How to call a function when a #State variable changes - swiftui

Question

I have a time selection subview with two wheel pickers, one for minutes and one for seconds. The values are bound to two (local) state variables in the parent view. I'm looking for a way to have a global state variable "time" changed every time when either one of the two local variables changes. I don't want to directly bind the two state variables for min/sec to the global state as I want only one variable there holding the time in seconds only. So there should be a conversion time = min * 60 + seconds.
I'm struggling to find a way of detecting a value change of the two local state variables.
Here's the subview:
struct TimePicker: View {
var min: Binding<Int>
var sec: Binding<Int>
var body: some View {
HStack() {
Spacer()
Picker(selection: min, label: EmptyView()) {
ForEach((0...9), id: \.self) { ix in
Text("\(ix)").tag(ix)
}
}.frame(width: 40).clipped().pickerStyle(WheelPickerStyle())
Text("Min.")
Picker(selection: sec, label: EmptyView()) {
ForEach((0...59), id: \.self) { ix in
Text("\(ix)").tag(ix)
}
}.frame(width: 40).clipped().pickerStyle(WheelPickerStyle())
Text("Sec.")
Spacer()
}
}
}

Answer 1

You may use combineLatest in the main view.
struct MainTimeView: View{
#State private var min : Int = 0
#State private var sec : Int = 0
#State private var myTime: Int = 0
var body: some View {
TimePicker(min: $min, sec: $sec).onReceive(Publishers.CombineLatest(Just(min), Just(sec))) {
self.myTime = $0 * 60 + $1
print(self.myTime)
}
}
}

Answer 2

i think you need to wrapped your global variable kinda
class TimeObject : BindableObject {
let didChange = PassthroughSubject<Void, Never>()
var time:Int = 0 {
didSet {
didChange.send(())
}
}
}
...
struct TimePicker: View {
var min: Binding<Int>
var sec: Binding<Int>
#EnvironmentObject var time : TimeObject
var body: some View {
HStack() {
Spacer()
Picker(selection: min, label: EmptyView()) {
ForEach((0...9), id: \.self) { ix in
Text("\(ix)").tag(ix)
}.gesture(TapGesture().onEnded(){
                        time.time = ix
                })
}.frame(width: 40).clipped().pickerStyle(WheelPickerStyle())
Text("Min.")
Picker(selection: sec, label: EmptyView()) {
ForEach((0...59), id: \.self) { ix in
Text("\(ix)").tag(ix)
}.gesture(TapGesture().onEnded(){
                        time.time = ix
                })
}.frame(width: 40).clipped().pickerStyle(WheelPickerStyle())
Text("Sec.")
Spacer()
}
}
}
...
TimePicker..environmentObject(TimeObject())
unfortunately don't have a chance to test