Flex3中的Interactivity

Sky-Tiger

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). All
display objects in a container, hence, can be thought of as residing in a visual stacking
order akin to a deck of playing cards, counted into a pile starting at zero.

Sky-Tiger

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

Sky-Tiger

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

Sky-Tiger

To retrieve the depth position of any object in a display object container, we use the
DisplayObjectContainer class’s instance method getChildIndex( ):

Sky-Tiger

To add a new object at a specific depth position, we use the DisplayObjectContainer
class’s instance method addChildAt( )

theContainer.addChildAt(theDisplayObject, depthPosition)

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The depthPosition must be an integer between 0 and theContainer.numChildren,
inclusive.
If the specified depthPosition is already occupied by an existing child, then
theDisplayObject is placed behind that existing child (i.e., the depth positions of all
display objects on or above that depth increases by one to make room for the new
child).

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To add a new object above all existing children, we use:
theContainer.addChildAt(theDisplayObject, theContainer.numChildren)
which is synonymous with the following:
theContainer.addChild(theDisplayObject)

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Typically, addChildAt( ) is used in combination with the DisplayObjectContainer
class’s instance method getChildIndex( ) to add an object below an existing child in a
given container. Here’s the general format:
theContainer.addChildAt(newChild, theContainer.getChildIndex(existingChild))

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To change the depth of an existing child, we can swap that child’s depth position
with another existing child via the DisplayObjectContainer class’s instance methods
swapChildren( ) or swapChildrenAt( ).

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The swapChildren( ) method takes the following form:
theContainer.swapChildren(existingChild1, existingChild2);
where existingChild1 and existingChild2 are both children of theContainer. The
swapChildren( ) method exchanges the depths of existingChild1 and existingChild2.