Inside the WinCE GUI

Example 1:
The Control Panel callback function

// if _declspec(export) doesn't work for this function (ie.  The 
// control panel app does not Link to it correctly), use the DEF file 
// to export this function from the DLL. You will need a 
// File name: ControlApplet.def 
LIBRARY ControlApplet
DESCRIPTION 'ControlPanel Applet'
EXPORTS
    CplApplet   @1 

// This is what ControlApplet.cpp will look like.
// This function takes a window handle, a message and a couple of 
// message specific parameters.   
// hWnd: handle to Control Panel window
LRESULT  __stdcall CplApplet (HWND  hWnd, UINT uMsg, 
                              LPARAM lParam1, LPARAM lParam2)
{
    switch (uMsg)
   {
        case CPL_INIT:
             // The message prompts CPlApplet to perform 
             // initialization.
        break;
        case CPL_GETCOUNT:
            // sent to Control Panel app to retrieve the
            // number of dialogs supported by the application.
        break;
        case CPL_IDNAME:
             _tcscpy ((LPTSTR)lParam2, TEXT("SampleApplet"));
              lParam1 = 1;
         return (lParam2);        
         case CPL_NEWINQUIRE:
            // Control Panel sends the CPL_NEWINQUIRE message 
            // once for each Dialog box supported by your 
            // application. 
        break;
        case CPL_DBLCLK:
            // This message sent to Control Panel application 
            // when the user double-clicks the icon in the 
            // control panel explorer.
        break;
        case CPL_STOP:
             // Sent once for each dialog box when the 
             // application  controlling the
             // Control Panel application closes.
        break; 
        case CPL_EXIT:
            // Sent once to a Control Panel application before 
            // the  controlling application 
            // releases the DLL that contains the application.
        break;      
   }
}