package {
    import flash.display.Sprite;
    import flash.events.Event;
    import flash.events.MouseEvent;
    import flash.geom.Rectangle;
    import flash.ui.Mouse;
    import flash.ui.MouseCursor;
 
    public class Spring1 extends Sprite {
        private var ball:Ball;
        private var spring:Number=0.02;
        private var targetX:Number=stage.stageWidth/2;
        private var rect:Rectangle;
        private var vx:Number=0;
        private var isDragging=false;
 
        public function Spring1() {
            init();
        }
 
        private function init():void {
            ball=new Ball(10);
            addChild(ball);
            ball.x=20;
            ball.y=stage.stageHeight/2;
            addEventListener(Event.ENTER_FRAME, onEnterFrame);
 
            ball.addEventListener(MouseEvent.MOUSE_DOWN,MouseDownHandler);
            ball.addEventListener(MouseEvent.MOUSE_OVER,function(){Mouse.cursor = MouseCursor.HAND});
            ball.addEventListener(MouseEvent.MOUSE_OUT,MouseOutHandler);
            stage.addEventListener(MouseEvent.MOUSE_UP,MouseUpHandler);
             
            //画辅助线
            graphics.lineStyle(1);
            graphics.moveTo(ball.x,ball.y);
            graphics.lineTo(stage.stageWidth-ball.x,ball.y);
            graphics.moveTo(stage.stageWidth/2,ball.y-10);
            graphics.lineTo(stage.stageWidth/2,ball.y+10);
 
            rect=new Rectangle(ball.x,ball.y,stage.stageWidth-2*ball.x,0);
        }
 
        private function MouseOutHandler() {
            if (! isDragging) {
                Mouse.cursor=MouseCursor.AUTO;
            }
        }
 
 
        //开始拖动
        private function MouseDownHandler(e:MouseEvent):void {
            ball.startDrag(true,rect);
            Mouse.cursor=MouseCursor.HAND;
            removeEventListener(Event.ENTER_FRAME, onEnterFrame);
            isDragging=true;
 
        }
         
        //结束拖动
        private function MouseUpHandler(e:MouseEvent):void {
            ball.stopDrag();
            addEventListener(Event.ENTER_FRAME, onEnterFrame);
            Mouse.cursor=MouseCursor.AUTO;
            isDragging=false;
        }
 
        private function onEnterFrame(event:Event):void {
            var dx:Number = targetX-ball.x;
            var ax:Number = dx*spring;//加速度与位移成正(反)比关系
            vx += ax;
            vx *= 0.97;//摩擦系数
            trace(ax,vx);
            ball.x+=vx;
 
        }
    }
}