I would like StateObject preserve state even after its view disappeared. But I failed. Here is my code:
import SwiftUI
struct ContentView: View {
#State var b: Bool = false
var body: some View {
VStack {
Toggle(isOn: $b, label: {Text("Show Button")})
if b {A()} else {Text("hi")}
}
}
}
struct A: View {
#StateObject var o: Obj = Obj()
var body: some View {
Button {o.i += 1} label: {Text("i == \(o.i.description)")}
}
}
class Obj: ObservableObject {
#Published var i: Int = 1
}
After the Toggle switched, the state o.i was reseted to 1. How can I preserve the state?
try this:
struct ContentView: View {
#State var b: Bool = false
#StateObject var o: Obj = Obj()
var body: some View {
VStack {
Toggle(isOn: $b, label: {Text("Show Button")})
if b {A(o: o)} else {Text("hi")}
}
}
}
struct A: View {
#ObservedObject var o: Obj
var body: some View {
Button {o.i += 1} label: {Text("i == \(o.i.description)")}
}
}
Related
When I press the Move button in the contextMenu, I change the isCopied and setOriginPath variables in the EnvironmentObject. When this change is made, the List view is cleared and I can't see anything on the screen. I don't have any problems when I don't use EnvironmentObject.
ContextMenu:
.contextMenu {
Button {
safeFileVM.hideSelectedFile(fileName: currentFile.fileName)
safeFileVM.takeArrayOfItems()
} label: {
HStack {
Text(!currentFile.isLock ? "Hide" : "Show")
Image(systemName: currentFile.isLock ? "eye" : "eye.slash")
}
}
Button {
safeFileClipboard.setOriginPath = URL(fileURLWithPath: currentFile.localPath)
safeFileClipboard.isCopied = true
} label: {
HStack {
Text("Move")
Image(systemName: "arrow.up.doc")
}
}
}
View:
struct DetailObjectView: View {
#ObservedObject var safeFileVM: SafeFileViewModel = SafeFileViewModel()
#EnvironmentObject var safeFileClipboard: SafeFileClipBoard
var currentFile: MyFile
var currentLocation = ""
var body: some View {
VStack {
.....
}
.contextMenu {
Button {
safeFileVM.hideSelectedFile(fileName: currentFile.fileName)
safeFileVM.takeArrayOfItems()
} label: {
HStack {
Text(!currentFile.isLock ? "Hide" : "Show")
Image(systemName: currentFile.isLock ? "eye" : "eye.slash")
}
}
Button {
safeFileClipboard.setOriginPath = URL(fileURLWithPath: currentFile.localPath)
safeFileClipboard.isCopied = true
} label: {
HStack {
Text("Move")
Image(systemName: "arrow.up.doc")
}
}
}
}
}
In the mini project below, when the EnvironmentObject value changes, navigation goes to the beginning. Why ? How can I fix this ?
Example Project:
Main:
#main
struct EnvironmentTestApp: App {
#StateObject var fooConfig: FooConfig = FooConfig()
var body: some Scene {
WindowGroup {
NavigationView {
ContentView()
.environmentObject(fooConfig)
}
}
}
}
ContentView:
struct ContentView: View {
#EnvironmentObject var fooConfig: FooConfig
private let numbers: [Number] = [.init(item: "1"), .init(item: "2"), .init(item: "3")]
var body: some View {
List {
ForEach(numbers, id: \.id) { item in
DetailView(itemNumber: item.item)
}
}
}
}
struct Number: Identifiable {
var id = UUID()
var item: String
}
DetailView:
struct DetailView: View {
#EnvironmentObject var fooConfig: FooConfig
var itemNumber: String = ""
var body: some View {
NavigationLink(destination: ContentView().environmentObject(fooConfig)) {
Text("\(itemNumber) - \(fooConfig.fooBool == true ? "On" : "Off")")
.environmentObject(fooConfig)
.contextMenu {
Button {
fooConfig.fooBool.toggle()
} label: {
HStack {
Text(fooConfig.fooBool != true ? "On" : "Off")
}
}
}
}
}
}
ObservableObject:
class FooConfig: ObservableObject {
#Published var fooBool: Bool = false
}
Move that from scene into ContentView, because scene is a bad place to update view hierarchy, it is better to do inside view hierarchy, so here
struct EnvironmentTestApp: App {
var body: some Scene {
WindowGroup {
ContentView() // only root view here !!
}
}
}
everything else is inside views, like
struct ContentView: View {
#StateObject private var foo = FooConfig()
var body: some View {
NavigationView {
MainView()
.environmentObject(foo) // << here !!
}
}
}
struct MainView: View {
#EnvironmentObject var fooConfig: FooConfig
private let numbers: [Number] = [.init(item: "1"), .init(item: "2"), .init(item: "3")]
var body: some View {
List {
ForEach(numbers, id: \.id) { item in
DetailView(itemNumber: item.item)
}
}
}
}
and so on...
Tested with Xcode 14 / iOS 16
My code is something like this:
class ViewModel: ObservableObject {
#Published var value = ""
}
struct ContentView: View {
#StateObject var viewModel = ViewModel()
var body: some View {
Group {
if viewModel.userSession != nil {
MyTabView()
} else {
LoginView()
}
}
.environmentObject(viewModel)
}
}
struct MyTabView: View {
var body: some View {
TabView {
View1()
.tabItem{}
View2()
.tabItem{}
View3()
.tabItem{}
View4()
.tabItem{}
}
}
}
struct View4: View {
#EnvironmentObject var viewModel: ViewModel
var body: some View {
NavigationView {
NavigationLink(destination: EditView().environmentObject(viewModel)){
Text("Edit")
}
}
}
}
struct EditView: View {
#EnvironmentObject var viewModel: ViewModel
var body: some View {
if viewModel.value != "" { //this is where I get the error
Text("\(viewModel.value)")
}
}
}
I've tried putting the environmentObject at MyTabView() in ContentView()
struct ContentView: View {
#StateObject var viewModel = ViewModel()
var body: some View {
Group {
if viewModel.userSession != nil {
MyTabView().environmentObject(viewModel)
} else {
LoginView()
}
}
}
}
I've tried putting the environmentObject at NavigationView in View4()
struct View4: View {
#EnvironmentObject var viewModel: ViewModel
var body: some View {
NavigationView {
NavigationLink(destination: EditView()){
Text("Edit")
}
}.environmentObject(viewModel)
}
}
The value from ViewModel is not getting passed into the EditView. I have tried many solutions I can find but non of those are helping with the error.
Can anyone please let me know what have I done wrong?
Here is the test code I used (entirely based on yours) that shows
"...The value from ViewModel is getting passed into the EditView...".
Unless I missed something, the code you provide does not reproduce the error you show.
class ViewModel: ObservableObject {
#Published var value = ""
#Published var userSession: String? // <-- for testing
}
struct ContentView: View {
#StateObject var viewModel = ViewModel()
var body: some View {
Group {
if viewModel.userSession != nil {
MyTabView()
} else {
LoginView()
}
}.environmentObject(viewModel)
}
}
struct MyTabView: View {
var body: some View {
TabView {
Text("View1").tabItem{Text("View1")}
Text("View2").tabItem{Text("View2")}
Text("View3").tabItem{Text("View3")}
View4().tabItem{Text("View4")}
}
}
}
struct View4: View {
#EnvironmentObject var viewModel: ViewModel
var body: some View {
NavigationView {
NavigationLink(destination: EditView().environmentObject(viewModel)){
Text("Edit")
}
}
}
}
struct EditView: View {
#EnvironmentObject var viewModel: ViewModel
var body: some View {
if viewModel.value != "" { // <-- here no error
Text(viewModel.value) // <-- here viewModel.value is a String
}
}
}
struct LoginView: View {
#EnvironmentObject var viewModel: ViewModel
var body: some View {
Button("Click me", action: {
viewModel.userSession = "something" // <-- to trigger the if in ContentView
viewModel.value = "testing-4-5-6" // <-- here change the value
})
}
}
Try this code and let us know if you get the error you show.
I have the following code in SwiftUI. I am expecting it to navigate from the list view to the PetView() with the proper name showing when tapping on one of the items in the ForEach loop or the button that says "Go to first pet". However, when I tap on an item or the button, the app doesn't do anything. What am I doing wrong? Thank you for your help!
import SwiftUI
#main
struct TestListAppApp: App {
var body: some Scene {
WindowGroup {
ContentView().environmentObject(ViewRouter())
}
}
}
import SwiftUI
struct ContentView: View {
#EnvironmentObject var viewRouter: ViewRouter
var body: some View {
ForEach(viewRouter.pets) { pet in
NavigationLink(
destination: PetView(),
tag: pet,
selection: $viewRouter.selectedPet,
label: {
Text(pet.name)
}
)
}
Button("Go to first pet.") {
viewRouter.selectedPet = viewRouter.pets[0]
}
}
}
import Foundation
class ViewRouter: ObservableObject {
#Published var selectedPet: Pet? = nil
#Published var pets: [Pet] = [Pet(name: "Louie"), Pet(name: "Fred"), Pet(name: "Stanley")]
}
import SwiftUI
struct PetView: View {
#EnvironmentObject var viewRouter: ViewRouter
var body: some View {
Text(viewRouter.selectedPet!.name)
}
}
import Foundation
struct Pet: Identifiable, Hashable {
var name: String
var id: String { name }
}
try this:
#main
struct TestListAppApp: App {
#StateObject var viewRouter = ViewRouter()
var body: some Scene {
WindowGroup {
ContentView().environmentObject(viewRouter)
}
}
}
struct PetView: View {
#EnvironmentObject var viewRouter: ViewRouter
var body: some View {
if let pet = viewRouter.selectedPet {
Text(pet.name)
} else {
EmptyView()
}
}
}
struct ContentView: View {
#EnvironmentObject var viewRouter: ViewRouter
var body: some View {
NavigationView {
List {
ForEach(viewRouter.pets) { pet in
NavigationLink(destination: PetView(),
tag: pet,
selection: $viewRouter.selectedPet,
label: {
Text(pet.name)
})
}
Button("Go to first pet.") {
viewRouter.selectedPet = viewRouter.pets[0]
}
}
}
}
}
The first part of question is answered. Let's elaborate this example to:
TextField view:
struct CreateNewCard: View {
#ObservedObject var viewModel: CreateNewCardViewModel
var body: some View {
TextField("placeholder...", text: $viewModel.definition)
.foregroundColor(.black)
}
}
ViewModel:
class CreateNewCardViewModel: ObservableObject {
#Published var id: Int
#Published var definition: String = ""
}
Main View:
struct MainView: View {
#State var showNew = false
var body: some View {
ForEach(0...10, id: \.self) { index in // <<<---- this represents the id
Button(action: { showNew = true }, label: { Text("Create") })
.sheet(isPresented: $showNew, content: {
// now I have to pass the id, but this
// leads to that I create a new viewModel every time, right?
CreateNewCard(viewModel: CreateNewCardViewModel(id: index))
})
}
}
My problem is now that when I type something into the TextField and press the return button on the keyboard the text is removed.
This is the most strange way of coding that i seen, how ever I managed to make it work:
I would like say that you can use it as leaning and testing, but not good plan for real app, How ever it was interesting to me to make it working.
import SwiftUI
struct ContentView: View {
var body: some View {
MainView()
}
}
class CreateNewCardViewModel: ObservableObject, Identifiable, Equatable {
init(_ id: Int) {
self.id = id
}
#Published var id: Int
#Published var definition: String = ""
#Published var show = false
static func == (lhs: CreateNewCardViewModel, rhs: CreateNewCardViewModel) -> Bool {
return lhs.id == rhs.id
}
}
let arrayOfModel: [CreateNewCardViewModel] = [ CreateNewCardViewModel(0), CreateNewCardViewModel(1), CreateNewCardViewModel(2),
CreateNewCardViewModel(3), CreateNewCardViewModel(4), CreateNewCardViewModel(5),
CreateNewCardViewModel(6), CreateNewCardViewModel(7), CreateNewCardViewModel(8),
CreateNewCardViewModel(9) ]
struct ReadModelView: View {
#ObservedObject var viewModel: CreateNewCardViewModel
var body: some View {
TextField("placeholder...", text: $viewModel.definition)
.foregroundColor(.black)
}
}
struct MainView: View {
#State private var arrayOfModelState = arrayOfModel
#State private var showModel: Int?
#State private var isPresented: Bool = false
var body: some View {
VStack {
ForEach(Array(arrayOfModelState.enumerated()), id:\.element.id) { (index, item) in
Button(action: { showModel = index; isPresented = true }, label: { Text("Show Model " + item.id.description) }).padding()
}
if let unwrappedValue: Int = showModel {
Color.clear
.sheet(isPresented: $isPresented, content: { ReadModelView(viewModel: arrayOfModelState[unwrappedValue]) })
}
}
.padding()
}
}
My code is a little more complex than this so I created an example that gets the same error.
When I navigate into a view, I have a function I want to perform with a variable passed into this view. That function then produces an array. I then want to put that array into a List, but I get an error.
How do I get the List to show the produced array?
I think the issue is the List can't be updated because it already has the declared blank array.
struct ContentView : View {
#State var array = [String]()
var body: some View {
List(self.array,id: \.self) { item in
Text("\(item)")
}
.onAppear(perform: createArrayItems)
}
func createArrayItems() {
array = ["item1", "item2", "item3", "item4", "item5"]
}
}
You can use ObservableObject data providers(eg : ViewModel) with #Published properties.
struct ListView: View {
#ObservedObject var viewModel = ListViewModel()
var body: some View {
NavigationView {
List(){
ForEach(viewModel.items) { item in
Text(item)
}
}
}
}
}
#if DEBUG
struct ContentView_Previews: PreviewProvider {
static var previews: some View {
ListView()
}
}
#endif
class ListViewModel: ObservableObject {
#Published var items = ["item1", "item2", "item3", "item4", "item5","item6"]
func addItem(){
items.append("item7")
}
}
You can use combine framework to update the list.
Whenever a change is made in DataProvider Object it will automatically update the list.
struct ContentView : View {
#EnvironmentObject var data: DataProvider
var body: some View {
NavigationView {
NavigationButton(destination: SecondPage()) {
Text("Go to Second Page")
}
List {
ForEach(data.array.identified(by: \.self)) { item in
Text("\(item)")
}
}
}
}
}
Add items in the list
struct SecondPage : View {
#State var counter = 1
#EnvironmentObject var tempArray: DataProvider
var body: some View {
VStack {
Button(action: {
self.tempArray.array.append("item\(self.counter)")
self.counter += 1
}) {
Text("Add items")
}
Text("Number of items added \(counter-1)")
}
}
}
It will simply notify the change
import Combine
final class DataProvider: BindableObject {
let didChange = PassthroughSubject<DataProvider, Never>()
var array = [String]() {
didSet {
didChange.send(self)
}
}
}
You also need to do some update in the SceneDelegate. This update ensures that ContentView has a DataProvider object in the environment.
window.rootViewController = UIHostingController(rootView: ContentView().environmentObject(DataProvider()))
#txagPman
I too have your problem to understand how to modify a list.
I was able to write this code.
I hope it's useful.
import SwiftUI
struct ContentView: View {
#State private var array = createArrayItems()
// #State private var array = [""] - This work
// #State private var array = [] - This not work
#State private var text = ""
var body: some View {
VStack {
TextField("Text", text: $text, onCommit: {
// self.array = createArrayItems() - This work after press return on textfield
self.array.append(self.text)
}).padding()
List (self.array, id: \.self) {item in
Text("\(item)")
}
}
// .onAppear {
// self.array = createArrayItems() - This not work
// }
}
}
func createArrayItems() -> [String] {
return ["item_01","item_02","item_03","item_04" ]
}
A dumb UI is a good UI
Keep your views dumb try the following code to create a dynamic List
import UIKit
import SwiftUI
import PlaygroundSupport
struct ContentView : View {
#State var array = [String]()
var body: some View {
List{
ForEach(array.identified(by: \.self)) { item in
Text("\(item)")
}
}
}
}
func createArrayItems()->[String] {
return ["item1", "item2", "item3", "item4", "item5","item6"]
}
PlaygroundPage.current.liveView = UIHostingController(rootView: ContentView(array: createArrayItems()))
Use this:
class ObservableArray<T>: ObservableObject {
#Published var array: [T]
init(array: [T] = ) {
self.array = array
}
init(repeating value: T, count: Int) {
array = Array(repeating: value, count: count)
}
}
struct YourView: View {
#ObservedObject var array = ObservableArray<String>()
var body: some View {
}
}