as2的Key.isDown方法在as3的代替

as3中没有了Key.isDown很不方便。所以你可以用以下方法用“isKeyPressed(keyCode);”代替：

import flash.events.KeyboardEvent;
import flash.ui.Keyboard;

var _keys:Array = new Array();
stage.addEventListener(KeyboardEvent.KEY_DOWN, this.handleKeyDown);
stage.addEventListener(KeyboardEvent.KEY_UP, this.handleKeyUp);

function handleKeyDown(evt:KeyboardEvent):void
{
    if (_keys.indexOf(evt.keyCode) == -1)
    {
        _keys.push(evt.keyCode);
    }
}

function handleKeyUp(evt:KeyboardEvent):void
{
    var i:int = _keys.indexOf(evt.keyCode);

    if (i > -1)
    {
        _keys.splice(i, 1);
    }
}

function isKeyPressed(key:int):Boolean
{
    return _keys.indexOf(key) > -1;
}