Preview Macro fails to load when using ObservedObject

Question

Created Dec ’23

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Participants 2

After spending some time trying to understand the difference between StateObject and ObservedObject, I learned that ObservedObject has to be added to child views. I want to be able to use my child view in a variety of parent views, so I decided to make the child view as a separate file and use ObservedObject. However, the preview fails to load and returns "Failed to build the scheme" error. I recreated the project into something as simple as possible. Let me provide some code here (comments are not copied here):

ViewModel: This will house all of the data that will be updated by the View. I have no child properties for the sake of simplicity.

import Foundation

public class ChildViewModel: ObservableObject
{
    
}

Now here is a child view that was added as a separate file:

import SwiftUI

struct ChildView: View {
    @ObservedObject var viewModel: ChildViewModel
    var body: some View {
        Text("Hello, World!")
    }
}

#Preview {
    @StateObject var cViewModel = ChildViewModel()
    ChildView(viewModel: cViewModel)
}

This is as simple as it gets and it still gives me problems. Coming from C#/XAML world, this has been a massive pain to figure out. I scoured every forum I could, used Apple's own documentation and have not found a single post that can explain what I am doing wrong.

Screenshot 2023-12-20 at 1.03.55 AM.png

Answered by jlilest in 775081022

You need to return the view...

#Preview {
    @StateObject var cViewModel = ChildViewModel()
    return ChildView(viewModel: cViewModel)
}

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Answer 1

jlilest OP

Dec ’23

Accepted Answer

You need to return the view...

#Preview {
    @StateObject var cViewModel = ChildViewModel()
    return ChildView(viewModel: cViewModel)
}

1