“NullReferenceException”错误

Question

我正在尝试为我的游戏添加评分系统。但是，每当我玩游戏时都会出现此错误，并且当小行星与玩家或子弹相撞时，它们不会再摧毁。

我的错误信息是这样的： NullReferenceException：对象引用未设置为对象的实例 DestroyByContact.OnTriggerEnter2D（UnityEngine.Collider2D 其他）（在 Assets/Scripts/DestroyByContact.cs:47）

我应该注意到，所有游戏对象上也都有正确的标签。

还有一些代码：

using UnityEngine;
using System.Collections;

public class DestroyByContact : MonoBehaviour {

    public GameObject explosion;
    public GameObject playerExplosion;
    public int scoreValue;
    private GameController gameController;

    void start () {
        GameObject gameControllerObject = GameObject.FindWithTag ("GameController");
        if (gameControllerObject != null) {
            gameController = gameControllerObject.GetComponent <GameController> ();
        }

        if (gameController == null)
        {
            Debug.Log ("Cannot find 'GameController' script");
        }
    }

    void OnTriggerEnter2D(Collider2D other){
        if (other.tag == "Boundary") {
            return;
        }

        Instantiate(explosion, transform.position, transform.rotation);

         if (other.tag == "Player") {
            Instantiate(playerExplosion, other.transform.position, other.transform.rotation);
        }

        gameController.AddScore (scoreValue);
        Destroy(other.gameObject);
        Destroy(gameObject);
    }
}

using UnityEngine;
using System.Collections;
using UnityEngine.UI;

public class GameController : MonoBehaviour {

    public GameObject[] asteroids;
    public Vector3 spawnValues;
    public int asteroidCount;
    public float spawnWait;
    public float startWait;
    public float waveWait;

    public GUIText scoreText;
    private int score;

    void Start () {
        score = 0;
        UpdateScore ();
        StartCoroutine (spawnWaves ());
    }

    IEnumerator spawnWaves () {

        yield return new WaitForSeconds (startWait);

        while (asteroidCount > 0) {
            for (int i = 0; i < asteroidCount; i++) {
                GameObject asteroid = asteroids[Random.Range(0, asteroids.Length)];
                Vector3 spawnPosition = new Vector3 (spawnValues.x, Random.Range (-spawnValues.y, spawnValues.y), spawnValues.z);
                Quaternion spawnRotation = Quaternion.identity;
                Instantiate (asteroid, spawnPosition, spawnRotation);
                yield return new WaitForSeconds (spawnWait);
            }
            yield return new WaitForSeconds (waveWait);

            if (asteroidCount <= 95) {
                asteroidCount += 5;
            }
        }
    }

    public void AddScore (int newScoreValue) {
        score += newScoreValue;
        UpdateScore ();
    }

    void UpdateScore () {
        scoreText.text = "Score:" + score;
    }
}

Answer 1

我想说更好的办法是在 Controller 中的 Instantiate 之后设置 gameController。如果我理解正确，您的GameController 会产生从预制/预定义集合中附加DestroyOnContact 的小行星？ 如果是这样，请考虑这样做：

游戏控制器

var go = Instantiate (asteroid, spawnPosition, spawnRotation) as GameObject;
if (destroyable != null)
{
   var destroyable = go.GetComponent<DestroyByContact>();
   if (destroyable == null)
   {
      //Something else got instantiated, destroy it as we don't need it here
      Destroy(destroyable);
   }
   else
   {
      destroyable.gameController = this;
   }
}

DestroyOnContact

//just change accessor from private to public
public GameController gameController;

//Get rid of stuff that would set gameController in Start()

//Also check if gameController != null before you call .AddScore()