private function createBall():void        {for(var i:int = 0; i < 10; i++)            {var ballDef:b2BodyDef = new b2BodyDef();                ballDef.type = b2Body.b2_dynamicBody;var radius:Number = 10+Math.random()*20;var circleShape:b2CircleShape  = new b2CircleShape(radius/PIXEL_TO_METER);var ballFixtureDef:b2FixtureDef = new b2FixtureDef();                ballFixtureDef.shape = circleShape;                ballFixtureDef.density = 1.0;                ballFixtureDef.restitution = 1.0;                ballFixtureDef.friction = 0.5;                ballDef.position.Set(stage.stageWidth/2/PIXEL_TO_METER,20/PIXEL_TO_METER);

//为每一个球创建一个相同大小的显示对象外观                var ballSprite:Ball = new Ball(radius,i+"");//将显示对象存入刚体定义的userData树形                ballDef.userData = ballSprite;//添加到容器中                addChild(ballSprite);

var ball:b2Body = world.CreateBody(ballDef);                ball.CreateFixture(ballFixtureDef);

            }        }

private function aysncSprite():void        {//遍历物理世界的所有刚体，此处为何如此遍历请参考Manual            //如果你已经给外观指定了变量，就不用遍历，直接调用变量            var body:b2Body = world.GetBodyList();while(body!=null)            {if(body.GetDefinition().userData is Sprite)                {var ballSprite:Sprite = body.GetDefinition().userData as Sprite;                    ballSprite.x = body.GetPosition().x * PIXEL_TO_METER;                    ballSprite.y = body.GetPosition().y * PIXEL_TO_METER;                    ballSprite.rotation = body.GetAngle() * (180 / Math.PI);                }                body = body.GetNext();            }        }

private function handleEnterFrame(evt:Event):void        {//更新鼠标位置            UpdateMouseWorld();//不断调用鼠标拖动方法            mouseDrag();

var timeStep:Number = 1/30;var velocityInterations:int = 10;var positionIterations:int = 10;

            world.Step(timeStep,velocityInterations,positionIterations);//同步显示对象和刚体            aysncSprite();//在2.1版本清除力，以提高效率            world.ClearForces();//绘制//            world.DrawDebugData();        }