Unity3d 如何使用Unity创建二维距离关节？NullReferenceException

我试图在一个脚本中创建一个Distance2dJoint来扩展monobhavior

不幸的是，我在这一行收到NullReferenceException异常：

dj2d.connectedBody = otherBody;

我做错了什么？dj2d似乎是空的，但当我实例化它时，它怎么可能是空的呢

void OnTriggerEnter2D( Collider2D other )
    {

        CatController otherCatController = other.GetComponentInParent<CatController> ();

        if ( otherCatController ) {
            Debug.Log("Hit a cat");
            if( otherCatController.index<index ){
                DistanceJoint2D dj2d = new DistanceJoint2D();
                Rigidbody2D otherBody = otherCatController.GetComponent<Rigidbody2D>();    
                dj2d.connectedBody = otherBody;

            }
        }

    }

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我从unity论坛找到了解决方案

            DistanceJoint2D dj2d = gameObject.AddComponent( "DistanceJoint2D" ) as DistanceJoint2D;
            dj2d.connectedBody = otherCatController.GetComponent<Rigidbody2D>();

可能重复的