Adding & Removing 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.

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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.

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Overview of Item Flow

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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

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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

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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

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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

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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

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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

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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

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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

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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

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When to Use Each Function

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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.