1. An event-driven method for programming a programmable logic controller, the method comprising: registering at least one event; storing at least one event handler program section corresponding to the at least one event; detecting an occurrence of the at least one event; adding the at least one event into an event queue of the programmable logic controller; extracting an event from the event queue; and executing an event handler program section corresponding to the extracted event, wherein registering the at least one event includes registering an event selected from at least one predefined event by a user, and registering a user-customized event input by a user, and wherein registering the user-customized event includes registering a logical combination of a plurality of predefined events including the at least one predefined event.