How can I trigger an action when a swiftUI toggle() is toggled?

Question

In my SwiftUI view I have to trigger an action when a Toggle() changes its state. The toggle itself only takes a Binding. I therefore tried to trigger the action in the didSet of the @State variable. But the didSet never gets called.

Is there any (other) way to trigger an action? Or any way to observe the value change of a @State variable?

My code looks like this:

struct PWSDetailView : View {

    @ObjectBinding var station: PWS
    @State var isDisplayed: Bool = false {
        didSet {
            if isDisplayed != station.isDisplayed {
                PWSStore.shared.toggleIsDisplayed(station)
            }
        }
    }

    var body: some View {
            VStack {
                ZStack(alignment: .leading) {
                    Rectangle()
                        .frame(width: UIScreen.main.bounds.width, height: 50)
                        .foregroundColor(Color.lokalZeroBlue)
                    Text(station.displayName)
                        .font(.title)
                        .foregroundColor(Color.white)
                        .padding(.leading)
                }

                MapView(latitude: station.latitude, longitude: station.longitude, span: 0.05)
                    .frame(height: UIScreen.main.bounds.height / 3)
                    .padding(.top, -8)

                Form {
                    Toggle(isOn: $isDisplayed)
                    { Text("Wetterstation anzeigen") }
                }

                Spacer()
            }.colorScheme(.dark)
    }
}

The desired behaviour would be that the action "PWSStore.shared.toggleIsDisplayed(station)" is triggered when the Toggle() changes its state.

Answer 1

iOS 14+

If you're using iOS 14 and higher you can use onChange:

struct ContentView: View {
    @State private var isDisplayed = false
    
    var body: some View {
        Toggle("", isOn: $isDisplayed)
            .onChange(of: isDisplayed) { value in
                // action...
                print(value)
            }
    }
}

Answer 2

Here is a version without using tapGesture.

@State private var isDisplayed = false
Toggle("", isOn: $isDisplayed)
   .onReceive([self.isDisplayed].publisher.first()) { (value) in
        print("New value is: \(value)")           
   }

Answer 3

iOS13+

Here is a more generic approach you can apply to any Binding for almost all built in Views like Pickers, Textfields, Toggle..

extension Binding {
    func didSet(execute: @escaping (Value) -> Void) -> Binding {
        return Binding(
            get: { self.wrappedValue },
            set: {
                self.wrappedValue = $0
                execute($0)
            }
        )
    }
}

And usage is simply;

@State var isOn: Bool = false
Toggle("Title", isOn: $isOn.didSet { (state) in
   print(state)
})

iOS14+

@State private var isOn = false

var body: some View {
    Toggle("Title", isOn: $isOn)
        .onChange(of: isOn) { _isOn in
            /// use _isOn here..
        }
}