Flex Training Day 4:Flex Events, Metadata & View States
What are Events? Events propagation in Flex Custom Events Metadata tags View States in Flex
Events let us know when something happens within an application Any user or system interaction with your application can generate events Components generate and dispatch events and consume (listen to) other events.
An event system consists of 3 main entities: dispatchers, listeners, and event objects. Event dispatchers are objects that dispatch events to objects that are registered as listeners
Almost all event classes extend the flash.events.Event class EventDispatcher gives the classes a capability to participate fully in the event model. All DisplayList items extend from EventDispatcher For non-visual components we can also implement the IEventDispatcher interface
When events are triggered, there arethree phases in which Flex checkswhether there are event listeners.These phases occur in the followingorder:•Capturing•Targeting•Bubbling‘target’ property refers to thedispatcher of the event.The ’currentTarget’ property refers tothe current node that is beingexamined for event listeners.
During any phase, you can stop the traversal of the display list by calling one of the following methods on the Event object: stopPropagation() stopImmediatePropagation()Both methods prevents the Eventobject from moving on to the next node,With the difference that stopImmediatePropagation () does not allow any other event listeners on the current node to execute
Metadata tag is the information to the Flex compiler that describes how components are used in a Flex application The metadata tags define component attributes, data binding properties, events, and other properties of the component. Flex interprets these statements during compilation; they are never interpreted during run time. Metadata statements are associated with a class declaration, an individual data field, or a method. 04/06/12 9
What are view states?In many rich Internet applications, the interface changes based on the task the user is performing. A simple example is an image that changes when the user rolls the mouse over it. View states let you A.Default view state B.Rich view state easily implement such applications.
A.Modified title of Panel container B.New form item C.Modified label of Button control D.New LinkButton control•Item Creation Policy – deferred or immediate