RPG Picking up items with polymorphism - probably quick :)

Question

Hello everyone, I know inventory questions get asked a lot but I have a particular problem that I have not been able to find the answer to because every tutorial and answer seems to conveniently avoid this issue.

Essentially, I'm working on a bit of an RPG, and so I have a BaseItem class (not MonoBehaviour) and a few classes that extend it like BaseWeapon, etc. Then I have a spawn game object in the world with a script attached to it. This script is called something like "SteelSwordSpawnScript" for example, which is MonoBehaviour, and in its start function I would initialize a new BaseItem of type BaseSword and fill the appropriate values for a steel sword in this case. When I pick up the item through a raycast, I obtain the script component and then from that I obtain the actual sword item and add it to an inventory array. The problem is, I need this to work for any possible item. In this way, I'd have to create hundreds of scripts for all the different items and so in my pick-up code I'd have to go through hundreds of possible script names. How can I just make one script, assign it any random BaseItem for any spawn object, and put it my inventory?

Thanks in advance :)

Answer 1

Hi @Andrzej828! From what I understand, you don't want to be defining each of these item types programmatically, but instead want to serialize data for each individual item and save them as assets in your project that you can reuse anywhere. That said, Unity does not support polymorphic serialization, so what you want to do is actually define a class for each item type and then create prefabs or other assets in your project to reference them.

For example, what I would do is something like this (obviously use real data for your game):

 public abstract class BaseItem : ScriptableObject {
     public float Weight {
         get { return m_Weight; } set { m_Weight = Mathf.Max (0f, value); }
     }
     [SerializeFloat, Range (0f, 100f)]
     private float m_Weight;

     protected BaseItem () {}
 }

 [CreateAssetMenu]
 public class Weapon : BaseItem {
     public float Durability {
         get { return m_Durability; } set { m_Durability = Mathf.Clamp01(value);
     }
     [SerializeFloat, Range (0f, 1f)]
     private float m_Durability = 0f;
     
     public float Power {
         get { return m_Power; } set { m_Power = Mathf.Clamp01(value);
     }
     [SerializeFloat, Range (0f, 1f)]
     private float m_Power = 0f;

     protected Weapon () {}
 }

 public class ItemSpawner : MonoBehaviour {
     [SerializeField]
     private BaseItem m_Item;

     protected virtual void Start () {
         // do this so you get a unique instance and don't modify the source asset
         m_Item = Instantiate (m_Item);
     }
 }

With this set up, you create each item as an asset in your project and serialize specific data for it. You can then reference any of these particular item definitions on any of your spawners.

RPG Picking up items with polymorphism - probably quick :)

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