My MFC Application Freezes if I Switch to Another App

Question

Commence V 2.0 of this question.

My VC++ MFC application compiles and runs just fine. That is, until I switch to another window. As soon as my program loses focus, it freezes; I cannot switch back to it and if I move a window that is in front of it, my app window displays white in the space that the other window was covering.

Since I first posted this question I have been able to pinpoint what portion of my program is causing this behavior, but I still don't know what lines of code are wrong or why.

The main dialog of my MFC application contains a CTabCtrl called m_MainTabControl. This main tab control holds onto two tabs labeled "Basic Design" and "Advanced Design", each of which are tied to their own dialogs. Both dialogs contain a CTabCtrl with several tabs. And thus my problem is born.

When I first created this tab-within-tab structure, I was having problems with my program freezing up when I tried to switch between inner tabs. Needless to say I was puzzled by this, until I noticed that if I first clicked on a control on one of the inner tabs I could then switch tabs just fine. So without fully understanding what the problem was, I set the focus to the first inner tab of the first inner tab on program startup. Problem half solved. When I ran the program I could click around on the first set of inner tabs just fine; if I switched to the second outer tab and tried clicking around its inner tabs without first clicking on a dialog control, it would freeze again. So I made a Focus function to focus the currently selected inner tab of the currently selected outer tab and called that in my tab change event (the one that goes off when you click on another tab).

That is how I got to the point I was at when I first asked this question. I thought my program was working just fine, until I played around with it a bit more and noticed it wasn't playing nicely when I flipped back and forth between it and another window or program. More specifically, as soon as my program goes out of focus some process goes haywire and takes up an entire CPU's worth of processing.

And now, the reason I explained my little tab structure and focus problems in such great detail: after much experimentation, I found that if I commented out the second tab on my outer tab structure (i.e. the "Advanced Design" dialog and all of its little children tabs) the remaining bit of my program runs fine, and I can switch to another window and back without a fight. "Great," I thought, "that's only about 90% of my program that I just commented out to get this working. Let's try and pare it down further." I put the "Advanced Design" tabbed dialog back in, but commented out the tabbed dialogs created by the tab control within "Advanced Design" and everything still worked fine. One by one I put back the tabbed dialogs belonging to "Advanced Design"'s tab control and every time I reintroduced The Error regardless of what tab I uncommented. I should also point out that one of the first tabs I tried putting back in (alone, of course) was my "Margins" tab, which is a MarginDlg class that I ALSO USE UNDER MY "Basic Design" TAB WITHOUT TROUBLE. This leads me to believe that there is something specific I have to do when creating tabbed dialogs within tabbed dialogs that I am not doing, or am doing incorrectly, kind of like how I had to mess with focusing to make it work at first.

I would be EXTREMELY grateful for any light that can be shed on the situation. I am including what I think are relevant snippets of code; as always, let me know if more is needed.

variable declarations from main dialog's .h file:

//tab stuff
CTabCtrl m_MainTabControl;
vector<CDialog*> m_tabPages;
SimpDesDlg* simpDesDlg;
AdvDesDlg* advDesDlg;

When my application starts up, it creates my main dialog, and the OnInitDialog() is called: (everything above the TODO: comment is default VS stuff dealing with the stupid about dialog)

BOOL CspAceDlg::OnInitDialog()
{
    CDialog::OnInitDialog();


    // Add "About..." menu item to system menu.

    // IDM_ABOUTBOX must be in the system command range.
    ASSERT((IDM_ABOUTBOX & 0xFFF0) == IDM_ABOUTBOX);
    ASSERT(IDM_ABOUTBOX < 0xF000);

    CMenu* pSysMenu = GetSystemMenu(FALSE);
    if (pSysMenu != NULL)
    {
     CString strAboutMenu;
     strAboutMenu.LoadString(IDS_ABOUTBOX);
     if (!strAboutMenu.IsEmpty())
     {
      pSysMenu->AppendMenu(MF_SEPARATOR);
      pSysMenu->AppendMenu(MF_STRING, IDM_ABOUTBOX, strAboutMenu);
     }
    }

    // Set the icon for this dialog.  The framework does this automatically
    //  when the application's main window is not a dialog
    SetIcon(m_hIcon, TRUE);   // Set big icon
    SetIcon(m_hIcon, FALSE);  // Set small icon

    // TODO: Add extra initialization here
    ///////////////////////////////////////

    DrawResultsArea();
    DrawTabs();
    theApp.Calculate();
    Focus();
    //simpDesDlg->Focus();
    //DrawToolbar();

    return FALSE;  // return TRUE  unless you set the focus to a control
}

DrawTabs() is where I create the tabs for my outer tab control:

void CspAceDlg::DrawTabs()
{
    simpDesDlg = new SimpDesDlg;
    m_tabPages.push_back(simpDesDlg);
    advDesDlg = new AdvDesDlg;
    m_tabPages.push_back(advDesDlg);

    // create a tcItem to hold the name of each tab during creation
    // and then get inserted, and arrays holding the tab names and IDs of
    // the dialogs they refer to
    TC_ITEM tcItem;
    PSTR pszTabNames[] = {"Basic Design", "Advanced Design"};
    UINT pszTabItems[] = {IDD_SIMPLEDESIGNTAB, IDD_ADVANCEDDESIGNTAB};

    //every member of m_tabPages[] will become a tab
    for (int i = 0; i < int(m_tabPages.size()); i++)
    {
     //set up the tab name
     tcItem.mask = TCIF_TEXT;
     tcItem.pszText = pszTabNames[i];
     tcItem.cchTextMax = int(strlen(pszTabNames[i]));
     //insert the new tab into the tab control and create the dialog window
     m_MainTabControl.InsertItem(i, &tcItem);
     m_tabPages[i]->Create(pszTabItems[i], &m_MainTabControl);
    }

    //redraw so that the dialogs don't appear in upper left corner and cover the tabs
    CRect tabRect, itemRect;
    int nX, nY, nXc, nYc;

    m_MainTabControl.GetClientRect(&tabRect);
    m_MainTabControl.GetItemRect(0, &itemRect);

    nX=itemRect.left;
    nY=itemRect.bottom+1;
    nXc=tabRect.right-itemRect.left-1;
    nYc=tabRect.bottom-nY-1;

    m_tabPages[0]->SetWindowPos(&wndTop, nX, nY, nXc, nYc, SWP_SHOWWINDOW);
    for(int nCount=1; nCount < int(m_tabPages.size()); nCount++){
     m_tabPages[nCount]->SetWindowPos(&wndTop, nX, nY, nXc, nYc, SWP_HIDEWINDOW);
    }
}

Main dialog's Focus() method:

void CspAceDlg::Focus()
{
    int curSel = m_MainTabControl.GetCurSel();
    m_tabPages[curSel]->SetFocus();

    //if it's the basic design, we need to focus its first tab
    if (curSel == 0)
    {
     simpDesDlg->Focus();
    }
    //if it's the advanced design, we need to focus its first tab
    else if (curSel == 1)
    {
     advDesDlg->Focus();
    }
}

code for m_MainTabControl's tab selection change event:

void CspAceDlg::OnTcnSelchangeBuildtabs(NMHDR *pNMHDR, LRESULT *pResult)
{
    for (int i = 0; i < int(m_tabPages.size()); i++)
    {
     m_tabPages[i]->ShowWindow(m_MainTabControl.GetCurSel() == i ? SW_SHOW :
                                                   SW_HIDE);
    }

    Focus();

    *pResult = 0;
}

SimpDesDlg and AdvDesDlg's tabs use identical code except for tab initialization (just creating different tabs for each) so here's the code for AdvDesDlg:

OnInitDialog():

BOOL AdvDesDlg::OnInitDialog()
{
    CDialog::OnInitDialog();

    DrawTabs();

    return false;
}

adding in the tabbed dialogs:

void AdvDesDlg::DrawTabs()
{
    //Make the dialogs for the tabs
    antennaDlg = new AntennaDlg;
    commSEDlg = new CommSEDlg;
    encryptorDlg = new EncryptorDlg;
    marginDlg = new MarginDlg;
    miscDlg = new MiscDlg;
    transRecDlg = new TransRecDlg;

    //add them all to the tabPages vector
    m_tabPages.push_back(antennaDlg);
    m_tabPages.push_back(commSEDlg);
    m_tabPages.push_back(encryptorDlg);
    m_tabPages.push_back(marginDlg);
    m_tabPages.push_back(miscDlg);
    m_tabPages.push_back(transRecDlg);

    //m_tabPages[0] = new AntennaDlg;
    //m_tabPages[1] = new CommSEDlg;
    //m_tabPages[2] = new EncryptorDlg;
    //m_tabPages[3] = new MarginDlg;
    //m_tabPages[4] = new MiscDlg;
    //m_tabPages[5] = new TransRecDlg;

    //antennaDlg = (AntennaDlg*) m_tabPages[0];
    //commSEDlg = (CommSEDlg*) m_tabPages[1];
    //encryptorDlg = (EncryptorDlg*) m_tabPages[2];
    //marginDlg = (MarginDlg*) m_tabPages[3];
    //miscDlg = (MiscDlg*) m_tabPages[4];
    //transRecDlg = (TransRecDlg*) m_tabPages[5];

    // create a tcItem to hold the name of each tab during creation
    // and then get inserted, and arrays holding the tab names and IDs of
    // the dialogs they refer to
    TC_ITEM tcItem;
    PSTR pszTabNames[] = {"Antenna", "Comm Support", "Encryptor", "Margins", "Misc", "Trasmitter/Receiver"};
    UINT pszTabItems[] = {IDD_ANTENNATAB, IDD_COMMSETAB, IDD_ENCRYPTORTAB, IDD_MARGINTAB, IDD_MISCTAB, IDD_TRANSRECTAB};

    //every member of m_tabPages[] will become a tab
    for (int i = 0; i < int(m_tabPages.size())/*(sizeof(m_tabPages)/sizeof(m_tabPages[0]))*/; i++)
    {
     //set up the tab name
     tcItem.mask = TCIF_TEXT;
     tcItem.pszText = pszTabNames[i];
     tcItem.cchTextMax = int(strlen(pszTabNames[i]));
     //insert the new tab into the tab control and create the dialog window
     advTab.InsertItem(i, &tcItem);
     m_tabPages[i]->Create(pszTabItems[i], &advTab);
    }

    //redraw so that the dialogs don't appear in upper left corner and cover the tabs
    CRect tabRect, itemRect;
    int nX, nY, nXc, nYc;

    advTab.GetClientRect(&tabRect);
    advTab.GetItemRect(0, &itemRect);

    nX=itemRect.left;
    nY=itemRect.bottom+1;
    nXc=tabRect.right-itemRect.left-1;
    nYc=tabRect.bottom-nY-1;

    //m_tabPages[0]->SetWindowPos(&wndTop, nX, nY, nXc, nYc, SWP_SHOWWINDOW);
    for(int nCount=/*1*/0; nCount < int(m_tabPages.size())/*(sizeof(m_tabPages)/sizeof(m_tabPages[0]))*/; nCount++){
     m_tabPages[nCount]->SetWindowPos(&wndTop, nX, nY, nXc, nYc, SWP_HIDEWINDOW);
    }
}

And the Focus() and tab changing:

void AdvDesDlg::Focus()
{
    this->SetFocus();
    for (int i = 0; i < int(m_tabPages.size())/*(sizeof(m_tabPages)/sizeof(m_tabPages[0]))*/; i++)
    {
     m_tabPages[i]->ShowWindow(advTab.GetCurSel() == i ? SW_SHOW :
                                                   SW_HIDE);
    }

    int curSel = advTab.GetCurSel();
    m_tabPages[curSel]->SetFocus();
}

void AdvDesDlg::OnTcnSelchangeAdvDesign(NMHDR *pNMHDR, LRESULT *pResult)
{
    for (int i = 0; i < int(m_tabPages.size())/*(sizeof(m_tabPages)/sizeof(m_tabPages[0]))*/; i++)
    {
     m_tabPages[i]->ShowWindow(advTab.GetCurSel() == i ? SW_SHOW :
                                                   SW_HIDE);
    }

    int curSel = advTab.GetCurSel();
    m_tabPages[curSel]->SetFocus();

    *pResult = 0;
}

Answer 1

Debug your app, get it into this state, then go Debug / Break All. Find the main thread in the Threads window, then look at the call stack. Somewhere in the call stack will be your code that's causing the hang.

Note that in order to get a sensible call stack you'll need to point Visual Studio at Microsoft's symbol servers; see http://msdn.microsoft.com/en-us/library/b8ttk8zy.aspx

Answer 2

The behavior you describe usually occurs when you are running some process without allowing the message pump to run.

What does your app do? I assume you start it, and then either hit a button or select a menu item to start some process.

If the program behaves normally when you first start it (before you click to start your processing), but then behaves as you describe after starting the process, then that's your problem.

You'll have to move that processing into another thread to allow the MFC GUI to remain responsive.