UnassignedReferenceException：敌人的可变射弹没有   被分配。您可能需要分配的射弹变量   检查器中的“敌人”脚本。   UnityEngine.Object.Internal_InstantiateSingle（UnityEngine.Object   数据，UnityEngine.Vector3 pos，UnityEngine.Quaternion腐烂）

GameObject laser = Instantiate(
        projectile,transform.position,Quaternion.identity) as GameObject;
laser.getcomponent<Rigidbody2D>().velocity = new Vector2(0,- projectileSpeed);