[Interest] QObjectListModel approach with Qt5 and QML crashes sometimes

[Railway Coder]

Hi,
issue is solved. I forgot to set a parent for C++ object.
QML was able to take ownership of the object.

http://doc.qt.io/qt-5/qtqml-cppintegration-data.html

Changing object creation to

*TestObject *testObject = new TestObject(&myObjectListModel);*

solves the problem with the crashes.
Git repository is also updated.

Best Regards,
railwaycoder



2015-02-03 6:55 GMT+01:00 Railway Coder <railwaycoder at gmail.com>:

> Hi,
>
> I'm currently writing an application using Qt5 (C++ and QML).
> It will get a big data backend in C++ which will get updated by different
> hardware in realtime.
>
> To get this data displayed in QtQuick. I found the QObjectListModel
> approach which was presented on QtDD12:
> http://qt-project.org/videos/watch/qml-for-desktop-apps
>
> I've updated the QObjectListModel implementation to work with Qt5.
>
> The application I've written sometimes crashes. It seems that this has to
> to with the QObjectListModel approach.
>
> I've put together a simple example to show this issue.
> A simple git import from QtCreator should make it very simple for you to
> test my
> example application.
>
> Clone URL:
> https://railwaycoder@bitbucket.org/railwaycoder/qobjectlistmodelqmltesting.git
>
> QObjectListModel is created in C++ and filled with 200 TestOBjects.
> The OBjectListModel is than exposed to QML using
> rootContext->setContextProperty(...)
> In Qml there is a simple ListView filled with data from the
> QObjectListModel childs.
> At this point there are no problems.
>
> But I want to do some actions with the TestObject selected in the ListView.
> Therefore I added the following code:
>
> onCurrentIndexChanged: {
>             console.log(currentIndex)
>             console.log(ObjectListModel.get(currentIndex))
>         }
>
> First testing looks also okay. But if you do fast scrolling up and down
> using
> keyboard or sometimes by simply selecting an item by mouse, the
> application crashes with following error:
>
> qml: TestObject(0x12e1820)
> qml: 51
> qml: TestObject(0x12e1610)
> qrc:/main.qml:35: TypeError: Cannot reat property 'name' of null
> qml: 50
> The program has unexpectedly finished.
>
> My idea about this issue is, that this has something to do with the
> seperate QtQuick rendering thread in Qt5.
> ListView sometimes needs to update it's data from the model and it seems
> if in the same moment ObjectListModel.get(currentIndex) is called this
> issue happens.
>
> Maybe I am completly wrong and there is a simple mistake in my code?
> Otherwise is this a bug? Or is it my task to take care of the QML
> rendering thread?
> Is QOBjectListModel approach best practise for accessing big data which is
> asynchronylsy updated by C++?
>
> Best Regards,
> railwaycoder
>
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