Using WM_COMMNOTIFY in an MFC Application

MORE INFORMATION

1. Specify a handler for the WM_COMMNOTIFY message using the OnMessage macro. The code to implement this step is shown below:

         // In the class header file,
         // generated message map functions protected:
         //{{AFX_MSG(CMfccommView)
              afx_msg LRESULT OnCommNotify(WPARAM wParam, LPARAM lParam);
              <other handlers>
         //}}AFX_MSG
         DECLARE_MESSAGE_MAP()
   
         // In the source file defining the class:
         BEGIN_MESSAGE_MAP(CMfccommView, CView)
              //{{AFX_MSG_MAP(CMfccommView)
              ON_MESSAGE(WM_COMMNOTIFY, OnCommNotify)
              <other mappings>
              //}}AFX_MSG_MAP
         END_MESSAGE_MAP()
   						

2. Write the handler procedure OnCommNotify() to trap the CN_EVENT, CN_RECEIVE, and CN_TRANSMIT notifications.
3. Because WM_COMMNOTIFY is a message, it is always sent to a window. If you do not already have a window handle to receive this message, use the Create() member of the CWnd class to create a hidden window (do not specify WS_VISIBLE) and use that handle (m_hWnd member) in the call to EnableCommNotification().
   
   NOTE: Remember that merely creating an instance of CWnd does not create a window. A common error is to derive a class from CWnd and to call EnableCommNotification() in the constructor of the derived class. This fails because the window handle, m_hWnd, is NULL at this point.
4. Because you cannot return values from the constructor, the constructor is not a suitable place for initializing the communications port and device. Perform all initializations outside of the constructor in a member function created for initialization purposes. Remember to check all the return values from the communications API.