Question

我有一个C++方案,它分出各种活动,例如:StatusEvent和Detection Event,向信息服务处(目前是活跃的MQ,通过积极的mq-cpp APU)提供不同的信息定义。我想写一个接收这些信息的听众,向他们说几句,并写上 co子,以图谋。听众有<代码>status_event_pb.h和detection_event_pb.h链接。

我的问题是:我如何在不了解所收到事件的类型的情况下加以区别? 我想做的是(在假冒法典中)

receive event
type = parseEventType(event);
if( type == events::StatusEventType) { 
    events::StatusEvent se = parseEvent(event);
    // do stuff with se
}
else {
    // handle the case when the event is a DetectionEvent
}

参看,但我不敢确定延期是否是这里的正确途径。简短的法典指明了前进的道路将受到高度赞赏。 pro夫的例子非常少!

感谢!

延期似乎确实是走的路,但我说,最后一点是清楚的。下面是我迄今为止的推论:

// A general event, can be thought as base Event class for other event types.
message Event {
    required int64 task_id = 1;     
    required string module_name = 2;    // module that sent the event

    extensions 100 to 199;               // for different event types
}

// Extend the base Event with additional types of events.
extend Event {
    optional StatusEvent statusEvent = 100;
    optional DetectionEvent detectionEvent = 101;
}

// Contains one bounding box detected in a video frame, 
// representing a region of interest.
message DetectionEvent {
    optional int64 frame = 2;   
    optional int64 time = 4;
    optional string label = 6;
}

// Indicate status change of current module to other modules in same service.
// In addition, parameter information that is to be used to other modules can
// be passed, e.g. the video frame dimensions.
message StatusEvent {
    enum EventType { 
        MODULE_START = 1; 
        MODULE_END = 2; 
        MODULE_FATAL = 3; 
    }
    required EventType type = 1;        
    required string module_name = 2;    // module that sent the event

    // Optional key-value pairs for data to be passed on.
    message Data {
        required string key = 1;
        required string value = 2;
    }
    repeated Data data = 3; 
}

我现在的问题是:(1) 如何知道事件信息包含哪些具体事件,(2) 确保其只包含one这种事件(根据定义,它可以包含一个<条码>-StatusEvent和<条码>。

Answer 1

我不会为此使用《Buffers议定书》,但这可能是很少使用和其他习惯的结合。

无论如何,我认为,我将在这里使用一个抽象的班子,以方便一般处理,并包含路线信息。不使用制革法界定的等级,包括制革电。

class Message
{
public:
  Type const& GetType() const;

  Origin const& GetOrigin() const;
  Destination const& GetDestination() const;

  // ... other informations

  template <class T>
  void GetContent(T& proto) const
  {
    proto.ParseFromIstream(&mContent); // perhaps a try/catch ?
  }

private:
  // ...

  std::stringstream mContent;
};

有了这种结构,你在主人面前既有一般性的,也有具体的处理:

void receive(Message const& message)
{
  LOG("receive - " << message.GetType() << " from " << message.GetOrigin()
                   << " to " << message.GetDestination());

  if (message.GetType() == "StatusEvent")
  {
    StatusEvent statusEvent;
    message.Decode(statusEvent);
    // do something
  }
  else if (message.GetType() == "DetectionEvent")
  {
    DetectionEvent detectionEvent;
    message.Decode(detectionEvent);
    // do something
  }
  else
  {
    LOG("receive - Unhandled type");
  }
}

当然,如果你使用<代码>std:unordered_map<Type,Handler>,那将是先令。如果+/否则链条,而不是硬编码的<代码>,但这一原则仍然相同:

Encode the type of message sent in the header
Decode only the header upon reception and dispatch based on this type
Decode the protobuf message in a part of the code where the type is known statically

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