I'm trying to build a simple SwiftUI view that displays a number of toggles. While I can get everything to display ok, I cannot get the toggles to flip. Here's is a simplified code example:
import SwiftUI
class StoreableParam: Identifiable {
let name: String
var id: String { name }
#State var isEnabled: Bool
let toggleAction: ((Bool) -> Void)?
init(name: String, isEnabled: Bool, toggleAction: ((Bool) -> Void)? = nil) {
self.name = name
self.isEnabled = isEnabled
self.toggleAction = toggleAction
}
}
class StoreableParamViewModel: ObservableObject {
#Published var storeParams: [StoreableParam] = []
init() {
let storedParam = StoreableParam(name: "Stored Param", isEnabled: false) { value in
print("Value changed")
}
storeParams.append(storedParam)
}
}
public struct UBIStoreDebugView: View {
#StateObject var viewModel: StoreableParamViewModel
public var body: some View {
VStack {
List {
ForEach(viewModel.storeParams, id: \.id) { storeParam in
Toggle(storeParam.name, isOn: storeParam.$isEnabled)
.onChange(of: storeParam.isEnabled) {
storeParam.toggleAction?($0)
}
}
}
}.navigationBarTitle("Toggle Example")
}
}
As mentioned in the comments, there are a couple of things going on:
#State is only for use in a View
Your model should be a struct
Then, you can get a Binding using the ForEach element binding syntax:
struct StoreableParam: Identifiable {
let name: String
var id: String { name }
var isEnabled: Bool
let toggleAction: ((Bool) -> Void)?
}
class StoreableParamViewModel: ObservableObject {
#Published var storeParams: [StoreableParam] = []
init() {
let storedParam = StoreableParam(name: "Stored Param", isEnabled: false) { value in
print("Value changed")
}
storeParams.append(storedParam)
}
}
public struct UBIStoreDebugView: View {
#StateObject var viewModel: StoreableParamViewModel
public var body: some View {
VStack {
List {
ForEach($viewModel.storeParams, id: \.id) { $storeParam in
Toggle(storeParam.name, isOn: $storeParam.isEnabled)
.onChange(of: storeParam.isEnabled) {
storeParam.toggleAction?($0)
}
}
}
}
}
}
Related
I wrote test code for NavigationStack. The behavior of the code is a two-step transition(ContentView -> SubsubTestView -> DetailView).
But I got an error when I have selected a name in SubsubTestView.
A NavigationLink is presenting a value of type “User” but there is no matching navigationDestination declaration visible from the location of the link. The link cannot be activated.
Is there anything wrong with the wrong part of the code?
ContentView.swift
import SwiftUI
class EnvObj: ObservableObject {
#Published var users = [User(name: "a"), User(name: "b"), User(name: "c")]
}
struct User: Hashable, Identifiable, Equatable {
var id = UUID()
var name = ""
static func == (lhs: User, rhs: User) -> Bool{
return lhs.id == rhs.id
}
}
struct ContentView: View {
#EnvironmentObject var envObj: EnvObj
#State var moveToSubsub = false
var body: some View {
NavigationStack {
Button("To subsub") {
moveToSubsub = true
}
.navigationDestination(isPresented: $moveToSubsub) {
SubsubTestView(vm: VM(envObj: envObj))
}
}
}
}
struct SubsubTestView: View {
#EnvironmentObject var envObj: EnvObj
#StateObject var vm: VM
var body: some View {
VStack {
List(self.vm.envObj.users) { user in
NavigationLink(value: user) {
Text(user.name)
}
}
.navigationDestination(for: User.self) { user in
DetailView(vm: VMD(envObj: envObj, selectedUser: user))
}
}
}
}
class VM: ObservableObject {
var envObj: EnvObj = .init()
init(envObj: EnvObj) {
self.envObj = envObj
}
}
struct DetailView: View {
#StateObject var vm: VMD
var body: some View {
VStack {
TextField("Name: ", text: (self.$vm.selectedUser ?? User()).name)
Text(self.vm.selectedUser?.name ?? User().name)
Button("submit", action: self.vm.submit)
}
}
}
class VMD: ObservableObject {
var envObj: EnvObj = .init()
#Published var selectedUser: User?
init(envObj: EnvObj, selectedUser: User? = nil) {
self.envObj = envObj
self.selectedUser = selectedUser
}
private(set) lazy var submit = {
if let user = self.selectedUser {
self.update(user: user)
}
}
func update(user: User) {
self.envObj.users = self.envObj.users.map {
return $0 == user ? user : $0
}
}
}
func ??<T>(binding: Binding<T?>, fallback: T) -> Binding<T> {
return Binding(get: {
binding.wrappedValue ?? fallback
}, set: {
binding.wrappedValue = $0
})
}
Thanks,
I have a rather strange problem with animation on adding elements to list in SwiftUI. I have a simple model class:
struct ShoppingList: Identifiable, Equatable {
let id: UUID
var name: String
var icon: String
var items: [Item]
init(id: UUID = UUID(), name: String, icon: String, items: [Item] = []) {
self.id = id
self.name = name
self.icon = icon
self.items = items
}
static func == (lhs: ShoppingList, rhs: ShoppingList) -> Bool {
return lhs.id == rhs.id
}
}
extension ShoppingList {
struct Item: Identifiable, Equatable {
let id: UUID
var name: String
init(id: UUID = UUID(), name: String) {
self.id = id
self.name = name
}
static func == (lhs: Item, rhs: Item) -> Bool {
return lhs.id == rhs.id
}
}
}
When I pass single ShoppingList object as binding to the view, adding animation basically doesn't happen at all:
Here is code of my view:
struct ShoppingListDetailView: View {
#Binding var shoppingList: ShoppingList
#State private var newItemName = ""
var body: some View {
List {
ForEach($shoppingList.items) { $item in
Text(item.name)
}
HStack {
TextField("Add item", text: $newItem)
Button(action: addNewItem) {
Image(systemName: "plus.circle.fill")
}
.disabled(newItemName.isEmpty)
}
}
.navigationTitle(shoppingList.name)
}
private func addNewItem() {
withAnimation {
let newItem = ShoppingList.Item(name: newItemName)
shoppingList.items.append(newItem)
}
}
}
And here is code of a parent view:
struct ShoppingListsView: View {
#Binding var shoppingLists: [ShoppingList]
var body: some View {
List {
ForEach($shoppingLists) { $list in
NavigationLink(destination: ShoppingListDetailView(shoppingList: $list)) {
ShoppingListItemView(shoppingList: $list)
}
}
}
.navigationTitle("Shopping List")
}
}
But once I pass whole list of ShoppingList objects and index for a particular one, everything works as expected:
Code with passing list to the view looks like that:
struct ShoppingListDetailView: View {
#Binding var shoppingList: [ShoppingList]
var index: Int
#State private var newItemName = ""
var body: some View {
List {
ForEach($shoppingList[index].items) { $item in
Text(item.name)
}
HStack {
TextField("Add item", text: $newItem)
Button(action: addNewItem) {
Image(systemName: "plus.circle.fill")
}
.disabled(newItemName.isEmpty)
}
}
.navigationTitle(shoppingList[index].name)
}
private func addNewItem() {
withAnimation {
let newItem = ShoppingList.Item(name: newItemName)
shoppingList[index].items.append(newItem)
}
}
}
And of course parent view:
struct ShoppingListsView: View {
#Binding var shoppingLists: [ShoppingList]
var body: some View {
List {
ForEach($shoppingLists) { $list in
NavigationLink(destination: ShoppingListDetailView(shoppingList: $shoppingLists, index: shoppingLists.firstIndex(of: list)!)) {
ShoppingListItemView(shoppingList: $list)
}
}
}
.navigationTitle("Shopping List")
}
}
I'm new to Swift (not to mention SwiftUI) and I have no idea what might be wrong here. Any ideas?
I'm struggling with some basic MVVM concepts in SwiftUI. I appreciate this is probably a simple question but my brain is frazzled I can't figure it out.
Here's my models/views/viewmodels etc.
import Foundation
struct Challenges {
var all: [Challenge]
init() {
all = []
}
}
struct Challenge: Identifiable, Codable, Hashable {
private(set) var id = UUID()
private(set) var name: String
private(set) var description: String
private(set) var gpxFile: String
private(set) var travelledDistanceMetres: Double = 0
init(name: String, description: String, gpxFile: String) {
self.name = name
self.description = description
self.gpxFile = gpxFile
}
mutating func addDistance(_ distance: Double) {
travelledDistanceMetres += distance
}
}
import SwiftUI
#main
struct ActivityChallengesApp: App {
var body: some Scene {
WindowGroup {
ChallengesView()
.environmentObject(ChallengesViewModel())
}
}
}
import SwiftUI
class ChallengesViewModel: ObservableObject {
#Published var challenges: Challenges
init() {
challenges = Challenges()
challenges.all = DefaultChallenges.ALL
}
func addDistance(_ distance: Double, to challenge: Challenge) {
challenges.all[challenge].addDistance(distance)
}
}
import SwiftUI
struct ChallengesView: View {
#EnvironmentObject var challengesViewModel: ChallengesViewModel
var body: some View {
NavigationView {
List {
ForEach(challengesViewModel.challenges.all) { challenge in
NavigationLink {
ChallengeView(challenge)
.environmentObject(challengesViewModel)
} label: {
VStack(alignment: .leading) {
Text(challenge.name)
Text("\(challenge.travelledDistanceMetres)")
}
}
}
}
.navigationTitle("Challenges")
}
}
}
import SwiftUI
struct ChallengeView: View {
var challenge: Challenge
#EnvironmentObject var challengesViewModel: ChallengesViewModel
init(_ challenge: Challenge) {
self.challenge = challenge
}
var body: some View {
VStack(alignment: .leading) {
Text(challenge.name)
Text("\(challenge.travelledDistanceMetres)")
}
.onTapGesture {
handleTap()
}
}
func handleTap() {
challengesViewModel.addDistance(40, to: challenge)
}
}
I understand the concepts but I'm confused as to what the ViewModel should be.
I feel like this is overkill, i.e. sending a model object to the view and the view model as an environment object. With this set up, I call the addDistance() function in the view model from within the view to make changes to the model.
ChallengeView(challenge)
.environmentObject(challengesViewModel)
Is it better to have a view model for the collection or one view model per model object?
This is the simplest version I could come up with.
I don't really understand the need for the challenges.all ? So I took it out.
I have
a struct for the single challenge
an observable class which is publishing the challenges array
instantiate this once with #StateObject and pass it down as you did
btw: You don't need explicit initializers for structs
this is it:
#main
struct ActivityChallengesApp: App {
// here you create your model once
#StateObject var challenges = ChallengesModel()
var body: some Scene {
WindowGroup {
ChallengesView()
.environmentObject(challenges)
}
}
}
struct Challenge: Identifiable, Codable, Hashable {
var id = UUID()
var name: String
var description: String
var gpxFile: String
var travelledDistanceMetres: Double = 0
mutating func addDistance(_ distance: Double) {
travelledDistanceMetres += distance
}
}
class ChallengesModel: ObservableObject {
#Published var challenges: [Challenge]
init() {
// Test data
challenges = [
Challenge(name: "Challenge One", description: "?", gpxFile: ""),
Challenge(name: "Challenge Two", description: "?", gpxFile: ""),
Challenge(name: "Last Challenge", description: "?", gpxFile: "")
]
}
func addDistance(_ distance: Double, to challenge: Challenge) {
// find the challenge and update it
if let i = challenges.firstIndex(where: {$0.id == challenge.id}) {
challenges[i].addDistance(distance)
}
}
}
struct ChallengesView: View {
#EnvironmentObject var challengesModel: ChallengesModel
var body: some View {
NavigationView {
List {
ForEach(challengesModel.challenges) { challenge in
NavigationLink {
ChallengeView(challenge: challenge)
.environmentObject(challengesModel)
} label: {
VStack(alignment: .leading) {
Text(challenge.name)
Text("\(challenge.travelledDistanceMetres)")
}
}
}
}
.navigationTitle("Challenges")
}
}
}
struct ChallengeView: View {
var challenge: Challenge
#EnvironmentObject var challengesModel: ChallengesModel
var body: some View {
VStack(alignment: .leading) {
Text(challenge.name)
Text("\(challenge.travelledDistanceMetres)")
}
.onTapGesture {
handleTap()
}
}
func handleTap() {
challengesModel.addDistance(40, to: challenge)
}
}
Is there a way to create an extension for Optional value so that we don't need to create custom binding individually.
class ViewModel: ObservableObject {
#Published var text: String?
}
struct ContentView: View {
#ObservedObject var model: ViewModel
var body: some View {
let binding = Binding(
get: { self.model.text ?? "" },
set: { self.model.text = $0 }
)
return VStack {
TextField("Text", text: binding)
}
}
}
I'm thinking about doing something like this
extension Optional where Wrapped == String {
func optionalBinding() -> Binding<String> {
return Binding(get: {
self ?? ""
}, set: { newValue in
self = newValue
})
}
}
Any suggestions on this?
You may try extending Binding instead of Optional:
extension Binding where Value == String? {
var optionalBinding: Binding<String> {
.init(
get: {
self.wrappedValue ?? ""
}, set: {
self.wrappedValue = $0
}
)
}
}
And use it like this:
class ViewModel: ObservableObject {
#Published var text: String?
}
struct ContentView: View {
#ObservedObject var model = ViewModel()
var body: some View {
VStack {
TextField("Text", text: $model.text.optionalBinding)
Text(String(describing: model.text))
}
}
}
Nil-coalescing operator.
public extension Binding {
static func ?? <Wrapped>(optional: Self, defaultValue: Wrapped) -> Binding<Wrapped>
where Value == Wrapped? {
.init(
get: { optional.wrappedValue ?? defaultValue },
set: { optional.wrappedValue = $0 }
)
}
}
var wrappedValue: String? = "📬"
#Binding(
get: { wrappedValue },
set: { wrappedValue = $0 }
) var string;
let stringOrDefault = $string ?? "📭"
XCTAssertEqual(stringOrDefault.wrappedValue, "📬")
string = nil
XCTAssertEqual(stringOrDefault.wrappedValue, "📭")
stringOrDefault.wrappedValue = "📪"
XCTAssertEqual(string, "📪")
To build on #pawello2222's answer, you can use a more generic extension catching all values:
extension Binding {
func unwrapped<T>(_ defaultValue: T) -> Binding<T> where Value == Optional<T> {
let binding = Binding<T>(get: { self.wrappedValue ?? defaultValue }, set: { self.wrappedValue = $0 })
return binding
}
}
And it is used like:
class ViewModel: ObservableObject {
#Published var text: String?
}
struct ContentView: View {
#ObservedObject var model = ViewModel()
var body: some View {
VStack {
TextField("Text", text: $model.text.unwrapped(String()))
Text(String(describing: model.text))
}
}
}
I'm an early bird in programming so I know this question can be ridiculous from the point of view of an expert but I'm stuck in this situation from several days.
I would like to update a row by using a button "Edit" (pencil) after having used another button to store the item with a TextField.
Here's the code:
class Food: Hashable, Codable, Equatable {
var id : UUID = UUID()
var name : String
init(name: String) {
self.name = name
}
static func == (lhs: Food, rhs: Food) -> Bool {
return lhs.name == rhs.name
}
func hash(into hasher: inout Hasher) {
hasher.combine(name)
}
}
class Manager: ObservableObject {
let objectWillChange = PassthroughSubject<Void, Never>()
#Published var shoppingChart: [Food] = []
init() {
let milk = Food(name: "Milk")
let coffee = Food(name: "Coffee")
shoppingChart.append(milk)
shoppingChart.append(coffee)
}
func newFood(name: String) {
let food = Food(name: name)
shoppingChart.insert(food, at: 0)
}
}
struct ContentView: View {
#ObservedObject var dm : Manager
#State var isAddFoodOpened = false
var body: some View {
VStack {
List {
ForEach(self.dm.shoppingChart, id:\.self) { food in
HStack {
Text(food.name)
Image(systemName: "pencil")
}
}
}
self.buttonAdd
}
}
var buttonAdd: some View {
Button(action: {
self.isAddFoodOpened.toggle()
}) {
Text("Add")
}
.sheet(isPresented: $isAddFoodOpened) {
Add(dm: self.dm, fieldtext: "", isAddFoodOpened: self.$isAddFoodOpened)
}
}
}
struct Add: View {
#ObservedObject var dm : Manager
#State var fieldtext : String = ""
#Binding var isAddFoodOpened : Bool
var body: some View {
VStack {
TextField("Write a food", text: $fieldtext)
buttonSave
}
}
var buttonSave : some View {
Button(action: {
self.dm.newFood(name: self.fieldtext)
self.isAddFoodOpened = false
}) {
Text("Save")
}
}
}
The #ObservedObject var dm : Manager object is never initialized.
Try initialized dm in ContentView like this:
#ObservedObject var dm = Manager()
Ok, so if I understand correctly you want to update/edit a row by using a button "Edit".
This will do it:
struct ContentView: View {
#ObservedObject var dm : Manager
#State var isAddFoodOpened = false
#State var isEditOpened = false
#State var fieldtext : String = ""
var body: some View {
VStack {
List {
ForEach(0..<self.dm.shoppingChart.count, id:\.self) { i in
HStack {
Text(self.dm.shoppingChart[i].name)
Button(action: { self.isEditOpened.toggle() }) {
Image(systemName: "pencil")
}.sheet(isPresented: self.$isEditOpened) {
TextField(self.dm.shoppingChart[i].name, text: self.$fieldtext, onEditingChanged: { _ in
self.dm.shoppingChart[i].name = self.fieldtext
})
}
}
}
}
self.buttonAdd
}
}
var buttonAdd: some View {
Button(action: {
self.isAddFoodOpened.toggle()
}) {
Text("Add")
}
.sheet(isPresented: $isAddFoodOpened) {
Add(dm: self.dm, fieldtext: "", isAddFoodOpened: self.$isAddFoodOpened)
}
}
}