How to create different views by using only one class instance?

Question

I want to create different views by using only one class instance. My goal is not to create a separate instance for each view(group), instead, I would like to pass data through all views. Every time I try to pass data from another view I am faced with "Cannot use instance member within property initializer" and "Generic parameter 'C' could not be inferred" errors. For clarifying my problem I added some example code and marked errors as a comment.

class DataService {
    
    static let group1: [Person] = [
        Person(name: "Jack", age: 21),
        Person(name: "Anna", age: 29),
        Person(name: "Steve", age: 12),
        Person(name: "Carl", age: 16),
    ]
    
    static let group2: [Person] = [
        Person(name: "Crag", age: 19),
        Person(name: "Daniel", age: 29),
        Person(name: "Katty", age: 36),
        Person(name: "Leo", age: 13),
    ]
    
}

struct Person {
    let name: String
    let age: Int
}

class PersonClass: ObservableObject {
    
    @Published var peopleArray: [Person]
    
    init(data: [Person]) {
        self.peopleArray = data
    }
}

struct humanView: View {
    
    let data: [Person]
    
    @StateObject var person = PersonClass(data: data) // Error1: Cannot use instance member 'data' within property initializer
    
    var body: some View {
        
        VStack {
            ForEach(person.peopleArray.indices, id: \.self) { index in // Error2: Generic parameter 'C' could not be inferred
                Rectangle()
                    .fill(Color.black)
                    .frame(width: 120, height: 120)
                    .cornerRadius(10)
                    .overlay(
                        Text(person.peopleArray[index].name)
                            .font(.headline)
                            .foregroundColor(.white)
                    )
            }
        }
    }
}
     
struct ContentView: View {
    var body: some View {
        NavigationView {
            NavigationLink("Group 1") {
                humanView(group: DataService.group1)
            }
            NavigationLink("Group 2") {
                humanView(group: DataService.group2)
            }
        }
    }
}

What's the reason in having PersonClass here? Use injected data directly in ForEach. Also this should be helpful stackoverflow.com/a/62636048/12299030. — Asperi
– Asperi, Commented Aug 3, 2022 at 19:52
Imagine I have a game view with different levels and I'd like to draw game components by level. I've check the article I think .onAppear() might be useful. Thank you. — Berke Keser
– Berke Keser, Commented Aug 3, 2022 at 21:15

Moon · Accepted Answer · 2022-08-04 15:33:20Z

1

You should use "@State" variable PersonClass. There is the anwser

class PersonClass {
    var peopleArray: [Person]
    
    init(data: [Person]) {
        self.peopleArray = data
    }
}

struct humanView: View {
    
    @State var personClass: PersonClass
    
    var body: some View {
        
        VStack {
            ForEach(personClass.peopleArray.indices, id: \.self) { index in // Error2: Generic parameter 'C' could not be inferred
                Rectangle()
                    .fill(Color.black)
                    .frame(width: 120, height: 120)
                    .cornerRadius(10)
                    .overlay(
                        Text(personClass.peopleArray[index].name)
                            .font(.headline)
                            .foregroundColor(.white)
                    )
            }
        }
    }
}
     
struct ContentView: View {
    var body: some View {
        NavigationView {
            VStack{
                NavigationLink("Group 1") {
                    humanView(personClass: PersonClass(data: DataService.group1))
                }
                NavigationLink("Group 2") {
                    humanView(personClass: PersonClass(data: DataService.group2))
                }
            }
        }
    }
}

answered Aug 4, 2022 at 15:33

Moon

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1 Comment

Berke Keser Over a year ago

When I use @State var personClass: PersonClass it creates view once but, when I change class properties view doesn't update accordingly. Instead, I've done the same approach with @StateObject and it works as expected. I could update view from another class and also I don't need to initialize different object each time. Thank you.

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