爲什麼我一直得到這個NullReferenceException錯誤？

Question

我的腳本...

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(); 
     } 
    } 
} 

錯誤：

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

我想不出什麼可能會造成這個錯誤。據我瞭解，這是試圖告訴我，一些東西不存在，但我想不出可能是什麼。 「score = GetComponent（）。score;」正在訪問包含分數值的另一個腳本，以便當計時器用完時它會告知玩家他們的分數，並讓他們選擇退出或重新開始遊戲。

此外，如果它幫助這裏是其它腳本...

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

公共類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，我覺得自己很蠢，但多虧了Reddit我終於找到了問題。原來，我把我的腳本附加到我的FPS控制器，這是造成null問題。

Answer 2

GetComponent<TriggerZone>() 

似乎返回null和您正嘗試訪問.score關閉null。您的解決方案是檢查null的回報，並採取適當的措施或確保呼叫永不返回null。

Answer 3

不論出於什麼原因，你可能會錯過你的CountDownTimer實例的TriggerZone腳本/組件，請嘗試以下屬性：

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

這RequireComponent屬性可以讓你自動添加所需的組件作爲一個依賴。下面是Unity3D官方文檔：

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：以下調用應該不會在更新（）調用，最好在開始（）或甲戌（）：

score = GetComponent<TriggerZone>().score;