get a list attribute

Unity Engine
,
1

Hi,

I’m working on an inventory system but I’m having a problem.

I use a “scriptable Object” for the different items:

[CreateAssetMenu]
public class ItemData : ScriptableObject
{
    public string displayName;
    public Sprite icon;
    public string description;
}

once picked up I store these in a game object which uses the following script which stores them in a list:

public class Inventory : MonoBehaviour
{
    public List<InventoryItem> inventory = new List<InventoryItem>();
    private Dictionary<ItemData, InventoryItem> itemDictionary= new Dictionary<ItemData, InventoryItem>();

8550053--1143152--upload_2022-10-10_15-53-17.png
8550053--1143152--upload_2022-10-10_15-53-17.png933×455 31.6 KB

My problem is that in another script I’m trying to retrieve this list and it’s doesnt seems to work

public Inventory invtPlayer;//gameObject Inventory
    //first try:
    public List<InventoryItem> inventLst = invtPlayer.inventory;
    //second try:
    public List<InventoryItem> inventLst = invtPlayer.GetComponent <List<InventoryItem>>;
2

A “List” is not a “Component”. So using a List type as the type argument of GetComponent wouldn’t work. You have already your Inventory instance reference. You just need to read the “inventory” field of it if you need access to that list.

Though you can not grab the reference to that list in a field initializer as during the time the field initializer runs, none of the serialized fields are initialized yet. You can only do this in a Unity callback like Awake or Start. Though I don’t really see a good reason why you would want to copy the List reference into another member variable of another class. This could cause many other issues (especially with hot-reloading). When you want to access the List of the Inventory, just use

invtPlayer.inventory

Of course this assumes you have actually assigned your Inventory script instance to the invtPlayer variable in the inspector (drag and drop).

3

Fairly common… these things (character customization, inventories, shop systems) are fairly tricky hairy beasts, definitely deep in advanced coding territory. They 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 an inventory 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.

Or… do like I like to do: just jump in and make it up as you go. It is SOFT-ware after all… evolve it as you go! :slight_smile:

Breaking down a large problem such as inventory:

https://discussions.unity.com/t/826141/4

Here is how to get started debugging:

You must find a way to get the information you need in order to reason about what the problem is.

What is often happening in these cases is one of the following:

  • the code you think is executing is not actually executing at all
  • the code is executing far EARLIER or LATER than you think
  • the code is executing far LESS OFTEN than you think
  • the code is executing far MORE OFTEN than you think
  • the code is executing on another GameObject than you think it is
  • you’re getting an error or warning and you haven’t noticed it in the console window

To help gain more insight into your problem, I recommend liberally sprinkling Debug.Log() statements through your code to display information in realtime.

Doing this should help you answer these types of questions:

  • is this code even running? which parts are running? how often does it run? what order does it run in?
  • what are the values of the variables involved? Are they initialized? Are the values reasonable?
  • are you meeting ALL the requirements to receive callbacks such as triggers / colliders (review the documentation)

Knowing this information will help you reason about the behavior you are seeing.

You can also supply a second argument to Debug.Log() and when you click the message, it will highlight the object in scene, such as Debug.Log("Problem!",this);

If your problem would benefit from in-scene or in-game visualization, Debug.DrawRay() or Debug.DrawLine() can help you visualize things like rays (used in raycasting) or distances.

You can also call Debug.Break() to pause the Editor when certain interesting pieces of code run, and then study the scene manually, looking for all the parts, where they are, what scripts are on them, etc.

You can also call GameObject.CreatePrimitive() to emplace debug-marker-ish objects in the scene at runtime.

You could also just display various important quantities in UI Text elements to watch them change as you play the game.

If you are running a mobile device you can also view the console output. Google for how on your particular mobile target, such as this answer or iOS: https://discussions.unity.com/t/700551 or this answer for Android: https://discussions.unity.com/t/699654

Another useful approach is to temporarily strip out everything besides what is necessary to prove your issue. This can simplify and isolate compounding effects of other items in your scene or prefab.

Here’s an example of putting in a laser-focused Debug.Log() and how that can save you a TON of time wallowing around speculating what might be going wrong:

https://discussions.unity.com/t/839300/3

When in doubt, print it out!™

Note: the print() function is an alias for Debug.Log() provided by the MonoBehaviour class.

4

Problem solved
Thank you :wink: