Flex3中的Interactivity

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The swapChildrenAt( ) method takes the following form:
theContainer.swapChildrenAt(existingDepth1, existingDepth2);
where existingDepth1 and existingDepth2 are both depths occupied by children of
theContainer. The swapChildrenAt( ) method exchanges the depths of the children at
existingDepth1 and existingDepth2.

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To remove an object from a display object container, we use the
DisplayObjectContainer class’s instance method removeChild( ), which takes the following
form:
theContainer.removeChild(existingChild)
where theContainer is a container that currently contains existingChild

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Alternatively, we can remove a child based on its depth using removeChildAt( ),
which takes the following form:
theContainer.removeChildAt(depth)

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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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It’s important to note that the removeChild( ) and removeChildAt( ) methods discussed
in the previous section do not necessarily cause the removed object to be
purged from memory; 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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To completely remove a display object from a program, we must both remove it from
the screen using removeChild( ) and also remove all references to it. To remove all
references to the object, we must manually remove it from every array that contains
it and assign null (or some other value) to every variable that references it. Once all
references to the object have been removed, the object becomes eligible for garbage
collection and will eventually be removed from memory by ActionScript’s garbage
collector.

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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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In ActionScript 3.0, it’s perfectly legal and common to remove a child from one
DisplayObjectContainer instance and move it to another. In fact, the mere act of adding
an object to a container automatically removes that object from any container it
is already in.

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we learned that child objects automatically
move, rotate, and transform when their ancestors are moved, rotated, and
transformed. We can use this feature to perform collective visual modifications to
groups of objects.

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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.