Qt signals/slot QThread > GUI with lambdas functions

OPit

Hello,
I use Qt6.4 on Windows and I have a mistake from a signal/slot error.

I have a QThread send a signal to my main GUI to show an error message :

connect(m_uploaderServer, &PortalUploader::error, [this](const QString & message)
    {
        m_labelError->setText(message);
        m_labelError->show();
    });

But when the signals is emitted, I have this error :

[09/01/2023-13:46:33.439] QBasicTimer::start: Timers cannot be started from another thread
[09/01/2023-13:46:33.439] QObject::setParent: Cannot set parent, new parent is in a different thread

I don't have this error if my QLabel is always visible (not use show() function).

I don't understand this error. If I call directly from my thead the show() function, I understand why it is not correct, but in this case ?? Do I not use correctly signal/slot mechanism ? Somebody knows why ?

Thanks

[EDIT] : it seems that the lambda function that makes problem. When I use a member slot function, it's OK. Somebody knows why ?

[EDIT2] I found the answer. In documentation, it says:

the lambda will be called in the thread of the event loop of the object used as context).

I keep my post, it can help someone else ...

Chris Kawa

@OPit said:

the lambda will be called in the thread of the event loop of the object used as context

A simple fix is to add that context i.e.

connect(m_uploaderServer, &PortalUploader::error, m_labelError, [this](...
                                                  ^
                                                  here

OPit

Oh great, thanks for your answer !