how can I know which object caused a specific event ?

[Radek]

Uff, this seems to be some kind of "VS" trick. The logic of the handler seems to be okay, sliderMoved(int) is a legal QSlider signal (so what "no matching signal?), the name of the slot handler is decided by you. No "special form" is prescribed. Sure, frmCustomNetwork must be a Q_OBJECT and the slot handler should be declared in the frmCustomNetwork class header in the public, private or protected slots section. The connect() calls seem to be okay. Supposing the handler is declared in frmCustomNetwork, the code should run.
In the Creator, you get useful hints when writing connect(). Once you type "SIGNAL(", you get available signals of the signaling class. You should see "sliderMoved(int)" on the list. Once you type "SLOT(", you get available slots of the target class. You should see your signal handler on the list. Selecting from the lists avoids most of errors.