Inventories

What is this?

Each Inventory you declare is stored as a single per-player weak_map (not N×2 individual variables), persisted across disconnects. Every slot holds an ItemId:int and a Qty:int. It's the building block for any gameplay that manages items beyond Fortnite's native loadout.

Inventories are not UEFN Item Granter / Item Remover devices. Those hand or strip Fortnite items in the player's native loadout (atoms grant_item, remove_item); an Inventory tracks your game's items in your own slot storage.

When do I need it?

• Backpack — a 20-slot grid of collected materials, potions, keys.
• Hotbar — 5 quick-access slots a HUD widget renders.
• Crafting grid — fixed slots that feed a recipe matcher.
• Quest items — 1-slot “quest log” holding the current objective token.

Walkthrough: add a backpack

1. 1

   Open Game Data → Inventories

   The empty state offers the 20-slot backpack pattern as a one-click starter.
2. 2

   Name + slot count

   + Add Inventory. Name it backpack, slot count 20. The slot count is fixed — pick something that fits the UI. The ID also doubles as the HUD prefix for the slot widgets.
3. 3

   Add items via rules

   In a rule: WHEN On Collectible Collected → DO Collect Item to Inventory (backpack, itemId). The Collect action checks for room first, then fills the first matching stack or empty slot; if there's no room it shows a “full” popup instead.
4. 4

   Display on HUD

   In the HUD editor, the Widgets panel shows an Inventory grids section — one click drops a grid bound to backpack. Each slot binds to backpack_N_id / backpack_N_qty (also pickable in any Text/Bar widget's Linked Variable dropdown).

React to inventory state

Inventories are not write-only. Two conditions let rules branch on their contents, and two actions mutate them safely:

• Inventory Has Item (inventory_has_item) — true when a given item ID is held in any slot.
• Inventory Is Full (inventory_is_full) — true when no slot is free.
• Collect Item to Inventory (inventory_collect) — add with a room check + feedback popups.
• Buy Item (Safe) (inventory_buy) — atomic spend-currency + add-item (no money lost if the bag is full).
• Reset Inventory Array (reset_inventory) — clear all slots (e.g. on respawn).

Common patterns

20-slot backpack

Default pattern. Per-player, persistent. Pairs with inventory_collect on collectible events and inventory_buy for shop purchases; gate the shop button with inventory_is_full.

Fixed hotbar

A 5-slot inventory pinned to the HUD. Often pre-filled on On Player Joined with starter items.

Quest log

Single-slot inventory holding the active quest token. Branch with inventory_has_item to check progress; pair with a tracker device.

Gotchas

What gets generated?

One shared slot class, a persistable container, and a single per-player weak_map — plus index-based helpers inside the device:

# Shared slot type (ItemId is an int; 0 = empty)
inventory_slot := class<final><persistable>:
    ItemId:int = 0
    Qty:int = 0

# Container — class as weak_map value (extensible post-publish)
inventory_store := class<final><persistable>:
    Version:int = 0
    Slots:[]inventory_slot = array{}

# Per-player persistent storage — one weak_map per inventory
var Backpack : weak_map(player, inventory_store) = map{}

# Inside the device — index-based helpers (excerpt)
GetBackpackQty(Player:player, Index:int):int = ...
FindBackpackEmpty(Player:player):int = ...   # first empty slot, or -1 if full
AddItemToBackpack(Player:player, ItemId:int, Qty:int):void = ...