组合.sink打印不打印

Question

我是新的组合和Sink，然而，我在其中放置的打印似乎没有日志，但行动的结果完成，因为用户是在AWS放大器内创建。

@objc private func createAccountButtonAction(sender: UIButton) {
    print("Create Account Button Action")
    signUp(password: self.password, email: self.email)
  }
  
  func signUp(password: String, email: String) -> AnyCancellable {
      let userAttributes = [AuthUserAttribute(.email, value: email)]
      let options = AuthSignUpRequest.Options(userAttributes: userAttributes)
      let sink = Amplify.Auth.signUp(username: email, password: password, options: options)
        .resultPublisher.sink(receiveCompletion: { (authError) in
          print("Failed with error: \(authError)")
        }, receiveValue: { (signUpResult) in
          print("Signed Up")
        })
    return sink
  }

Answer 1

使用.sink运算符时，它将返回一个类型为AnyCancellable的令牌。当该令牌被销毁时，它会调用cancel，这会撕毁它所代表的订阅。您没有保存令牌，所以Swift会在订阅有机会交付任何输出之前立即销毁它。

通常的解决方案是找到存储令牌的位置，例如在控制器对象的属性中：

class AccountCreationController: UIViewController {
    private var token: AnyCancellable? = nil
// NEW          ^^^^^ storage for the AnyCancellable

    @objc private func createAccountButtonAction(sender: UIButton) {
        print("Create Account Button Action")
        signUp(password: self.password, email: self.email)
    }

    func signUp(password: String, email: String) {
        let userAttributes = [AuthUserAttribute(.email, value: email)]
        let options = AuthSignUpRequest.Options(userAttributes: userAttributes)
        token = Amplify.Auth.signUp(username: email, password: password, options: options)
// NEW  ^^^^^ store the AnyCancellable to keep the subscription alive
            .resultPublisher.sink(
                receiveCompletion: { (authError) in
                    print("Failed with error: \(authError)")
                },
                receiveValue: { (signUpResult) in
                    print("Signed Up")
                })
    }
}

如果您确定永远不想取消订阅(例如，用户不能按“取消”按钮退出)，则可以直接创建Subscribers.Sink，而不是使用sink操作符，并使用subscribe方法将Sink订阅到Publisher。subscribe方法执行而不是返回AnyCancellable。Sink对象本身就是一个Cancellable，而不是一个AnyCancellable，您不必将它存储在任何地方以保持订阅活动。

class AccountCreationController: UIViewController {
    @objc private func createAccountButtonAction(sender: UIButton) {
        print("Create Account Button Action")
        signUp(password: self.password, email: self.email)
    }

    func signUp(password: String, email: String) {
        let userAttributes = [AuthUserAttribute(.email, value: email)]
        let options = AuthSignUpRequest.Options(userAttributes: userAttributes)
        Amplify.Auth.signUp(username: email, password: password, options: options)
// NEW  ^ There is no AnyCancellable to store.
            .resultPublisher
            .subscribe(
// NEW      ^^^^^^^^^^ use the subscribe method instead of sink.
                Subscribers.Sink(
// NEW          ^^^^^^^^^^^^^^^^ Create a Sink object.
                    receiveCompletion: { (authError) in
                        print("Failed with error: \(authError)")
                    },
                    receiveValue: { (signUpResult) in
                        print("Signed Up")
                    }
                )
            )
    }
}