Appsync订阅无法正常工作，但查询和变异工作正常

Question

我正在构建一个简单的React Native应用程序。测试AppSync API。我能够查询，修改；但订阅似乎无效。我正在Android模拟器上进行尝试。

这是我建立客户和创建订阅的方式。

    const client = new AWSAppSyncClient({
      url: awsconfig.aws_appsync_graphqlEndpoint,
      region: awsconfig.aws_appsync_region,
      auth: {
        type: AUTH_TYPE.API_KEY, // or type: awsconfig.aws_appsync_authenticationType,
        apiKey: awsconfig.aws_appsync_apiKey,
      }
    });

    subscription = client.subscribe({ query: gql(onCreateBook) }).subscribe({
        next: data => {
          console.log("got a book--->");
        },
        error: error => {
          console.warn("errror getting book");
        }
      });

这是我的架构（相关部分）和订阅gql（由codeGen自动生成）

架构

type Book {
    title: String!
    description: String
}

type Mutation {
    createBook(input: CreateBookInput!): Book
    updateBook(input: UpdateBookInput!): Book
    deleteBook(input: DeleteBookInput!): Book
}

type Query {
    getBook(title: String!): Book
    listBooks(filter: TableBookFilterInput, limit: Int, nextToken: String): BookConnection
}

type Subscription {
    onCreateBook(title: String, description: String): Book
        @aws_subscribe(mutations: ["createBook"])
    onUpdateBook(title: String, description: String): Book
        @aws_subscribe(mutations: ["updateBook"])
    onDeleteBook(title: String, description: String): Book
        @aws_subscribe(mutations: ["deleteBook"])
}

订阅gql

// eslint-disable
// this is an auto generated file. This will be overwritten

export const onCreateBook = `subscription OnCreateBook($title: String, $description: String) {
  onCreateBook(title: $title, description: $description) {
    title
    description
  }
}
`;
export const onUpdateBook = `subscription OnUpdateBook($title: String, $description: String) {
  onUpdateBook(title: $title, description: $description) {
    title
    description
  }
}
`;
export const onDeleteBook = `subscription OnDeleteBook($title: String, $description: String) {
  onDeleteBook(title: $title, description: $description) {
    title
    description
  }
}
`;

注意：我已验证订阅可以很好地触发AWS Console中的突变，但是我看不到ReactNative应用程序中的任何错误。