为什么我在 Unity 中的操纵杆会出现此错误？

Question

我目前正在制作一个 2D 游戏作为初学者，我想在我的游戏中添加操纵杆控件。我做的一切都像 Brackeys 的 youtube 视频，但我总是得到这个错误：

NullReferenceException: Object reference not set to an instance of an object
PlayerMovement.Update () (at Assets/Scripts/PlayerMovement.cs:21)

有人能帮我吗？ YouTube 视频和时间戳的 link 是：

https://youtu.be/bp2PiFC9sSs?t=780

我当前的脚本：

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

public class PlayerMovement : MonoBehaviour {

    public CharacterController2D controller;
    public Animator animator;

    public Joystick joystick;

    public float runSpeed = 40f;

    float horizontalMove = 0f;
    bool jump = false;
    bool crouch = false;

    // Update is called once per frame
    void Update() {

        if (joystick.Horizontal >= .2f)
        {
            horizontalMove = runSpeed;
        } else if (joystick.Horizontal <= -.2f)
        {
            horizontalMove = -runSpeed;
        } else
        {
            horizontalMove = 0f;
        }

        float verticalMove = joystick.Vertical;

        animator.SetFloat("Speed", Mathf.Abs(horizontalMove));

        if (verticalMove >= .5f)
        {
            jump = true;
            animator.SetBool("IsJumping", true);
        }

        if (verticalMove <= -.5f)
        {
            crouch = true;
        }
        else
        {
            crouch = false;
        }

    }

    public void OnLanding ()
    {
        animator.SetBool("IsJumping", false);
    }

    public void OnCrouching (bool isCrouching)
    {
        animator.SetBool("IsCrouching", isCrouching);
    }

    void FixedUpdate ()
    {
        // Move our character
        controller.Move(horizontalMove * Time.fixedDeltaTime, crouch, jump);
        jump = false;
    }
}

Answer 1

根据视频，您必须将场景层次结构中的 FixedJoystick 对象拖放到 PlayerMovement 的操纵杆字段中在检查器中（从视频中查看 11:24）

为什么我在 Unity 中的操纵杆会出现此错误？

Why do I get this error for a joystick in Unity?

c#

unity3d

controller

joystick