Missing reference exception unity как исправить

I’m trying to create Arkanoid 3d game using Unity with C#. I’ve created simple Menu (Scene 0), where I can start my game, my main scene where actual game takes place(Scene 1) and Scoreboard (Scene 2), which is shown after losing all 3 balls Player has at start. After pressing any key i go back to Menu and can start game again. And this is where problem begins.

During second game after loosing 1st ball, my game goes crazy. I get loads of “MissingReferenceException”s like one below (but some linked to other objects (like GUIText’s etc):

MissingReferenceException: The object of type 'Player' has been destroyed but
you are still trying to access it.
Your script should either check if it is null or you should not destroy the object.
Player.BallLost () (at Assets/Player/Player.cs:164)
GameEventManager.TriggerBallLost () (at Assets/Menagers/GameEventManager.cs:30)
Ball.Update () (at Assets/Ball/Ball.cs:47)

I noticed loads of MissingReferenceExceptions that are casued by not assigning variables. But this feels kinda diffrent for me since it all works perfectly during “1st play”. What can cause this problem? I cheked in inspector after launching game for the second game and all variables are assigned to objects.

I’m not sure if shoudl insert game code since it has grown rather big and is split into >10 scripts.

Вернуться в Почемучка

Кто сейчас на конференции

Сейчас этот форум просматривают: нет зарегистрированных пользователей и гости: 33



Value type vs Reference type

In many programming languages, variables have what is called a “data type”. The two primary data types are value types (int, float, bool, char, struct, …) and reference type (instance of classes). While value types contains the value itself, references contains a memory address pointing to a portion of memory allocated to contain a set of values (similar to C/C++).

For example, Vector3 is a value type (a struct containing the coordinates and some functions) while components attached to your GameObject (including your custom scripts inheriting from MonoBehaviour) are reference type.

When can I have a NullReferenceException?

NullReferenceException are thrown when you try to access a reference variable that isn’t referencing any object, hence it is null (memory address is pointing to 0).

Some common places a NullReferenceException will be raised:

Manipulating a GameObject / Component that has not been specified in the inspector

// t is a reference to a Transform.
public Transform t ;

private void Awake()
{
     // If you do not assign something to t
     // (either from the Inspector or using GetComponent), t is null!
     t.Translate();
}

Retrieving a component that isn’t attached to the GameObject and then, trying to manipulate it:

private void Awake ()
{
    // Here, you try to get the Collider component attached to your gameobject
    Collider collider = gameObject.GetComponent<Collider>();

    // But, if you haven't any collider attached to your gameobject,
    // GetComponent won't find it and will return null, and you will get the exception.
    collider.enabled = false ;
}

Accessing a GameObject that doesn’t exist:

private void Start()
{
    // Here, you try to get a gameobject in your scene
    GameObject myGameObject = GameObject.Find("AGameObjectThatDoesntExist");

    // If no object with the EXACT name "AGameObjectThatDoesntExist" exist in your scene,
    // GameObject.Find will return null, and you will get the exception.
    myGameObject.name = "NullReferenceException";
}

Note: Be carefull, GameObject.Find, GameObject.FindWithTag, GameObject.FindObjectOfType only return gameObjects that are enabled in the hierarchy when the function is called.

Trying to use the result of a getter that’s returning null:

var fov = Camera.main.fieldOfView;
// main is null if no enabled cameras in the scene have the "MainCamera" tag.

var selection = EventSystem.current.firstSelectedGameObject;
// current is null if there's no active EventSystem in the scene.

var target = RenderTexture.active.width;
// active is null if the game is currently rendering straight to the window, not to a texture.

Accessing an element of a non-initialized array

private GameObject[] myObjects ; // Uninitialized array

private void Start()
{
    for( int i = 0 ; i < myObjects.Length ; ++i )
        Debug.Log( myObjects[i].name ) ;
}

Less common, but annoying if you don’t know it about C# delegates:

delegate double MathAction(double num);

// Regular method that matches signature:
static double Double(double input)
{
    return input * 2;
}

private void Awake()
{
    MathAction ma ;

    // Because you haven't "assigned" any method to the delegate,
    // you will have a NullReferenceException
    ma(1) ;

    ma = Double ;

    // Here, the delegate "contains" the Double method and
    // won't throw an exception
    ma(1) ;
}

How to fix ?

If you have understood the previous paragraphes, you know how to fix the error: make sure your variable is referencing (pointing to) an instance of a class (or containing at least one function for delegates).

Easier said than done? Yes, indeed. Here are some tips to avoid and identify the problem.

The “dirty” way : The try & catch method :

Collider collider = gameObject.GetComponent<Collider>();

try
{
    collider.enabled = false ;
}       
catch (System.NullReferenceException exception) {
    Debug.LogError("Oops, there is no collider attached", this) ;
}

The “cleaner” way (IMHO) : The check

Collider collider = gameObject.GetComponent<Collider>();

if(collider != null)
{
    // You can safely manipulate the collider here
    collider.enabled = false;
}    
else
{
    Debug.LogError("Oops, there is no collider attached", this) ;
}

When facing an error you can’t solve, it’s always a good idea to find the cause of the problem. If you are “lazy” (or if the problem can be solved easily), use Debug.Log to show on the console information which will help you identify what could cause the problem. A more complex way is to use the Breakpoints and the Debugger of your IDE.

Using Debug.Log is quite useful to determine which function is called first for example. Especially if you have a function responsible for initializing fields. But don’t forget to remove those Debug.Log to avoid cluttering your console (and for performance reasons).

Another advice, don’t hesitate to “cut” your function calls and add Debug.Log to make some checks.

Instead of :

 GameObject.Find("MyObject").GetComponent<MySuperComponent>().value = "foo" ;

Do this to check if every references are set :

GameObject myObject = GameObject.Find("MyObject") ;

Debug.Log( myObject ) ;

MySuperComponent superComponent = myObject.GetComponent<MySuperComponent>() ;

Debug.Log( superComponent ) ;

superComponent.value = "foo" ;

Even better :

GameObject myObject = GameObject.Find("MyObject") ;

if( myObject != null )
{
   MySuperComponent superComponent = myObject.GetComponent<MySuperComponent>() ;
   if( superComponent != null )
   {
       superComponent.value = "foo" ;
   }
   else
   {
        Debug.Log("No SuperComponent found onMyObject!");
   }
}
else
{
   Debug.Log("Can't find MyObject!", this ) ;
}

Sources:

1. http://answers.unity3d.com/questions/47830/what-is-a-null-reference-exception-in-unity.html
2. https://stackoverflow.com/questions/218384/what-is-a-nullpointerexception-and-how-do-i-fix-it/218510#218510
3. https://support.unity3d.com/hc/en-us/articles/206369473-NullReferenceException
4. https://unity3d.com/fr/learn/tutorials/topics/scripting/data-types

I am making a game in unity 3d and I have missing reference exception.The error
don’t appear in my script editor so I don’t know what is this error related to.
Here is the Gamemanager script:

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

public class Gamemanager : MonoBehaviour
{
public List<Character> Characters = new List<Character>();
public List <Item> AllItems = new List<Item> ();
bool ShowCharWheel;
public int SelectedCharacter;
int LastCharacter;
public static Gamemanager Instance;
public bool CanShowSwitch = true;
public Character CurrentCharacter; 

void Awake()
{
    foreach (Character c in Characters)
    {
        c.Instance = Instantiate(c.PlayerPrefab, c.HomeSpawn.position, c.HomeSpawn.rotation) as GameObject;
        c.Instance.GetComponent<PlayerController> ().LocalCharacter = c;
    }
    ChangeCharacterStart(Characters[PlayerPrefs.GetInt("SelectedChar")]);
}
// Use this for initialization
void Start()
{

}
void ChangeCharacterStart(Character c)
{

    LastCharacter = SelectedCharacter;
    SelectedCharacter = Characters.IndexOf(c);
    CurrentCharacter = c;
    Characters [LastCharacter].Instance.GetComponent<PlayerController> ().CanPlay = false;
    Characters[SelectedCharacter].Instance.GetComponent<PlayerController>().CanPlay = true;
    Camera.main.GetComponent<SmoothFollow>().target = Characters[SelectedCharacter].Instance.transform;
    PlayerPrefs.SetInt("SelectedChar", SelectedCharacter);
}
// Update is called once per frame
void Update()
{
    if (CanShowSwitch) {
        if (Input.GetKey (KeyCode.C)) {
            ShowCharWheel = true;

        } else if (Input.GetKey (KeyCode.V)) {
            ShowCharWheel = false;

        }

    }
}

void ChangeCharacter(Character c)
{
    c.Instance.GetComponent<AI> ().DoneHome = false;
    if (Vector3.Distance (Characters [SelectedCharacter].Instance.transform.position, c.Instance.transform.position) > 10) {
        sequencemanager.Instance.StartCoroutine ("DoCharSwitch", c);
        CanShowSwitch = false;
        LastCharacter = SelectedCharacter;
        SelectedCharacter = Characters.IndexOf (c);
        CurrentCharacter = c;
        Characters [LastCharacter].Instance.GetComponent<PlayerController> ().CanPlay = false;
        Characters [SelectedCharacter].Instance.GetComponent<PlayerController> ().CanPlay = true;
        PlayerPrefs.SetInt ("SelectedChar", SelectedCharacter);

    } else {
        LastCharacter = SelectedCharacter;
        SelectedCharacter = Characters.IndexOf(c);
        CurrentCharacter = c;
        Characters [LastCharacter].Instance.GetComponent<PlayerController> ().CanPlay = false;
        Characters [SelectedCharacter].Instance.GetComponent<PlayerController> ().CanPlay = true;
        PlayerPrefs.SetInt ("SelectedChar", SelectedCharacter);
        Camera.main.GetComponent<SmoothFollow> ().target = Characters [SelectedCharacter].Instance.transform;

    }


}


void OnGUI()
{
    if (ShowCharWheel)
    {
        GUILayout.BeginArea(new Rect(Screen.width - 64, Screen.height - 256, 64, 208), GUIContent.none, "box");
        foreach (Character c in Characters)
        {
            if (GUILayout.Button(c.Icon, GUILayout.Width(64), GUILayout.Height(64)))
            {
                ChangeCharacterStart(c);
            }
        }
    GUILayout.EndArea();
    }
}
    }

  [System.Serializable]
  public class Character
  {
public string Name;
public Texture2D Icon;
public GameObject PlayerPrefab;
public GameObject Instance;
public Transform HomeSpawn;
   }

[System.Serializable]
 public class Item
{
public string Name;
public Texture2D Icon;
public ItemInstance InstancePrefab;
 }

The error is on line

c.Instance = Instantiate(c.PlayerPrefab, c.HomeSpawn.position, c.HomeSpawn.rotation) as GameObject;

This is my editor image with error.The main problem is when I start the game it destroy the gamemanager script.
And another important thing.I migrated this project.I had to reinstall windows.Before that the error didn’t appeared.And now it do.And I am sure I took the whole pro