Signals and slots are used to connect between an event from gui and a function. In other words, you can manage situations what happens after an situations.
on this example, we say that, call the onButtonClicked() function after button clicked:
QObject::connect(ui.btnStart, SIGNAL(clicked()), this, SLOT(onButtonClicked()));
If you want to get signals, you must connect these to slots. Slots are functions defined as slot like this example:
private slots: void onButtonClicked();
this code on header file.
And last important think is that, signals and slots must have same parameters. It works:
QObject::connect(ui.comboBox, SIGNAL(activated(int)), this, SLOT(onComboboxActivated(int)));
But there is no connection in this example:
QObject::connect(ui.comboBox, SIGNAL(activated(int)), this, SLOT(onComboboxActivated()));