Register Component Hit

December 01, 2017

UE4 Version: 4.18.3

Github Link: https://github.com/Harrison1/unrealcpp/tree/master/OnComponentHit

For this tutorial we are using the standard first person C++ template with starter content. If you don't know how to add a new actor class to your project, please visit the Add C++ Actor Class post.

In this tutorial we will learn how to register a hit event on a component. Create a new C++ actor class and call it OnComponentHit. In the header file will declare a UBoxComponent variable and a void function to run when the component registers a hit. Below is the final header file.

OnHitComponent.h

#pragma once

#include "CoreMinimal.h"
#include "GameFramework/Actor.h"
#include "OnComponentHit.generated.h"

UCLASS()
class UNREALCPP_API AOnComponentHit : public AActor
{
	GENERATED_BODY()
	
public:	
	// Sets default values for this actor's properties
	AOnComponentHit();

protected:
	// Called when the game starts or when spawned
	virtual void BeginPlay() override;

public:	
	// Called every frame
	virtual void Tick(float DeltaTime) override;

	UPROPERTY(VisibleAnywhere)
	class UBoxComponent* MyComp;

	UFUNCTION()
	void OnCompHit(UPrimitiveComponent* HitComp, AActor* OtherActor, UPrimitiveComponent* OtherComp, FVector NormalImpulse, const FHitResult& Hit);
	
};

In .cpp file first #include the BoxComponent header file.

include files

#include "OnComponentHit.h"
// include files
#include "Components/BoxComponent.h"

Next, we'll set the default values for our actor in the actor's init function. We'll initialize the actor with a UBoxComponent and set it as the RootComponent. Then, we'll add OnComponentHit to the component and connect it to our function OnCompHit. We'll make OnCompHit in the next step. I'm also setting the default CollisionProfileName to BlockAllDynamic, this can be changed later in the editor.

init function

// Sets default values
AOnComponentHit::AOnComponentHit()
{
 	// Set this actor to call Tick() every frame.  You can turn this off to improve performance if you don't need it.
	PrimaryActorTick.bCanEverTick = true;

	// Use a sphere as a simple collision representation
	MyComp = CreateDefaultSubobject<UBoxComponent>(TEXT("BoxComp"));
	MyComp->SetSimulatePhysics(true);
    MyComp->SetNotifyRigidBodyCollision(true);
    
	MyComp->BodyInstance.SetCollisionProfileName("BlockAllDynamic");
	MyComp->OnComponentHit.AddDynamic(this, &AOnComponentHit::OnCompHit);

	// Set as root component
	RootComponent = MyComp;

}

Now let's create our simple OnCompHit function that will print to screen the other actor's name when our actor hits it. For more information on OnComponentHit you can visit some good AnswerHub posts here and here or visit the ue4 documentation here

OnCompHit

void AOnComponentHit::OnCompHit(UPrimitiveComponent* HitComp, AActor* OtherActor, UPrimitiveComponent* OtherComp, FVector NormalImpulse, const FHitResult& Hit)
{
	if ((OtherActor != NULL) && (OtherActor != this) && (OtherComp != NULL))
	{
		if (GEngine) GEngine->AddOnScreenDebugMessage(-1, 5.f, FColor::Green, FString::Printf(TEXT("I Hit: %s"), *OtherActor->GetName()));
	}
}

Below is the final .cpp file.

OnComponentHit.cpp

#include "OnComponentHit.h"
#include "Components/BoxComponent.h"

// Sets default values
AOnComponentHit::AOnComponentHit()
{
 	// Set this actor to call Tick() every frame.  You can turn this off to improve performance if you don't need it.
	PrimaryActorTick.bCanEverTick = true;

	// Use a sphere as a simple collision representation
	MyComp = CreateDefaultSubobject<UBoxComponent>(TEXT("BoxComp"));
	MyComp->SetSimulatePhysics(true);
	MyComp->SetNotifyRigidBodyCollision(true);
	MyComp->BodyInstance.SetCollisionProfileName("BlockAllDynamic");
	MyComp->OnComponentHit.AddDynamic(this, &AOnComponentHit::OnCompHit);

	// Set as root component
	RootComponent = MyComp;

}

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

// Called every frame
void AOnComponentHit::Tick(float DeltaTime)
{
	Super::Tick(DeltaTime);

}

void AOnComponentHit::OnCompHit(UPrimitiveComponent* HitComp, AActor* OtherActor, UPrimitiveComponent* OtherComp, FVector NormalImpulse, const FHitResult& Hit)
{
	if ((OtherActor != NULL) && (OtherActor != this) && (OtherComp != NULL))
	{
		if (GEngine) GEngine->AddOnScreenDebugMessage(-1, 5.f, FColor::Green, FString::Printf(TEXT("I Hit: %s"), *OtherActor->GetName()));
	}
}

Compile the code. Drag and drop the actor into the game scene. Add a static mesh to the actor and fit inside the hit box. Now when you push play the actor should register the hit events.

Author

Harrison McGuire

Harrison McGuire