SwiftUI Picker不再适用于Xcode 11 beta 7

Question

I'm using a Picker to have the user select a font type. This code used to work, but it no longer works correctly. I think it may have stopped working after I updated to Xcode 11 beta 7. I can tap on the Picker to bring up the Picker options list, but my previous selection no longer shows a checkmark next to it, and tapping on an option no longer does anything. Am I doing something wrong or is this just a beta bug?

SettingsFont view:

struct SettingsFont: View {

  @EnvironmentObject var userSettings: UserSettings

  let fontNames = FontName.allCases

  var body: some View {
    Form {
      Section {
        Picker(selection: $userSettings.fontName, label: Text("Font Type")) {
          ForEach(fontNames, id: \.self) { fontName in
            Text(fontName.rawValue).tag(fontName.rawValue)
              .font(FontFactory.noteFont(for: fontName))
          }
        }
      }
    }
    .listStyle(GroupedListStyle())
    .navigationBarTitle(Text("Font"))
  }

}

UserSettings:

import Foundation
import Combine

class UserSettings: ObservableObject {

  var objectWillChange = PassthroughSubject<Void, Never>()

  enum StringSettingsKey: String {
    case fontName
  }

  struct Default {
    static let fontName = FontName.sanFrancisco
  }

  @Published var fontName: FontName = Default.fontName {
    willSet { objectWillChange.send() }
    didSet { set(string: fontName.rawValue, for: .fontName) }
  }

  init() {
    setFromUserDefaults(settingsKey: .fontName)
  }

  private func setFromUserDefaults(settingsKey: StringSettingsKey) {
    if let storedString = UserDefaults.standard.string(forKey: settingsKey.rawValue) {
      switch settingsKey {
      case .fontName: fontName = FontName(rawValue: storedString) ?? Default.fontName
      }
      return
    }
  }

  private func set(string: String, for settingsKey: StringSettingsKey) {
    UserDefaults.standard.set(string, forKey: settingsKey.rawValue)
  }

  private func storedString(for settingsKey: StringSettingsKey) -> String? {
    return UserDefaults.standard.string(forKey: settingsKey.rawValue)
  }

}

FontName:

enum FontName: String, CaseIterable {
  case sanFrancisco = "San Francisco"
  case bitter = "Bitter"
  case helvetica = "Helvetica"
  case georgia = "Georgia"
  case avenir = "Avenir"
  case menlo = "Menlo"
}

Answer 1

You need to wrap your view in a navigation view:

struct SettingsFont: View {

    @EnvironmentObject var userSettings: UserSettings

    let fontNames = FontName.allCases

    var body: some View {
        NavigationView {
            Form {
                Section {
                    Picker(selection: $userSettings.fontName, label: Text("Font Type")) {
                        ForEach(fontNames, id: \.self) { fontName in
                            Text(fontName.rawValue).tag(fontName.rawValue)
                                .font(FontFactory.noteFont(for: fontName))
                        }
                    }
                }
            }
        }
        .navigationBarTitle(Text("Font"))
    }

}

The navigation view is needed to navigate to the screen with options and then to navigate back.