flash as3.0中用代码控制元件的运动，怎么使元件不超出舞台外面

function FoodPosition():void { food.x = int(Math.random() * rows) * 2 * radius + 2 * radius; food.y = int(Math.random() * cols) * 2 * radius + 2 * radius; if (food.x > 580 || food.y > 580 || food.x < 0 || food.y < 0) { food.visi... function FoodPosition():void { food.x = int(Math.random() * rows) * 2 * radius + 2 * radius; food.y = int(Math.random() * cols) * 2 * radius + 2 * radius; if (food.x > 580 || food.y > 580 || food.x < 0 || food.y < 0) { food.visible = false; } } 当元件的坐标超出舞台时，让其可见性为false，这样写发现总是没有效果