Learn SwiftUI (Day 19/100)

import SwiftUI

struct ContentView: View {
    @State private var f: Double = 68
    @State private var c: Double = 0
    @FocusState private var isFocusedF
    @FocusState private var isFocusedC

    func f2c(_ f: Double) -> Double {
        Double(String(format: "%.2f", (f-32) * 5 / 9))!
    }

    func c2f(_ c: Double) -> Double {
        Double(String(format:"%.2f", c * 9 / 5 + 32))!
    }

    var body: some View {
        NavigationStack {
            Form {
                Section("Temperature") {
                    VStack(alignment: .leading) {
                        HStack {
                            TextField("F", value: $f, format: .number)
                                .keyboardType(.numberPad)
                                .onChange(of: f) { (oldValue, newValue) in
                                    if isFocusedF {
                                        self.c = f2c(newValue)
                                    }
                                }
                                .focused($isFocusedF)
                            Text("°F").foregroundColor(.gray)
                        }
                        Divider().padding(.vertical)
                        HStack {
                            TextField("C", value: $c, format: .number)
                                .keyboardType(.numberPad)
                                .onChange(of: c) { (oldValue, newValue) in
                                    if isFocusedC {
                                        self.f = c2f(newValue)
                                    }
                                }
                                .focused($isFocusedC)
                            Text("°C").foregroundColor(.gray)
                        }
                        .onAppear {
                            self.c = f2c(f)
                        }
                    }
                    .padding()
                }
            }
            .navigationTitle("Simple Metrics")
        }
    }
}