Flex3中的Interactivity

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When an object has keyboard focus, it acts as the logical recipient of all keyboard
input and becomes the target of all keyboard-input event dispatches. An object can
gain keyboard focus either programmatically (via the Stage class’s instance variable
focus) or through user interaction, via the mouse, the Tab key, or the arrow keys.
However, in order to gain keyboard focus, an object must be an instance of a class
that inherits from InteractiveObject. Furthermore, in Flash Player, only one object
can have keyboard focus at a time.

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in order for an object to receive focus via those keys, it must be part of
Flash Player’s tab order. The tab order is the set of all objects on the display list that
can potentially receive focus via the keyboard. The tab order also determines the
sequence in which objects receive focus when the user presses the Tab key.

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There are two distinct tab orders in Flash Player: the automatic tab order and the
custom tab order. The automatic tab order is Flash Player’s default tab order, used
when no custom tab order is defined.

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The automatic tab order includes the following
objects:
• Instances of TextField that are on the display list and have their type variable set
to TextFieldType.INPUT
• Instances of Sprite or MovieClip that are on the display list and have their
buttonMode variable set to true or their tabEnabled variable set to true
• Instances of SimpleButton that are on the display list

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The root of the display list is an instance of the Stage class, which is automatically
created when the Flash runtime starts. This special, automatically created Stage
instance serves two purposes. First, it acts as the outermost container for all graphical
content displayed in the Flash runtime (i.e., it is the root of the display list).

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Second,
it provides information about, and control over, the global characteristics of the
display area.

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When an empty Flash runtime opens a new .swf file, it locates that .swf file’s main
class, creates an instance of it, and adds that instance to the display list as the Stage
instance’s first child.

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The .swf file’s main class instance is both the program entry point and the first visual
object displayed on screen. Even if the main class instance does not create any graphics
itself, it is still added to the display list, ready to contain any graphics created by
the program in the future. The main class instance of the first .swf file opened by the
Flash runtime plays a special role in ActionScript; it determines certain global environment
settings, such as relative-URL resolution and the type of security restrictions
applied to external operations.

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Once an instance of a .swf file’s main class has been added to the Stage instance, a
program can add new content to the screen by following these general steps:
1. Create a displayable object (i.e., an instance of any core display class or any class
that extends a core display class).
2. Invoke the DisplayObjectContainer class’s instance method addChild( ) on either
the Stage instance or the main-class instance, and pass addChild( ) the displayable
object created in Step 1.

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A display object’s depth is an integer
value that determines how that object overlaps other objects in the same display
object container.