Skip to main content
While ItemDataAsset defines the type of item, FItemInstance represents a specific instance of that item with unique properties. Location: /Public/Inventory/Structures/ItemInstance.h

​
The Difference

Think of it like this:
  • ItemDataAsset = “The concept of an Iron Sword”
  • FItemInstance = “Bob’s Iron Sword with 75% durability that he crafted on Tuesday”

​
FItemInstance Structure

FName ItemID;                              // Which item type
int32 Quantity;                            // Stack size
UItemDataAsset* ItemData;                  // Reference to definition
FGameplayTag RarityTag;                    // Instance rarity
TArray<FStatModifier> StatModifiers;       // Custom stats
FText CrafterName;                         // Who crafted this
TArray<FItemModSlot> Infusions;            // Mods/enchantments
float Durability;                          // Current durability
FDateTime CreationTime;                    // When created
FGuid UniqueID;                            // Globally unique ID
FName OwnerID;                             // Ownership tracking

​
Key Properties Explained

ItemID & ItemData
  • ItemID: Quick reference to item type
  • ItemData: Full reference to the ItemDataAsset
  • Both are kept for performance (ID is faster to check, Data has all info)
Quantity
  • How many items in this stack
  • Must be ≤ ItemData’s MaxStackSize
  • Used for commodities, ammo, resources
Rarity Tag
  • Can override the ItemDataAsset’s default rarity
  • Allows the same sword to drop as Common or Epic
  • Used by loot system for random quality
Stat Modifiers
  • Additional stats beyond the base item
  • Can be additive, multiplicative, or override
  • Example: +5 Attack on top of sword’s base 10 attack
FStatModifier ExtraDamage;
ExtraDamage.StatTag = "Stat.Attack";
ExtraDamage.ModifierType = EStatModifierTypes::Additive;
ExtraDamage.Value = 5.0f;
Crafter Name
  • Displays who crafted the item
  • “Crafted by Thorin”
  • Used for provenance-based stacking
Infusions
  • Applied mods/enchantments
  • Fire damage, frost effect, etc.
  • Each has a power level
FItemModSlot FireMod;
FireMod.SlotTag = "Mod.Element.Fire";
FireMod.ModID = "BurningBrand";
FireMod.ModPower = 1.5f;
FireMod.DisplayName = FText::FromString("Flame Brand");
Durability
  • Current durability value (0.0 to MaxDurability)
  • Used for equipment wear and tear
  • Affects item stacking with durability-based policies
Creation Time
  • When this item was created
  • Used for decay system
  • Freshness for food items
Unique ID
  • Globally unique identifier (GUID)
  • Used for save/load
  • Tracks specific item instances across sessions
Owner ID
  • Tracks who owns this item
  • Used for loot rights
  • Prevents item theft in multiplayer

​
Common Operations

Check if Empty 
if (ItemInstance.IsEmpty())
{
    // No item in this slot
}
Check Stacking Compatibility 
if (ItemInstance.IsStackableWith(OtherInstance))
{
    // Can merge these stacks
}
Get Max Durability 
float MaxDurability = ItemInstance.GetMaxDurability();
Serialization 
// Save
FItemRecord Record = ItemInstance.ToRecord();

// Load
FItemInstance LoadedInstance = FItemInstance::FromRecord(Record);

​
When Are Item Instances Created?

  1. Picking up items: WorldItemActor creates instance
  2. Loot drops: LootComponent generates instances
  3. Crafting: CraftingComponent creates new instance
  4. Quest rewards: Manually created in code/Blueprint
  5. Admin commands: Debug/testing tools