Camera.main上出现Unity2D NullReferenceException错误。ScreenToWorldPoint(输入.鼠标位置);复制

当我在Unity编辑器中构建/玩游戏并构建自己时,Unity在SelectScript.cs:19上不断向我显示NullReferenceException错误

originPoint = Camera.main.ScreenToWorldPoint(Input.mousePosition);

有人知道如何解决这个错误吗?

下面我发送此文件的完整代码:

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class SelectScript : MonoBehaviour
{
    private Vector3 originPoint, endPoint;
    public Sprite selectAreaSprite;
    private GameObject area;
    private BoxCollider2D areaCollider;
    public List<GameObject> SelectedGameObjects;
    [SerializeField] private GameObject menu;
    private bool wasClicked;
    public Vector3 connection;
    private void Update()
    {
        if(Input.GetMouseButton(0) == false)
        {
            originPoint = Camera.main.ScreenToWorldPoint(Input.mousePosition);
        }
        if (Input.GetMouseButtonDown(0))
        {
            CreateSelectArea();
        }
        if (Input.GetMouseButton(0))
        {
            endPoint = Camera.main.ScreenToWorldPoint(Input.mousePosition);
            area.transform.position = (originPoint + endPoint) / 2;
            area.transform.localScale = new Vector3(originPoint.x - endPoint.x, originPoint.y - endPoint.y, 0);
        }
        else if (Input.GetMouseButtonUp(0))
        {
            GameObject areaToDestroy = GameObject.Find("SelectArea");
            if(areaToDestroy != null)
            {
                Destroy(areaToDestroy);
            } 
        }
        if (Input.GetMouseButtonDown(1))
        {
            menu.transform.position = Input.mousePosition + new Vector3(0, 0, 10);
            menu.SetActive(true);
        }
    }
    private void CreateSelectArea()
    {
        area = new GameObject();
        area.name = "SelectArea";
        area.transform.position = originPoint - endPoint;
        var spriteRenderer = area.AddComponent<SpriteRenderer>();
        spriteRenderer.sprite = selectAreaSprite;
        spriteRenderer.color = new Color(0, 0.8f, 0, 1f);
        spriteRenderer.sortingOrder = -2;
        areaCollider = area.AddComponent<BoxCollider2D>();
        areaCollider.isTrigger = true;
    }
    public void Move()
    {
        wasClicked = false;
        StartCoroutine("waitForMouseClick");
    }
    private IEnumerator waitForMouseClick()
    {
        yield return new WaitForEndOfFrame();
        wasClicked = Input.GetMouseButton(0);
        if (!wasClicked)
        {
            StartCoroutine("waitForMouseClick");
        }
        else
        {
            foreach(GameObject g in SelectedGameObjects)
            {
                g.GetComponent<CardScript>().isSelected = false;
                g.transform.position = Camera.main.ScreenToWorldPoint(Input.mousePosition + new Vector3(0, 0, 10));
                if(g.GetComponent<LineRenderer>() != null)
                {
                    g.GetComponent<LineRenderer>().SetPosition(0, transform.position);
                }
            }
            Unselect();
        }
    }
    public void AddConnection()
    {
        StartCoroutine("waitForConnectionChange");
    }
    private IEnumerator waitForConnectionChange()
    {
        yield return new WaitForEndOfFrame();
        foreach (GameObject g in SelectedGameObjects)
        {
            g.GetComponent<CardScript>().AddConnection(Camera.main.ScreenToWorldPoint(Input.mousePosition));
        }
        if (!Input.GetMouseButton(0))
        {
            StartCoroutine("waitForConnectionChange");
        }
        else if(Input.GetMouseButton(0))
        {
            var mousePos = new GameObject();
            mousePos.name = "MousePosForConnection";
            mousePos.transform.position = Camera.main.ScreenToWorldPoint(Input.mousePosition);
            mousePos.AddComponent<CircleCollider2D>();
            mousePos.GetComponent<CircleCollider2D>().radius = 0.1f;
            mousePos.GetComponent<CircleCollider2D>().isTrigger = true;
            Unselect();
        }
        else if(connection != null)
        {
            foreach (GameObject g in SelectedGameObjects)
            {
                g.GetComponent<CardScript>().AddConnection(connection);
            }
            connection = new Vector3(0,0,0);
            Unselect();
        }
    }
    public void DeleteConnection()
    {
        foreach(GameObject g in SelectedGameObjects)
        {
            g.GetComponent<CardScript>().DeleteConnection();
        }
    }
    public void Unselect()
    {
        foreach(GameObject g in SelectedGameObjects)
        {
            g.GetComponent<CardScript>().isSelected = false;
        }
        SelectedGameObjects.Clear();
    }
}

我尝试将Vector2更改为Vector3,但没有成功。早些时候它起到了应有的作用,但现在不起作用了。可能是什么原因导致的,以及如何解决?