Unity中脚本多次测试后抛出NullReferenceException问题求助

问题背景 #

C#基础薄弱，学校项目包含两个Unity脚本：Game_Handler负责游戏核心逻辑，Game_Set_Handler管理题目字典。项目初始运行正常，但测试6-7次后会触发空引用异常；复制脚本修改类名后可正常运行几次，之后仍会出现相同问题。

相关代码 #

Game_Set_Handler 完整代码 #

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using System.Linq;
using UnityEngine.UI;
using System.Threading.Tasks;
using System.Diagnostics;
using Random = System.Random;


public class Game_Set_Handler : MonoBehaviour
{
    public class Set
    {
        public string? Question { get; set; }
        public int StartingPoints { get; set; }
        public string Answer1 { get; set; }
        public string Answer2 { get; set; }
        public string Answer3 { get; set; }
        public string? Answer4 { get; set; }
        public string? Answer5 { get; set; }

    }

    public Dictionary<int, Set> Sets;

    public void Handler()
    {
        Sets = new Dictionary<int, Set>()
        {
            {1,new Set { Question="sports to play outside", StartingPoints=250, Answer1 = "football", Answer2 = "baseball", Answer3 = "basketball", Answer4 = "soccer", Answer5 = "golf"}},
            {2,new Set { Question="board games", StartingPoints=375, Answer1 = "chess", Answer2 = "checkers", Answer3 = "monopoly",Answer4 = "battleship",Answer5 = "mancala"}},
            {3,new Set { Question="famous religions", StartingPoints=400, Answer1 = "christianity", Answer2 = "islam", Answer3 = "judaism",Answer4 = "buddhism",Answer5 = "hinduism"}},
            {4,new Set { Question="types of bread in the USA", StartingPoints=225, Answer1 = "banana", Answer2 = "sourdough", Answer3 = "white",Answer4 = "wheat",Answer5 = "pumpkin"}},
            {5,new Set { Question="car brands in the USA", StartingPoints=100, Answer1 = "ford", Answer2 = "chevrolet", Answer3 = "toyota",Answer4 = "honda",Answer5 = "volkswagen"}},

        };
    }

    void Start()
    {
        Handler();
    }


    public int Get_Question()
    {
        int value = new Random().Next(0, Sets.Count + 1);
        return value;
    }
}

Game_Handler 关联代码 #

var dictionary = Parent.GetComponent<Game_Set_Handler>().Sets; //Parent是Canvas，两个脚本都挂载其上
int dict_key = Parent.GetComponent<Game_Set_Handler>().Get_Question();

触发的错误信息 #

NullReferenceException: Object reference not set to an instance of an object
Game_Set_Handler.Get_Question () (at Assets/Scripts/Game_Set_Handler.cs:53)
Game_Handler.Start_Game () (at Assets/Scripts/Game_Handler.cs:60)
Game_Handler.Start () (at Assets/Scripts/Game_Handler.cs:121)

问题根源与修复方案 #

核心问题点 #

1. Sets字典可能未初始化：Game_Set_Handler的Start方法执行时机晚于Game_Handler的Start时，Sets仍为null，调用Get_Question时访问Sets.Count会触发空引用。
2. 随机数生成逻辑错误：Random.Next(0, Sets.Count +1)会生成0到5的随机数，但字典的键是1-5，生成0时后续访问字典会出错；且每次调用Get_Question都新建Random实例，短时间内多次调用会生成重复随机数，甚至因系统时钟精度问题导致异常。
3. 重复调用GetComponent：Game_Handler中每次访问都调用GetComponent，不仅效率低，还可能因对象状态变化获取到null。

具体修复步骤 #

1. 提前初始化字典并调整初始化时机：
   将Sets声明改为直接初始化，并将字典初始化移到Awake方法（Awake比Start执行更早，确保Game_Handler访问时字典已就绪）：

   public Dictionary<int, Set> Sets = new Dictionary<int, Set>();
   
   void Awake()
   {
       Handler();
   }
   

2. 优化随机数生成逻辑：
   声明静态Random实例避免重复创建，同时调整随机数范围为1到Sets.Count，确保生成的键一定存在于字典中：

   private static Random _random = new Random();
   
   public int Get_Question()
   {
       // 双重保险，确保字典已初始化
       if (Sets == null || Sets.Count == 0)
       {
           Handler();
       }
       // 生成1到Sets.Count之间的随机数（包含两端）
       return _random.Next(1, Sets.Count + 1);
   }
   

3. 优化Game_Handler中的组件访问逻辑：
   缓存Game_Set_Handler实例，增加空值检查，避免重复调用GetComponent：

   var setHandler = Parent.GetComponent<Game_Set_Handler>();
   if (setHandler == null)
   {
       Debug.LogError("Canvas上未挂载Game_Set_Handler组件");
       return;
   }
   var dictionary = setHandler.Sets;
   int dict_key = setHandler.Get_Question();
   

内容的提问来源于stack exchange，提问作者Issaiah Teneyck