Unity预设名称“mainCamera”在当前上下文中不存在

我得到错误的名字 mainCamera' does not exist in the current context for the line targetpos=(vector2)maincamera.main.screentownorldpoint(input.mouseposition);`。我在寻找答案,但找不到方法来阻止这一切。

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

public class PlayerController : MonoBehaviour {

    float speed = 2f;
    Vector2 targetPos;

    private Rigidbody2D myRigidbody;
    private Animator myAnim;

    private static bool playerExists;
    public GameObject cameraPrefab;

    private void Start()
    {
        myRigidbody = GetComponent<Rigidbody2D>();
        myAnim = GetComponent<Animator>();

        if(!playerExists){
            playerExists = true;
            DontDestroyOnLoad(transform.gameObject);
        } else {
            Destroy(gameObject);
        }

        targetPos = transform.position;

        GameObject mainCamera = (GameObject)Instantiate(cameraPrefab);
    }

    void Update()
    {
        if (Input.GetMouseButtonDown(0))
        {

            targetPos = (Vector2)mainCamera.main.ScreenToWorldPoint(Input.mousePosition);
        }
        if ((Vector2)transform.position != targetPos)
        {
            Move();
        } else {
            myAnim.SetBool("PlayerMoving", false);
        }
    }