SwiftUI @Binding update doesn't refresh view

Question

I feel like I\'m missing something very basic, but this example SwiftUI code will not modify the view (despite the Binding updating) when the button is clicked

Tutorials

Answer 1

Looking into this some more I think I understand what's happening.

In this instance I want to use @Binding as I'm building a custom control (like SwiftUI's native Toggle, which also binds to a Bool)

The issue is that the static state in ContentView_Previews (i.e., the line @State static var selected: Bool = false) does not trigger a re-render of the preview when the state changes, so even though the selected state has changed due to interaction with the control, the control (a child of ContentView_Previews) does not re-render itself

This makes it tough to test controls in isolation in the SwiftUI preview, however moving the state into a dummy ObservableObject instance functions correctly. Here's the code:

import SwiftUI
import Combine

class SomeData: ObservableObject {
    @Published var isOn: Bool = false
}

struct MyButton: View {
    @Binding var isSelected: Bool

    var body: some View {
        Button(action: {
            self.isSelected.toggle()
        }) {
            Text(isSelected ? "Selected" : "Not Selected")
        }
    }
}

struct ContentView: View {
    @EnvironmentObject var data: SomeData

    var body: some View {
        MyButton(isSelected: $data.isOn)
    }
}

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

It seems that a change in @State static var doesn't trigger a preview re-render. In the above code my @Binding example is moved into MyButton and the content view's dummy environment instance is bounds to its isSelected property. Tapping the button updates the view as expected in the SwiftUI preview.