Minimizing Mfc application with open Qt dialog

Question

Hello

I am using QtWinMigrate solution to show dialogs from my plugin dlls that are loaded in third party Mfc application. The problem is the following :

When I minimize the main window of my Mfc application, and when I restore it back again, all of my open Qt dialogs are lost. I found out that actually my Qt dialogs are destroyed i.e destructors are called.

I did some debugging and discovered the following :

When I close my Mfc main window my Qt dialog gets WM_SHOWWINDOW message with SW_PARENTCLOSING wparam parametar. Then QtWndProc is called, which for the SW_PARENTCLOSING case issues sends QHideEvent:

in QtWndProc() function in file qapplication_win.cpp line 2160

case WM_SHOWWINDOW :

if(lparam==SW_PARENTCLOSING) {
   QHideEvent e;
   qt_sendSpontaneousEvent(widget,e);
   widget->hideChildren(true); ////////////////////

and the eventFilter of QWinWidget sends DefferedDelete who deletes my dialog :

in QWinWidget.cpp in line 280

QWinWidget::eventFilter(OObject* o, QEvent* e){

    case QEvent::Hide: 

    if(w->testAtrribute(Qt::WA_DeleteOnClose)

    deleteLater();

}

Can someone please explain this behavior to me? This seems like bug to me .

Thanks

Answer 1

You have the answer in your question. See the documentation on WA_DeleteOnClose. You will need to call setAttribute(WA_DeleteOnClose, false) on your dialogs that you don't want deleted when they are hidden.