使用 SwiftUI 选择器，我的 MacBook 温度高达 50 度

Question

一使用代码，我的 MacBook 就会升温至 50 度。我有 4 个枚举，每个枚举都有一个选择器，一旦我将 3 个选择器放入 if-else 语句中然后进行调试，我的 MacBook 就会发热太多，以至于我几乎无法再触摸它了。错误 ->

编译器无法在合理的时间内对该表达式进行类型检查；尝试将表达式分解为不同的子表达式

我将枚举与协议 Int16、Hashable、CaseIterable 结合使用。我想要 Int16 作为我的 CoreData 属性。如果我将 Int16 更改为 Int，则代码有效。我将 "Taggs" 转换为 int 这样我就可以使用 else if statemant.

Import SwiftUI
struct EnumsInEnums: View {
          @State  var pickMain = 0
          @State  var pickA = 0
          @State  var pickB = 0
          @State  var pickC = 0

enum MainEnum :  Int16, Hashable, CaseIterable
        {
        case AEnum
        case BEnum
        case CEnum
        var name: String { return "\(self)" }
        }
enum AEnum :  Int16, Hashable, CaseIterable
        {
        case Aa
        case Ba
        case Ca
        var name: String { return "\(self)" }
        }
enum BEnum :  Int16, Hashable, CaseIterable
        {
        case Ab
        case Bb
        case Cb
        var name: String { return "\(self)" }
        }
enum CEnum :  Int16, Hashable, CaseIterable
        {
        case Ac
        case Bc
        case Cc
        var name: String { return "\(self)" }
}
var body: some View {
 NavigationView {
  Form {
   Section {

   Picker(selection: $pickMain, label: Text("Pick \(pickMain)")) {
                 ForEach(MainEnum.allCases, id: \.self){ x in
                 Text("\(x.name)").tag(Int(x.rawValue))
                 }
                    }
    if pickMain == 0 {
       Picker(selection: $pickA, label: Text("Pick \(pickA)")) {
                  ForEach(AEnum.allCases, id: \.self){ x in
                  Text("\(x.name)").tag(Int(x.rawValue))
                  }
             }
       } else if pickMain == 1 {
       Picker(selection: $pickB, label: Text("Pick \(pickB)")) {
                  ForEach(BEnum.allCases, id: \.self){ x in
                  Text("\(x.name)").tag(Int(x.rawValue))
                  }
             }
       } else if pickMain == 2 {
       Picker(selection: $pickC, label: Text("Pick \(pickC)")) {
                  ForEach(CEnum.allCases, id: \.self){ x in
                  Text("\(x.name)").tag(Int(x.rawValue))
                  }
            }
      }
     }
    }
   }
  }
 }

我希望 select Main，然后第二个选择器会向我显示 selected，就好像我 select 一个汽车制造商，第二个选择器会显示相应的汽车模型。

Answer 1

在 beta 5 中，ForEach 存在一个已知问题。来自发行说明：

Using a ForEach view with a complex expression in its closure can may result in compiler errors. Workaround: Extract those expressions into their own View types. (53325810)

你的ForEach视图，好像不太复杂，封装它的内容并不能解决问题。但是，如果您封装整个选择器就可以正常工作。仔细检查代码，因为我可能在封装时引入了错别字。

import SwiftUI

struct ContentView: View {
    var body: some View {
        EnumsInEnums()
    }
}

struct EnumsInEnums: View {
    @State  var pickMain = 0
    @State  var pickA = 0
    @State  var pickB = 0
    @State  var pickC = 0

    enum MainEnum :  Int16, Hashable, CaseIterable
    {
        case AEnum
        case BEnum
        case CEnum
        var name: String { return "\(self)" }
    }
    enum AEnum :  Int16, Hashable, CaseIterable
    {
        case Aa
        case Ba
        case Ca
        var name: String { return "\(self)" }
    }
    enum BEnum :  Int16, Hashable, CaseIterable
    {
        case Ab
        case Bb
        case Cb
        var name: String { return "\(self)" }
    }
    enum CEnum :  Int16, Hashable, CaseIterable
    {
        case Ac
        case Bc
        case Cc
        var name: String { return "\(self)" }
    }

    var body: some View {
        NavigationView {
            Form {
                Section {

                    PickerMain(pickMain: $pickMain)

                    if pickMain == 0 {
                        PickerA(pickA: $pickA)
                    }
                    else if pickMain == 1 {
                        PickerB(pickB: $pickB)
                    } else if pickMain == 2 {
                        PickerC(pickC: $pickC)

                    }
                }
            }
        }
    }

    struct PickerMain: View {
        @Binding var pickMain: Int

        var body: some View {
            Picker(selection: $pickMain, label: Text("Pick \(pickMain)")) {
                ForEach(MainEnum.allCases, id: \.self){ x in
                    Text("\(x.name)").tag(Int(x.rawValue))
                }
            }
        }
    }

    struct PickerA: View {
        @Binding var pickA: Int

        var body: some View {
            Picker(selection: $pickA, label: Text("Pick \(pickA)")) {
                ForEach(AEnum.allCases, id: \.self){ x in
                    Text("\(x.name)").tag(Int(x.rawValue))
                }
            }
        }
    }

    struct PickerB: View {
        @Binding var pickB: Int

        var body: some View {
            Picker(selection: $pickB, label: Text("Pick \(pickB)")) {
                ForEach(BEnum.allCases, id: \.self){ x in
                    Text("\(x.name)").tag(Int(x.rawValue))
                }
            }
        }
    }

    struct PickerC: View {
        @Binding var pickC: Int

        var body: some View {
            Picker(selection: $pickC, label: Text("Pick \(pickC)")) {
                ForEach(CEnum.allCases, id: \.self){ x in
                    Text("\(x.name)").tag(Int(x.rawValue))
                }
            }
        }
    }
}

使用 SwiftUI 选择器，我的 MacBook 温度高达 50 度

Used SwiftUI picker and my MacBook heats up to 50 degrees

enums

if-statement

picker

swiftui

编译器无法在合理的时间内对该表达式进行类型检查；尝试将表达式分解为不同的子表达式