Advanced MFC Programming

Chapter 13. Adding Special Features to Application
GetLastActivePopup(), which will find out the most recently activated pop-up window. 2)
::ShowWindow(…), which will restore the original state of the window being minimized (parameter
SW_RESTORE can be used for this purpose). 3) CWnd::SetForegroundWindw(), which will bring the child
window to foreground if there is a such kind of window. Steps 1) and 3) are necessary here because a
mainframe window may own some pop up windows (For example, a dialog box implemented by an SDI or
MDI application). Once the mainframe window is brought to the top, we also need to bring its child pop up
window to foreground.
After this is done, we need to return a FALSE value, which indicates that the procedure of creating
mainframe window, document and view is not successful. This will cause the application to exit.
If no window with the same class name is found, we can proceed to register our own window class.
This can be done by stuffing a WNDCLASS type object and passing the object address to function
AfxRegisterClass(…), whose only parameter is a WNDCLASS type pointer:
BOOL AFXAPI AfxRegisterClass(WNDCLASS *lpWndClass);
In order to make sure that our application is the same with those implemented by default MFC window
classes, we must stuff the class with appropriate values. Here is how this is done in the sample:
……
……
memset(&wndcls, 0, sizeof(WNDCLASS));
wndcls.style=CS_DBLCLKS | CS_HREDRAW | CS_VREDRAW;
wndcls.lpfnWndProc=::DefWindowProc;
wndcls.hInstance=AfxGetInstanceHandle();
wndcls.hIcon=LoadIcon(IDR_MAINFRAME);
wndcls.hCursor=LoadCursor(IDC_ARROW);
wndcls.hbrBackground=(HBRUSH)(COLOR_WINDOW+1);
wndcls.lpszMenuName=NULL;
wndcls.lpszClassName=ONCE_CLASSNAME;
if(!AfxRegisterClass(&wndcls))
{
TRACE("Class Registration Failed\n");
return FALSE;
}
The class name string is defined using ONCE_CLASSNAME macro. Of course, when we override function
CMainFrame::OnPreCreateWindow(…), we need to replace the default class name with it. The following
code fragment shows how this function is overridden in the sample:
BOOL CMainFrame::PreCreateWindow(CREATESTRUCT& cs)
{
cs.lpszClass=ONCE_CLASSNAME;
return CMDIFrameWnd::PreCreateWindow(cs);
}
Before the application exits, we must unregister the window class if it has been registered successfully.
For this purpose, a Boolean type variable m_bRegistered is declared in class COnceApp, which will be set to
TRUE after the class is registered successfully. When overriding function CWinApp::ExitInstance()
(which should be overridden if we want to do some cleanup job before the application exits), we need to
unregister the window class name if the value of m_bRegistered is TRUE. The following is the overridden
function implemented in the sample:
int COnceApp::ExitInstance()
{
if(m_bRegistered == TRUE)
{
::UnregisterClass(ONCE_CLASSNAME, AfxGetInstanceHandle());
}
return CWinApp::ExitInstance();
}
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