All Flex components, including Application, have a common, standard life cycle. These life cycles are most easily described and understood from the view of the events they dispatch. We are primarily concerned with the following three major events in a component life cycle:

The events always occur in this order: preinitialize, initialize, and creationComplete.

Components are always created from descriptors. The use of descriptors allows the Flex framework a lot of flexibility in terms of how and when it instantiates components. Each component that can contain child components will have a list of descriptors for the child components. As you’ll see in Chapter 10, you can control the creation policy for some components. In those cases, if you were to defer instantiation of child components, such a component would dispatch a preinitialize event right away, but it would not dispatch the initialize event until the code explicitly created the child components from the descriptors.

The initialize event occurs when the child components have been created. However, at this point the layout of the child components has not yet occurred. The initialize event means you can successfully reference the child components, targeting them with ActionScript commands.

The creationComplete event occurs at the point when we would conventionally think of a component as being truly complete: the child components are created, and everything is laid out.

These life cycle events occur within all components, and we’ll return to these events throughout the book. We mention this life cycle in this chapter because it can help you to better understand what happens when an application first starts. That is, once an Application instance is created, it dispatches a preinitialize event. However, it hasn’t yet created any child components. It then recursively creates child components. Here’s an example to help you better understand the process. If an Application contains a VBox that contains a Label component, the Application instantiates its child, the VBox. The VBox then dispatches a preinitialize event. The VBox creates its child, the Label component. The VBox can then dispatch an initialize event. The Application can then do the same. Only after everything is laid out will the Application dispatch a creationComplete event.