Detect Whether the index Change in ComboBox is by user or programatically

[deepakkakkeel]

Hi,

I have a QComboBox. I have connected SIGNAL currentIndexChanged to a SLOT update(). So may is there any way that i can check whether the currentIndexChanged is called because of user interaction on comboBox or programatically.

Thanks
Deepak

[sierdzio]

When you change it programatically, "block signals":http://qt-project.org/doc/qt-5.0/qtcore/qobject.html#blockSignals and update by hand. You can pass a boolean value to indicate that, for example. So:
@
combobox->blockSignals(true);
// change the index here. Combobox will not send any signals!
// so you need to call your slot yourself - here is where you can inform it that it's not user change
combobox->blockSignals(false);
@

[deepakkakkeel]

Hi,

In my piece of code the SIGNAL currentIndexChanged() is called which will call my SLOT update(). So inside that function i need to check whether the index change has been caused by user or programatically.

Deepak.

[sierdzio]

Yeah, just add a boolean to your update:
@
void YourClass::update(bool changeByUser = false);

/// then
combobox->blockSignals(true);
// change the index here. Combobox will not send any signals!
update(true);
combobox->blockSignals(false);
@

[butterface]

Some time ago I read you should not use blockSignals but disconnect instead. Is that true?

[sierdzio]

I don't know, I have not heard anything said against blockSignals, please provide a link if you have one - I'm interested in knowing the reason. Documentation does not hint at blockSignals being bad in any way.

You can disconnect if you prefer, it takes just a bit more typing.

[butterface]

Of course if I can find the link again.

[vezprog]

I have used blockSignals in multiple occasions for combo boxes as well as radio buttons for state changes. It has always worked perfect for me!

[butterface]

It is some time ago and I cannot find the link anymore. It is also possible that either the link or I was wrong.
Apparently if no one knows such a fact it is not correct.