Making calculations based on state of segmented picker - swiftui

Question

I know the below is incorrect, and I feel dumb that i can't solve this, but I'm struggling to undertand where to put the 'logic' (and if statment or other) for handeling calculations in my app, based on the entered value and the state of a segmented picker. I can't add it as part of the picker, and it throws an error if i tey and make totalTime a computed property like the below.
I created a quick example to make it simpler to undertand my question. I want to hold the value for use on another screen as well.
struct ContentView: View {
#AppStorage("totalTime") var totalTime: Double {
onChange(of: timeSelected) {
if timeSelected == "hours" {
totalTime = (Double(enteredValue) ?? 0) * multipier
} else {
totalTime = (Double(enteredValue) ?? 0)
}
}
}
#State var enteredValue = ""
#State var timeSelected = "hours"
let multipier = 2.0
let arrayLabel = ["hours", "minutes"]
var body: some View {
VStack {
Form {
Section(header: Text("Time Test")){
TextField("enter value", text: $enteredValue)
Picker("timeValue",selection: $timeSelected) {
ForEach(arrayLabel, id: \.self){
Text("\($0)")
}
}
.pickerStyle(.segmented)
}
}
}
}
}

Answer 1

I reworked your code so that it works like you asked, that the computation is done when the Picker is changed. However, this never triggers if the Picker isn't changed:
struct ContentView: View {
#AppStorage("totalTime") var totalTime: Double = 0.0
#State var enteredValue = ""
#State var timeSelected = "hours"
let multipier = 2.0
let arrayLabel = ["hours", "minutes"]
var body: some View {
VStack {
Form {
Section(header: Text("Time Test")){
TextField("enter value", text: $enteredValue)
Picker("timeValue",selection: $timeSelected) {
ForEach(arrayLabel, id: \.self){
Text("\($0)")
}
}
.pickerStyle(.segmented)
Text("Total time: \(totalTime, format: .number)")
}
// This can be most places within the view
.onChange(of: timeSelected) { _ in
computeTotal()
}
}
}
}
// Refactor to its own function for cleaner code.
private func computeTotal() {
if timeSelected == "hours" {
totalTime = (Double(enteredValue) ?? 0) * multipier
} else {
totalTime = (Double(enteredValue) ?? 0)
}
}
}
A better version may be:
struct TimeSelectedView: View {
#AppStorage("totalTime") var totalTime: Double = 0.0
#State var enteredValue = ""
#State var timeSelected = "hours"
// Use a computed variable that makes its computations based on enteredValue
// Every time that changes, the computed variable will update setting totalTime
var total: Double {
if timeSelected == "hours" {
totalTime = (Double(enteredValue) ?? 0) * multipier
} else {
totalTime = (Double(enteredValue) ?? 0)
}
return totalTime
}
let multipier = 2.0
let arrayLabel = ["hours", "minutes"]
var body: some View {
VStack {
Form {
Section(header: Text("Time Test")){
TextField("enter value", text: $enteredValue)
Picker("timeValue",selection: $timeSelected) {
ForEach(arrayLabel, id: \.self){
Text("\($0)")
}
}
.pickerStyle(.segmented)
Text("Total time: \(total, format: .number)")
}
}
}
}
}
This will update continuously for either a changed in enteredValue or a change in timeSelected.