MtFeedAddin.h

Data

As discussed above, the data received by the client consists of two strings: a topic string and a field list. The message class is therefore as follows:

class CMtFeedAddinMsg : public CXllMtMsg {
public:
    CMtFeedAddinMsg(LPCSTR pszTopic, LPCSTR pszData)
    : m_strTopic(pszTopic),
      m_strData(pszData)
    {
    }
    CString m_strTopic;
    CString m_strData;
};

The data cache is equally simple. It just maps topic strings to field lists.

class CMtFeedAddinDataCache {
public:
    void Set(LPCSTR pszTopic, LPCSTR pszData) {
        m_map[pszTopic] = pszData;
    }
    BOOL Lookup(LPCSTR pszTopic, CString& strData) const {
        map_type::const_iterator itF = m_map.find(pszTopic);
        if (itF == m_map.end()) 
            return FALSE;
        strData = itF->second;
        return TRUE;
    }
protected:
    typedef std::map<CString, CString> map_type;
    map_type m_map;
};

Application class

Most of the application class, CMtBackgroundApp, is shown below. The areas that have been changed from the AppWizard-produced original are shown in grey.

class CMtFeedAddinApp : public CXllPushApp
{
public:
    CMtFeedAddinApp();

// Names
public:
    static LPCSTR m_pszDefName;

// Implementation
    mtcHandle               m_client;                         
    CMtFeedAddinDataCache   m_cache;                          
    std::set<CString>       m_advises;                        

    static BOOL ExtractField(LPCSTR pszData, LPCSTR pszField, 
        double& dValue);                                      
    BOOL Reconnect();                                         

// Overrides
    virtual int OnXllOpenEx();                                
    virtual void OnXllClose();                                
    virtual void ProcessAsyncMessage(CXllMtMsg* msg);         
    virtual void OnTopicAdd(LPCSTR pszTopic);                 
    virtual void OnTopicRemove(LPCSTR pszTopic);              
    ...
};

Let us examine each of these blocks in turn.

The data member m_client is a handle to the communications channel. The data cache, m_cache is a data member of the application, and shares its lifetime. m_advises contains the list of topics currently being advised on.

ExtractField() is a utility function that extracts the value of a named field from a field list.

Reconnect() closes and then reopens the channel to the server.

We have encountered the three standard overrides before, in the MtBackground sample. The two new event handlers are OnTopicAdd() and OnTopicRemove(). These are called by the push engine when a new topic is added to the list of connections (i.e. when the first connection to a particular topic is made) and when a topic is removed from the list (i.e. when the last connection to a topic is removed). The add-in handles these by sending Advise or Unadvise requests to the server.

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