Unity提示对象引用未设置错误，已声明变量仍触发NullReferenceException

问题描述 #

Unity开发过程中触发NullReferenceException（对象引用未设置为对象实例）报错，报错定位在代码第14、26行，已在第8行声明对应变量但依然触发报错。

HealthPoint类定义代码 #

using UnityEngine;

public class HealthPoint
{
    public float max;
    public float min = 0;
    public float current;
}

触发报错的Obstacle类代码 #

using UnityEngine;

public class Obstacle : MonoBehaviour
{
    [SerializeField] private float MaxHp = 100;
    [SerializeField] private float MinHp = 0;

    private HealthPoint hp;

    SpriteRenderer spriteRenderer;

    private void Start()
    {
        hp.max = MaxHp;
        hp.min = MinHp;
        hp.current = MaxHp;
    }

    public void GotHit(float HitPoint)
    {
        hp.current -= 20;
    }

    private void Update()
    {
        float color = (int)(hp.current / 100);
        spriteRenderer.color = new Color(color, color, color);
    }
}

问题根源 #

引用类型变量仅声明未初始化，默认值为null，调用null对象的属性/方法就会触发对象引用不存在报错：

• 自定义类HealthPoint是引用类型，仅声明private HealthPoint hp未创建实例
• SpriteRenderer组件未通过GetComponent获取挂载在当前GameObject上的实例

修复后完整代码 #

using UnityEngine;

public class Obstacle : MonoBehaviour
{
    [SerializeField] private float MaxHp = 100;
    [SerializeField] private float MinHp = 0;

    private HealthPoint hp;
    private SpriteRenderer spriteRenderer;

    private void Start()
    {
        spriteRenderer = gameObject.GetComponent<SpriteRenderer>();
        hp = new HealthPoint();

        hp.max = MaxHp;
        hp.min = MinHp;
        hp.current = MaxHp;
    }

    public void GotHit(float HitPoint)
    {
        hp.current -= HitPoint;
    }

    private void Update()
    {
        float color = hp.current / 100;
        spriteRenderer.color = new Color(color, color, color);
    }
}

修复点说明 #

• 新增hp = new HealthPoint()创建HealthPoint类实例
• 新增spriteRenderer = gameObject.GetComponent<SpriteRenderer>()获取当前物体上的SpriteRenderer组件实例
• 修复GotHit方法逻辑，将固定扣20改为使用传入的HitPoint参数
• 移除Update方法中多余的int强制转换，避免颜色值被截断为0或1，实现血量对应的灰度渐变效果

内容的提问来源于stack exchange，提问作者semih yılmaz