value of type 'String' to expected argument type 'Binding<String>'
TextField("add notes", text: (self.$item as! Binding<Product>).notes) // ⚠️ Cast from 'Binding<PurchasableProduct>' to unrelated type 'Binding<Product>' always fails
}
} else {
Text("Digital Good")
}
}
}
}
What I'm trying to achieve is:
I have a collection of items that depends on a class should be drawn differently
Items have different editable sync that should be binded into CartView
Not sure if thats syntax issue or my approach issue ... how to cast this on body to get the correct view based on type?
You may create a custom binding:
struct CartItemView: View {
#Binding var item: PurchasableProduct
var product: Binding<Product>? {
guard item is Product else { return nil }
return .init(
get: {
self.$item.wrappedValue as! Product
}, set: {
self.$item.wrappedValue = $0
}
)
}
var body: some View {
VStack {
if product != nil {
TextField("add notes", text: product!.notes)
} else {
Text("Digital Good")
}
}
}
}
So, I have the following View Model where I fetch the data:
import Foundation
import SwiftUI
import Combine
import Alamofire
class AllStatsViewModel: ObservableObject {
#Published var isLoading: Bool = true
#Published var stats = [CountryStats]()
func fetchGlobalStats() {
let request = AF.request("https://projectcovid.deadpool.wtf/all")
request.responseDecodable(of: AllCountryStats.self) { (response) in
guard let globalStats = response.value else { return }
DispatchQueue.main.async {
self.stats = globalStats.data
}
self.isLoading = false
}
}
}
And this is the view:
struct CardView: View {
#ObservedObject var allStatsVM = AllStatsViewModel()
var body: some View {
VStack {
Text(self.allStatsVM.stats[0].country)
}
.onAppear {
self.allStatsVM.fetchGlobalStats()
}
}
}
I'd like to access only the first element of the data, but the problem I face is that when the view loads, the data is not loaded, so I get an index out of range error at
Text(self.allStatsVM.stats[0].country)
Is there a way, I can access the first element?
try this:
struct CardView: View {
#ObservedObject var allStatsVM = AllStatsViewModel()
var body: some View {
VStack {
if self.allStatsVM.stats.count > 0 {
Text(self.allStatsVM.stats[0].country)
} else {
Text ("data loading")
}
}
.onAppear {
self.allStatsVM.fetchGlobalStats()
}
}
}