How to listen to a computed property in SwiftUI? - swift

Question

I am trying to disable a button based on a computed property from the View Model, but is only disabled after the view is reloaded.
This is the View Model :
class VerifyFieldViewModel : ObservableObject {
#ObservedObject var coreDataViewModel = CoreDataViewModel()
func isValidFirstName() -> Bool {
guard coreDataViewModel.savedDetails.first?.firstName?.count ?? 0 > 0 else {
return false
}
return true
}
func isValidLastName() -> Bool {
guard coreDataViewModel.savedDetails.first?.lastName?.count ?? 0 > 0 else {
return false
}
return true
}
var isFirstNameValid : String {
if isValidFirstName() {
return ""
} else {
return "Name is empty"
}
}
var isLastNameValid : String {
if isValidLastName() {
return ""
} else {
return "Surname is empty"
}
}
var isSignUpComplete: Bool {
if !isValidFirstName() || !isValidLastName() {
return false
}
return true
}
}
This is how I am disabling the button .
struct CartsView: View {
#State var onboardingState: Int = 0
#StateObject var coreDataViewModel = CoreDataViewModel()
#ObservedObject var verifyFieldViewModel = VerifyFieldViewModel()
var body: some View {
ZStack {
switch onboardingState {
case 0 :
VStack {
detailOrder
.transition(transition)
Spacer()
bottomButton
.padding(30)
}
case 2 :
VStack {
detailOrder2
.transition(transition)
Spacer()
bottomButton
.padding(30)
.opacity(verifyFieldViewModel.isSignUpComplete ? 1 : 0.6)
.disabled(!verifyFieldViewModel.isSignUpComplete)
}
default:
EmptyView()
}
}
}
}
This is the Core Data View Model :
class CoreDataViewModel : ObservableObject {
let manager = CoreDataManager.instance
#Published var savedDetails : [Details] = []
init() {
fetchSavedDetails()
}
func fetchSavedDetails() {
let request = NSFetchRequest<Details>(entityName: "Details")
do {
savedDetails = try manager.context.fetch(request)
} catch let error {
print("Error fetching \(error)")
}
}
func saveContext() {
DispatchQueue.main.async {
self.manager.save()
self.fetchSavedDetails()
}
}
}
NOTE : It works, but only when the view is reloaded.
EDITED : I updated the question to make it easier to understand. Hope that you can help me now.
EDITED2: Added Core Data View Model .

Answer 1

As mentioned above you don't need a computed property in this case. I made a small example of Login procedure which demonstrates the same behavior.
class LoginViewModel: ObservableObject {
#Published var username: String = ""
#Published var password: String = ""
var isValid: Bool {
(username.isNotEmpty && password.isNotEmpty)
}
func login() {
// perform login
}
}
struct ContentView: View {
#StateObject private var vm: LoginViewModel = LoginViewModel()
var body: some View {
Form {
TextField("User name", text: $vm.username)
TextField("Password", text: $vm.password)
Button("Login") {
vm.login()
}.disabled(!vm.isValid)
}
}
}