拖动精灵的三种方法比较

 构建Ball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 ();
        }
    }
}

 

第一种方法：会出现拖动时突然跳跃，使自身的中心与鼠标的中心对齐。

package
{
    import flash.events.MouseEvent;
    import flash.display.Sprite;
    
    public class MouseMoveDrag extends Sprite
    {
        private var ball:Ball;
        
        public function MouseMoveDrag()
        {
            Init();
        }
        public function Init():void
        {
            ball=new Ball(40,0xFFFF00);
            ball.x=stage.stageWidth/2;
            ball.y=stage.stageHeight/2;
            addChild(ball);
            ball.addEventListener(MouseEvent.MOUSE_DOWN,MouseDown);
        }
        public function MouseDown(e:MouseEvent):void
        {
            stage.addEventListener(MouseEvent.MOUSE_UP,MouseUp);
            stage.addEventListener(MouseEvent.MOUSE_MOVE,MouseMove);
        }
        public function MouseUp(e:MouseEvent):void
        {
            stage.removeEventListener(MouseEvent.MOUSE_UP,MouseUp);
            stage.removeEventListener(MouseEvent.MOUSE_MOVE,MouseMove);
        }
        public function MouseMove(e:MouseEvent):void
        {
            ball.x=mouseX;
            ball.y=mouseY;
        }
    }
}

 

第二种方法：完全正确，稍微有点繁琐。

package
{
    import flash.events.MouseEvent;
    import flash.display.Sprite;
    
    public class MouseMoveDrag extends Sprite
    {
        private var ball:Ball;
        private var dx:Number;
        private var dy:Number;
        
        public function MouseMoveDrag()
        {
            Init();
        }
        public function Init():void
        {
            ball=new Ball(40,0xFFFF00);
            ball.x=stage.stageWidth/2;
            ball.y=stage.stageHeight/2;
            addChild(ball);
            ball.addEventListener(MouseEvent.MOUSE_DOWN,MouseDown);
        }
        public function MouseDown(e:MouseEvent):void
        {
            stage.addEventListener(MouseEvent.MOUSE_UP,MouseUp);
            stage.addEventListener(MouseEvent.MOUSE_MOVE,MouseMove);
            dx=ball.x-mouseX;
            dy=ball.y-mouseY;
        }
        public function MouseUp(e:MouseEvent):void
        {
            stage.removeEventListener(MouseEvent.MOUSE_UP,MouseUp);
            stage.removeEventListener(MouseEvent.MOUSE_MOVE,MouseMove);
        }
        public function MouseMove(e:MouseEvent):void
        {
            ball.x=mouseX+dx;
            ball.y=mouseY+dy;
        }
    }
}

 

第三种方法：简单，但是startDrag()和stopDrag()每次只能拖动一个物体。

package
{
    import flash.events.MouseEvent;
    import flash.display.Sprite;
    
    public class MouseMoveDrag extends Sprite
    {
        private var ball:Ball;
        
        public function MouseMoveDrag()
        {
            Init();
        }
        public function Init():void
        {
            ball=new Ball(40,0xFFFF00);
            ball.x=stage.stageWidth/2;
            ball.y=stage.stageHeight/2;
            addChild(ball);
            ball.addEventListener(MouseEvent.MOUSE_DOWN,MouseDown);
        }
        public function MouseDown(e:MouseEvent):void
        {
            stage.addEventListener(MouseEvent.MOUSE_UP,MouseUp);
            ball.startDrag();
        }
        public function MouseUp(e:MouseEvent):void
        {
            stage.removeEventListener(MouseEvent.MOUSE_UP,MouseUp);
            ball.stopDrag();
        }
    }
}