问在编辑另一个TextField时更改TextField
EN

Stack Overflow用户

提问于 2021-06-27 14:03:41

回答 1查看 66关注 0票数 0

我最近开始学习SwiftUI，我想做一个单位转换器。在这个过程中，我遇到了一个问题:必须确保当将一个数值输入其中一个TextField时，会触发其余的TextField公式，并显示总值。

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)
    }
}

swift

swiftui

回答 1

Stack Overflow用户

发布于 2021-06-27 16:52:27

在SwiftUI 3中，@FocusState可以用来检测TextField是否被聚焦，这使得可以根据它的值执行不同的工作。您可以将一个变量设置为主变量，并从中计算其他值。对于每个值，使用两个函数进行正向和反向计算：

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
    }
}