Setting QPixmap to Qlabel gives segmentation fault and app crashes

[vicky_mac]

@SGaist No i was directly updating as given above in the coed.

I am not able to figure out on which event i should write the slot for label updation.

please suggest.

[SGaist]

Which code exactly ?

[vicky_mac]

@SGaist
In the question it self I have given code where I am updating the label.

As I receive a frame in gst reamer thread I update it.

But how to do it in signal slot mechanism I am not able to feagure out. As you suggested above using qmetaobject how to use it in code.?

[Christian Ehrlicher]

@vicky_mac said in Setting QPixmap to Qlabel gives segmentation fault and app crashes:

As I receive a frame in gst reamer thread I update it.

You are not allowed to modify the GUI from any thread except the main thread (better: the thread where QApplication lives in). Use signals/slots to update your ui.

[SGaist]

Something like:

QMetaObject::invokeMethod(ui->label, "setPixmap", Qt::QueuedConnection, Q_ARG(pixmap));

[vicky_mac]

@SGaist hi thanx for advise..
I did Qmetaobject::Invokemethod(self-ui->vdolabel, "setPixel", qtqueuedconnection, Q_Args(Qpixmap, P)) :

And updating qlabel from setPixmap function in mainwidown.cpp its working fine.

Is it ok now or should have to anything else.
Is this OK passing the object reference and derefenrecing it like this?
MainWindow* self = static_cast<MainWindow* >(gSelf);

[SGaist]

Do you mean pass your MainWindow instance as the opaque data to your callback ?

[vicky_mac]

@SGaist yes, because without that we would not Abe able to invoke method.
MainWindow* self = static_cast<MainWindow* >(gSelf);
This line...

Because now by using Invokemethod I am updating qlabel in main thread and not child or gstreamer thread that seems OK.

[SGaist]

I'd go a step further and pass directly the pointer to the QLabel object, it's even less instructions to use.

[vicky_mac]

@SGaist didn't get your point.
Can you please give example for above scenario

[SGaist]

Rather than giving the pointer to your MainWindow instance, pass directly the pointer to your label. Basically:

mainwindow->ui->label