Qt 5.0.2 & 5.1.0 Drag and Drop crash

[SoulSharer]

Updated information with callstack at the bottom of the topic

Hello there, I've been using Qt for a while and it is great, however I encountered a problem in the newer version.
When I start dragging and drop immediately - application just crashes with an error message "Access violation reading location", I swear I checked everything twice, made a lot if/else for sanity checks, still nothing. (looked into sample code, documentation, everything)

It crashes before it gets a chance to call dropEvent() function, even though dragEnterEvent() and dragMoveEvent() being called.
What could it be? I have no debugging symbols and call stack is just helpless.
Drag and drop action happens between two QMainWindows that are owned by the main QMainWindow (dragging from QListWidget and dropping to QTableWidget that are inherited by custom classes).
It is crashing in both Debug and Release.

P.s. if I wait a little before dropping all seems to be working

!http://i.imgur.com/VJre463.png(Screen_of_the_call_stack)! (probably worthless) :(
http://i.imgur.com/IAdr8CW.png New, captured with application verifier on. (all options enabled except for "Low resource simulation")
Looks like a similar issue: http://stackoverflow.com/questions/15050300/visual-studio-2010-access-violation-reading-location-debuging-not-much-info

Don't know if that will help, but here is what verifier outputted.
@First-chance exception at 0x664d1d9a in pleaseWork.exe: 0xC0000005: Access violation reading location 0x00000004.

===========================================================
VERIFIER STOP 0000000000000013: pid 0x6454: first chance access violation for current stack trace

0000000000000004 : Invalid address being accessed
00000000664D1D9A : Code performing invalid access
00000000001CEA00 : Exception record. Use .exr to display it.
00000000001CE510 : Context record. Use .cxr to display it.

This verifier stop is continuable.
After debugging it use 'go' to continue.

=======================================
VERIFIER STOP 00000013: pid 0x6454: First chance access violation for current stack trace.

00000004 : Invalid address causing the exception.
664D1D9A : Code address executing the invalid access.
002EB0A8 : Exception record.
002EB0F8 : Context record.
@

Thanks for any help!

---Environment
Windows 7 x64 SP1
Qt 5.0.0 (one that is provided with installer)
Visual Studio 2010 SP1

[SoulSharer]

Added additional information, spent a day debugging, still out of luck. :(

[SoulSharer]

-Finally managed to temporary fix this issue with-
@setAttribute(Qt::WA_DontCreateNativeAncestors, true); @
-Just in case someone will run into the same problem.-

Was wrong, still the same thing..

P.s. I updated to 5.0.2 and it didn't help

[bodzio131]

Hi,
Could you load *.pdb files for Qt binaries and then provide callstack?
As far as I can see you use visual leak detector (vld_x86.dll). Do you encounter your problems without it?
Could you try to build your program on linux and use valgrind?

[raven-worx]

can you show some lines of code ... or even share your project for inspection?

[SoulSharer]

Thanks for replies guys, I did try to turn off visual leak detector (and it is off by default in release) - same situation and I don't have a chance to build it on Linux I'm afraid. (mostly because I depend on Microsofts stuff, like DirectX for example)

Not sure where would I get .pdb files for binaries, other than by compiling myself which is a pain for Qt 5 with this new libraries (icu, angle) as far as I see.

[quote author="raven-worx" date="1365878204"]can you show some lines of code ... or even share your project for inspection?[/quote]
There is a lot of code and a lot of unrelated to the issue (also it is a closed project so I can't open the whole thing to the public, even if I want to), so I can only provide small snippets from it I guess, not sure what is need though. So I will post what I'm doing with drag and drop.

Starting with (SpriteDBList : QListWidget):
@void SpriteDBList::mousePressEvent( QMouseEvent *event )
{
QListWidget::mousePressEvent(event);

if (this->selectedItems().count() == 0) return;

if (event->button() == Qt::LeftButton)
dragStartPosition = event->pos();
}

void SpriteDBList::mouseMoveEvent( QMouseEvent *event )
{
if (selectedItems().count() == 0 || !(event->buttons() & Qt::LeftButton) || (event->pos() - dragStartPosition).manhattanLength()
< QApplication::startDragDistance())
{
QListWidget::mouseMoveEvent(event);
return;
}

if (!currentItem()) {
return;
}

seString spriteFrameName = currentItem()->text().toStdString();
seString spriteFrameFullPath = m_dbWidget->GetCurrentDir() + "\" + spriteFrameName;

QDrag *drag = new QDrag(this);
QMimeData *mimeData = new QMimeData();
QByteArray data(spriteFrameFullPath.c_str());
mimeData->setData("joi/spriteframe_path", data);
drag->setMimeData(mimeData);
drag->setPixmap(currentItem()->icon().pixmap(80, 80)); //icon with which we will move
drag->setHotSpot(QPoint(drag->pixmap().width()/2,
drag->pixmap().height()/2)); //where our cursor will be relative to topleft of pixmap

Qt::DropAction dropAction = drag->exec(Qt::CopyAction, Qt::CopyAction);
}
@
and ending in (AnimationFrameTable : QTableWidget):
@
void AnimationFrameTable::dragEnterEvent(QDragEnterEvent *event) {
Qt::DropAction action = event->proposedAction();

if (action == Qt::IgnoreAction) {
event->ignore();
return;
}

QObject* source = event->source();

if (event->mimeData() == NULL) {
event->ignore();
return;
} else {
const QMimeData* mime = event->mimeData();

if (mime->hasFormat("joi/spriteframe_path")) {
event->accept(); //looks like crash happens after this line
} else {
event->ignore();
}
}
}

void AnimationFrameTable::dragMoveEvent(QDragMoveEvent *e) {
Qt::DropAction action = e->proposedAction();
if (action == Qt::IgnoreAction) {
e->ignore();
return;
}

QObject* source = e->source();
const QMimeData* mime = e->mimeData();
if (mime == NULL) {
e->ignore();
} else if (mime->hasFormat("joi/spriteframe_path")) {
e->accept();
} else {
e->ignore();
}
}

void AnimationFrameTable::dropEvent(QDropEvent *event) {
Qt::DropAction action = event->proposedAction();
if (action == Qt::IgnoreAction) {
event->ignore();
return;
}

if (event->mimeData() == NULL || !event->mimeData()->hasFormat("joi/spriteframe_path")) {
event->ignore();
return;
}

QByteArray data = event->mimeData()->data("joi/spriteframe_path");
QString fullpath = data;
m_animWindow->AddSpriteFrame(fullpath.toStdString());

event->accept();
}@

There are a lot of checks just because I wanted to nail down the issue, still didn't help at all.
I checked everything in what I've posted. For example I commented strings just to see whether it is a heap corruption and passed mimeData with empty QByteArray, didn't help either.

And it crashes before it gets to dropEvent() function as I've mentioned before

[SoulSharer]

Ok, I've managed to load in .pdb and here is a callstack, now it looks useful:

Updated callstacks:
http://i.imgur.com/BAoL8mC.png
http://i.imgur.com/XIEbyvp.png

and where it stopped
http://i.imgur.com/BJdc8SP.png

• looks like scoped pointer was destroyed or something

[SGaist]

Hi,

Hope you don't mind me asking that, but would aren't you reinventing the wheel ? Drag and Drop support are already supported in QTableWidget and QListWidget.

You might better go overloading "QTableWidget::dropMimeData":http://qt-project.org/doc/qt-4.8/qtablewidget.html#dropMimeData and "QListWidget::mimeData":http://qt-project.org/doc/qt-4.8/qlistwidget.html#mimeData

You would then only have to care about your data.

Hope it helps

[SoulSharer]

[quote author="SGaist" date="1365890494"]Hi,

Hope you don't mind me asking that, but would aren't you reinventing the wheel ? Drag and Drop support are already supported in QTableWidget and QListWidget.

You might better go overloading "QTableWidget::dropMimeData":http://qt-project.org/doc/qt-4.8/qtablewidget.html#dropMimeData and "QListWidget::mimeData":http://qt-project.org/doc/qt-4.8/qlistwidget.html#mimeData

You would then only have to care about your data.

Hope it helps[/quote]

Didn't know about that, thanks. I might use it for most of the stuff, but I still want to find out what's wrong with current code if possible.

[raven-worx]

This code looks good so far ... the problem must be somewhere else.

[bodzio131]

Do you manage QObject descendants by yourself? Maybe you delete such objects directly (instead of deleteLater) or you use smart pointers with such objects. It could be a real problem if you interfere with Qt objects management model.

I think you need to narrow your project by cutting whatever you can step by step, or try to use the same drag-drop logic in simpler app. However, I suppose the problem can be far away from part which shows crash :(

[SoulSharer]

Thanks for the help.

[quote author="Bogdan" date="1365933102"]Do you manage QObject descendants by yourself? Maybe you delete such objects directly (instead of deleteLater) or you use smart pointers with such objects. It could be a real problem if you interfere with Qt objects management model.

I think you need to narrow your project by cutting whatever you can step by step, or try to use the same drag-drop logic in simpler app. However, I suppose the problem can be far away from part which shows crash :([/quote]

No I don't manage anything related to QObject myself and don't use smart pointers at all. The maximum I do is subclassing existing widgets to reimplement drag and drop actions.

And yeah I will try to cut it into something testable.

[SoulSharer]

For some reason in notifyInternal() receiver is NULL (0) after dropping, which causes all of this. Still trying to recreate this issue.

[raven-worx]

this means that you probably deleting objects before the drag has finished.
Or creating them on the wrong storage location (e.g. stack).

[SoulSharer]

Thing is I don't allocate on stack or delete them at all, my windows are allocated on heap and are not deleted until main window closes.
-Checked it once more, everything alright

Could it be because of some broken relationship between QMainWindows or QWidgets?

And Dropping does work if I don't do it fast, if I do it fast it gets reciever that is null and so it crashes.

[raven-worx]

Hard to tell if you can't show more code...

[SoulSharer]

Never mind, thanks for help anyway.

[wizzhard]

Hello,

I also experience a crash during drag n drop with the very same callstack after the crash.

In my case the crash occurs in a qtreeview when i drag n drop item internally.

In fact everything works fine until I double click an item of the view to rename it.

1 - I fill the item delegate with the new name
2 - Press enter to validate
3 - setData of the model is called (but does nothing).
4 - I try to drag & drop an item
5 - dragEnterEvent is called once.
6 - dragMoveEvent is called once
7 - program crash in QScopedPointer line134

@0 QScopedPointer<QObjectData,QScopedPointerDeleter<QObjectData> >::data qscopedpointer.h 134 0x651f1d4a
1 qGetPtrHelper<QScopedPointer<QObjectData,QScopedPointerDeleter<QObjectData> > > qglobal.h 991 0x651df58b
2 QObject::d_func qobject.h 119 0x651f0323
3 QCoreApplication::notifyInternal qcoreapplication.cpp 764 0x65468230
4 QCoreApplication::sendSpontaneousEvent qcoreapplication.h 206 0x65577098
5 QWidgetWindow::handleDropEvent qwidgetwindow.cpp 566 0x65d3e759
6 QWidgetWindow::event qwidgetwindow.cpp 195 0x65d3d30c
7 QApplicationPrivate::notify_helper qapplication.cpp 3398 0x65cc291e
8 QApplication::notify qapplication.cpp 2829 0x65cc035a
9 QCoreApplication::notifyInternal qcoreapplication.cpp 767 0x65468264
10 QCoreApplication::sendEvent qcoreapplication.h 203 0x6546d5e9
11 QGuiApplicationPrivate::processDrop qguiapplication.cpp 2228 0x66673045
12 QWindowSystemInterface::handleDrop qwindowsysteminterface.cpp 556 0x6665860c
13 QWindowsOleDropTarget::Drop qwindowsdrag.cpp 683 0x64eef4dd
14 CPrivDragDrop::PrivDragDrop getif.cxx 960 0x770f2b79
15 PrivDragDrop getif.cxx 1099 0x770f2d78
16 CDropTarget::Drop drag.cpp 2492 0x770ca04d
17 CDragOperation::CompleteDrop drag.cpp 1601 0x770c9ede
18 DoDragDrop drag.cpp 1964 0x770ca8dd
19 QWindowsDrag::drag qwindowsdrag.cpp 802 0x64eef9fa
20 QDragManager::drag qdnd.cpp 143 0x666831c8
21 QDrag::exec qdrag.cpp 282 0x66681daa
22 QAbstractItemView::startDrag qabstractitemview.cpp 3581 0x65faf1a5
23 QAbstractItemView::mouseMoveEvent qabstractitemview.cpp 1761 0x65fa9d9b
24 QTreeView::mouseMoveEvent qtreeview.cpp 1924 0x65ff6a8b
25 QWidget::event qwidget.cpp 7842 0x65d0a0ed
26 QFrame::event qframe.cpp 534 0x65e67772
27 QAbstractScrollArea::viewportEvent qabstractscrollarea.cpp 1163 0x65f089c4
28 QAbstractItemView::viewportEvent qabstractitemview.cpp 1680 0x65fa971b
29 QTreeView::viewportEvent qtreeview.cpp 1260 0x65ff3ece
30 QAbstractScrollAreaPrivate::viewportEvent qabstractscrollarea_p.h 105 0x65caaf28
31 QAbstractScrollAreaFilter::eventFilter qabstractscrollarea_p.h 121 0x65f0a919
32 QCoreApplicationPrivate::sendThroughObjectEventFilters qcoreapplication.cpp 863 0x654684f3
33 QApplicationPrivate::notify_helper qapplication.cpp 3394 0x65cc2902
34 QApplication::notify qapplication.cpp 2962 0x65cc098c
35 QCoreApplication::notifyInternal qcoreapplication.cpp 767 0x65468264
36 QCoreApplication::sendSpontaneousEvent qcoreapplication.h 206 0x65577098
37 QApplicationPrivate::sendMouseEvent qapplication.cpp 2469 0x65cbfab5
38 QWidgetWindow::handleMouseEvent qwidgetwindow.cpp 403 0x65d3dd00
39 QWidgetWindow::event qwidgetwindow.cpp 155 0x65d3d274
40 QApplicationPrivate::notify_helper qapplication.cpp 3398 0x65cc291e
41 QApplication::notify qapplication.cpp 2829 0x65cc035a
42 QCoreApplication::notifyInternal qcoreapplication.cpp 767 0x65468264
43 QCoreApplication::sendSpontaneousEvent qcoreapplication.h 206 0x65577098
44 QGuiApplicationPrivate::processMouseEvent qguiapplication.cpp 1417 0x6666ffe4
45 QGuiApplicationPrivate::processWindowSystemEvent qguiapplication.cpp 1249 0x6666f852
46 QWindowSystemInterface::sendWindowSystemEventsImplementation qwindowsysteminterface.cpp 536 0x66658561
47 QWindowSystemInterface::sendWindowSystemEvents qwindowsysteminterface.cpp 516 0x666584e9
48 QWindowsGuiEventDispatcher::sendPostedEvents qwindowsguieventdispatcher.cpp 86 0x64ecc014
49 qt_internal_proc qeventdispatcher_win.cpp 423 0x654f08d7
50 InternalCallWinProc USER32 0x766662fa
51 UserCallWinProcCheckWow USER32 0x76666d3a
52 DispatchMessageWorker USER32 0x766677c4
53 DispatchMessageW USER32 0x7666788a
54 QEventDispatcherWin32::processEvents qeventdispatcher_win.cpp 744 0x654f19c3
55 QWindowsGuiEventDispatcher::processEvents qwindowsguieventdispatcher.cpp 78 0x64ecbf7e
56 QEventLoop::processEvents qeventloop.cpp 137 0x65464ea1
57 QEventLoop::exec qeventloop.cpp 212 0x65464ffe
58 QCoreApplication::exec qcoreapplication.cpp 1020 0x6546879d
59 QGuiApplication::exec qguiapplication.cpp 1184 0x6666f5e8
60 QApplication::exec qapplication.cpp 2674 0x65cc0009
61 main main.cpp 20 0xbaf6fe
62 WinMain qtmain_win.cpp 131 0xc5f5ea
63 __tmainCRTStartup crtexe.c 547 0xc5d440
64 WinMainCRTStartup crtexe.c 371 0xc5d1cf
65 BaseThreadInitThunk kernel32 0x775f33aa
66 __RtlUserThreadStart ntdll32 0x77bd9f72
67 _RtlUserThreadStart ntdll32 0x77bd9f45 @

[wizzhard]

I just found something that seems to fix the issue here.

http://stackoverflow.com/questions/17373591/qt5-custom-lineedit-widget-qlineedit-subclass-private-variable-crashes-applica

I have unchecked acceptDrop on the qtreeview that own the items and it doesn't crash anymore.

EDIT : it doesn't works finally, it was the interruption of the debugger that prevented the problem to occur by interrupting the item delegate validation.

[SoulSharer]

Well, I've updated to 5.1.0, it still crashes. But now it also outputs this:

bq. QAccessibleTree::indexFromLogical: invalid index: 1 0 for QTreeWidget(0x4b06408)
Cannot creat accessible child interface for object: QTreeWidget(0x4b06408) index: 1
QAccessibleTree::indexFromLogical: invalid index: 2 0 for LayersTreeWidget(0x4a69668, name = "treeWidget")
Cannot creat accessible child interface for object: LayersTreeWidget(0x4a69668, name = "treeWidget") index: 2
QAccessibleTree::indexFromLogical: invalid index: 2 0 for LayersTreeWidget(0x4a69668, name = "treeWidget")
Cannot creat accessible child interface for object: LayersTreeWidget(0x4a69668, name = "treeWidget") index: 2
First-chance exception at 0x74c2c41f in JOI_Editor.exe: 0x80010001: Вызов был отклонен.
QAccessibleTree::indexFromLogical: invalid index: 3 0 for LayersTreeWidget(0x4a69668, name = "treeWidget")
Cannot creat accessible child interface for object: LayersTreeWidget(0x4a69668, name = "treeWidget") index: 3
First-chance exception at 0x6631232a in JOI_Editor.exe: 0xC0000005: Access violation reading location 0x00000004.
Unhandled exception at 0x770815de in JOI_Editor.exe: 0xC0000005: Access violation reading location 0x00000004.
The program '[7544] JOI_Editor.exe: Native' has exited with code -1073741819 (0xc0000005).