动作电缆：在通道中调用自定义方法

Question

我正在尝试实现动作电缆。这运行良好，但我想在连接到频道时接收一些数据（这里我想知道有多少用户已连接）。

我在我的频道上创建了一个自定义方法 nbUsers ：

class OnTheSamePageChannel < ApplicationCable::Channel

  @count = 0

  def subscribed
    ...
    @count++
    stream_for(params[:url])
  end

  def unsubscribed
    ...
    @count--
  end

  def nbUsers
    pp 'debug: nbUsersCalled'
    @count
  end

还有我的javascript：

export default class OnSamePageSubscription extends React.Component {

    constructor(props) {
        super(props);

        this.cable = ActionCable.createConsumer(WEB_SOCKET_HOST);
        this.subscribe = () => {
            this.channel = this.cable.subscriptions.create(
                {
                    channel: 'OnTheSamePageChannel',
                    url: props.url,
                    current_user: props.current_user
                },
                {
                    connected: this.connected,
                    disconnected: this.disconnected,
                    received: this.received,
                    rejected: this.rejected
                }
            );
        };
        this.unsubscribe = () => {
            this.channel.unsubscribe()
        };
    }

    received = (data) => {
        console.log(`Connected user : ${data.user}`);

        this.props.onUpdate(data);
    };

    connected = () => {
        console.log(`Tracking connection`);
    };

    disconnected = () => {
        console.warn(`Tracking disconnected.`);
    };

    rejected = () => {
        console.warn('Tracking rejected');
    };

}

问题是：如何调用这个方法（nbUsers）并得到结果？

我试过https://robots.thoughtbot.com/talking-to-actioncable-without-rails 但这不起作用

Answer 1

class OnTheSamePageChannel < ApplicationCable::Channel

  @count = 0

  def subscribed
    # ...
    @count++
    stream_for(params[:url])
    transmit(number_of_users: nbUsers)
  end
  # ...
end


export default class OnSamePageSubscription extends React.Component {
  // ...
  received = (data) => {
    console.log(`Number of users: ${data.number_of_users}`);

    this.props.onUpdate(data);
  };
}

• 以上是对您问题的直接回答...

  如何调用这个方法（nbUsers）并得到结果？

  ...但是，您当前的代码中仍然存在很多问题：

  • class OnTheSamePageChannel < ApplicationCable::Channel
      @count = 0 
      # ^ this is a class-level instance-variable
      # ...and not an instance-level instance-variable (that I think you were under the impression of
    end
    
    # To demonstrate:
    # OnTheSamePageChannel.new.instance_variable_get(:@count)
    # => nil
    # OnTheSamePageChannel.instance_variable_get(:@count)
    # => 0
    

  • 要解决此问题，您需要执行以下操作：

    class OnTheSamePageChannel < ApplicationCable::Channel
      attr_accessor :count
      @count = 0 
    
      def subscribed
        # ...
        self.class.count += 1
      end
    
      def unsubscribed 
        # ...
        self.class.count -= 1
      end
    
      def nbUsers
        # ...
        self.class.count
      end
    end
    

  • 重要提示：上面的代码只能在单进程服务器上运行，如果您已经有多个服务器或进程，或者其他依赖于 Rails 的应用程序（如 Sidekiq 或 (rails-console)），它将无法完全工作正是因为内存（其中存储了@count）在它们之间没有共享。据我所知，如果已经考虑了“缩放”，还没有（还没有？）一种简单的内置 Rails 方法来检查连接用户的数量。随意查看其他SO question

Answer 2

您可以使用 perform 调用它。这是代码 this.perform("nbUsers")