Designer plugin segfaults designer :(

[tmarki]

Hi,
I'm trying to extend Designer with a custom widget, but my widget keeps killing it with a segfault whenever I try to save the dialog the widget is on or I just try to preview it.

My custom widget is a rather simple QScrollArea derivative. Here's a (partial) backtrace of the crash:

#0 0xb7c0730f in DomWidget::write (this=0x0, doc=@0xbfc66fd0, tagName=@0xbfc66c38) at uilib/ui4.cpp:2859
#1 0xb7c07e04 in DomWidget::write (this=0x858f290, doc=@0xbfc66fd0,
tagName=@0xbfc66dd8) at uilib/ui4.cpp:2916
#2 0xb7c07e04 in DomWidget::write (this=0x858e808, doc=@0xbfc66fd0,
tagName=@0xbfc66ef4) at uilib/ui4.cpp:2916
#3 0xb7c09271 in DomUI::write (this=0x858f388, doc=@0xbfc66fd0,
tagName=@0xbfc66fe0) at uilib/ui4.cpp:271
#4 0xb7bd43d3 in QAbstractFormBuilder::save (this=0xbfc6707c,
dev=0xbfc670c0, widget=0x84fc768) at
uilib/abstractformbuilder.cpp:1037
#5 0xb7ebf2ca in qdesigner_internal::QDesignerResource::save
(this=0xbfc6707c, dev=0xbfc670c0, widget=0x84fc768) at
../formeditor/qdesigner_resource.cpp:158
#6 0xb7ecbdf2 in qdesigner_internal::FormWindow::contents
(this=0x84f0900) at ../formeditor/formwindow.cpp:1375
#7 0xb7c6927e in
qdesigner_internal::QDesignerFormBuilder::createPr eview (fw=0x84f0900,
styleName=@0xbfc67430, appStyleSheet=@0xbfc67434,
scriptErrors=0xbfc67208, errorMessage=0xbfc67458)
at shared/qdesigner_formbuilder.cpp:323
#8 0xb7c6a100 in
qdesigner_internal::QDesignerFormBuilder::createPr eview (fw=0x84f0900,
styleName=@0xbfc67430, appStyleSheet=@0xbfc67434,
errorMessage=0xbfc67458) at shared/qdesigner_formbuilder.cpp:373
#9 0xb7cffb5d in qdesigner_internal::PreviewManager::createPreview
(this=0x83eebe0, fw=0x84f0900, pc=@0xbfc67430,
errorMessage=0xbfc67458) at shared/previewmanager.cpp:270
#10 0xb7d00a9e in qdesigner_internal::PreviewManager::showPreview
(this=0x83eebe0, fw=0x84f0900, pc=@0xbfc67430,
errorMessage=0xbfc67458) at shared/previewmanager.cpp:309
#11 0x0808fd7d in QList<QString>::append ()
#12 0x080a8f82 in QList<QString>::append ()
#13 0xb6c4d859 in QMetaCallEvent:laceMetaCall (this=0x8404818,
object=0x83e7230) at kernel/qobject.cpp:491
#14 0xb6c5096b in QObject::event (this=0x83e7230, e=0x4901) at
kernel/qobject.cpp:1104
#15 0xb70cf39f in QApplicationPrivate::notify_helper (this=0x81434e8,
receiver=0x83e7230, e=0x8404818) at kernel/qapplication.cpp:3712
#16 0xb70d23e9 in QApplication::notify (this=0xbfc67b84,
receiver=0x83e7230, e=0x8404818) at kernel/qapplication.cpp:3271
#17 0xb6c3fe9a in QCoreApplication::notifyInternal (this=0xbfc67b84,
receiver=0x83e7230, event=0x8404818) at
kernel/qcoreapplication.cpp:546
#18 0xb6c412ed in QCoreApplicationPrivate::sendPostedEvents
(receiver=0x0, event_type=0, data=0x8143310) at
../../include/QtCore/../../src/corelib/kernel/qcoreapplication.h:205
#19 0xb6c4158d in QCoreApplication::sendPostedEvents (receiver=0x0,
event_type=0) at kernel/qcoreapplication.cpp:1016
#20 0xb6c688d4 in postEventSourceDispatch (s=0x814a700) at
../../include/QtCore/../../src/corelib/kernel/qcoreapplication.h:210
[snip]

I tried everything I could think of without success.
I'd be glad if someone would be able to help me out. I'm using the Qt 4.4 snapshot on Debian.
Thanks!

[wysota]

Does your widget work properly without using the plugin?

[tmarki]

Does your widget work properly without using the plugin?

Sure, it already works in an application, and the need arose to have it available in Designer, hence this new problem.

[wysota]

Could we see the plugin implementation?

[tmarki]

It seems like I found what the problem was.

In the constructor of the said widget I created a QLabel and assigned it to the ScrollArea with setWidget ().

After commenting out the setWidget line (and using setWidget later, when the QLabel actually got it's content set up) I can preview an save the dialog without a segfault.

I am puzzled why this helped, so if someone has an explanation it would be nice to know.