Application Development with Qt Creator - Second Edition

Debugging Qt's signal-slot connections

What do you do if you think that you've correctly connected a signal to a slot and yet your slot's not being fired?

Here's a bunch of things you can try:

• Check the compile log for error messages about undefined signals and slots.
• Check the runtime log for errors on connection. If need be, ensure that the connection succeeds by testing its return value (it should return true).
• Check to make sure that the connect code, the emit code, and the slot code is reached. (Odds are one of them isn't.)
• Make sure that you declare the connection as follows:

  connect(sender, SIGNAL(someSignal(type)), receiver,     
          SLOT(received(type)))

• The signal and slot specifications should have the argument types, but not the arguments themselves. ...