Example: Interaction + Inventory Loop (Blueprint)

This runnable example stitches together Interaction (trace + interface) and Inventory (DataAssets + replication) into a minimal, network-ready flow.

Goal

• Look at an item, press Use to pick it up, it goes to inventory, UI updates, save/load works, and it replicates correctly.

What you build

• Player Controller: Enhanced Input mapping for Use (IE_Triggered from an Action "IA_Use").
• Character: Line Trace for Objects + Interface call IInteractable.Interact(Instigator) on focus actor.
• Item Actor: Implements IInteractable; has a PrimaryDataAsset reference defining ItemID, StackSize, Tags.
• Inventory Component: ActorComponent with ReplicatedUsing array of FItemStacks; RPCs Server_AddItem, Server_RemoveItem.
• UI: MVVM ViewModel observes Inventory; Widget binds to VM; shows item list.
• SaveGame: Struct snapshot of Inventory; Save/Load Service calls UGameplayStatics save functions.

Blueprint steps (high level)

1. Create GameplayTags: Item.Consumable, Item.Weapon, Item.Currency.
2. Create PDA DA_Item_<Name> with fields: FName ItemID, FGameplayTagContainer Tags, int32 MaxStack.
3. Interface BPI_Interactable: Interact(Actor Instigator).
4. Actor BP_Pickup_<Name>: StaticMesh, PDA ref; Implements BPI_Interactable → On Interact: GetOwnerInventory(Instigator) → Server_AddItem(PDA, Count=1) → DestroyActor.
5. Character BP_Character: Camera; Tick or timer → LineTraceSingleByChannel (Visibility), if Hit Actor ImplementsInterface, set FocusedActor; On Use Input: Execute_Interact(FocusedActor, self).
6. Component BP_InventoryComponent: Replicates true; Array Items of FItemStack { PDA, Count } with ReplicatedUsing OnRep_Items. RPCs: Server_AddItem(PDA, Count); validate and merge stacks; OnRep_Items → Broadcast OnInventoryChanged.
7. ViewModel BP_InventoryVM: Expose Items as Array of FItemView { Name, Icon, Count }; Bind to Inventory component via OnInventoryChanged.
8. Widget WBP_Inventory: ListView bound to VM Items.
9. Save/Load: USaveGame_BP_Inventory with TArray<FItemSave { ItemID, Count }>; Service saves/loads and reconstructs using AssetManager GetPrimaryAssetIdList.
10. Networking: Ensure Use input runs on owning client; Interact triggers Server RPC to mutate inventory; pickups are bReplicates with bNetLoadOnClient false.

Testing

• Singleplayer: pick up/destroy, UI updates, save then reload map, inventory restored.
• Multiplayer PIE 2 clients: authority-only mutations; late joiner sees current inventory via replication and OnRep.

Suggested prompts

• Add/extend prompts from the Interaction and Inventory pages to generate specific Blueprints and validation tests.

Prompts for this example

• "Generate the Blueprint steps to add BP_InventoryComponent with Server_AddItem RPC and OnRep_Items hook; include variables and replication settings."
• "Generate the Interactable interface (BPI_Interactable) and implement it in BP_Pickup_Apple to add one item to the instigator's inventory on interact, then destroy self."
• "Generate the MVVM ViewModel BP_InventoryVM that maps inventory items into a TArray view for a ListView; detail bindings on the WBP_Inventory widget."
• "Write a Save/Load service Blueprint that snapshots and restores the inventory using USaveGame; include a quick test sequence to verify."