Create Scriptable Object with constant, Unique ID

Question

I use Scriptable Objects to create Items for my Unity Game. Let's say I create a Stick, a Sword and a Helmet. Now to use them, I need to drag them into a list and on game start, each item get's an ID assigned which is also the position in the list, as I simply loop through the list to assign ID's. Now I can access the item by using the index it has or, as shown in most of the tutorials about ScriptableObjects, we can then add the item and the id to a Dictionary to better access them.

Stick is 0, Sword is 1 and Helmet is 2. Now I decide to remove the sword with a patch so helmet gets the ID of 1. Now every savegame is broken as swords become helmets.

How can I handle assigning fixed ID's which wont change and wont be taken by another item until I really want to assign it again? I could of course hard-code the id for every ScriptableObject I create but as you can imagine, managing hard-coded IDs seems not like a good idea.

Answer 1

Here is my take on it :

1. Create a custom attribute "ScriptableObjectIdAttribute", you can use it in front of whatever you need to be an id.
2. Make a custom property drawer in order to initialize the id the first time you access the object in the inspector and also to make it non-editable by the inspector.
3. (Optional) Make a base class with that Id property and extend all your ScriptableObjects which need a unique Id from it.

BaseScriptableObject.cs :

using System;
using UnityEditor;
using UnityEngine;

public class ScriptableObjectIdAttribute : PropertyAttribute { }

#if UNITY_EDITOR
[CustomPropertyDrawer(typeof(ScriptableObjectIdAttribute))]
public class ScriptableObjectIdDrawer : PropertyDrawer {
    public override void OnGUI(Rect position, SerializedProperty property, GUIContent label) {
        GUI.enabled = false;
        if (string.IsNullOrEmpty(property.stringValue)) {
            property.stringValue = Guid.NewGuid().ToString();
        }
        EditorGUI.PropertyField(position, property, label, true);
        GUI.enabled = true;
    }
}
#endif

public class BaseScriptableObject : ScriptableObject {
    [ScriptableObjectId]
    public string Id;
}

Weapon.cs :

using System;
using UnityEngine;

[CreateAssetMenu(fileName = "weapon", menuName = "Items/Weapon")]
public class Weapon : BaseScriptableObject {
    public int Attack;
    public int Defence;
}

Result :