SwiftUI call function on variable change

Question

I am trying to convert a view of my watchOS App to Swift UI. I wanted to port the volume control that can be found in watchKit to SwiftUI with custom controls. In the image

Answer 1

You can use a custom Binding, that calls some code in set. For example from :

extension Binding {
    /// Execute block when value is changed.
    ///
    /// Example:
    ///
    ///     Slider(value: $amount.didSet { print($0) }, in: 0...10)
    func didSet(execute: @escaping (Value) ->Void) -> Binding {
        return Binding(
            get: {
                return self.wrappedValue
            },
            set: {
                self.wrappedValue = $0
                execute($0)
            }
        )
    }
}

Answer 2

As you said "In the past I would have done this with a didSet, but this is no longer available" I test below code it works perfectly

struct pHome: View {
 @State var prog:Int = 2 {
    willSet{
        print("willSet: newValue =\(newValue)  oldValue =\(prog)") 
    }
    didSet{
        print("didSet: oldValue=\(oldValue) newValue=\(prog)")
        //Write code, function do what ever you want todo 
    }
} 
 var body: some View {
VStack{
                Button("Update"){
                    self.prog += 1
                }
                Text("\(self.prog)%")
  }
 }
}