为什么我一直得到这个NullReferenceException错误？

Question

我的脚本...

using UnityEngine; 
using System.Collections; 

public class CountDownTimer : MonoBehaviour { 

    public int score; 
    float timeRemaining = 15; 

    // Use this for initialization 
    void Start() { 
    } 

    // Update is called once per frame 
    void Update() { 
     timeRemaining -= Time.deltaTime; 
     score = GetComponent<TriggerZone>().score; 
    } 

    void OnGUI(){ 
     if (timeRemaining > 0) { 
      GUI.Label(new Rect(100, 100, 200, 100), "Time Remaining: "+(int)timeRemaining); 
     } 
     else{ 
      GUI.Label(new Rect(100, 100, 200, 100), "Times up your score was: " + score + ". Press the r button to restart, or ESC to quit."); 
      if (Input.GetKeyDown("r")) 
       Application.LoadLevel("Testing Grounds"); 
      if (Input.GetKey("escape")) 
       Application.Quit(); 
     } 
    } 
} 

错误：

NullReferenceException: Object reference not set to an instance of an object CountDownTimer.Update() (at Assets/Scripts/CountDownTimer.cs:16)

我想不出什么可能会造成这个错误。据我了解，这是试图告诉我，一些东西不存在，但我想不出可能是什么。 “score = GetComponent（）。score;”正在访问包含分数值的另一个脚本，以便当计时器用完时它会告知玩家他们的分数，并让他们选择退出或重新开始游戏。

此外，如果它帮助这里是其它脚本...

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

公共类TriggerZone：MonoBehaviour {

public Text MyText; 
public int score; 

// Use this for initialization 
void Start() { 

    MyText.text = ""; 

} 


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

    MyText.text = "$" + score; 

} 

void OnTriggerEnter(Collider coll) { 

    if (coll.gameObject.HasTag ("ValueLevel1")) 
     score = score + 5; 

    if (coll.gameObject.HasTag ("ValueLevel2")) 
     score = score + 25; 

    if (coll.gameObject.HasTag ("ValueLevel3")) 
     score = score + 50; 

    if (coll.gameObject.HasTag ("ValueLevel4")) 
     score = score + 100; 

    if (coll.CompareTag ("Pickable")) { 
     coll.gameObject.SetActive(false); 
    } 

} 

}

Answer 1

嗯，我觉得自己很蠢，但多亏了Reddit我终于找到了问题。原来，我把我的脚本附加到我的FPS控制器，这是造成null问题。

Answer 2

GetComponent<TriggerZone>() 

似乎返回null和您正尝试访问.score关闭null。您的解决方案是检查null的回报，并采取适当的措施或确保呼叫永不返回null。

Answer 3

不论出于什么原因，你可能会错过你的CountDownTimer实例的TriggerZone脚本/组件，请尝试以下属性：

[RequireComponent (typeof (TriggerZone))] //Try add this 
public class CountDownTimer : MonoBehaviour { 
... 
} 

这RequireComponent属性可以让你自动添加所需的组件作为一个依赖。下面是Unity3D官方文档：

When you add a script which uses RequireComponent, the required component will automatically be added to the game object. This is useful to avoid setup errors. For example a script might require that a rigid body is always added to the same game object. Using RequireComponent this will be done automatically, thus you can never get the setup wrong.

BTW：以下调用应该不会在更新（）调用，最好在开始（）或甲戌（）：

score = GetComponent<TriggerZone>().score;