访问自定义 class 的 IEnumerable<T> 时出现 NullReferenceException

Question

目标

我正在使用 Unity 设计一个 boid 系统。我通过在 "Swarm" 列表进入对撞机时添加一个 boid 来处理感知半径。为了找到每个 boid 的力，我需要循环遍历 swarm 列表，访问 "Boid" class，并检索速度和位置。

问题

来自每个群体实体的 Boid classes 被添加到一个新列表中，并传递给物理控制器。但是，在第 96 行抛出 NullReferenceException，我不明白为什么该变量会为 null。据我所知，使用 foreach 访问填充的 Enumerable<Boid> 应该有变量。

NullReferenceException: Object reference not set to an instance of an object Boid.Alignment (System.Collections.Generic.IEnumerable`1[T] boids) (at Assets/Scripts/Boid.cs:96) Boid.Update () (at Assets/Scripts/Boid.cs:42)

经测试，似乎在访问新的Boids列表的任何部分时都会抛出。

为什么我的新列表中没有数据？有没有更好的方法来处理 3D space 中 boid 的 2D 实现？有没有我可以用来更好地理解 Linq 的资源？

P.S。我对使用 Linq 系统很陌生，大部分代码来自 this video and this Unity project script

代码

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

public class Boid : MonoBehaviour
{
// Global Variables
public Boid_Settings settings;

// Local Variables
public Rigidbody body;
public Vector2 acceleration;
public Vector2 velocity
{
    get
    { return new Vector2(body.velocity.x, body.velocity.z); }
    set
    { body.velocity = new Vector3(value.x, body.velocity.y, value.y); }
}
public Vector2 position
{
    get
    { return new Vector2(transform.position.x, transform.position.z); }
}
public List<GameObject> swarm = new List<GameObject>();
public List<GameObject> targets = new List<GameObject>();


// Functions
private void Start()
{
    float angle = Random.Range(0, 2 * Mathf.PI);
    transform.rotation = Quaternion.Euler(new Vector3(0, 0, angle));
    velocity = new Vector2(Mathf.Cos(angle), Mathf.Sin(angle));
}

private void Update()
{
    IEnumerable<Boid> boids = swarm.Select(o => o.GetComponent<Boid>()).ToList(); //Line 40

    Vector2 alignment = Alignment(boids); //LINE 42
    Vector2 separation = Separation(boids);
    Vector2 cohesion = Cohesion(boids);

    acceleration = settings.alignmentWeight * alignment + settings.cohesionWeight * cohesion + settings.seperationWeight * separation;

    UpdatePhysics();
}

// Entity Awareness Assignment
private void OnTriggerEnter(Collider collider)
{
    if (collider.CompareTag("Zombie"))
    { swarm.Add(collider.gameObject); }
    else if (collider.CompareTag("Player") || collider.CompareTag("Lure"))
    { targets.Add(collider.gameObject); }
}

private void OnTriggerExit(Collider collider)
{
    if (collider.CompareTag("Zombie"))
    { swarm.Remove(collider.gameObject); }
    else if (collider.CompareTag("Player") || collider.CompareTag("Lure"))
    {
        targets.Remove(collider.gameObject);
        StartCoroutine(LingerTarget(collider.gameObject));
    }
}

IEnumerator LingerTarget(GameObject target)
{
    targets.Add(target);
    yield return new WaitForSeconds(settings.lingerTime);
    targets.Remove(target);
}


// Core Boid Logic
public void UpdatePhysics()
{
    // Apply the acceleration, and then limit the speed to the maximum.
    Vector2 UncappedVelocity = velocity + acceleration;
    velocity = ApplyLimit(UncappedVelocity, settings.maxSpeed);

    float angle = Mathf.Atan2(velocity.y, velocity.x) * Mathf.Rad2Deg;
    body.transform.rotation = Quaternion.Euler(new Vector3(0, 0, angle));
}

private Vector2 Alignment(IEnumerable<Boid> boids)
{
    Vector2 velocity = Vector2.zero;
    if (!boids.Any()) return velocity;

    foreach (Boid boid in boids)
    { velocity += boid.velocity; } //LINE 96
    velocity /= boids.Count();

    Vector2 steer = Steer(velocity.normalized * settings.maxSpeed);
    return steer;
}

private Vector2 Cohesion(IEnumerable<Boid> boids)
{
    if (!boids.Any()) return Vector2.zero;

    Vector2 sumPositions = Vector2.zero;
    foreach (Boid boid in boids)
    { sumPositions += boid.position; }
    Vector2 average = sumPositions / boids.Count();
    Vector2 direction = average - position;

    Vector2 steer = Steer(direction.normalized * settings.maxSpeed);
    return steer;
}

private Vector2 Separation(IEnumerable<Boid> boids)
{
    Vector2 direction = Vector2.zero;
    boids = boids.Where(o => Vector3.Distance(o.transform.position, position) <= settings.avoidanceRadius);
    if (!boids.Any()) return direction;

    foreach (Boid boid in boids)
    {
        Vector2 difference = position - boid.position;
        direction += difference.normalized / difference.magnitude;
    }
    direction /= boids.Count();

    Vector2 steer = Steer(direction.normalized * settings.maxSpeed);
    return steer;
}

private Vector2 Steer(Vector2 desired)
{
    Vector2 steer = desired - velocity;
    steer = ApplyLimit(steer, settings.maxSteerForce);

    return steer;
}

// Calculation Helpers
private Vector2 ApplyLimit(Vector2 baseVector, float limit)
{
    if (baseVector.sqrMagnitude > limit * limit)
    { baseVector = baseVector.normalized * limit; }
    return baseVector;
}
}

Boid_Settings模块：

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

[CreateAssetMenu]
public class Boid_Settings : ScriptableObject
{
// Boid
public float maxSpeed = 5;
public float avoidanceRadius = 1;
public float maxSteerForce = 3;

public float lingerTime = 2.5f;
public float alignmentWeight = 1;
public float cohesionWeight = 1;
public float seperationWeight = 1;
public float targetWeight = 1;

// Spawner
public float awarenessRadius = 2.5f;
}

上下文图片

证明boid classes有数据要读取 Unity 环境和 Boid.cs 附件 Unity Boid Boid.body 组件当游戏运行时，每个 Boid 找到两个 swarm 伙伴

Answer 1

原来我分配的是空数据，因为第 40 行的 GetComponent 函数找到了没有附加 Boid 脚本的 boid 的 "Body"。使用 GetComponentInChildren 进行搜索时，会填充数组并给出值。

旧线：

IEnumerable<Boid> boids = swarm.Select(o => o.GetComponent<Boid>()).ToList();

新线：

IEnumerable<Boid> boids = swarm.Select(o => o.GetComponentInChildren<Boid>()).ToList();

访问自定义 class 的 IEnumerable<T> 时出现 NullReferenceException

NullReferenceException when accessing an IEnumerable<T> of a custom class

c#

linq

ienumerable

boids

目标

问题

代码

上下文图片