Error: "Use of unassigned local variable 'BoxPrefab'".,"Use of unassigned local variable 'BoxPrefab'

Questions & Answers
1

I’m working on my game, it’s my first project on Unity. In short, it has 3d Grid and box in each grid cell. I need to instantiate Box prefab in each cell, but I’m getting this error: “Assets\BoxGrid.cs(26,67): error CS0165: Use of unassigned local variable ‘BoxPrefab’”.

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

public class BoxGrid
{
    private GameObject BoxPrefab = GameObject.Find("Box");

    private int width;
    private int height;
    private int length;
    private float CellSize;
    private int[,,] BoxGridArray;

    public BoxGrid(int width, int height, int length, float CellSize) {
        this.width = width;
        this.height = height;
        this.length = length;
        this.CellSize = CellSize;

        BoxGridArray = new int[width, height, length];

        for (int x = 0; x < BoxGridArray.GetLength(0); x++) {
            for (int y = 0; y < BoxGridArray.GetLength(1); y++) {
                for (int z = 0; z < BoxGridArray.GetLength(2); z++) {
                    GameObject BoxPrefab = GameObject.Instantiate(BoxPrefab, GetPosition(x, y, z) + new Vector3(CellSize, CellSize, CellSize) * .5f, Quaternion.identity) as GameObject;
                    
                    Debug.DrawLine(GetPosition(x, y, z), GetPosition(x, y, z + 1), Color.white, 100f);
                    Debug.DrawLine(GetPosition(x, y, z), GetPosition(x, y + 1, z), Color.white, 100f);
                    Debug.DrawLine(GetPosition(x, y, z), GetPosition(x + 1, y, z), Color.white, 100f);
                }
            }
        }
    }
    private Vector3 GetPosition(int x, int y, int z) {
        return new Vector3(x, y, z) * CellSize;
    }
}

Code below is other script with MonoBehaviour.

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

public class GridCreate : MonoBehaviour
{
    public void Start() {
        BoxGrid Grid = new BoxGrid(4, 4, 4, 25f);
    }
}

How do I fix this error?

2

In general the underlying issue is that either the GameObject.Find(...) is never executed or the object is not found.

To fix the first possibility i’d suggest you move the initialization code into the constructor:

   public BoxGrid(int width, int height, int length, float CellSize) {
          BoxPrefab = GameObject.Find("Box");

If that still does not work then obviously the Prefab is not Found. Are you sure that the Scene in which you execute this code contains a GameObject that has no parent which has the name "Box"?