FInventoryArray

A replicated container for all inventory slots within an UInventoryComponentBase. Handles replication, synchronization, and change tracking via Unreal’s FFastArraySerializer.

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Overview

FInventoryArray is the core replicated data structure used by the Inventory System to manage and synchronize item data between the server and connected clients.

It holds a list of FInventorySlot entries and provides a custom fast array serializer for efficient delta replication.

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Struct Declaration

class UInventoryComponentBase;

USTRUCT(BlueprintType)
struct FInventoryArray : public FFastArraySerializer
{
    GENERATED_BODY()

    UPROPERTY(VisibleAnywhere, BlueprintReadOnly, Category = "Inventory")
    TArray<FInventorySlot> Items;

    UPROPERTY(VisibleAnywhere, Category = "Inventory")
    TWeakObjectPtr<UInventoryComponentBase> OwningInventory;
    
    bool NetDeltaSerialize(FNetDeltaSerializeInfo & DeltaParms)
    {
        return FFastArraySerializer::FastArrayDeltaSerialize<FInventorySlot, FInventoryArray>(
            Items, DeltaParms, *this
        );
    }

    void MarkInventorySlotDirty(FInventorySlot& InventorySlot, FInventorySlot NewSlotInfo, bool bDeferred);
};

template<>
struct TStructOpsTypeTraits<FInventoryArray> : public TStructOpsTypeTraitsBase2<FInventoryArray>
{
    enum { WithNetDeltaSerializer = true };
};

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Key Responsibilities

• Manages the internal array of inventory slots (Items).
• Handles fast delta serialization for network replication.
• Notifies the owning inventory when a slot is updated or changed.
• Supports deferred or immediate dirty marking for optimized network updates.

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Properties

Property	Type	Description
Items	TArray<FInventorySlot>	Holds all inventory slot entries belonging to this inventory.
OwningInventory	TWeakObjectPtr<UInventoryComponentBase>	Weak pointer to the inventory component that owns this array.

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Replication

FInventoryArray leverages Unreal Engine’s FFastArraySerializer for efficient network replication of the inventory’s state.

When items are added, removed, or modified, only changed entries are sent over the network rather than the entire array.

bool NetDeltaSerialize(FNetDeltaSerializeInfo& DeltaParms)
{
    return FFastArraySerializer::FastArrayDeltaSerialize<FInventorySlot, FInventoryArray>(
        Items, DeltaParms, *this
    );
}

template<>
struct TStructOpsTypeTraits<FInventoryArray> : public TStructOpsTypeTraitsBase2<FInventoryArray>
{
    enum { WithNetDeltaSerializer = true };
};

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Function: MarkInventorySlotDirty

Marks a specific inventory slot as dirty (changed), which triggers replication updates and informs the owning inventory of the modification.

void FInventoryArray::MarkInventorySlotDirty(
    FInventorySlot& InventorySlot, 
    FInventorySlot NewSlotInfo, 
    bool bDeferred
)
{
    if (bDeferred)
    {
        UE_LOG(LogTemp, Warning, TEXT("Marking Inventory Slot Dirty Deferred"));
    }
    else
    {
        UE_LOG(LogTemp, Warning, TEXT("Marking Inventory Slot Dirty"));

        InventorySlot.Item = NewSlotInfo.Item;
        InventorySlot.Quantity = NewSlotInfo.Quantity;
        InventorySlot.ServerIndex = NewSlotInfo.ServerIndex;

        MarkItemDirty(InventorySlot);

        if (OwningInventory.IsValid())
        {
            OwningInventory->OnItemChanged(InventorySlot);
        }
    }
}

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Parameters

Name	Type	Description
InventorySlot	FInventorySlot&	The existing slot in the array to update.
NewSlotInfo	FInventorySlot	The new slot data (item, quantity, index).
bDeferred	bool	Whether to defer replication marking (for batch updates).

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Behavior

• When bDeferred == true, the change is logged but not immediately replicated.
• When bDeferred == false, the slot is updated, marked dirty for replication, and the owning inventory’s OnItemChanged event is triggered.

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Integration

FInventoryArray is owned and managed by the UInventoryComponentBase, which uses it for all item storage, replication, and change handling.

Relationship Diagram

UInventoryComponentBase
        │
        ▼
  FInventoryArray
        │
        ▼
  TArray<FInventorySlot>

Each FInventorySlot represents a single stack of items (object reference + quantity).

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Example Usage

void FInventoryArray::MarkInventorySlotDirty(FInventorySlot& InventorySlot, FInventorySlot NewSlotInfo, bool bDeferred)
{
    if (!bDeferred)
    {
        InventorySlot = NewSlotInfo;
        MarkItemDirty(InventorySlot);
        
        if (OwningInventory.IsValid())
        {
            OwningInventory->OnItemChanged(InventorySlot);
        }
    }
}

When MarkItemDirty() is called, Unreal Engine automatically triggers replication updates for that entry.

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Summary

• FInventoryArray is the replication backbone of the inventory system.

• It maintains all inventory slots and syncs them efficiently over the network.

• Handles slot change notifications and replication optimization through FFastArraySerializer.

• Works closely with:

  • FInventorySlot
  • UInventoryComponentBase