Seems the issue is solved: The whole stuff is related to some COM library we (have to) use. During my tests I came along this code snippet in my main.cpp:
CoInitializeEx( NULL, COINIT_APARTMENTTHREADED ); // (a) InitialUseOfCOMObject(); // (b) CoUninitialize(); // (c) Using the call sequence (1)-(3) below, I can comment whatever part of (a) to (c), but (3) will never succeed. That might be what you would expect, either. However, if I uncomment (a) to (c), even (1) did not succeed! Taking a closer look at the return value of CoInitializeEx() showed that it returned RPC_E_CHANGED_MODE, i.e. that some startup code in the COM library already initialized it in a way incompatible with Qt. The CoUnitialize then made the CoInitialize inside Qt to succeed. Apparently some code behind QPrinter then again did a CoInitialize in the wrong mode, causing the second call to fail. For a workaround, I ended up in re-initializing COM myself and keeping this initialization until the end of my app. So, as often: Qt is clear from guilt... :-) Thanks to Henry and Harri for their assistance! On Wed, Dec 20, 2017 at 10:42 PM, Rainer Wiesenfarth < rainer_wiesenfa...@trimble.com> wrote: > Hi all, > > I have a strange problem that is bugging me for a couple of days now. > Although I think the chances are low to find someone who experienced the > same issue, I would like to give it a try. > > I was able to strip the interesting part of my application down to these > lines: > > QString sProject = QFileDialog::getOpenFileName( this, tr( "Select > Project File" ), > m_sProjectFile, tr( "Project File (*.prj);;" "All Files (*.*)" ) ); > // (1) > > QPrinter p; // (2) > > sProject = QFileDialog::getOpenFileName( this, tr( "Select Project File" > ), > m_sProjectFile, tr( "Project File (*.prj);;" "All Files (*.*)" ) ); > // (3) > > Case 1: Running my application on Windows 10 (four different machines): > - (1) succeeds > - (2) succeeds > - (3) hangs the application in QWindowsNativeFileDialogBase::doExec() > at m_fileDialog->Show(owner) > > Case 2: Embedding the above snippet into a small sample application on > Windows 10: > - (1) to (3) all succeed > > Case 3: Setting the QFileDialog::DontUseNativeDialog option on Windows 10: > - (1) to (3) all succeed > > Case 4: Running my application on Windows 7 (several machines): > - (1) to (3) all succeed > > I took a close look at the m_fileDialog in QWindowsNativeFileDialogBase > for the Windows 10 case that gets stuck: > - at (1), m_fileDialog references a vtable in comdlg32.dll!const > CFileOpenSave > - at (3), m_fileDialog references a vtable in > OneCoreUAPCommonProxyStub.dll!0x... > > So it seems to be related to Windows "umbrella" libraries, but I have no > idea how. I looked even deeper into where m_fileDialog is getting assigned > and found the call to CoCreateInstance(), where CLSID_FileOpenDialog and > IID_IFileOpenDialog is passed in both (1) and (3), but in (1) the comdlg32 > object is returned while in (3) it is the OneCore... object. > > My guess so far: > 1. The constructor or destructor of QPrinter could lead to the replacement > of the object behind CLSID_FileOpenDialog, but > 2. this replacement not done always, but is triggered by the "some magic" > part in my application that is executed before (1) > > Any ideas what the "some magic" part could be? Unfortunately my > application is quite complex and can not be stripped down easily... > > Cheers, Rainer > > -- > Software Engineer | Trimble Imaging Division > Rotebühlstraße 81 | 70178 Stuttgart | Germany > Office +49 711 22881 0 | Fax +49 711 22881 11 <+49%20711%202288111> > http://www.trimble.com/imaging/ | http://www.inpho.de/ > > Trimble Germany GmbH, Am Prime Parc 11, 65479 Raunheim > Eingetragen beim Amtsgericht Darmstadt unter HRB 83893, > Geschäftsführer: Dr. Frank Heimberg, Jürgen Kesper > -- Software Engineer | Trimble Imaging Division Rotebühlstraße 81 | 70178 Stuttgart | Germany Office +49 711 22881 0 | Fax +49 711 22881 11 http://www.trimble.com/imaging/ | http://www.inpho.de/ Trimble Germany GmbH, Am Prime Parc 11, 65479 Raunheim Eingetragen beim Amtsgericht Darmstadt unter HRB 83893, Geschäftsführer: Dr. Frank Heimberg, Jürgen Kesper
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