Use Desktop Handle in case of no valid app HWND for QPrintDialog

The call Win32 API PrintDlgEx needs in the PRINTDLGEX struct a valid
window handle for hwndOwner to show up. In case there is no window
created, as seen in the example, the call to PrintDlgEx fails with
COM error code E_HANDLE. Using the Desktop HWND, in case of no valid
app HWND creates a valid call to PrintDlgEx with showing up the dialog.

Pick-to: 6.6
Fixes: QTBUG-118899
Change-Id: Ie7009c8e6e8285a0b6312e310b3d065c532f9e17
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@qt.io>

1 files changed, 6 insertions, 1 deletions

diff --git a/src/printsupport/dialogs/qprintdialog_win.cpp b/src/printsupport/dialogs/qprintdialog_win.cpp
index 6ac3bea4c0..6d8c2d0f4d 100644
--- a/src/printsupport/dialogs/qprintdialog_win.cpp
+++ b/src/printsupport/dialogs/qprintdialog_win.cpp
@@ -101,7 +101,12 @@ static void qt_win_setup_PRINTDLGEX(PRINTDLGEX *pd, QWindow *parentWindow,
 
     if (d->ep->printToFile)
         pd->Flags |= PD_PRINTTOFILE;
-    pd->hwndOwner = parentWindow ? (HWND)QGuiApplication::platformNativeInterface()->nativeResourceForWindow("handle", parentWindow) : 0;
+
+    WId wId = parentWindow ? parentWindow->winId() : 0;
+    //QTBUG-118899 PrintDlg needs valid window handle in hwndOwner
+    //So in case there is no valid handle in the application,
+    //use the desktop as valid handle.
+    pd->hwndOwner = wId != 0 ? HWND(wId) : GetDesktopWindow();
     pd->lpPageRanges[0].nFromPage = qMax(pdlg->fromPage(), pdlg->minPage());
     pd->lpPageRanges[0].nToPage   = (pdlg->toPage() > 0) ? qMin(pdlg->toPage(), pdlg->maxPage()) : 1;
     pd->nCopies = d->printer->copyCount();