Using @State resolves into 'self' used before all stored properties are initialized

Question

I ran into an issue when using the @State property.

My ContentView.swift looks like this:

import SwiftUI

struct ContentView: View {
    @State var showText: Bool = true
    
    var Mod: Modifier
    init() {
        Mod = Modifier(showText: $showText) // Throws error -> 'self' used before all stored properties are initialized ('self.Mod' not initialized)
    }
    
    var body: some View {
        VStack {
            if showText == true {
                Text("Hello, World!")
            }
            Mod
        }
    }
}

struct ContentView_Previews: PreviewProvider {
    static var previews: some View {
        ContentView()
    }
}

And my Modifier.swift from which the Modifier view is called has following code:

import SwiftUI

struct Modifier: View {
    @Binding var showText: Bool
    
    var body: some View {
        VStack {
            Button("Hide Text") {
                self.showText.toggle()
            }
        }
    }
}

I created this simplified code from my actual project that my problem is easier to understand.

Problem

The problem is that the code in the init function results into an error and I don't know how to resolve it.

What I tried and what I would need

Because this is just a simplified version of my actual code there are some requirements I need to my code:

• Mod can't be a computed variable
• I somehow need the Modifier view as a variable called Mod in my ContentView
• When I remove the @State property and the @Binding property and the $ the code works and results with 0 errors. But I need to use the @State property (which unfortunately results into errors with my code)
• Also the button to hide and show the text should work

I would be very thankful if anyone could give me a hint. I really appreciate your help!

Answer 1

Mod = Modifier(showText: _showText.projectedValue)

You can make it let instead of var if you'd like.

Answer 2

I did actually find a way to do this. I'm not sure whether it'll be suitable but here are the details.

The problem was that SwiftUI didn't seem to allow setting the Binding outside of body. So this solution returns a new instance of Modifier

struct Modifier: View {
    @Binding var showText: Bool
    
    var body: some View {
        VStack {
            Button("Hide Text") {
                self.showText.toggle()
            }
        }
    }
    
    // this function returns a new instance with the binding
    func bind(to binding: Binding<Bool>) -> Self {
        return Modifier(showText: binding)
    }
}

And the code for ContentView, where we can call this function from within body:

struct ContentView: View {
    @State var showText: Bool = true
    var Mod: Modifier
    
    init() {
        Mod = Modifier(showText: .constant(true)) // .constant() gives a placeholder Binding
    }
    
    var body: some View {
        return VStack {
            if showText == true {
                Text("Hello, World!")
            }
            Mod.bind(to: $showText)
        }
    }
}

Tested and the text can be hidden/shown. Hope this can help.

Answer 3

Use views inside body context

struct ContentView: View {
    @State var showText: Bool = true
    
    var body: some View {
        VStack {
            if showText == true {
                Text("Hello, World!")
            }
            Modifier(showText: $showText)
        }
    }
}