In this lesson, you will learn how to use Interfaces to allow C++ and Blueprints to talk to each other without needing to know each other's specific class types.
The Problem: Tight Coupling
When you write code that directly references a specific class (like AEnemy), your project becomes brittle. If you want a Player to be able to "Interact" with both a Chest and an NPC, you would normally have to cast to both types. This creates a mess of dependencies. Interfaces solve this by creating a "contract" that says, "I don't care what you are, as long as you promise to perform this action."
Defining the Interface
In C++, you define an interface by inheriting from UInterface. This creates two classes: the interface itself and its configuration class.
UINTERFACE(MinimalAPI)
class UInteractable : public UInterface { GENERATED_BODY() };
class IInteractable {
GENERATED_BODY()
public:
// This allows Blueprints to implement this logic
UFUNCTION(BlueprintNativeEvent, Category = "Interaction")
void OnInteract();
};
Decoupled Communication
The magic happens when you trigger this interface from your C++ code. Instead of checking if an object is an AChest or an ANPC, you simply check if the object implements IInteractable.
if (OtherActor->GetClass()->ImplementsInterface(UInteractable::StaticClass()))
{
// This calls the function on the actor, whether it's C++ or a Blueprint
IInteractable::Execute_OnInteract(OtherActor);
}
Why This Matters
By using BlueprintNativeEvent, you create a powerful bridge. You can write default logic in C++ and let your designers override that logic in a specific Blueprint (like a BP_TreasureChest) without the C++ class ever needing to "know" about the chest’s existence.
This creates polymorphic communication: the player simply sends an "Interact" message, and the receiving object handles it based on its own implementation. You no longer need long chains of Cast nodes, making your codebase cleaner and much easier to maintain as your project grows.
Key Takeaway: Interfaces allow you to define common behaviors that disparate C++ and Blueprint classes can implement, enabling your objects to communicate effectively without being tightly coupled to one another.