Interface

Official Documentation: docs.unrealengine.com.

Create Interface

First, Create a new C++ file in the Unreal Engine Editor and select Unreal Interface as the Parent Class. Also, if you want to trigger it OnOverlap, dont forget to enable OverlapAllDynamics in your Details Panel for the Actors that Interact with eachother.

tip

Interface is great to interact between Actors

YourInterface.h
#pragma once

#include "CoreMinimal.h"
#include "UObject/Interface.h"
#include "YourInterface.generated.h"

// This class does not need to be modified.
UINTERFACE(MinimalAPI)
class UYourInterface : public UInterface
{
  GENERATED_BODY()
};

/**
* 
*/
class YOURGAME_API IYourInterface
{
  GENERATED_BODY()

  // Add interface functions to this class. This is the class that will be inherited to implement this interface.
public:
  // for this example were creating a Interact function
  virtual void Interact() = 0; // = 0; so we signal, to the compiler that there is no implementation of this function in the YourInterface.cpp
};

Setup the Actor you want to Interact with, in this case SomeActor

SomeActor.h
#pragma once

#include "CoreMinimal.h"
#include "GameFramework/Actor.h"
#include "YourInterface.h" // include your Interface file
#include "SomeActor.generated.h"

UCLASS()
// extend your class with your Interface
class YOURGAME_API ASomeActor : public AActor, public IYourInterface // add Interface here
{
  GENERATED_BODY()

public:	
  ASomeActor();
  
  // Our Interact function from YourInterface.h
  virtual void Interact() override;
...
}

SomeActor.cpp
#include "SomeActor.h"

ASomeActor::ASomeActor()
{
  //
}

// Called when the game starts or when spawned
void ASomeActor::BeginPlay()
{
  Super::BeginPlay();
}

void ASomeActor::Interact()
{
  // define what SomeActor should do on Interact
  // in this case we just print a log to the console
  UE_LOG(LogTemp, Warning, TEXT("You Successfully Interacted with SomeActor"));
}

For this example we'll call the interface from YourCharacter Class

YourCharacter.h
#include "YourInterface.h" // add the Interface file

YourCharacter.cpp
#include "YourCharacter.h

AYourCharacter::AYourCharacter()
{
  //
}

// Called when the game starts or when spawned
void AYourCharacter::BeginPlay()
{
  Super::BeginPlay();
}

// For demonstration purposes: We'll just cast a LineTrace every Tick
// You obviously can set up your Inputs then cast a LineTrace from there
void AYourCharacter::Tick(float DeltaSeconds)
{
  Super::Tick(DeltaSeconds);

  // LineTrace Parameters
  FHitResult Hit;
  FVector Forward = FollowCamera->GetForwardVector() * 1000.f;
  FVector Start = GetCapsuleComponent()->GetComponentLocation();
  FVector End = Start + Forward;
  FCollisionQueryParams CollisionParams;
  CollisionParams.AddIgnoredActor(this);

  if (Controller != nullptr) // PlayerController is not null
    // add the parameters to the LineTrace
    GetWorld()->LineTraceSingleByChannel(Hit, Start, End, ECC_Visibility, CollisionParams);
    // Visualize the LineTrace with DrawDebugLine
    DrawDebugLine(GetWorld(), Start, End, Hit.bBlockingHit ? FColor::Blue : FColor::Red, false, 5.0f, 1.0f, 10.0f);

    if (Hit.bBlockingHit && IsValid(Hit.GetActor())) // check if a Actor got got
    {
      // Cast YourInterface and check if its not null
      IYourInterface* Interface = Cast<IYourInterface>(Hit.GetActor());
      if (Interface)
      {
        // if Interface is not null call the Interact function
        Interface->Interact(); 
        // This prints the following in the console: 
        // "You Successfully Interacted with SomeActor" from SomeActor
      }
    }
    else
    {
      // If the LineTrace does not hit an Actor
      UE_LOG(LogTemp, Log, TEXT("No Actor got got"));
    }
}

This was an example on how to use Interfaces in Unreal Engine C++.

Interface

Create Interface​

Create Interface