ActionScript for Flash MX: The Definitive Guide, Second Edition

Key.removeListener() Method

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The onKeyDown( ) and onKeyUp( ) events are triggered precisely once for each keypress

and key release. When using onKeyUp( ) and onKeyDown( ), you need not concern yourself

with whether the key is still being pressed at any given instant. Using these events allows

you to detect keypresses accurately even if the user releases the key between frames, and it

also prevents you from checking the same key twice if it was pressed only once. In any case,

you will ordinarily use the Key.getCode( ) and Key.getAscii( ) methods to check for the last

key pressed within an onKeyDown( ) or onKeyUp( ) listener.

The onKeyUp( ) event executes immediately when a key is released, independent of the

code on a movie’s timeline(s). However, visual changes to the movie made by the listener

are not rendered until the next frame refresh, which is determined by the frame rate of the

movie. Unfortunately, in Flash 6, updateAfterEvent( ) cannot be used to force a screen

refresh from onKeyUp( ); updateAfterEvent( ) has an effect only when invoked either from a

movie clip mouse or key event, or a setInterval( ) callback.

Usage

To emulate onKeyUp( ) in Flash 5, use the MovieClip class’s on(keyUp) clip event attached

to a movie clip at authoring time. For ...