I am creating a page settingView for saving userdata where I call a class with @ObservedObject. And I also made some func in the settingView page for load and save the userdata. But there I get the error "Cannot assign to property: 'self' is immutable in SettingView". How can I solve this.

Here is a part of my class

class UserData: ObservableObject, Codable {
    @Published var name = ""
    @Published var firstname = ""
    @Published var email = ""
}

And here a part of the SettingView

struct SettingsView: View {
    @ObservedObject var userdata = UserData()

var body: some View {

        NavigationView{
            Form {
                Section(header: Text("User")){
                    TextField("Name", text: $userdata.name)
                    TextField("Firstname", text: $userdata.firstname)
                    TextField("Email...", text: $userdata.email)
                   //more code
                }
                Section{
                    Button(action: {
                        self.saveData()
                        self.showingAlert = true
                    }){
                        Text("Save")
                    }
            }
        }

        .onAppear(perform: {
            self.loadData()
        })
    }

    func getDocumentsDirectory() -> URL {
        let paths = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask)
        return paths[0]
    }

    func loadData() {
        let filename = getDocumentsDirectory().appendingPathComponent("SavedData")

        do {
            let data = try Data(contentsOf: filename)
            userdata = try JSONDecoder().decode(UserData.self, from: data) //<-- error on userdata
            print("File is loaded")
        } catch {
            print("Unable to load saved data.")
        }
    }
}

The problem is that by changing userdata within a function called from body, you are trying to mutate the SettingsView struct from within body which, as a computed property with a non-mutating getter, cannot mutate the struct.

Change your @ObservedObject to @StateObject and load the data in your SettingsView initializer. I think that should fix it. (NOTE: I haven't actually tried any code to back this up; I'm flying by the seat of my pants here!)

Hi thanks for your advice. But I made a @state var NewUserData and used that in my LoadData and then I set all my userdata equal to NewUserData. Now I can load the data on appear.