persistent value in a picker changing views in Swift

I don’t understand how implementing in Swift a simple picker showing a list of values that retain the selected value switching between different views. I’m able to use the selected value to update the Model via Combine framework by the way.

here’s the code, but the onAppear{}/onDisappear{} doesn’t work as expected:

struct CompanyView: View {

    @ObservedObject var dataManager: DataManager = DataManager.shared

    @State var selTipoAzienda = 0

    var body: some View {
        VStack {
            companyPhoto
            Text("Company view")
            Form {
                Picker(selection: $selTipoAzienda, label: Text("Tipo Azienda")) {
                    ForEach(0 ..<  self.dataManager.company.tipoAziendaList.count) {
                        Text(self.dataManager.company.tipoAziendaList[$0])
                    }
                }
            }

            Button(action:  {self.dataManager.cambiaTipoAzienda(tipoAzienda: self.dataManager.company.tipoAziendaList[self.selTipoAzienda]) }) {
                Image(systemName: "info.circle.fill")
                    .font(Font.system(size: 28))
                    .padding(.horizontal, 16)
            }
        }
//        .onAppear{
//            self.selTipoAzienda = self.dataManager.company.tipoAziendaList.firstIndex(of: self.dataManager.company.tipoAzienda) ?? 0
//        }
//        .onDisappear{
//            self.dataManager.cambiaTipoAzienda(tipoAzienda: self.dataManager.company.tipoAziendaList[self.selTipoAzienda])
//        }
    }

I think binding and didSet would be the answer but I don’t know how they have to be implemented

Source: Swift