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UInventoryComponentBase ​

Base component responsible for managing items, usage, transfer, and replication in the Inventory System.

Overview ​

The UInventoryComponentBase class handles all core inventory logic for adding, removing, using, transferring, and dropping items. It ensures that all operations are authority-validated and replicated correctly across the network.

All externally accessible functions are BlueprintCallable and automatically perform server validation when called from clients.

Network Behavior ​

All inventory actions follow this flow:

  1. Authority Check If executed on a client, the function calls its Server RPC counterpart automatically.

  2. Validation Ensures that the item is valid and implements IInventoryItemInterface.

  3. Execution Calls the appropriate authority-only internal method (e.g., AttemptAddItem, AttemptRemoveItem).

Inventory Workflow ​

Adding Items ​

Function:

cpp
bool AddItem(UObject* Item, int32 Quantity, int32& RemainingAmount);

Description: Attempts to add an item to the inventory while performing authority and validity checks.

Authority Chain:

AddItem → AttemptAddItem → Server_AddItem

Related Interface Function:IInventoryItemInterface::CanBeAddedToInventory()

Blueprint Events & Delegates:

  • K2_OnItemAdded
  • OnItemChanged_Delegate

Removing Items ​

Functions:

cpp
bool RemoveItem(UObject* Item, int32 Quantity, int32& RemainingAmount);
bool RemoveItemAtIndex(int32 Index, int32 Quantity, int32& RemainingAmount, bool bUseLocalIndex);

Description: Removes an item or quantity from the inventory by object or slot.

Related Interface Function:IInventoryItemInterface::CanBeRemovedFromInventory()

Blueprint Events & Delegates:

  • K2_OnItemRemovedFromInventory
  • OnItemRemovedFromInventoryDelegate

Using Items ​

Functions:

cpp
bool UseItem(UObject* Item, int32 Quantity);
bool UseItemAtIndex(int32 Index, int32 Quantity, bool bUseLocalIndex);

Description: Uses an item, triggering its custom OnUse logic.

Related Interface Function:IInventoryItemInterface::CanBeUsed()

Example Flow:

  1. Validate authority and item.
  2. Check that the Item can be used via IInventoryItemInterface::CanBeUsed()
  3. Call the item’s OnUse implementation.
  4. Update inventory if necessary (e.g., consume item).

Transferring Items ​

Functions:

cpp
bool TransferItem(UObject* Item, int32 Quantity, UInventoryComponentBase* TargetInventory);
bool TransferItemAtIndex(int32 Index, int32 Quantity, UInventoryComponentBase* TargetInventory, bool bUseLocalIndex);

Description: Transfers items from one inventory to another with validation and replication.

Related Interface Function:IInventoryItemInterface::CanBeTransferred()

Dropping Items ​

Functions:

cpp
bool DropItem(UObject* Item, int32 Quantity);
bool DropItemAtIndex(int32 Index, int32 Quantity, bool bUseLocalIndex);

Description: Drops items into the world or environment, triggering the item’s drop logic.

Related Interface Function:IInventoryItemInterface::CanBeDropped()

Item Callback:

cpp
void OnDrop(UInventoryComponentBase* InventoryComponent, int Quantity);

Utility Functions ​

FunctionDescription
GetFreeSlot()Returns the first empty slot index.
GetItemAtIndex(int32 Index)Returns the UObject* stored in a slot.
GetServerIndex(int32 Index)Converts a client-local index to the authoritative server index.
GetInventorySlot(int32 Index)Returns an FInventorySlot struct at the given index.

Replication ​

PropertyTypeDescription
InventoryFInventoryArrayReplicated array containing all inventory slots and items.
InventorySizeintNumber of available slots in the inventory.

Inventory updates trigger replication through OnRep callbacks and OnItemChanged events.

Example: Add & Use Item (C++) ​

cpp
UInventoryComponentBase* Inventory = PlayerCharacter->FindComponentByClass<UInventoryComponentBase>();
UObject* Item = NewObject<UMyPotionItem>();

// This needs to be on the server in order to be used like this
int32 Remaining = 0;
if (Inventory->AddItem(Item, 5, Remaining))
{
    Inventory->UseItem(Item, 1);
}

Flow:

  1. Validate item and authority.
  2. Add item to replicated inventory.
  3. Call the item’s OnUse() implementation.

Best Practices ​

  • ✅ Always implement IInventoryItemInterface in your item classes.
  • ✅ Use delegates (OnItemChanged_Delegate) to update UI efficiently.
  • ✅ Avoid calling authority-only methods from clients.
  • ✅ Use BlueprintImplementableEvent to extend gameplay logic cleanly.

Last Updated: October 2025 Version: 1.1.0