Using a Window

Because this is Microsoft Windows we're developing for, sometimes it's handy to be able to put up a window or a dialog box. For example, the MessageBox call we made earlier yielded a somewhat boring advertisement, as shown in Figure 1.12.

Figure 1.12. Boring message box

Normally, putting up a custom dialog box is kind of a pain. For the average Win32 programmer, either it involves lots of procedural code, which we don't like, or it involves building a bunch of forwarding code to map Windows messages to member functions (a dialog box is an object, after all). As with MFC, ATL has a great deal of functionality for building windows and dialog boxes. To add a new dialog box, select Add Class from the Project menu and then select ATL Dialog from the list of available templates, as shown in Figure 1.13.

Figure 1.13. Inserting a dialog box class

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The ATL Dialog Wizard (see Figure 1.14) is much simpler than many other ATL class templates. It allows you to enter only C++ name information because a dialog box is a Win32 object, not a COM object.

Figure 1.14. ATL Dialog Wizard

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The generated code creates a class that derives from CAxDialogImpl and uses a new dialog box resource, also provided by the wizard. The derived class routes messages to handlers using the MSG_MAP macros, as shown here:

class CAdvert : public CAxDialogImpl<CAdvert> {                
public:                                                        
  CAdvert() {}                                                 
  ~CAdvert() {}                                                
  enum { IDD = IDD_ADVERT };                                   
                                                               
BEGIN_MSG_MAP(CAdvert)                                         
    MESSAGE_HANDLER(WM_INITDIALOG, OnInitDialog)               
    COMMAND_HANDLER(IDOK, BN_CLICKED, OnClickedOK)             
    COMMAND_HANDLER(IDCANCEL, BN_CLICKED, OnClickedCancel)     
    CHAIN_MSG_MAP(CAxDialogImpl<CAdvert>)                      
END_MSG_MAP()                                                  
                                                               
  LRESULT OnInitDialog(UINT uMsg, WPARAM wParam, LPARAM lParam,
                      BOOL& bHandled) {                        
    if( m_bstrClient.Length() ) {
      CComBSTR bstrCaption = OLESTR("CalcPi sponsored by ");
      bstrCaption += m_bstrClient;

      USES_CONVERSION;
      SetWindowText(OLE2CT(bstrCaption));
    }
    return 1; // Let the system set the focus                  
  }                                                            
                                                               
  LRESULT OnClickedOK(WORD wNotifyCode, WORD wID, HWND hWndCtl,
     BOOL& bHandled) {                                          
    EndDialog(wID);                                            
    return 0;                                                  
}                                                              
                                                               
  LRESULT OnClickedCancel(WORD wNotifyCode, WORD wID,          
    HWND hWndCtl, BOOL& bHandled) {                            
    EndDialog(wID);                                            
    return 0;                                                  
  }                                                            
                                                               
  CComBSTR m_bstrClient;
};

If you want to handle another message, you can add the appropriate entries to the message map and add the handler member functions by hand. If you prefer, you can add a message handler by right-clicking the name of the CAxDialogImpl-based class in Class view, choosing Properties, and clicking the Messages toolbar button. Figure 1.15 shows the resulting window.

Figure 1.15. Adding a Windows message handler

For more information on ATL's extensive support for windowing, including building standalone Windows applications, see Chapter 10, "Windowing."