菜鸟求助Flex的问题

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The eventPhase variable indicates whether the current event dispatch is in the capture
phase, the target phase, or the bubbling phase

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Immediately before ActionScript dispatches a given event, it predetermines the entire
event flow for that dispatch based on the current state of the event target’s display
hierarchy. That is, the list of objects that will be notified of the event, and the order
in which those objects will be notified, is predetermined before the event dispatch
begins. Once the event dispatch begins, objects are notified of the event according to
that predetermined order—even if the structure of the target object’s display hierarchy
is modified by event listeners during the event dispatch.

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Event Listener List Mutation
As we’ve just learned, when a given event occurs, ActionScript notifies the appropriate
objects according to the predetermined order of the event flow. In turn, when
each object receives notification of the event, its event listeners are triggered. The
specific list of listeners that are triggered by a given event notification is determined
immediately before that notification occurs. Once the notification has begun, that
listener list cannot be altered.

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The event object is always an
instance of the Event class or one of its descendants.Every type of event in ActionScript—whether built-in or custom—is given a string name.

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Each event dispatch in ActionScript has an event target, which is the object to which
the event conceptually pertains.
To respond to a given event, listeners typically register with the event target

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The general process for responding to an event in ActionScript is as follows:
1. Determine the name of the event’s event type.
2. Determine the datatype of the event object representing the event.
3. Create an event listener to respond to the event. The event listener must define a
single parameter matching the datatype of the event object from Step 2.
4. Use EventDispatcher class’s instance method addEventListener( ) to register the
event listener with the event target (or, any display ancestor of the event target).
5. Sit back and wait for the event to occur.

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During every event dispatch, the Event object passed to every event listener defines a
currentTarget variable that provides a reference to the object with which the event
listener registered.

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For events targeted at nondisplay objects, the value of the Event class’s instance variable
currentTarget is always equal to target

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Some events in ActionScript are associated with a side effect known as a default
behavior. For example, the default behavior of a TextEvent.TEXT_INPUT event is text
being added to the target text field.
In some cases, events with a default behavior offer the option to prevent that behavior
programmatically
Events with a default behavior that can be prevented are said
to be cancelable.

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To prevent the default behavior for a cancelable event, we invoke the Event class’s
instance method preventDefault( ) on the Event object passed to any listener registered
for that event.