Quote Originally Posted by ulmly View Post
The on_objectName_signalSignature() slot is automatically connected to the signalSignature() signal from objectName. This is done by default. Also, I should not spend an extra effort to make signal-slot connection, even in Qt Designer. Just declare it in header file and define in implementation one.
It's better to make the connection graphically and name the slot in a way that it gives more information about what it does instead of a vague information when it is triggered.

However, why am I not able to see the 'second' connect() statement ? Is the statement hidden from us ?
The second connection is done by
QMetaObject::connectSlotsByName() that is called from setupUi() in the file generated by uic from your Designer form.