> ## Documentation Index
> Fetch the complete documentation index at: https://docs.warpathstudios.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Adding & Removing Items

> The UMI Inventory System provides a flexible and modular way to add, remove, use, transfer, and drop items.

The UMI Inventory System provides a flexible and modular way to **add**, **remove**, **use**, **transfer**, and **drop** items. These actions form the core workflows for any inventory-driven game, including survival, RPG, crafting, and MMO-style mechanics.

This section explains the high-level logic behind how the system handles item flow and links to dedicated pages with detailed Blueprint + C++ examples.

***

## **How UMI Handles Items Internally**

Every item in UMI exists as an **Item Instance** (`FItemInstance`) which contains:

* Item ID
* Reference to its `UItemDataAsset`
* Stack quantity
* Quality / durability / custom fields
* Crafter name (optional)
* Any additional metadata

When adding or removing items, UMI always modifies **item instances**, not data assets.

***

## **Overview of Item Flow**

### **1. Adding Items**

You can add items to an inventory in several ways:

* **By Data Asset** (e.g., adding "5 Health Potions")
* **By Item Instance** (customized items with durability, crafter name, etc.)
* **With Overflow Handling** (e.g., generate world drops when inventory is full)

UMI automatically:

* Finds valid slots
* Merges stacks when possible
* Respects slot/container restrictions
* Respects weight / encumbrance limits
* Returns overflow if items do not fit

🔗 *See:* **Adding Items**

***

### **2. Removing Items**

Items can be removed:

* By Item ID
* By Data Asset
* By slot index
* By taking an item instance directly

UMI calculates exact quantities and prevents partial removes unless requested.

🔗 *See:* **Removing Items**

***

### **3. Using Items**

The inventory can execute an item’s **use behavior**, such as:

* Consuming food / potions
* Triggering abilities
* Reducing stack count
* Destroying or replacing the instance

Usage can be invoked via slot index, UI interaction, or hotbar input.

🔗 *See:* **Using Items**

***

### **4. Weight & Encumbrance**

UMI supports weight-based carry limits. When enabled:

* Items contribute to total weight
* Adding items may fail if too heavy
* Designers may impose movement penalties

Weight is fully optional and can be disabled (MaxWeight = 0).

🔗 *See:* **Weight / Encumbrance**

***

### **5. Container & Slot Restrictions**

UMI allows fine-grained control over what items can be placed in:

* Entire inventories (containers)
* Individual slots (e.g., weapon-only slots)

Restrictions can use:

* Gameplay tags
* Whitelists / blacklists
* Custom Blueprint logic

🔗 *See:* **Container Restrictions**

***

### **6. Sorting & Compacting**

Inventories can be automatically or manually sorted by:

* Name
* Rarity
* Quantity
* Category
* Value
* Custom sorting logic

UMI also supports compacting (removing empty slot gaps).

🔗 *See:* **Sorting System**

***

### **7. Transferring Items Between Inventories**

Items can be transferred:

* Between player inventories
* Between containers
* Into equipment slots
* From hotbar → inventory or vice-versa

Transfers support quantity control and restriction validation.

🔗 *See:* **Transferring Items**

***

### **8. Splitting Stacks**

Stacks can be split either:

* Automatically (half split)
* With custom logic in Blueprint or UI
* During drag-drop operations

🔗 *See:* **Splitting Stacks**

***

### **9. Dropping Items into the World**

Items can be spawned as physical world objects using:

* Drop by slot
* Drop by instance
* Drop at target location
* Overflow drop during AddItem operations

World items integrate with the Interaction System.

🔗 *See:* **Dropping Items**

***

## **When to Use Each Function**

| Action                        | When to Use It                                                  |
| ----------------------------- | --------------------------------------------------------------- |
| **AddItem**                   | Standard item grants, pickups, crafting outputs                 |
| **AddItemInstance**           | Items with durability, quality, custom metadata                 |
| **TryAddItem**                | Adding items when space/weight restrictions may block placement |
| **RemoveItem / TakeItem**     | Consuming items, moving items to UI widgets or equipment        |
| **UseItem**                   | Potions, food, consumables, abilities                           |
| **TransferItem**              | Looting containers, trading, stash systems                      |
| **SplitStack**                | Drag/drop UIs, inventory management                             |
| **DropItem / SpawnWorldItem** | Throwing items, world pickups, death drop behaviors             |

***

## **System Responsibilities Summary**

UMI handles:

* Slot searching and stack merging
* Quantity validation
* Weight and capacity checks
* Restriction enforcement
* Overflow handling
* Instance creation and replication
* UI event broadcasting

You only need to call the appropriate function — UMI takes care of the internal logic.