Why update variable in observable object does not update the view? - ios

Question

I am new to SwiftUI. Learning new properties such as #State, #Binding, #EnvironmentObject etc.
I am currently working on the login template, define a binding #Published variable in observable object which allows to switch between login page and main page. However, when I update the variable inside the observable object, the main page does not show up. It is still in the login page. What is missing in my code?
struct ContentView: View {
#EnvironmentObject var loginViewModel: LoginViewModel
var body: some View {
return Group {
if loginViewModel.signInSuccess {
MainPageView()
}
else {
LoginView(signInSuccess: $loginViewModel.signInSuccess).environmentObject(LoginViewModel())
}
}
}
}
final class LoginViewModel: ObservableObject {
#Published var signInSuccess:Bool = false;
func performLogin() {
signInSuccess = true;
}
}
struct LoginView: View {
#EnvironmentObject var loginViewModel: LoginViewModel
#Binding var signInSuccess: Bool;
var body: some View {
Button(action: submit) {
Text("Login")
.foregroundColor(Color.white)
}
}
func submit() {
loginViewModel.performLogin()
// signInSuccess = true;
}
}
If I tried to update binding 'signInSuccess' in the loginView, it can successfully update the view to the mainView. However, is there a way that I can update signInSuccess inside the Observable Object that also update the ContentView to the MainView?

Answer 1

Yes, you just change the view code as the following.
The binding actually is not necessary.
struct ContentView: View {
#EnvironmentObject var loginViewModel: LoginViewModel
var body: some View {
return Group {
if loginViewModel.signInSuccess {
MainPageView()()
}
else {
LoginView(signInSuccess: $loginViewModel.signInSuccess).environmentObject(self.loginViewModel)
}
}
}
}
window.rootViewController = UIHostingController(rootView: ContentView().environmentObject(LoginViewModel())

Answer 2

If you want to use an environmental variable, you have to declare it in your SceneDelegate and set it on the ContontentView:
class SceneDelegate: UIResponder, UIWindowSceneDelegate {
var window: UIWindow?
var loginViewModel = LoginViewModel()
func scene(_ scene: UIScene,
willConnectTo session: UISceneSession,
options connectionOptions: UIScene.ConnectionOptions) {
let contentView = ContentView()
if let windowScene = scene as? UIWindowScene {
let window = UIWindow(windowScene: windowScene)
window.rootViewController = HostingViewController(rootView: contentView.environmentObject(loginViewModel))
self.window = window
window.makeKeyAndVisible()
}
}
// etc.
Then in your ContenView you don't need to set it in any way on the LoginView as it is held by the enviroment:
struct ContentView: View {
#EnvironmentObject var loginViewModel: LoginViewModel
var body: some View {
return Group {
if loginViewModel.signInSuccess {
MainPageView()
} else {
LoginView()
}
}
}
}
In your model, make sure you declare your signInSuccess as private(set) so it can only be set from within the class and only read from elsewhere:
final class LoginViewModel: ObservableObject {
#Published private(set) var signInSuccess:Bool = false;
func performLogin() {
signInSuccess = true;
}
}
And finally in the LoginView you just need to include the #EnvironmentObject and everything else will work.
struct LoginView: View {
#EnvironmentObject var loginViewModel: LoginViewModel
var body: some View {
Button(action: { self.loginViewModel.performLogin() }) {
Text("Login")
.foregroundColor(Color.white)
}
}
}