Inventory System Problem

Here is my codes :

Item Database:

Code (CSharp):

1. using System.Collections;
2. using System.Collections.Generic;
3. using UnityEngine;
4. using LitJson;
5. using System.IO;
6. using UnityEngine.UI;
7.  
8. public class ItemDatabase : MonoBehaviour {
9.     private List<Item> database = new List<Item>();
10.     private JsonData itemData;
11.  
12.  
13.     void Start()
14.     {
15.         itemData = JsonMapper.ToObject(File.ReadAllText(Application.dataPath + "/StreamingAssets/Item.json"));
16.         ConstructItemDatabase();
17.         Debug.Log(FetchItemByID(1).Description);
18.     }
19.  
20.     public Item FetchItemByID(int id) {
21.         for (int i = 0; i < database.Count; i++)
22.         {
23.  
24.             if (database[i].ID == id)
25.  
26.                 return database[i];
27.         }
28.             return null;
29.      
30.     }
31.  
32.  
33.  
34.     void ConstructItemDatabase() {
35.         for (int i = 0; i < itemData.Count; i++) {
36.             database.Add(new Item((int)itemData[i]["id"], itemData[i]["title"].ToString(), (int)itemData[i]["value"], (int)itemData[i]["stats"]["power"], (int)itemData[i]["stats"]["defence"], (int)itemData[i]["stats"]["weight"], itemData[i]["description"].ToString(), (bool)itemData[i]["stackable"], (int)itemData[i]["rarity"], itemData[i]["slug"].ToString(), itemData[i]["type"].ToString()));
37.         }
38.     }
39. }
40.  
41. public class Item {
42.     public int ID { get; set; }
43.     public string Title { get; set; }
44.     public int Value { get; set; }
45.     public int Power { get; set; }
46.     public int Defence { get; set; }
47.     public int Weight { get; set; }
48.     public string Description { get; set; }
49.     public bool Stackable { get; set; }
50.     public int Rarity { get; set; }
51.     public string Slug { get; set; }
52.     public string Type { get; set; }
53.  
54.     public Item(int id, string title, int value, int power, int defence, int weight, string description, bool stackable, int rarity, string slug, string type){
55.         this.ID = id;
56.         this.Title = title;
57.         this.Value = value;
58.         this.Power = power;
59.         this.Defence = defence;
60.         this.Weight = weight;
61.         this.Description = description;
62.         this.Stackable = stackable;
63.         this.Rarity = rarity;
64.         this.Slug = slug;
65.         this.Type = type;
66.  
67.     }
68.  
69.    public Item() {
70.         this.ID = -1;
71.     }
72. }

Inventory Database:

Code (CSharp):

1. using System.Collections;
2. using System.Collections.Generic;
3. using UnityEngine;
4. using UnityEngine.UI;
5.  
6. public class InventoryDatabase : MonoBehaviour {
7.  
8.     GameObject InvPanel;
9.     GameObject SlotPanel;
10.     ItemDatabase database;
11.     public GameObject InvSlots;
12.     public GameObject InvItems;
13.  
14.     public int slotAmount = 20;
15.     public List<Item> items = new List<Item>();
16.     public List<GameObject> slots = new List<GameObject>();
17.  
18.     // Use this for initialization
19.     void Start () {
20.         AddItem(0);
21.         database = GetComponent<ItemDatabase>();
22.         InvPanel = GameObject.Find("InvPanel");
23.         SlotPanel = InvPanel.transform.Find("SlotPanel").gameObject;
24.         for (int i = 0; i < slotAmount; i++) {
25.             items.Add(new Item());
26.             slots.Add(Instantiate(InvSlots));
27.             slots[i].transform.SetParent(SlotPanel.transform);
28.         }
29.     }
30.  
31.  
32.  
33.  
34.     public void AddItem (int id) {
35.        Item itemToAdd = database.FetchItemByID(id);
36.        for (int i = 0; i < items.Count; i++) {
37.             if (items[i].ID == -1) {
38.                 items[i] = itemToAdd;
39.                 GameObject itemObj = Instantiate(InvItems);
40.                 itemObj.transform.SetParent(slots[i].transform);
41.                 itemObj.transform.position = Vector2.zero;
42.                 break;
43.             }
44.         }
45.     }
46. }
47.  

and it returns :
NullReferenceException: Object reference not set to an instance of an object
InventoryDatabase.AddItem (Int32 id) (at Assets/Scripts/InventoryDatabase.cs:35)
InventoryDatabase.Start () (at Assets/Scripts/InventoryDatabase.cs:20)

the error is clearly on this "Item itemToAdd = database.FetchItemByID(id);" line of code, yet i cannot seem to fix it, the function FetchByItemID() is alright, it works, yet i have no clue what happend

 

It might be the starts weren't in the right order. Maybe try putting the database in the awake.

 

database is null. You're doing this:

Code (csharp):

1. AddItem(0);
2. database = GetComponent<ItemDatabase>();

so you're trying to add an item to the database before you've fetched it. That won't work. Just swap the lines.

 

Thank you!!!!! I am so dumb!