The prefab you want to instantiate is null

Scripting
1

This is a simple problem but I can’t figure it out. I’ve declared a public variable in the class definition:

public GameObject cube;

I have then created a test prefab which contains a sphere, and dragged it onto this public variable in the editor. Then back in my script I attampt to instantiate when a button is pressed:

Instantiate(cube,new Vector3(0,0,0),Quaternion.identity);

But I always get the error:
NullReferenceException: The prefab you want to instantiate is null.

I’m going to insert the whole class underneath here in case its something else thats messing things up.

using UnityEngine;

using System.Collections;


public class GuiBehaviour : MonoBehaviour
{
    // define and create our GUI delegate
    private delegate void GUIMethod();
    private GUIMethod currentGUIMethod;
    private int length = 10;
    private int buttonHeight = 30;
    private int spacer = 2;
    //public TopTweetController gameController;
    public GameObject cube;
    
           
    void Start ()
    {
        // start with the main menu GUI
        this.currentGUIMethod = MainMenu;
        iPhoneSettings.screenOrientation = iPhoneScreenOrientation.Portrait;
       
    }
   
    public void MainMenu()
    {
    	
    	// Make a background box
		GUI.Box (new Rect (10,10,300,460), "Main Menu");
		GUI.Label(new Rect(20,350,300,40),"Test String");
		
		for(int i=0;i<length;i++) 
		{
			
			if(GUI.Button (new Rect (20,(spacer*i)+(buttonHeight*i)+30,280,30), "Game "+i.ToString()))
			
			{
				this.currentGUIMethod = threeDView;
			}
		}
		
        if (GUI.Button (new Rect (20,Screen.height-70,280,30), "Options"))
        {
            // options button clicked, switch to new menu
            this.currentGUIMethod = OptionsMenu;
        }
    }
   
    private void OptionsMenu()
    {
    	 // Make a background box
		GUI.Box (new Rect (10,10,300,460), "Options Menu");
		GUI.Label(new Rect(20,350,300,40),"Test String");
		
        if (GUI.Button (new Rect (20,Screen.height-70,280,30), "Main Menu"))
        {
            // go back to the main menu
            this.currentGUIMethod = MainMenu;
        }
    }   
    
    private void threeDView() 
    {
    	GUI.Box (new Rect (10,10,300,460), "3D View");
		GUI.Label(new Rect(20,350,300,40),"Test String");
		
        if (GUI.Button (new Rect (20,Screen.height-70,280,30), "Main Menu"))
        {
            // go back to the main menu
            this.currentGUIMethod = MainMenu;
        }

    	
    	Instantiate(cube,new Vector3(0,0,0),Quaternion.identity);
    }
    


    // Update is called once per frame
    public void OnGUI ()
    {
        this.currentGUIMethod();
    }




}
2

As the error says, the only thing that can be happening is that the instance of your script doesn’t have a prefab in the cube variable.

Did you drag it onto an instance of the script inside the game world or onto the script declaration inside the Unity hierarchy? It doesn’t really work unless you drag it onto an instance of the script. To test this, start your game and click on the object holding the script. If the cube variable is marked as empty, then that’s your problem.