Null Reference Exception

[RomarioRaven]

Hi,

I have an error in my Console after clicking ‘Play Game’ on the scene ‘Start’. Is in some ways similar issue to the one that Steven have (here is a link).

Here is a Console output:

The mentioned ‘Level.cs’ code lines 26-30:

    public void LoadGame()
    {
        SceneManager.LoadScene("Game");
        FindObjectOfType<PlaySession>().ResetGame();
    }

The code in ‘PlaySession.cs’ (in a unity tutorial the name for this file is GameSession):

    public void ResetGame()
    {
        Destroy(gameObject);
    } 

I’m not sure what is wrong with that section. Any ideas?

Thanks
RR

[Nina]

Hi Romario,

Welcome to our community!

NullReferenceException means that a reference (“link”) to an instance is missing. Is there a PlaySession object in your scene?

[RomarioRaven]

Yes, it is.

Here is an screen grab from ‘Game’ scene hierarchy:

Here is a screen grab from ‘Game’ scene ‘Play Session’ inspector:

RR

[Nina]

Thank you. That looks fine so far.

Is your PlaySession object a “singleton”? If so, check if you have gameObject.SetActive(false); in the same code block as the Destroy method.

[RomarioRaven]

Nina,

I have a singleton in in ‘PlaySession’ that is added to Play Session object:

    private void Awake()
    {
        ScreenScore();
    }

but don’t have a gameObject.SetActive(false); added to ‘RestedGame’ destroy method.

I will add it and check if that’s help.

RR

[RomarioRaven]

Updating ‘ResetGame’ to:

    public void ResetGame()
    {
        gameObject.SetActive(false);
        Destroy(gameObject);
    } 

didn’t help

RR

[Nina]

That isn’t the “singleton”.

[RomarioRaven]

The ‘ScreenScore’ is a singleton. Here is a rest of the code:

    private void Awake()
    {
        ScreenScore();
    }

    private void ScreenScore()
    {
        int numberOfSessions = FindObjectsOfType<PlaySession>().Length;

        if (numberOfSessions > 1)
        {
            Destroy(gameObject);
        }
        else
        {
            DontDestroyOnLoad(gameObject);
        }
    }

It’s based on the unity course, section 115 (31_id_cud), You can watch video. I didn’t use method name ‘SetUpSingleton’. Used my own naming convention.

RR

[Nina]

I meant this potential fix:

        if (numberOfSessions > 1)
        {
            gameObject.SetActive(false);
            Destroy(gameObject);
        }

[RomarioRaven]

Thanks Nina, but this solution didn’t help. The error is still showing.

I think I forgot to mentioned that the error appears when I click ‘Play Game’ at the beginning. I mean when I run the game preview from ‘Start’.

RR

[Nina]

In which scene do you press the play button? In the Start scene? And then you click on Play Game? If so, double click on the error message in your console.

[RomarioRaven]

Yes, I click the ‘Play Game’ button in the ‘Start’ scene. If I double click the error message in my VS I have highlighted this line:

        FindObjectOfType<PlaySession>().ResetGame();

line in 'Level.cs"

Here is the rest of the error message:

UnityEngine.Events.InvokableCall.Invoke () (at <480508088aee40cab70818ff164a29d5>:0)
UnityEngine.Events.UnityEvent.Invoke () (at <480508088aee40cab70818ff164a29d5>:0)
UnityEngine.UI.Button.Press () (at D:/App/Unity/2019.3.13f1/Editor/Data/Resources/PackageManager/BuiltInPackages/com.unity.ugui/Runtime/UI/Core/Button.cs:68)
UnityEngine.UI.Button.OnPointerClick (UnityEngine.EventSystems.PointerEventData eventData) (at D:/App/Unity/2019.3.13f1/Editor/Data/Resources/PackageManager/BuiltInPackages/com.unity.ugui/Runtime/UI/Core/Button.cs:110)
UnityEngine.EventSystems.ExecuteEvents.Execute (UnityEngine.EventSystems.IPointerClickHandler handler, UnityEngine.EventSystems.BaseEventData eventData) (at D:/App/Unity/2019.3.13f1/Editor/Data/Resources/PackageManager/BuiltInPackages/com.unity.ugui/Runtime/EventSystem/ExecuteEvents.cs:50)
UnityEngine.EventSystems.ExecuteEvents.Execute[T] (UnityEngine.GameObject target, UnityEngine.EventSystems.BaseEventData eventData, UnityEngine.EventSystems.ExecuteEvents+EventFunction`1[T1] functor) (at D:/App/Unity/2019.3.13f1/Editor/Data/Resources/PackageManager/BuiltInPackages/com.unity.ugui/Runtime/EventSystem/ExecuteEvents.cs:261)
UnityEngine.EventSystems.EventSystem:Update() (at D:/App/Unity/2019.3.13f1/Editor/Data/Resources/PackageManager/BuiltInPackages/com.unity.ugui/Runtime/EventSystem/EventSystem.cs:377)

[Naxos84]

I’m not a c# developer (yet).

But the only point where a “null exception” can occur is when invoking “ResetGame()” on something that is “null”.

Could you please try the following:
print(FindObjectOfType<PlaySession>());

and check wether it prints something other than null

[Coach_Butters]

I have the same issue. Debug.Log(FindObjectOfType< PlaySession>()); returns null

[Coach_Butters]

Issue was resolved by putting a PlaySession Prefab into the starting scene.

[Naxos84]

Good that you have found the problem.