changing a TextField while editing another TextField - swift

Question

I recently started learning SwiftUI and I want to make a unit converter. In the process I ran into a problem: it is necessary to make sure that when a numerical value is entered into one of the TextField, the rest of the TextField formulas are triggered and the total values are displayed.
import SwiftUI
import Combine
struct ContentView: View {
#State var celsius: String = ""
#State var kelvin: String = ""
#State var farenheit: String = ""
#State var reyumur: String = ""
#State var rankin: String = ""
var body: some View {
NavigationView {
Temperature(celsius: $celsius, kelvin: $kelvin, farenheit: $farenheit, reyumur: $reyumur, rankin: $rankin)
}
}
}
struct ContentView_Previews: PreviewProvider {
static var previews: some View {
ContentView()
}
}
struct Temperature: View {
#Binding var celsius: String
#Binding var kelvin: String
#Binding var farenheit: String
#Binding var reyumur: String
#Binding var rankin: String
var body: some View {
List {
Section(
header: Text("Международная система (СИ)")) {
HStack {
TextField("Enter value", text: $celsius)
.keyboardType(.numbersAndPunctuation)
.onReceive(Just(celsius)) { newValue in
let filtered = newValue.filter { "0123456789.".contains($0) }
if filtered != newValue {
self.celsius = filtered
}
}
Text("°C")
.padding(.horizontal)
.font(.headline)
.foregroundColor(.blue)
}
HStack {
TextField("Enter value", text: $kelvin)
.keyboardType(.numbersAndPunctuation)
.onReceive(Just(kelvin)) { newValue in
let filtered = newValue.filter { "0123456789.".contains($0) }
if filtered != newValue {
self.kelvin = filtered
}
}
Text("K")
.padding(.horizontal)
.font(.headline)
.foregroundColor(.blue)
}
}
Section(
header: Text("США и Британия")) {
HStack {
TextField("Enter value" , text: $farenheit)
.keyboardType(.numbersAndPunctuation)
.onReceive(Just(farenheit)) { newValue in
let filtered = newValue.filter { "0123456789.".contains($0) }
if filtered != newValue {
self.farenheit = filtered
}
}
Text("F")
.padding(.horizontal)
.font(.headline)
.foregroundColor(.blue)
}
}
Section(
header: Text("Редкоиспользуемые")) {
HStack {
TextField("Enter value" , text: $reyumur)
.keyboardType(.numbersAndPunctuation)
.onReceive(Just(reyumur)) { newValue in
let filtered = newValue.filter { "0123456789.".contains($0) }
if filtered != newValue {
self.reyumur = filtered
}
}
Text("Re")
.padding(.horizontal)
.font(.headline)
.foregroundColor(.blue)
}
HStack {
TextField("Enter value" , text: $rankin)
.keyboardType(.numbersAndPunctuation)
.onReceive(Just(rankin)) { newValue in
let filtered = newValue.filter { "0123456789.".contains($0) }
if filtered != newValue {
self.rankin = filtered
}
}
Text("R")
.padding(.horizontal)
.font(.headline)
.foregroundColor(.blue)
}
}
}
.navigationBarTitle("Temperature")
.navigationBarTitleDisplayMode(.inline)
}
}

Answer 1

With SwiftUI 3, #FocusState can be used to detect if TextField is focused, which enables doing different works according to its value. You could set one variable to be the main, and other values should be calculated from it. For each value, calculate in the forward and reverse direction with two functions:
struct CelsiusAndKelvin: View {
#State private var celsius: String = "" // Assume all other values are based on celsius
#FocusState private var isKelvinFocused: Bool // When focused,
#State private var kelvinWhenFocused: String? // you may not want it to be calculated from other values
private var kelvinMask: Binding<String> {
Binding { // If `isKelvinFocused` turns true, this getter will be called first
if isKelvinFocused && kelvinWhenFocused != nil {
return kelvinWhenFocused!
}
if let x = Double(celsius) {
return String(format: "%.2f", c2k(x))
}
return ""
} set: {
if isKelvinFocused { kelvinWhenFocused = $0 }
if let x = Double($0) {
celsius = String(format: "%.2f", k2c(x))
} else {
celsius = ""
}
}
}
var body: some View {
Form {
TextField("°C", text: $celsius)
TextField("K", text: kelvinMask)
.focused($isKelvinFocused)
}
.onChange(of: isKelvinFocused) {
// Make `isKelvinFocused` always equal to `kelvinWhenFocused != nil`
if !$0 { kelvinWhenFocused = nil }
}
}
}
extension CelsiusAndKelvin {
private func c2k(_ x: Double) -> Double {
return x + 273.15
}
private func k2c(_ x: Double) -> Double {
return x - 273.15
}
}