简单的物体二段跳效果

package {
/*author : CYPL*/
        import flash.display.*;
        import flash.events.*;
        import flash.utils.Timer;
        public class JumpTest extends Sprite {
                private static  const G:int=1;
                private var box:Sprite;
                private var landObject:Sprite;
                private var ySpeed:int=0;
                private var jumpSpeed:int=-15;
                private var keyPressed:Boolean= false;
                private var keyReleased:Boolean=true;
                private var comboJump:Boolean=false;
                private var inAir:Boolean=true;
                private var timer:Timer;
                public function JumpTest() {
                        box=drawRect((stage.stageWidth-50)/2,100,50,50,0xff0000);
                        landObject=drawRect(0,300,stage.stageWidth,20);
                        (timer=new Timer(30)).start();
                        configureControl();
                }
                private function configureControl():void {
                        stage.addEventListener(KeyboardEvent.KEY_DOWN,keyDownHandler,false,0,true);
                        stage.addEventListener(KeyboardEvent.KEY_UP,keyUpHandler,false,0,true);
                        timer.addEventListener(TimerEvent.TIMER,timerHandler,false,0,true);

                }
                private function drawRect(posX:Number,posY:Number,w:Number,h:Number,color:uint=0):Sprite {
                        var rect:Sprite;
                        with (rect=new Sprite) {
                                graphics.beginFill(color);
                                graphics.drawRect(0,0,w,h);
                                x=posX;
                                y=posY;
                        }
                        return Sprite(addChild(rect));
                }
                private function keyDownHandler(evt:KeyboardEvent):void {
                        keyReleased && inAir && !comboJump&&(comboJump=true,ySpeed=jumpSpeed,trace("comboJump"));
                        !keyPressed&&(keyPressed=true,inAir=true,ySpeed=jumpSpeed,timer.start());
                        keyReleased=false;
                }
                private function keyUpHandler(evt:KeyboardEvent):void {
                        keyReleased=true;
                        ySpeed<-5&&(ySpeed+=8)&&ySpeed>0&&ySpeed=0;
                }
                private function timerHandler(evt:TimerEvent):void {
                        evt.updateAfterEvent();
                        ySpeed+=G;
                        box.y+=ySpeed;
                        ySpeed>0&&(box.hitTestObject(landObject))&&(trace(landObject.y),box.y=landObject.y-box.height,timer.stop(),keyPressed=false,inAir=false,comboJump=false);
                }



        }
}