'QMessageBox::critical' : none of the 4 overloads could convert all the argument type

[anda_skoa]

This looks reasonable.

You can do the connect in main()

QObject::connect( &mThread, SIGNAL(alertSignal(QString)), &w, SLOT(alertSlot(QString)), Qt::QueuedConnection);

QObject::connect( &mThread, SIGNAL(alertSignal(QString)), &w, SLOT(alertSlot(QString)), Qt::QueuedConnection);

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Cheers,
_

[Lesiok]

And the last parameter is not needed because its default value is Qt::AutoConnection which means that for objects from different threads it is Qt::QueuedConnection.

[anda_skoa]

And the last parameter is not needed because its default value is Qt::AutoConnection which means that for objects from different threads it is Qt::QueuedConnection.

True, however in this case both objects belong to the same thread. It will still work with auto connection because another check is which thread is executing the emit and that is a different thread then the owner of the reciever object.

Doesn't hurt to explicitly specify Qt::QueuedConnection though.

Cheers,
_

[ChrisW67]

GUI objects in threads aside, the original error message:

QMessageBox::critical' : none of the 4 overloads could convert all the argument

is caused by:

QMessageBox::critical(this,tr("ERROR"),tr("Large change in illumination.\nPlease re-capture reference image.\n"));

QMessageBox::critical(this,tr("ERROR"),tr("Large change in illumination.\nPlease re-capture reference image.\n"));

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because the first argument, this, is not a pointer to a QWidget and cannot be converted to one.