Bug NullReferenceException Error

Hi everyone!
I'm trying to make an inventory system that allows the player to take an object that they just bought and place it into a chest with "slots" available to drag and drop the object into


using System.Collections.Generic;
using System.Runtime.InteropServices;
using UnityEngine;
using UnityEngine.EventSystems;
using UnityEngine.UI;
public class Spawn : MonoBehaviour, IBeginDragHandler, IDragHandler, IEndDragHandler
{
public string itemName;
public int itemPrice;
private Image image;
private Slotscript _slotscript;
//gptcode
private Transform _originalParent;
private Vector3 _originalPosition;

private void Awake()
{
image = GetComponent<Image>();
_slotscript= GetComponent<Slotscript>();

}
public void OnBeginDrag(PointerEventData PointerEventData)
{
_originalParent = transform.parent;
_originalPosition = transform.localPosition;
transform.SetParent(transform.root);
transform.SetAsLastSibling();
}
public void OnDrag(PointerEventData eventData)
{
transform.position = eventData.position;
}
public void OnEndDrag(PointerEventData pointerEventData)
{
Debug.Log($"{gameObject.name} -- OnEndDrag");
var chestGraphicRaycaster = SceneResources.Instance.ChestCanvasRaycaster;
List<RaycastResult> hits = new List<RaycastResult>();
chestGraphicRaycaster.Raycast(pointerEventData, hits);

foreach (var hit in hits)
{
var _name = hit.gameObject.name;
Debug.Log($"Chest Canvas: { _name}");
var gameObject = hit.gameObject;
var slotScript = gameObject.GetComponent<Slotscript>();
if ( slotScript != null )
{
slotScript.AddItemToSlot(itemName, image.sprite, itemPrice);
transform.SetParent(gameObject.transform);
transform.localPosition = Vector3.zero;

_slotscript.IsEmpty();
return;




}
}
}
}

This is the script attached to the items that player purchases that they can then drag into a chest.
The item stores into the slots however the console shows the following error:

NullReferenceException: Object reference not set to an instance of an object
Spawn.OnEndDrag (UnityEngine.EventSystems.PointerEventData pointerEventData) (at Assets/Scripts/Spawn.cs:64)

line 64 being : _slotscript.IsEmpty();

I'm confused as to how to solve this error

 

Null reference exception means your object is null (has not been assigned yet). I think you're confusing _slotscript with slotscript.

 

I want to eat an apple, I put my hand into a bag, and there is none. If there is none (nothing, null) I can't eat an apple. I must fill the bag with apples.

Function _slotscript.IsEmpty() is equal to function apple.Eat().

 

How to fix a NullReferenceException error

https://forum.unity.com/threads/how-to-fix-a-nullreferenceexception-error.1230297/

Three steps to success:
- Identify what is null <-- any other action taken before this step is WASTED TIME
- Identify why it is null
- Fix that

Before you get too far down this rabbit hole:

Just beware:

These things (inventory, shop systems, character customization, dialog tree systems, crafting, etc) are fairly tricky hairy beasts, definitely deep in advanced coding territory.

Inventory code never lives "all by itself." All inventory code is EXTREMELY tightly bound to prefabs and/or assets used to display and present and control the inventory. Problems and solutions must consider both code and assets as well as scene / prefab setup and connectivity.

Inventories / shop systems / character selectors all contain elements of:

- a database of items that you may possibly possess / equip
- a database of the items that you actually possess / equip currently
- perhaps another database of your "storage" area at home base?
- persistence of this information to storage between game runs
- presentation of the inventory to the user (may have to scale and grow, overlay parts, clothing, etc)
- interaction with items in the inventory or on the character or in the home base storage area
- interaction with the world to get items in and out
- dependence on asset definition (images, etc.) for presentation

Just the design choices of such a system can have a lot of complicating confounding issues, such as:

- can you have multiple items? Is there a limit?
- if there is an item limit, what is it? Total count? Weight? Size? Something else?
- are those items shown individually or do they stack?
- are coins / gems stacked but other stuff isn't stacked?
- do items have detailed data shown (durability, rarity, damage, etc.)?
- can users combine items to make new items? How? Limits? Results? Messages of success/failure?
- can users substantially modify items with other things like spells, gems, sockets, etc.?
- does a worn-out item (shovel) become something else (like a stick) when the item wears out fully?
- etc.

Your best bet is probably to write down exactly what you want feature-wise. It may be useful to get very familiar with an existing game so you have an actual example of each feature in action.

Once you have decided a baseline design, fully work through two or three different inventory tutorials on Youtube, perhaps even for the game example you have chosen above.

Breaking down a large problem such as inventory:

https://forum.unity.com/threads/weapon-inventory-and-how-to-script-weapons.1046236/#post-6769558

If you want to see most of the steps involved, make a "micro inventory" in your game, something whereby the player can have (or not have) a single item, and display that item in the UI, and let the user select that item and do things with it (take, drop, use, wear, eat, sell, buy, etc.).

Everything you learn doing that "micro inventory" of one item will apply when you have any larger more complex inventory, and it will give you a feel for what you are dealing with.

Breaking down large problems in general:

https://forum.unity.com/threads/opt...n-an-asteroid-belt-game.1395319/#post-8781697

If you insist on continuing and you are using a tutorial, BE SURE YOU DO IT PROPERLY:

Tutorials and example code are great, but keep this in mind to maximize your success and minimize your frustration:

How to do tutorials properly, two (2) simple steps to success:

Step 1. Follow the tutorial and do every single step of the tutorial 100% precisely the way it is shown. Even the slightest deviation (even a single character!) generally ends in disaster. That's how software engineering works. Every step must be taken, every single letter must be spelled, capitalized, punctuated and spaced (or not spaced) properly, literally NOTHING can be omitted or skipped.

Fortunately this is the easiest part to get right: Be a robot. Don't make any mistakes.
BE PERFECT IN EVERYTHING YOU DO HERE!!

If you get any errors, learn how to read the error code and fix your error. Google is your friend here. Do NOT continue until you fix your error. Your error will probably be somewhere near the parenthesis numbers (line and character position) in the file. It is almost CERTAINLY your typo causing the error, so look again and fix it.

Step 2. Go back and work through every part of the tutorial again, and this time explain it to your doggie. See how I am doing that in my avatar picture? If you have no dog, explain it to your house plant. If you are unable to explain any part of it, STOP. DO NOT PROCEED. Now go learn how that part works. Read the documentation on the functions involved. Go back to the tutorial and try to figure out WHY they did that. This is the part that takes a LOT of time when you are new. It might take days or weeks to work through a single 5-minute tutorial. Stick with it. You will learn.

Step 2 is the part everybody seems to miss. Without Step 2 you are simply a code-typing monkey and outside of the specific tutorial you did, you will be completely lost. If you want to learn, you MUST do Step 2.

Of course, all this presupposes no errors in the tutorial. For certain tutorial makers (like Unity, Brackeys, Imphenzia, Sebastian Lague) this is usually the case. For some other less-well-known content creators, this is less true. Read the comments on the video: did anyone have issues like you did? If there's an error, you will NEVER be the first guy to find it.

Beyond that, Step 3, 4, 5 and 6 become easy because you already understand!

Finally, when you have errors, don't post here... just go fix your errors! Here's how:

Remember: NOBODY here memorizes error codes. That's not a thing. The error code is absolutely the least useful part of the error. It serves no purpose at all. Forget the error code. Put it out of your mind.

The complete error message contains everything you need to know to fix the error yourself.

The important parts of the error message are:

- the description of the error itself (google this; you are NEVER the first one!)
- the file it occurred in (critical!)
- the line number and character position (the two numbers in parentheses)
- also possibly useful is the stack trace (all the lines of text in the lower console window)

Always start with the FIRST error in the console window, as sometimes that error causes or compounds some or all of the subsequent errors. Often the error will be immediately prior to the indicated line, so make sure to check there as well.

Look in the documentation. Every API you attempt to use is probably documented somewhere. Are you using it correctly? Are you spelling it correctly?

All of that information is in the actual error message and you must pay attention to it. Learn how to identify it instantly so you don't have to stop your progress and fiddle around with the forum.

 

ALSO... what on earth are you using InteropServices for?!!! Is that just the Jet-For-Brains Rider adding extra usings???

For future reference;

If you post a code snippet, ALWAYS USE CODE TAGS:

How to use code tags: https://forum.unity.com/threads/using-code-tags-properly.143875/