Being able to handle events in Flex is very important because you will most likely need to use them to interact with Flex controls, custom controls, and components. This section provides you with basic information about the event model in Flex 2, and describes the Event object, its subclasses, and the event dispatching model.
Events inform a developer that something has happened within a Flex application. They can be generated when the visual appearance of a component changes, when the component is created and destroyed, and by using user devices such as the mouse and keyboard. In other words, any user interaction will most likely trigger an event, or even data that is returned from the server may trigger an event. This happens without any user interaction.
The developer can listen for these events by adding event listeners, which are functions used to respond to the triggered events. They are commonly referred to as event handlers. To give you an example, a user clicks a button that downloads data from the server. An event handler listens for an event to be triggered once the data has been fully downloaded. The event is fired, which, in turn, calls the event-handler function and parses the data into some meaningful information to be used in a DataGrid control, for example.
All or most components in Flex have built-in events that can be handled in ActionScript in your MXML applications
