I'd appreciate any help with this, I'm just a beginner so I'm not sure if I'm misunderstanding, or have the implementation wrong or if this is a bug.
I'm trying to have my MacOS app segue to the main screen after a successful login. I have an appState to share state with the rest of the app. The AppState is a class conforming to Observable object and I added an observer to print whenever the isLoggedIn property changes:
class AppState : ObservableObject {
#Published var isLoggedIn = false {
didSet {
print("AppState isLoggedin: \(isLoggedIn)")
}
}
}
I also have a MasterView struct to deal with changing the main view.
struct MasterView: View {
#ObservedObject var appState: AppState = AppState()
var body: some View {
return Group {
if appState.isLoggedIn {
NavView()
} else {
LoginView()
}
}.frame(width: 1200, height: 800)
}
}
I have a bunch of code to handle doing the login which I won't post for the sake of brevity, suffice to say that it works, isLoggedIn is set to true and prints to the console after a successful login. The issue is that the view never updates to reflect this so I'm still stuck on the login screen.
Any help is greatly appreciated, I've spent more time on this than I care to admit. Thanks!
Update: I remember having trouble with #EnvironmentObject and so I switched to #ObservableObject and #Published. After re-implementing #EnvironmentObject I now remember why: I have a networking class which causes a crash as it is not an ancestor view. Per Paul Hudson's comment, "Note: Environment objects must be supplied by an ancestor view – if SwiftUI can’t find an environment object of the correct type you’ll get a crash. This applies for previews too, so be careful."
For More Information.
I figured it out, working code below.
AppState:
final class AppState : ObservableObject {
#Published var isLoggedIn = false {
didSet {
print("AppState isLoggedIn: \(isLoggedIn)")
}
}
}
Content View :
struct ContentView: View {
#ObservedObject var appState: AppState
var body: some View {
return Group {
if appState.isLoggedIn {
MainView(appState: appState)
} else {
LoginView(appState: appState)
}
}.frame(maxWidth: 1200, maxHeight: 800)
}
}
Login View:
struct LoginView: View {
#ObservedObject var appState: AppState
var body: some View {
Button(action: {
withAnimation {
self.appState.isLoggedIn.toggle()
}
}) {
Text("Go to Main View")
}.padding()
}
}
Finally, Main View:
struct MainView: View {
#ObservedObject var appState: AppState
var body: some View {
Button(action: {
withAnimation {
self.appState.isLoggedIn.toggle()
}
}) {
Text("Back To Login View")
}.padding()
}
}
Related
I am struggling with a bug and I just can't seem to solve it, or where to look further.
The problem occurs when I try to remove a view (which holds a NavigationView) from the view hierarchy. It crashes with: Thread 1: EXC_BAD_ACCESS (code=1, address=0x10)
After experimenting with the sanitizer I got this output in the debugger: *** -[_TtGC7SwiftUI41StyleContextSplitViewNavigationControllerVS_19SidebarStyleContext_ removeChildViewController:]: message sent to deallocated instance 0x10904c880
Which pointed me to figure out that it was the NavigationView that cause it somehow. But I still can't figure out how to get from here.
This problem ONLY occurs on a real device, it works just fine in a simulator and you may have to hit the login, and then log out and log back in a few times before the crash happens.
I made a sample app with the example: https://github.com/Surferdude667/NavigationRemoveTest
The code is as follows:
NavigationRemoveTestApp
#main
struct NavigationRemoveTestApp: App {
var body: some Scene {
WindowGroup {
RootView()
}
}
}
RootView
struct RootView: View {
#StateObject private var viewModel = RootViewModel()
var body: some View {
if !viewModel.loggedIn {
WelcomeView()
} else {
ContentView()
}
}
}
RootViewModel
class RootViewModel: ObservableObject {
#Published var loggedIn = false
init() {
LogInController.shared.loggedIn
.receive(on: DispatchQueue.main)
.assign(to: &$loggedIn)
}
}
WelcomeView
struct WelcomeView: View {
var body: some View {
NavigationView {
VStack {
Text("Welcome")
NavigationLink("Go to login") {
LogInView()
}
}
}
}
}
LogInView
struct LogInView: View {
var body: some View {
VStack {
Text("Log in view")
Button("Log in") {
LogInController.shared.logIn()
}
}
}
}
ContentView
struct ContentView: View {
var body: some View {
VStack {
Text("Content view")
Button("Log out") {
LogInController.shared.logOut()
}
}
}
}
LogInController
import Combine
class LogInController {
static let shared = LogInController()
var loggedIn: CurrentValueSubject<Bool, Never>
private init() {
self.loggedIn = CurrentValueSubject<Bool, Never>(false)
}
func logIn() {
self.loggedIn.send(true)
}
func logOut() {
self.loggedIn.send(false)
}
}
I found a few solutions.
Either you wrap the if statement in the RootView with a NavigationView instead of having the NavigationView inside the actual views, it works. This is however not very convenient since everything is now wrapped in a NavigationView.
Replacing NavigationView with the new iOS 16 NavigationStack also solves it.
Omg mate, I had the same problem, because of this post it's solved. But don't you think it is a really weird bug? Did you find out more about the root cause? Nevertheless you made my day.
The app has a model that stores the user's current preference for light/dark mode, which the user can change by clicking on a button:
class DataModel: ObservableObject {
#Published var mode: ColorScheme = .light
The ContentView's body tracks the model, and adjusts the colorScheme when the model changes:
struct ContentView: View {
#StateObject private var dataModel = DataModel()
var body: some View {
NavigationStack(path: $path) { ...
}
.environmentObject(dataModel)
.environment(\.colorScheme, dataModel.mode)
As of Xcode Version 14.0 beta 5, this is producing a purple warning: Publishing changes from within view updates is not allowed, this will cause undefined behavior. Is there another way to do this? Or is it a hiccup in the beta release? Thanks!
Update: 2022-09-28
Xcode 14.1 Beta 3 (finally) fixed the "Publishing changes from within view updates is not allowed, this will cause undefined behavior"
See: https://www.donnywals.com/xcode-14-publishing-changes-from-within-view-updates-is-not-allowed-this-will-cause-undefined-behavior/
Full disclosure - I'm not entirely sure why this is happening but these have been the two solutions I have found that seem to work.
Example Code
// -- main view
#main
struct MyApp: App {
#StateObject private var vm = ViewModel()
var body: some Scene {
WindowGroup {
ViewOne()
.environmentObject(vm)
}
}
}
// -- initial view
struct ViewOne: View {
#EnvironmentObject private var vm: ViewModel
var body: some View {
Button {
vm.isPresented.toggle()
} label: {
Text("Open sheet")
}
.sheet(isPresented: $vm.isPresented) {
SheetView()
}
}
}
// -- sheet view
struct SheetView: View {
#EnvironmentObject private var vm: ViewModel
var body: some View {
Button {
vm.isPresented.toggle()
} label: {
Text("Close sheet")
}
}
}
// -- view model
class ViewModel: ObservableObject {
#Published var isPresented: Bool = false
}
Solution 1
Note: from my testing and the example below I still get the error to appear. But if I have a more complex/nested app then the error disappears..
Adding a .buttonStyle() to the button that does the initial toggling.
So within the ContentView on the Button() {} add in a .buttonStyle(.plain) and it will remove the purple error:
struct ViewOne: View {
#EnvironmentObject private var vm: ViewModel
var body: some View {
Button {
vm.isPresented.toggle()
} label: {
Text("Open sheet")
}
.buttonStyle(.plain) // <-- here
.sheet(isPresented: $vm.isPresented) {
SheetView()
}
}
}
^ This is probably more of a hack than solution since it'll output a new view from the modifier and that is probably what is causing it to not output the error on larger views.
Solution 2
This one is credit to Alex Nagy (aka. Rebeloper)
As Alex explains:
.. with SwiftUI 3 and SwiftUI 4 the data handling kind of changed. How SwiftUI handles, more specifically the #Published variable ..
So the solution is to have the boolean trigger to be a #State variable within the view and not as a #Published one inside the ViewModel. But as Alex points out it can make your views messy and if you have a lot of states in it, or not be able to deep link, etc.
However, since this is the way that SwiftUI 4 wants these to operate, we run the code as such:
// -- main view
#main
struct MyApp: App {
var body: some Scene {
WindowGroup {
ViewOne()
}
}
}
// -- initial view
struct ViewOne: View {
#State private var isPresented = false
var body: some View {
Button {
isPresented.toggle()
} label: {
Text("Open sheet")
}
.sheet(isPresented: $isPresented) {
SheetView(isPresented: $isPresented)
// SheetView() <-- if using dismiss() in >= iOS 15
}
}
}
// -- sheet view
struct SheetView: View {
// I'm showing a #Binding here for < iOS 15
// but you can use the dismiss() option if you
// target higher
// #Environment(\.dismiss) private var dismiss
#Binding var isPresented: Bool
var body: some View {
Button {
isPresented.toggle()
// dismiss()
} label: {
Text("Close sheet")
}
}
}
Using the #Published and the #State
Continuing from the video, if you need to still use the #Published variable as it might tie into other areas of your app you can do so with a .onChange and a .onReceive to link the two variables:
struct ViewOne: View {
#EnvironmentObject private var vm: ViewModel
#State private var isPresented = false
var body: some View {
Button {
vm.isPresented.toggle()
} label: {
Text("Open sheet")
}
.sheet(isPresented: $isPresented) {
SheetView(isPresented: $isPresented)
}
.onReceive(vm.$isPresented) { newValue in
isPresented = newValue
}
.onChange(of: isPresented) { newValue in
vm.isPresented = newValue
}
}
}
However, this can become really messy in your code if you have to trigger it for every sheet or fullScreenCover.
Creating a ViewModifier
So to make it easier for you to implement it you can create a ViewModifier which Alex has shown works too:
extension View {
func sync(_ published: Binding<Bool>, with binding: Binding<Bool>) -> some View {
self
.onChange(of: published.wrappedValue) { newValue in
binding.wrappedValue = newValue
}
.onChange(of: binding.wrappedValue) { newValue in
published.wrappedValue = newValue
}
}
}
And in use on the View:
struct ViewOne: View {
#EnvironmentObject private var vm: ViewModel
#State private var isPresented = false
var body: some View {
Button {
vm.isPresented.toggle()
} label: {
Text("Open sheet")
}
.sheet(isPresented: $isPresented) {
SheetView(isPresented: $isPresented)
}
.sync($vm.isPresented, with: $isPresented)
// .onReceive(vm.$isPresented) { newValue in
// isPresented = newValue
// }
// .onChange(of: isPresented) { newValue in
// vm.isPresented = newValue
// }
}
}
^ Anything denoted with this is my assumptions and not real technical understanding - I am not a technical knowledgeable :/
Try running the code that's throwing the purple error asynchronously, for example, by using DispatchQueue.main.async or Task.
DispatchQueue.main.async {
// environment changing code comes here
}
Task {
// environment changing code comes here
}
Improved Solution of Rebel Developer
as a generic function.
Rebeloper solution
It helped me a lot.
1- Create extension for it:
extension View{
func sync<T:Equatable>(_ published:Binding<T>, with binding:Binding<T>)-> some View{
self
.onChange(of: published.wrappedValue) { published in
binding.wrappedValue = published
}
.onChange(of: binding.wrappedValue) { binding in
published.wrappedValue = binding
}
}
}
2- sync() ViewModel #Published var to local #State var
struct ContentView: View {
#EnvironmentObject var viewModel:ViewModel
#State var fullScreenType:FullScreenType?
var body: some View {
//..
}
.sync($viewModel.fullScreenType, with: $fullScreenType)
I have a MVVM SwiftUI app that will navigate to another view based on the value of a #Published property of a view model:
class ViewModel: ObservableObject {
#Published public var showView = false
func doShowView() {
showView = true
}
}
struct MyView: View {
#StateObject var viewModel = ViewModel()
var body: some View {
NavigationView {
MySubView().environmentObject(viewModel)
}
}
}
struct MySubView: View {
#EnvironmentObject private var viewModel: ViewModel
var body: some View {
VStack {
Button(action: {
viewModel.doShowView()
}) {
Text("Button")
}
NavigationLink(
destination: SomeOtherView(),
isActive: $viewModel.showView,
label: {
EmptyView()
})
}
}
}
The problem is sometimes when I run the app it will work only every other time and sometimes it works perfectly as expected.
The cause seems to be that sometimes when the property is set in the view model (in doShowView()) SwiftUI will immediately render my view with the old value of showView and in the working case the view is rendered on the next event cycle with the updated value.
Is this a feature (due to the fact #Published is calling objectWillChange under the hood and the view is rendering due to that) or a bug?
If it is a feature (and I just happen to get lucky when it works as I want it to) what is the best way to guarantee it renders my view after the new value is set?
Note this is only a simple example, I cannot use a #State variable in the button action since in the real code the doShowView() method may or may not set the showView property in the view model.
The issue here is that SwiftUI creates the SomeOtherView beforehand. Then, this view is not related with the viewModel in any way, so it's not re-created when viewModel.showView changes.
A possible solution is to make SomeOtherView depend on the viewModel - e.g. by explicitly injecting the environmentObject:
struct MySubView: View {
#EnvironmentObject private var viewModel: ViewModel
var body: some View {
VStack {
Button(action: {
viewModel.doShowView()
}) {
Text("Button")
}
NavigationLink(
destination: SomeOtherView().environmentObject(viewModel),
isActive: $viewModel.showView,
label: {
EmptyView()
}
)
}
}
}
I came upon a working solution. I did add a #State variable and set it by explictly watching for changes of showView:
class ViewModel: ObservableObject {
#Published public var showView = false
var disposables = Set<AnyCancellable>()
func doShowView() {
showView = true
}
}
struct MyView: View {
#StateObject var viewModel = ViewModel()
var body: some View {
NavigationView {
MySubView().environmentObject(viewModel)
}
}
}
struct MySubView: View {
#EnvironmentObject private var viewModel: ViewModel
#State var showViewLink = false
var body: some View {
VStack {
Button(action: {
viewModel.doShowView()
}) {
Text("Button")
}
NavigationLink(
destination: SomeOtherView(),
isActive: $showViewLink,
label: {
EmptyView()
})
}
.onAppear {
viewModel.$showView
.sink(receiveValue: { showView in
showViewLink = showView
})
.store(in: &viewModel.disposables)
}
}
}
My app has 4 views (let's call them View_A[root] -> View_B -> View_C -> View_D). The navigation between them was made using NavigationView/NavigationLink.
When I call self.presentationMode.wrappedValue.dismiss() from the last view(View_D) I expect it to dismiss the current view (D) only, but for some reason it dismissed ALL the views and stops at view A (root view).
That's weird.
I spent a couple of hours trying to figure out what's going on there and I found that
- if I remove "ForEach" from "View_A" it works correctly and only the last view is dismissed. Even though ForEach gets just 1 static object in this example.
The second weird thing is that
- if I don't change "self.thisSession.stats" to false it also works correctly dismissing only the last view.
This is super weird as View_A (as far as I understand) is not dependent on thisSession environment variable.
Any ideas on how to prevent View_C and View_B from being dismissed in this case? I wanna end up at View_C after clicking the link, not at View_A.
Any help is appreciated, it took me a while to find out where it comes from but I'm not smart enough to proceed any further ;)
import SwiftUI
struct A_View: View {
#EnvironmentObject var thisSession: CurrentSession
var body: some View {
NavigationView {
VStack {
Text("View A")
ForEach([TestObject()], id: \.id) { _ in
NavigationLink(destination: View_B() ) {
Text("Move to View B")
}
}
}
}
}
}
struct View_B: View {
var body: some View {
NavigationView {
NavigationLink(destination: View_C()
) {
Text("GO TO VIEW C")
}
}
}
}
struct View_C: View {
var body: some View {
ZStack {
NavigationView {
NavigationLink(destination: View_D()) {
Text("GO TO VIEW D")
}
}
}
}
}
struct View_D: View {
#EnvironmentObject var thisSession: CurrentSession
#Environment(\.presentationMode) var presentationMode: Binding<PresentationMode>
var body: some View {
ZStack {
VStack {
Button(action: {
self.thisSession.stats = false
self.presentationMode.wrappedValue.dismiss()
}) {
Text("Return!")
}
}
}
}
}
class CurrentSession: ObservableObject {
#Published var stats: Bool = false
#Published var user: String = "user"
}
struct TestObject: Identifiable, Codable {
let id = UUID()
}
Your issue is with:
NavigationView
There is only supposed to be one NavigationView in an entire view stack. Try removing the NavigationView from views B and C
I am trying to rewrite my app using SwiftUI only and I am having difficulty with the EnvironmentObject, trying to understand how it works…
I want to redirect my app users to the appropriate page at launch, depending on:
if this is their first time
if they have a login,
if they want to start using without login
If it is the first time the app is launched, LocalStorage has no data so I present the app on a welcome page
I offer the choice of 2 buttons to click on:
“New User” which redirect to the main page of the app and create a new user
“Login” which present the login page to retrieve the last backup
If the app has previously been launched, I present the main page straight away.
Now said, if I initiate my “currentPage” as “MainView” or “LoginView”, it works - but NOT if it is set as “WelcomeView”.
I presume the problem comes when the variable gets changed from a subview? I thought the use of #EnvironmentObject was the way to get around this…
Can someone explain to me how it works?
My various files are:
import SwiftUI
import Combine
class ViewRouter: ObservableObject {
let objectWillChange = PassthroughSubject<ViewRouter,Never>()
var currentPage: String = "WelcomeView" {
didSet {
objectWillChange.send(self)
}
}
}
import SwiftUI
struct ParentView : View {
#EnvironmentObject var viewRouter: ViewRouter
var body: some View {
VStack {
if viewRouter.currentPage == "WelcomeView" {
WelcomeView()
}
else if viewRouter.currentPage == "MainView" {
MainView()
}
else if viewRouter.currentPage == "LoginView" {
LoginView()
}
}
}
}
import SwiftUI
struct WelcomeView: View {
#EnvironmentObject var viewRouter: ViewRouter
var body: some View {
ZStack{
// VStack { [some irrelevant extra code here] }
VStack {
LoginButtons().environmentObject(ViewRouter())
}
// VStack { [some irrelevant extra code here] }
}
}
}
import SwiftUI
struct LoginButtons: View {
#EnvironmentObject var viewRouter: ViewRouter
var body: some View {
VStack {
Button(action: {
self.viewRouter.currentPage = "MainView"
}) {
Text("NEW USER")
}
Button(action: {
self.viewRouter.currentPage = "LoginView"
}) {
Text("I ALREADY HAVE AN ACCOUNT")
}
}
}
}
import SwiftUI
struct MainView : View {
#EnvironmentObject var viewRouter: ViewRouter
var body: some View {
VStack {
// Just want to check if it is working for now before implementing the appropriate Views...
Button(action: {
self.viewRouter.currentPage = "WelcomeView"
}) {
Text("BACK")
}
}
}
}
import SwiftUI
struct LoginView : View {
#EnvironmentObject var viewRouter: ViewRouter
var body: some View {
VStack {
// Just want to check if it is working for now before implementing the appropriate Views...
Button(action: {
self.viewRouter.currentPage = "WelcomeView"
}) {
Text("BACK")
}
}
}
}
Many Thanks in advance! :wink:
Ok so in your main view, the one that you are going to decide where to send your user, you could check for the app if it was lunched before or not, depending on that do whatever you want. Once you know how to do this, you can adapt to the other things. This is how you can check for it, again, in your main view router:
init() {
// Create initial Data if not data has been setup
if (InitialAppSetup().initialDataLoaded == false) {
InitialAppSetup().createInitialData()
}
// Onboarding screen
if !UserDefaults.standard.bool(forKey: "didLaunchBefore") {
UserDefaults.standard.set(true, forKey: "didLaunchBefore")
currentPage = "onboardingView"
} else {
currentPage = "homeView"
}
}
The InitialAppSetup() class has a UserDefault which goes like this:
#Published var initialDataLoaded: Bool = UserDefaults.standard.bool(forKey: "InitialData") {
didSet {
UserDefaults.standard.set(self.initialDataLoaded, forKey: "InitialData")
}
}
Ok... My 'mistake' was to add an extra ".environmentObject(ViewRouter())" when calling my subview "LoginButtons".
If I remove it, it works!.. But why?!?
struct WelcomeView: View {
#EnvironmentObject var viewRouter: ViewRouter
var body: some View {
ZStack{
// VStack { [some irrelevant extra code here] }
VStack {
LoginButtons()
// --> .environmentObject(ViewRouter())
}
// VStack { [some irrelevant extra code here] }
}
}
}