对象引用未设置为对象的实例。NullReferenceException：[重复]

Question

我是一名初学者，正在尝试使用 Unity 制作 2D 多人游戏，但我发现了一个难以解决的错误。我试图找到解决方案，但仍然没有找到。你能帮助我吗？ 这是我的代码：

public class PlayerController : MonoBehaviourPun, IPunObservable
{

    public float speed;
    private Rigidbody2D rb2d;
    public Animator animator;

    public PhotonView pv;
    private Vector3 smoothMove;

    private GameObject sceneCamera;
    public GameObject playerCamera;

    // Use this for initialization
    void Start()
    {
        rb2d = GetComponent<Rigidbody2D>();

        if (photonView.IsMine)
        {
            playerCamera = GameObject.Find("Main Camera").GetComponent<GameObject>();
            //sceneCamera = playerCamera;

            sceneCamera.SetActive(false); // this is line 29
            playerCamera.SetActive(true);
        }
    }
}

this is my code 并出现此错误消息：

NullReferenceException：对象引用未设置为对象的实例 PlayerController.Start () (在 Assets/Scripts/PlayerController.cs:29)

Answer 1

sceneCamera 从未设置过，它的值始终为null，因为您评论了这一行：

            //sceneCamera = playerCamera;

1. 您可以将sceneCamera 字段公开给编辑器（例如，将其公开）
2. 你可以用Camera.main找到主场景相机

但你应该在尝试禁用它之前检查它是否为空

public class PlayerController : MonoBehaviourPun, IPunObservable
{

    public float speed;
    private Rigidbody2D rb2d;
    public Animator animator;

    public PhotonView pv;
    private Vector3 smoothMove;

    public GameObject sceneCamera;
    public GameObject playerCamera;

    // Use this for initialization
    void Start()
    {
        rb2d = GetComponent<Rigidbody2D>();

        if (photonView.IsMine)
        {
            playerCamera = GameObject.Find("Main Camera").GetComponent<GameObject>();

            if (sceneCamera != null)
            {
                sceneCamera.SetActive(false);
            }
            if (playerCamera != null)
            {
                playerCamera.SetActive(true);
            }
        }
    }
}