In Qt, this action-response scheme is handled by signals and slots. This section will include a few definitions, and then we shall jump into an example for further explanation.
A signal is a message that is passed to communicate that the state of an object has changed. This signal may carry information about the change that has occurred. For instance, when a window has been resized, the signal will usually carry the coordinates of the new state (or size) of the window. Sometimes, a signal may carry no extra information, such as that of a button click.
A slot is a specific function of an object that is called whenever a certain signal has been emitted. Since slots are functions, they will embody lines of code that perform an action, such as closing a window, disabling a button, and sending an email, to mention but a few.
Signals and slots have to be connected...