FLEX3笔记！

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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. When two display objects overlap, the one with the greater depth
position (the “higher” of the two) obscures the other (the “lower” of the two).

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The
lowest object in the stacking order has a depth position of 0, and the highest object
has a depth position equal to the number of child objects in the display object container,
minus one

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Display objects added to a container using addChild( ) are assigned depth positions
automatically. Given an empty container, the first child added via addChild( ) is
placed at depth 0, the second is placed at depth 1, the third is placed at depth 2, and so on

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After removeChild( ) or removeChildAt( ) runs, the removed child’s parent variable is
set to null because the removed child has no container. If the removed child was on
the display list before the call to removeChild( ) or removeChildAt( ), it is removed
from the display list. If the removed child was visible on screen before the call to
removeChild( ) or removeChildAt( ), it is also removed from the screen. If the removed
child is, itself, a DisplayObjectContainer with its own children, those children are
also removed from the screen.

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they only remove the object from the parent
DisplayObjectContainer object’s display hierarchy. If the removed object is referenced
by a variable or array element, it continues to exist and can be re-added to
another container at a later time.

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even after all references to an object have been
removed, that object continues to be active until the garbage collector deletes it from
memory.

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ActionScript does not provide a direct method for removing all of an object’s children.
Hence, to remove every display child from a given object, we must use a while
loop or a for loop.

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Color and coordinate transformations made to a container via the DisplayObject
class’s instance variable transform are also inherited by its descendants

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When a new child display object is added to a DisplayObjectContainer object,
ActionScript dispatches an Event.ADDED event targeted at the new child. Likewise,
when an existing child display object is removed from a DisplayObjectContainer
object, ActionScript dispatches an Event.REMOVED event targeted at the removed child.

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• A DisplayObjectContainer instance can use the Event.ADDED and Event.REMOVED
events to detect when it has gained or lost a display descendant.
• A DisplayObject instance can use the Event.ADDED and Event.REMOVED events to
detect when it has been added to or removed from a parent container.