快速组合 : subsequent Publisher that consumes other Publishers (using CombineLatest) doesn't "fire"

Question

我正在尝试复制 WWDC 2019 session “结合实践”中给出的“Wizard School Signup”示例 https://developer.apple.com/videos/play/wwdc2019/721/从 22:50 开始使用 SwiftUI(与在 session 期间使用的 UIKit 相反)。

我已经根据示例创建了所有发布者:validatedEMail、validatedPassword 和 validatedCredentials。虽然 validatedEMail 和 validatedPassword 工作正常，但使用 CombineLatest 消耗两个发布者的 validatedCredentials 永远不会触发

//
//  RegistrationView.swift
//
//  Created by Lars Sonchocky-Helldorf on 04.07.19.
//  Copyright © 2019 Lars Sonchocky-Helldorf. All rights reserved.
//

import SwiftUI
import Combine

struct RegistrationView : View {
    @ObjectBinding var registrationModel = RegistrationModel()

    @State private var showAlert = false
    @State private var alertTitle: String = ""
    @State private var alertMessage: String = ""

    @State private var registrationButtonDisabled = true

    @State private var validatedEMail: String = ""
    @State private var validatedPassword: String = ""

    var body: some View {
        Form {
            Section {
                TextField("Enter your EMail", text: $registrationModel.eMail)
                SecureField("Enter a Password", text: $registrationModel.password)
                SecureField("Enter the Password again", text: $registrationModel.passwordRepeat)
                Button(action: registrationButtonAction) {
                    Text("Create Account")
                }
                .disabled($registrationButtonDisabled.value)
                    .presentation($showAlert) {
                        Alert(title: Text("\(alertTitle)"), message: Text("\(alertMessage)"))
                }
                .onReceive(self.registrationModel.validatedCredentials) { newValidatedCredentials in
                    self.registrationButtonDisabled = (newValidatedCredentials == nil)
                }
            }

            Section {
                Text("Validated EMail: \(validatedEMail)")
                    .onReceive(self.registrationModel.validatedEMail) { newValidatedEMail in
                        self.validatedEMail = newValidatedEMail != nil ? newValidatedEMail! : "EMail invalid"
                }
                Text("Validated Password: \(validatedPassword)")
                    .onReceive(self.registrationModel.validatedPassword) { newValidatedPassword in
                        self.validatedPassword = newValidatedPassword != nil ? newValidatedPassword! : "Passwords to short or don't matchst"
                }
            }
        }
        .navigationBarTitle(Text("Sign Up"))
    }

    func registrationButtonAction() {
        let trimmedEMail: String = self.registrationModel.eMail.trimmingCharacters(in: .whitespaces)

        if (trimmedEMail != "" && self.registrationModel.password != "") {
            NetworkManager.sharedInstance.registerUser(NetworkManager.RegisterRequest(uid: trimmedEMail, password: self.registrationModel.password)) { (status) in
                if status == 200 {
                    self.showAlert = true
                    self.alertTitle = NSLocalizedString("Registration successful", comment: "")
                    self.alertMessage = NSLocalizedString("please verify your email and login", comment: "")
                } else if status == 400 {
                    self.showAlert = true
                    self.alertTitle = NSLocalizedString("Registration Error", comment: "")
                    self.alertMessage = NSLocalizedString("already registered", comment: "")
                } else {
                    self.showAlert = true
                    self.alertTitle = NSLocalizedString("Registration Error", comment: "")
                    self.alertMessage = NSLocalizedString("network or app error", comment: "")
                }
            }
        } else {
            self.showAlert = true
            self.alertTitle = NSLocalizedString("Registration Error", comment: "")
            self.alertMessage = NSLocalizedString("username / password empty", comment: "")
        }
    }
}

class RegistrationModel : BindableObject {
    @Published var eMail: String = ""
    @Published var password: String = ""
    @Published var passwordRepeat: String = ""

    public var didChange = PassthroughSubject<Void, Never>()

    var validatedEMail: AnyPublisher<String?, Never> {
        return $eMail
            .debounce(for: 0.5, scheduler: RunLoop.main)
            .removeDuplicates()
            .flatMap { username in
                return Future { promise in
                    self.usernameAvailable(username) { available in
                        promise(.success(available ? username : nil))
                    }
                }
        }
        .eraseToAnyPublisher()
    }

    var validatedPassword: AnyPublisher<String?, Never> {
        return Publishers.CombineLatest($password, $passwordRepeat)
            .debounce(for: 0.5, scheduler: RunLoop.main)
            .map { password, passwordRepeat in
                guard password == passwordRepeat, password.count > 5 else { return nil }
                return password
        }
        .eraseToAnyPublisher()
    }

    var validatedCredentials: AnyPublisher<(String, String)?, Never> {
        return Publishers.CombineLatest(validatedEMail, validatedPassword)
            .map { validatedEMail, validatedPassword in
                guard let eMail = validatedEMail, let password = validatedPassword else { return nil }
                return (eMail, password)
        }
        .eraseToAnyPublisher()
    }


    func usernameAvailable(_ username: String, completion: (Bool) -> Void) {
        let isValidEMailAddress: Bool = NSPredicate(format:"SELF MATCHES %@", "[A-Z0-9a-z._%+-]+@[A-Za-z0-9.-]+\\.[A-Za-z]{2,64}").evaluate(with: username)

        completion(isValidEMailAddress)
    }
}

#if DEBUG
struct RegistrationView_Previews : PreviewProvider {
    static var previews: some View {
        RegistrationView()
    }
}
#endif

我希望在提供有效用户名(有效电子邮件地址)和两个长度正确的匹配密码时启用表单按钮。负责这两项任务的两个发布者工作，我可以在我为调试目的添加的两个文本中的用户界面中看到经过验证的电子邮件和经过验证的密码。

只有第三个发布者(也与上面视频中 32:20 处显示的代码进行比较)永远不会触发。我确实在这些发布者中设置了断点，在行的 validatedPassword 发布者中:

guard password == passwordRepeat, password.count > 5 else { return nil }

在那里停得很好，但在 validatedCredentials Publisher 中有一个类似的断点:

guard let eMail = validatedEMail, let password = validatedPassword else { return nil }

从未达到。

我做错了什么？

编辑:

为了让上面的代码在Xcode-beta 11.0 beta 4下运行 didChange 需要替换成 willChange

Answer 1

我在这里回答了这个问题:https://forums.swift.org/t/crash-in-swiftui-app-using-combine-was-using-published-in-conjunction-with-state-in-swiftui/26628/9由非常友好和乐于助人的 Nanu Jogi 编写，他不在 stackoverflow 上。

这很简单:

添加这一行:

        .receive(on: RunLoop.main) // run on main thread 

在 validatedCredentials 中，它看起来像这样:

var validatedCredentials: AnyPublisher<(String, String)?, Never> {
    return Publishers.CombineLatest(validatedEMail, validatedPassword)

        .receive(on: RunLoop.main) // <<—— run on main thread

        .map { validatedEMail, validatedPassword in
            print("validatedEMail: \(validatedEMail ?? "not set"), validatedPassword: \(validatedPassword ?? "not set")")

            guard let eMail = validatedEMail, let password = validatedPassword else { return nil }

            return (eMail, password)

    }
    .eraseToAnyPublisher()

这就是所有需要的。

这里再放一遍完整的引用代码(针对 Xcode 11.0 beta 5 (11M382q) 进行了更新):

//
//  RegistrationView.swift
//  Combine-Beta-Feedback
//
//  Created by Lars Sonchocky-Helldorf on 09.07.19.
//  Copyright © 2019 Lars Sonchocky-Helldorf. All rights reserved.
//

import SwiftUI
import Combine

struct RegistrationView : View {
    @ObservedObject var registrationModel = RegistrationModel()

    @State private var registrationButtonDisabled = true

    @State private var validatedEMail: String = ""
    @State private var validatedPassword: String = ""

    var body: some View {
        Form {
            Section {
                TextField("Enter your EMail", text: $registrationModel.eMail)
                SecureField("Enter a Password", text: $registrationModel.password)
                SecureField("Enter the Password again", text: $registrationModel.passwordRepeat)
                Button(action: registrationButtonAction) {
                    Text("Create Account")
                }
                .disabled($registrationButtonDisabled.wrappedValue)
                    .onReceive(self.registrationModel.validatedCredentials) { newValidatedCredentials in
                        self.registrationButtonDisabled = (newValidatedCredentials == nil)
                }
            }

            Section {
                Text("Validated EMail: \(validatedEMail)")
                    .onReceive(self.registrationModel.validatedEMail) { newValidatedEMail in
                        self.validatedEMail = newValidatedEMail != nil ? newValidatedEMail! : "EMail invalid"
                }
                Text("Validated Password: \(validatedPassword)")
                    .onReceive(self.registrationModel.validatedPassword) { newValidatedPassword in
                        self.validatedPassword = newValidatedPassword != nil ? newValidatedPassword! : "Passwords to short or don't match"
                }
            }
        }
        .navigationBarTitle(Text("Sign Up"))
    }

    func registrationButtonAction() {

    }
}

class RegistrationModel : ObservableObject {

    @Published var eMail: String = ""
    @Published var password: String = ""
    @Published var passwordRepeat: String = ""

    var validatedEMail: AnyPublisher<String?, Never> {
        return $eMail
            .debounce(for: 0.5, scheduler: RunLoop.main)
            .removeDuplicates()
            .map { username in
                return Future { promise in
                    print("username: \(username)")
                    self.usernameAvailable(username) { available in
                        promise(.success(available ? username : nil))
                    }
                }
        }
        .switchToLatest()
            .eraseToAnyPublisher()
    }

    var validatedPassword: AnyPublisher<String?, Never> {
        return Publishers.CombineLatest($password, $passwordRepeat)
            .debounce(for: 0.5, scheduler: RunLoop.main)
            .map { password, passwordRepeat in
                print("password: \(password), passwordRepeat: \(passwordRepeat)")
                guard password == passwordRepeat, password.count > 5 else { return nil }
                return password
        }
        .eraseToAnyPublisher()
    }

    var validatedCredentials: AnyPublisher<(String, String)?, Never> {
        return Publishers.CombineLatest(validatedEMail, validatedPassword)
            .receive(on: RunLoop.main)
            .map { validatedEMail, validatedPassword in
                print("validatedEMail: \(validatedEMail ?? "not set"), validatedPassword: \(validatedPassword ?? "not set")")
                guard let eMail = validatedEMail, let password = validatedPassword else { return nil }
                return (eMail, password)
        }
        .eraseToAnyPublisher()
    }


    func usernameAvailable(_ username: String, completion: (Bool) -> Void) {
        let isValidEMailAddress: Bool = NSPredicate(format:"SELF MATCHES %@", "[A-Z0-9a-z._%+-]+@[A-Za-z0-9.-]+\\.[A-Za-z]{2,64}").evaluate(with: username)

        completion(isValidEMailAddress)
    }
}

#if DEBUG
struct RegistrationView_Previews : PreviewProvider {
    static var previews: some View {
        RegistrationView()
    }
}
#endif