stage按键监听

package tools{
        public class KeyIsDown{
                private static var obj;
                
                public static function init(stage){
                        obj = new Object();
                        stage.addEventListener("keyDown", keydownHandler);
                        stage.addEventListener("keyUp", keyupHandler);
                }
                
                public static function isDown(key){
                        return(obj[key] ? true : false);
                }
                
                private static function keydownHandler(event){
                        obj[event.keyCode] = true;
                }
                
                private static function keyupHandler(event){
                        obj[event.keyCode] = false;
                }
                
        }
}

开始的时候在文档类构造的时候KeyIsDown.init(stage)一下
然后在任何地方KeyIsDown.isDown(keycode)都可以返回keycode有没有按下了