拖动和运动模拟

1.构建小球精灵

package 
{
    import flash.display.Sprite;

    public class Ball extends Sprite
    {
        public var radius:Number;
        public var color:uint;

        public function Ball (radius:Number,color:uint)
        {
            this.radius=radius;
            this.color=color;
            Init ();
        }
        public function Init ():void
        {
            graphics.beginFill (color);
            graphics.drawCircle (0,0,radius);
            graphics.endFill ();
        }
    }
}

 

2.构建拖动和运动动画

package 
{
    import flash.display.Sprite;
    import flash.display.StageScaleMode;
    import flash.display.StageAlign;
    import flash.events.MouseEvent;
    import flash.events.Event;

    public class DragAndMove extends Sprite
    {
        private var ball:Ball;
        private var vx:Number;
        private var vy:Number;
        private var bounce:Number=-0.8;
        private var gravity:Number=0.9;

        public function DragAndMove ()
        {
            Init ();
        }
        public function Init ():void
        {
            stage.scaleMode=StageScaleMode.NO_SCALE;
            stage.align=StageAlign.TOP_LEFT;

            ball=new Ball(20,0xFFF000);
            ball.x=stage.stageWidth/2;
            ball.y=stage.stageHeight/2;
            vx=Math.random()*20-10;
            vy=-20;
            addChild (ball);
            ball.addEventListener (MouseEvent.MOUSE_DOWN,MouseDown);
            addEventListener (Event.ENTER_FRAME,EnterFrame);
        }
        private function EnterFrame (e:Event):void
        {
            vy+=gravity;
            ball.x+=vx;
            ball.y+=vy;
            if (ball.x<ball.radius)
            {
                ball.x=ball.radius;
                vx*=bounce;
            }
            else if (ball.x+ball.radius>stage.stageWidth)
            {
                ball.x=stage.stageWidth-ball.radius;
                vx*=bounce;
            }
            if (ball.y<ball.radius)
            {
                ball.y=ball.radius;
                vy*=bounce;
            }
            else if (ball.y+ball.radius>stage.stageHeight)
            {
                ball.y=stage.stageHeight-ball.radius;
                vy*=bounce;
            }
        }
        private function MouseDown (e:MouseEvent):void
        {
            stage.addEventListener (MouseEvent.MOUSE_UP,MouseUp);
            ball.startDrag ();
            removeEventListener (Event.ENTER_FRAME,EnterFrame);
        }
        private function MouseUp (e:MouseEvent):void
        {
            stage.removeEventListener (MouseEvent.MOUSE_UP,MouseUp);
            ball.stopDrag ();
            addEventListener (Event.ENTER_FRAME,EnterFrame);
        }
    }
}