Creating Only One Instance

Here is what I am trying to do: I have a Dialog Application and I only want to have one instance running at a time.

Here is the code that I have, but it still allows for mulitple instances.

LPCTSTR lpszUniqueClass = _T("MsdSaveData");

BOOL CGSaveApp::InitInstance()
{
// InitCommonControls() is required on Windows XP if an application
// manifest specifies use of ComCtl32.dll version 6 or later to enable
// visual styles. Otherwise, any window creation will fail.

// check for previous instance of Software
if(FirstInstance()== FALSE)
{
return(FALSE);
}

InitCommonControls();

CWinApp::InitInstance();

AfxEnableControlContainer();

// Register our unique class name that we wish to use
WNDCLASS wndcls;
memset(&wndcls, 0, sizeof(WNDCLASS)); // start with NULL defaults
wndcls.style = CS_DBLCLKS |CS_HREDRAW |CS_VREDRAW;
wndcls.lpfnWndProc = ::DefWindowProc;
wndcls.hInstance = AfxGetInstanceHandle();
wndcls.hIcon = NULL;
wndcls.hCursor = LoadCursor(IDC_ARROW);
wndcls.hbrBackground = (HBRUSH) (COLOR_BTNFACE + 1);
wndcls.lpszMenuName = NULL;
wndcls.cbWndExtra = DLGWINDOWEXTRA;
wndcls.lpszClassName = lpszUniqueClass;
// register MsdSaveData class name
if(!AfxRegisterClass(&wndcls))
{
return FALSE;
}


CGSaveDlg dlg;
m_pMainWnd = &dlg;
INT_PTR nResponse = dlg.DoModal();
if (nResponse == IDOK)
{
// TODO: Place code here to handle when the dialog is
// dismissed with OK
}
else if (nResponse == IDCANCEL)
{
// TODO: Place code here to handle when the dialog is
// dismissed with Cancel
}

// Since the dialog has been closed, return FALSE so that we exit the
// application, rather than start the application's message pump.
return FALSE;
}




BOOL CGSaveApp::FirstInstance(void)
{
CWnd *pWndPrev, *pWndParent, *pWndChild;
// check for another copy of wnd class running
pWndPrev = CWnd::FindWindow(lpszUniqueClass,NULL);
if(pWndPrev)
{
pWndPrev->SetWindowText("TRUE");
pWndParent = pWndPrev->GetParent();
// find child popup
pWndChild = pWndParent->GetLastActivePopup();
// pWndParent->BringWindowToTop();
// activate previous copy
if(pWndParent->IsIconic())
{
pWndParent->ShowWindow(SW_SHOWNORMAL);
}
pWndChild->SetForegroundWindow();
return(FALSE);
}
// first instance
return(TRUE);
}

Thanks I have not been able to figure this out!!

Use singleton ...

http://www.codeproject.com/cpp/singletonrvs.asp

http://www-h.eng.cam.ac.uk/help/tpl/...+/tic0282.html

What do you mean by still allows multiple instances ?

Does it mean that multiple dialogs are shown ?

How fast are you invoking these multiple apps? There is a chance that the FindWindow may fail to look for certain classes if you are doing it too fast.

A named mutex might me a better option ...

I guess for instance, if I have the application Icon on the Desktop and I start the first application, let it run, then minimize it.

Next I double click the same application and another instance begins as opposed to just Maximizing the previous instance.

I just want to make it to where I only have One instance running at a time to keep people from constantly Double Clicking on the application Icon!

I think I see the problem. You are registering a class but you are not creating a window using that class. So FindWindow will naturally fail !!

BOOL CMyApp::InitInstance()
{
HANDLE hMutex = NULL;
hMutex = CreateMutex (NULL, TRUE, "Exists");
if (GetLastError() == ERROR_ALREADY_EXISTS)
{
return false; // if exist then exit
}

CDialog has the "PreCreateWindow(CREATESTRUCT& cs)" method. You can insert it from the ClassWizard.
Please change parameters of your window in this method.

Take a look at the following FAQ...

Quote:

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... I only want to have one instance running at a time.

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The best article describing "HOW TO DO IT" I ever seen is:
Avoiding Multiple Instances of an Application

Try this...

Code:

---

if( IsWindow(m_hDlg) )
{
    // Make it ShowWindow, Foreground etc
    return 1;
}
// Create a new dialog

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Hope this helps,
Regards,
Usman.

I think most of the other suggestions should have solved the problem, but here is another link for completeness:

http://support.microsoft.com/default...NoWebContent=1

Quote:

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Originally posted by Valery B.
CDialog has the "PreCreateWindow(CREATESTRUCT& cs)" method. You can insert it from the ClassWizard.
Please change parameters of your window in this method.

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Have you done that? As far as I know, that won't work.