package {
    import flash.display.Sprite;
    import flash.display.StageAlign;
    import flash.display.StageScaleMode;
    import flash.events.Event;
    import flash.events.MouseEvent;
    import flash.ui.Mouse;
    import flash.ui.MouseCursor;
     
    public class 对象拖拽 extends Sprite {
         
        private var ball:Ball;
        private var vx:Number;
        private var vy:Number;
        private var bounce:Number=-0.8;//反弹速度百分比
        private var gravity:Number=0.9;//重力加速度百分比
        private var frictionX:Number=0.98;//摩擦力因子--水平方向
        private var frictionY:Number=0.99;//摩擦力因子--垂直方向
         
        //public function Bouncing2() {
        public function 对象拖拽() {
            init();
        }
         
        private function init():void {
            stage.scaleMode=StageScaleMode.NO_SCALE;
            stage.align=StageAlign.TOP_LEFT;
            ball=new Ball(20)  ;
            ball.x=stage.stageWidth/2;
            ball.y=stage.stageHeight/2;
            vx=(Math.random()*2-1) * 20;
            vy=-10;
            addChild(ball);
            ball.addEventListener(MouseEvent.MOUSE_DOWN,MouseDownHandler);
            ball.addEventListener(MouseEvent.MOUSE_OVER,function(){ Mouse.cursor = MouseCursor.HAND;});
            ball.addEventListener(MouseEvent.MOUSE_OUT,function(){ Mouse.cursor = MouseCursor.AUTO;});
            addEventListener(Event.ENTER_FRAME,EnterFrameHandler);
        }
        private function EnterFrameHandler(event:Event):void {
            vy+=gravity; //加入重力加速度，所以肯定会向下掉
            vx *= frictionX; //加入摩擦力，所以最终会停下来
            vy *= frictionY;
            ball.x+=vx;//产生移动
            ball.y+=vy;
             
            var left:Number=0;
            var right:Number=stage.stageWidth;
            var top:Number=0;
            var bottom:Number=stage.stageHeight;
             
            //水平方向边界检测
            if (ball.x+ball.radius>right) {
                ball.x=right-ball.radius;
                vx*=bounce;
            } else if (ball.x - ball.radius < left) {
                ball.x=left+ball.radius;
                vx*=bounce;
            }
             
            //垂直方向边界检测
            if (ball.y+ball.radius>bottom) {
                ball.y=bottom-ball.radius;
                vy*=bounce;
            } else if (ball.y - ball.radius < top) {
                ball.y=top+ball.radius;
                vy*=bounce;
            }
        }
        private function MouseDownHandler(e:MouseEvent):void {
            stage.addEventListener(MouseEvent.MOUSE_UP,MouseUpHandler);
            ball.startDrag();
            removeEventListener(Event.ENTER_FRAME,EnterFrameHandler);//移除EnterFrame事件，否则在拖动过程中，小球还在不断下掉
        }
        private function MouseUpHandler(e:MouseEvent):void {
            stage.removeEventListener(MouseEvent.MOUSE_UP,MouseUpHandler);
            ball.stopDrag();
            addEventListener(Event.ENTER_FRAME,EnterFrameHandler);//拖动完成后，恢复EnterFrame事件监听，以便小球能不断运动
        }
    }
}