How do I correctly create a reference to a Unity object?

Question

I am new to C# and Unity and am having trouble finding a clear answer to my problem.

I am trying to create a simple TextMeshProUGUI text log buffer in a panel. The buffer itself works fine until I try to access it from another class - I believe because I am not creating the reference to the panel correctly.

Here is my code for the TextMeshProUGUI object collector:

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

public class TextLogControl : MonoBehaviour
{
    public TextMeshProUGUI textPrefab;  // Unity prefab 

    public  List<TextMeshProUGUI> textItems = new List<TextMeshProUGUI>();

    [SerializeField]
    public int maxItems = 100;


    public void LogText(string newTextString, Color newColor)
    {

    Instantiate(textPrefab, transform);

        textPrefab.text = newTextString;

        if (textItems.Count >= maxItems)
        {
            textItems.RemoveAt(0); // I should probably be destroying something, but that's another question
        }

        textPrefab.gameObject.SetActive(true);

        textItems.Add(textPrefab);
    }

    // The above function works correctly if I write a test function within this same class

}

Here is the code for the class that is trying to access the LogText() function:

using System;
using UnityEngine;

public class World : MonoBehaviour
{
    Color defaultColor = Color.black;

    public TextLogControl textLog; 


    public void Init()
    {
        // I need to create a reference here somewhere, but nothing I am trying is working

        textLog.LogText("Welcome - you made it!", defaultColor);

    }
}

I am putting the TextLogControl script on the Unity GameObject that is holding the TMP objects, and that works on its own.

I thought that I was creating a reference to the holder GameObject by dragging it onto my World object in Unity as below, but I am still getting an NRE when I call World.Init(), which means that I'm doing something wrong, but I cannot figure out what.

I thought this would create the reference that is not being created

Edit: The error I'm receiving is

NullReferenceException: Object reference not set to an instance of an object

When trying to run World.Init() - specifically, textLog is null, even though I have got it dragged onto the appropriate spot in Unity (I believe).

Answer 1

As this is so long for comment, A null reference means that it is trying to access something that doesn't exist. You either forgot to drag something in the editor, or you are a step ahead and have something un-commented that should still be commented. Your code is using something that isn't there. I recommend you to add this piece of code to your files to check either the error is coming from NullRefrence of class or the else code.

    TextMeshProUGUIs = textPrefab.GetComponent<TextMeshProUGUI>();
    if (TextMeshProUGUIs == null)
    {
        Debug.LogError("No TextMeshProUGUI component found.");  
    }