Creating a Foundation Classes Dialog Box with Custom Icon

ID: Q87976

The information in this article applies to:

SUMMARY

Using the Microsoft Foundation Classes supplied with Microsoft C/C++ versions 7.0 and Microsoft Visual C++, you can create a main application window based on a dialog box. However if a dialog is used as the application's main window, and the dialog is created with a minimize button and then minimized, the default application icon will be displayed. This article briefly describes two approaches that can be taken to change the default icon to a custom (application-defined) icon.

Starting with Visual C++ 4.0, AppWizard supports creation of dialog based applications that have custom icons. The method described in this article works with Visual C++ 4.0, but it is preferred to use the AppWizard generated code.

The CFormView class is a useful alternative to the "dialog as main window technique" when using Microsoft Foundation Classes, and provides additional features. For more information on CFormView, see the documentation supplied with Microsoft Visual C++, the VIEWEX and CHKBOOK samples, and query on the following words in the Microsoft Knowledge Base:

CFormView
A discussion of CFormView based applications is beyond the scope of this article.


MORE INFORMATION

One technique for using a dialog as the main window is documented in the "Class Libraries User's Guide" which shipped with Microsoft C/C++ version 7.0 on page 334, and in both versions via the TRACER sample application. Neither of these techniques illustrates how to change the default icon to a custom icon.

The first technique below, illustrated with code fragments, shows the modifications required to allow the TRACER sample to display a custom icon when minimized. This is the simplest approach to the problem.

The second technique is illustrated using a sample from the Software/Data Library. While more complex, it illustrates how to use the Windows ::RegisterClass() API to register a class with an application defined icon.

Add OnPaint to CPromptDlg of the TRACER sample

This technique will work for versions 1.0 and 2.0 of the Microsoft Foundation Classes.

  1. Add the following public declarations to the CPromptDlg class definition in tracer.cpp: 
    
  afx_msg void OnPaint();
  afx_msg BOOL OnEraseBkgnd(CDC* pDC);
  afx_msg HCURSOR OnQueryDragIcon();


  2. Add the following macros to the CPromptDlg message map in tracer.cpp: 
    
  ON_WM_PAINT()
  ON_WM_ERASEBKGND()
  ON_WM_QUERYDRAGICON()


  3. Add the following function definitions in tracer.cpp: 
    
  void CPromptDlg::OnPaint()
  {
     CPaintDC dc(this); // device context for painting
     if (IsIconic())
     {
        // Erase the icon background when placed over other app window
        DefWindowProc(WM_ICONERASEBKGND, (WORD)dc.m_hDC, 0L);

        // Center the icon
        CRect rc;
        GetClientRect(&rc);
        rc.left = (rc.right  - ::GetSystemMetrics(SM_CXICON)) >> 1;
        rc.top  = (rc.bottom - ::GetSystemMetrics(SM_CYICON)) >> 1;

        // Draw the icon
        HICON hIcon = AfxGetApp()->LoadIcon(AFX_IDI_STD_FRAME);
        dc.DrawIcon(rc.left, rc.top, hIcon);
     }
     // Do not call CDialog::OnPaint() for painting messages
  }

  BOOL CPromptDlg::OnEraseBkgnd(CDC* pDC)
  {
     if (IsIconic())
        return TRUE;
     else
        return CDialog::OnEraseBkgnd(pDC);
  }


  HCURSOR CPromptDlg::OnQueryDragIcon()
  {
     return AfxGetApp()->LoadIcon(AFX_IDI_STD_FRAME);
  }
    In this example, AFX_IDI_STD_FRAME is the ID of an icon contained in the application's resource file, and the dialog template contains the WS_MINIMIZEBOX style.


The PRIVDLG sample program from the Software/Data Library

An example can be found in the Software/Data Library by searching on the word PRIVDLG, the Q number of this article, or S13583. PRIVDLG was archived using the PKware file-compression utility.

If you are creating a standard frame window, the only step required for your application to use a custom icon is to define an icon resource in your .RC file with the constant AFX_IDI_STD_FRAME. When the Microsoft Foundation Classes libraries register the window class for your frame window, they will use this icon as the window icon.

Alternatively, if your application uses a dialog box as its main window, the procedure for using a custom icon is a bit more involved. The main reason you can't simply use AFX_IDI_STD_FRAME for MFC 1.0 or IDR_MAINFRAME for MFC 2.0 and MFC 2.5 is that all Windows dialog boxes use a pre-registered window class, and the icon used for this class cannot be changed easily.

The solution is to register a private window class to be used for your dialog box. Because the name of this window class must be specified in the dialog template, the Microsoft Foundation Classes function AfxRegisterWndClass will not work, because it creates a new class name dynamically at run time.

The restrictions on registering your own private dialog class in Microsoft Foundation Classes are the same as in standard C Windows programming. For more information, query on the following words in the Microsoft Knowledge Base:
private and dialog and class
To register a private dialog class with a custom icon, do the following three steps:

  1. Register a new private dialog class using the ::RegisterClass() function with a unique class name. Fill in your own icon for the hIcon field of the WNDCLASS structure, and add your custom icon to the .RC file. This class should only be registered once for your application. Be sure to follow the standard Windows rules for registering a private dialog class (see the Knowledge Base reference above).


  2. Add the CLASS "classname" directive to your dialog box resource file, using the unique class name you registered in step 1. Make sure your dialog contains the WS_MINIMIZEBOX style bit if you want to allow the dialog to be minimized.


  3. Create a dialog using the template from step 2.


Additional query words: kbinf 7.00 1.00 1.50 2.00 2.50 2.50 2.51 2.52 


Keywords          : kbMFC KbUIDesign kbVC 
Version           : 7.00   | 1.00 1.50 1.51 1.52 | 1
Platform          : MS-DOS NT WINDOWS 
Issue type        :

Last Reviewed: July 26, 1999