选择器中的 SwiftUI 和枚举

Question

我在游乐场工作，试图学习 SwiftUI。我正在创建一个视图，其中包含一个标签、一个文本字段、用于显示选取器和选取器值的文本。

我目前拥有的是这个

import UIKit
import PlaygroundSupport
import SwiftUI

enum Units: String, CaseIterable, Identifiable
{
    case Inches = "in"
    case Millimeters = "mm"
    case Centimeters = "cm"
    
    var id: String { self.rawValue }
}

struct VariableView: View
{
    let name: String
    let labelValue: String
    @State private var inputValue = ""
    @State private var inputUnits = Units.Inches
    
    init(name: String, label: String)
    {
        self.name = name
        labelValue = label
    }
    
    var body: some View
    {
        VStack(alignment: .leading, spacing: 0)
        {
            Text(self.labelValue)
                .font(.subheadline)
                .frame(width: .infinity, alignment: .leading)
                .padding(.horizontal, 4)
            HStack
            {
                TextField("Value", text: $inputValue)
                    .padding(.horizontal, 4)
                    .keyboardType(.numbersAndPunctuation)
                Text(inputUnits.id)
                Picker("...", selection: $inputUnits)
                {
                    /*
                    Text("Inches").tag(Units.Inches)
                    Text("Millimeters").tag(Units.Millimeters)
                    Text("Centimeters").tag(Units.Centimeters)
                     */
                    ForEach(Units.allCases)
                    {
                        unit in Text(unit.rawValue.capitalized)
                    }
                }
                .padding(10)
                .pickerStyle(MenuPickerStyle())
            }
            Divider()
             .frame(height: 1)
             .padding(.horizontal, 30)
             .background(Color.black)
        }
    }
}

// Make a SwiftUI view
struct ContentView: View
{
    var body: some View
    {
        VariableView(name: "value1", label: "Value 1")
        VariableView(name: "value1", label: "Value 2")
        VariableView(name: "value1", label: "Value 3")
        VariableView(name: "value1", label: "Value 4")
        VariableView(name: "value1", label: "Value 5")
    }
}

// Make a UIHostingController
let viewController = UIHostingController(rootView: ContentView())

// Assign it to the playground's liveView
PlaygroundPage.current.liveView = viewController

当我单击“...”时，它会崩溃。变为黑色并停止运行。没有错误，只是停止。

如果我使用三个文本行（当前已注释掉）而不是 ForEach，它可以工作 - 但最终我需要能够为每个输入动态设置允许的单位，所以我需要 ForEach 工作。

Answer 1

inputTypes 的类型是 Units，硬编码 Texts 上的标签与该类型匹配。在 ForEach 中，标签是 Units.rawValue，类型是 String。看看这是否适用于 Playground：

struct PickFromEnumView: View {
    @State private var inputUnits = Units.none
    
    var body: some View {
        VStack {
            Picker(inputUnits.rawValue, selection: $inputUnits) {
                ForEach(Units.allCases) { unit in
                    unit.label.tag(unit)
                }
            }
            .padding(10)
            .pickerStyle(MenuPickerStyle())
            Spacer()
        }
    }
    
    enum Units: String, CaseIterable, Identifiable
    {
        case none = "…"
        case inches = "in"
        case millimeters = "mm"
        case centimeters = "cm"
        
        var id: String { self.rawValue }
        
        var label : some View {
            switch(self) {
            case .none: return Label("…", systemImage: "circle")
            case .inches: return Label("inch", systemImage: "1.circle")
            case .millimeters: return Label("millimeter", systemImage: "2.circle")
            case .centimeters: return Label("centimeter", systemImage: "3.circle")
            }
        }
    }
}