“在视图更新期间修改状态，这将导致未定义的行为。”在文本字段（SwiftUI）上输入时出错

我有两个文本字段，分配给：

@State  private var emailAddress: String = ""
@State  private var password: String = ""

现在，每当我在上面输入内容时，该应用程序似乎都会卡住并给出以下错误：

“在视图更新期间修改状态，这将导致未定义的行为。”

我有一个StartView():

class UserSettings: ObservableObject {

var didChange = PassthroughSubject<Void, Never>()

@Published var loggedIn : Bool = false {
     didSet {
         didChange.send(())
     }
 }
}

struct StartView: View {
@EnvironmentObject var settings: UserSettings

var body: some View {
    if settings.loggedIn {
        return AnyView(TabbarView())
    }else {
        return AnyView(ContentView())
    }
}

}

我创建了一个 UserSettings 的 ObservableObject 类，它具有loggedIn布尔值。当用户点击“登录”按钮时LogInView()，这个布尔值变成true并出现一个新视图（TabbarView())

这是LogInView()：

struct LogInView: View {
@EnvironmentObject var settings: UserSettings

@State  private var emailAddress: String = ""
@State  private var password: String = ""

var body: some View {
GeometryReader { geometry in
        VStack (alignment: .center){
            HStack {
                Image("2")
                .resizable()
                .frame(width: 20, height: 20)
                Text("Social App")
                    .font(.system(size: 12))

            }.padding(.top, 30)
                .padding(.bottom, 10)

            Text("Log In to Your Account")
                .font(.title)
                .font(.system(size: 14, weight: .bold, design: Font.Design.default))
                .padding(.bottom, 50)

            TextField("Email", text: self.$emailAddress)
                .frame(width: geometry.size.width - 45, height: 50)
                .textContentType(.emailAddress)
                .padding(EdgeInsets(top: 0, leading: 5, bottom: 0, trailing: 0))
                .accentColor(.red)
                .background(Color(red: 242 / 255, green: 242 / 255, blue: 242 / 255))
                .cornerRadius(5)


            TextField("Password", text: self.$password)
                .frame(width: geometry.size.width - 45, height: 50)
                .padding(EdgeInsets(top: 0, leading: 5, bottom: 0, trailing: 0))
                .foregroundColor(.gray)
                .background(Color(red: 242 / 255, green: 242 / 255, blue: 242 / 255))
                .textContentType(.password)
                .cornerRadius(5)

             Button(action: {
                self.settings.loggedIn = true
             }) {
                    HStack {
                        Text("Log In")
                    }
                        .padding()
                        .frame(width: geometry.size.width - 40, height: 40)
                        .foregroundColor(Color.white)
                        .background(Color.blue)
                        .cornerRadius(5)
                }
                 .padding(.bottom, 40)

            Divider()

            Button(action: {
                    print("Take to forget password VC")
                    }) {
                    Text("Forgot your password?")
            }

            Spacer()

            }
            .padding(.bottom, 90)
        }
}
}

我知道如果我在修改状态时更新视图（在文本字段中输入时），则会出现此错误。但我没有更新登录屏幕中任何地方的视图。那为什么会出现这个错误呢。帮助将不胜感激！

这对我有用，你甚至不需要导入合并！当你使用@Published，SwiftUI会自动合成objectWillChangesubject，并且每当属性发生变化时就会调用 send。您仍然可以致电.send()如果需要，可以手动执行，但大多数情况下您不会。

class UserSettings: ObservableObject {
    @Published var loggedIn : Bool = false
}

Beta 5 发行说明摘录：

您可以通过定义一个来手动遵守 ObservableObject 在对象更改之前发出的 objectWillChange 发布者。 然而，默认情况下，ObservableObject会自动合成 objectWillChange 并在任何 @Published 属性更改之前发出。

这是对我来说运行良好的完整代码（iPhone Xr 和真实设备，iPad 6th Gen）：

window.rootViewController = UIHostingController(rootView: ContentView().environmentObject(UserSettings()))

import SwiftUI

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

class UserSettings: ObservableObject {
    @Published var loggedIn : Bool = false
}

struct StartView: View {
    @EnvironmentObject var settings: UserSettings

    var body: some View {
        if settings.loggedIn {
            return AnyView(Text("LOGGED IN"))
        } else {
            return AnyView(LogInView())
        }
    }
}

struct LogInView: View {
    @EnvironmentObject var settings: UserSettings


    @State  private var emailAddress: String = ""
    @State  private var password: String = ""

    var body: some View {
        GeometryReader { geometry in
            VStack (alignment: .center){
                HStack {
                    Image(systemName: "2.circle.fill")
                        .resizable()
                        .frame(width: 20, height: 20)
                    Text("Social App")
                        .font(.system(size: 12))

                }.padding(.top, 30)
                    .padding(.bottom, 10)

                Text("Log In to Your Account")
                    .font(.title)
                    .font(.system(size: 14, weight: .bold, design: Font.Design.default))
                    .padding(.bottom, 50)

                TextField("Email", text: self.$emailAddress)
                    .frame(width: geometry.size.width - 45, height: 50)
                    .textContentType(.emailAddress)
                    .padding(EdgeInsets(top: 0, leading: 5, bottom: 0, trailing: 0))
                    .accentColor(.red)
                    .background(Color(red: 242 / 255, green: 242 / 255, blue: 242 / 255))
                    .cornerRadius(5)


                TextField("Password", text: self.$password)
                    .frame(width: geometry.size.width - 45, height: 50)
                    .padding(EdgeInsets(top: 0, leading: 5, bottom: 0, trailing: 0))
                    .foregroundColor(.gray)
                    .background(Color(red: 242 / 255, green: 242 / 255, blue: 242 / 255))
                    .textContentType(.password)
                    .cornerRadius(5)

                Button(action: {
                    self.settings.loggedIn = true
                }) {
                    HStack {
                        Text("Log In")
                    }
                    .padding()
                    .frame(width: geometry.size.width - 40, height: 40)
                    .foregroundColor(Color.white)
                    .background(Color.blue)
                    .cornerRadius(5)
                }
                .padding(.bottom, 40)

                Divider()

                Button(action: {
                    print("Take to forget password VC")
                }) {
                    Text("Forgot your password?")
                }

                Spacer()

            }
            .padding(.bottom, 90)
        }
    }
}