How to make a binding computed property update on an ObservableObject class? - swiftui

Question

I have this class:
class MyModel:ObservableObject {
var selectedObjectIndex:Int {
set {}
get {
let selectedResult = objects.filter({ $0 == selectedObject })
if selectedResult == 0 { return 0 }
return objects.firstIndex(of: selectedResult.first!)!
}
}
}
This selectedObjectIndex would normally be a #Published var selectedObjectIndex:Int but because it is a computed property, I cannot use #Published there.
So I was forced to add this to the model
func getselectedObjectIndexBinding() -> Binding<Int> {
let binding = Binding<Int>(
get: { () -> Int in
return self.selectedObjectIndex
}) { (newValue) in
self.selectedObjectIndex = newValue
}
return binding
}
In the view I have a Picker, using this like
Picker(selection: myModel.getselectedObjectIndexBinding(),
label: Text("select")) {
The picker appears correctly but If I set a new value on it, the model selectedObjectIndex is not updated.

Answer 1

You can try something like below, whenever a binding is updated, your selectedObjectIndex can trigger ObjectWillChange notification after doing some relevant work. I have created selectedObjectIndex as propertyObserver.
struct CreditCardFront: View {
#ObservedObject var myModel:MyModel
var body: some View {
Picker(selection: myModel.getselectedObjectIndexBinding(),
label: Text("select")) {
ForEach(1..<10) { value in
Text("\(value)")
}
}
Text("\(myModel.selectedObjectIndex ?? 0)")
}
}
class MyModel:ObservableObject {
var selectedObjectIndex:Int?{
didSet{
// Your work here
update() // call notification on specific change
}
}
func getselectedObjectIndexBinding() -> Binding<Int> {
let binding = Binding<Int>(
get: { () -> Int in
return self.selectedObjectIndex ?? 0
}) { (newValue) in
self.selectedObjectIndex = newValue
}
return binding
}
func update(){
self.objectWillChange.send()
}
}
#main-:
#main
struct WaveViewApp: App {
#StateObject var model:MyModel
init() {
let model = MyModel()
_model = StateObject(wrappedValue: model)
}
var body: some Scene {
WindowGroup {
CreditCardFront(myModel: model)
}
}
}