How to spawn a simple cube in C++?

Development Programming & Scripting
2

Beginner here, but ill give it a go:

Create a new project, then extract the static mesh from the box brush as detailed here.

Save it somewhere

Go File->AddCodeToProject
Add a new actor, call it ‘CubeActor’

Exit from the unreal editor

change CubeActor.h to the following:

UCLASS()
class SOMEPROJECT_API ACubeActor : public AActor
{
	GENERATED_UCLASS_BODY()

	UPROPERTY(Category = Meshes, VisibleAnywhere)
	TSubobjectPtr<UStaticMeshComponent> CubeMesh;
    	
    };

Change CubeActor.cpp to the following:

ACubeActor::ACubeActor(const class FPostConstructInitializeProperties& PCIP)
	: Super(PCIP)
{
	CubeMesh = PCIP.CreateDefaultSubobject<UStaticMeshComponent>(this, TEXT("CubeMesh"));
}

Recompile your project, should build fine.

Back in the editor , select new from the content browser in the bottom left, select blueprint - select your newly created CubeActor:

22966-parentclass.png

save your blueprint as ‘BP_Cube’

Open up your new blueprint.
Under ‘Defaults’, choose the static mesh you saved eariler:

22967-bp_mesh.png
22967-bp_mesh.png1259×785 116 KB

Compile and save your blueprint.

Close the editor

Now thats done, you’ll want to change your ACubeActor to the following:

UCLASS()
class SOMEPROJECT_API ACubeActor : public AActor
{
	GENERATED_UCLASS_BODY()

	UPROPERTY(Category = Meshes, VisibleAnywhere)
	TSubobjectPtr<UStaticMeshComponent> CubeMesh;

public:
	TSubclassOf<class ACubeActor> CubeBlueprint;
};

ACubeActor.cpp:

ACubeActor::ACubeActor(const class FPostConstructInitializeProperties& PCIP)
	: Super(PCIP)
{
	CubeMesh = PCIP.CreateDefaultSubobject<UStaticMeshComponent>(this, TEXT("CubeMesh"));

	static ConstructorHelpers::FObjectFinder<UBlueprint> CubeBP(TEXT("Blueprint'/Game/BP_Cube.BP_Cube'"));
	if (CubeBP.Object){
		CubeBlueprint = (UClass*)CubeBP.Object->GeneratedClass;
	}
}

Now, you’ll want to add a new header library (this is so we can have a reference to cube blueprint anywhere)

Create ‘BP_Libs.h’ (if you build it straight in VS, it’ll put it by default in intermediate/projectfiles/, you’ll need to move this to source/someproject/ to be able to reference it)

then add the following:

#include "SomeProject.h"

static TSubclassOf<class ACubeActor> GetCubeBP()
{
	static ConstructorHelpers::FObjectFinder<UBlueprint> CubeBP(TEXT("Blueprint'/Game/BP_Cube.BP_Cube'"));
	if (CubeBP.Object){
		return (UClass*)CubeBP.Object->GeneratedClass;
	}
}

template <typename ObjectType>
static FORCEINLINE ObjectType* SpawnBP(
	UWorld* TheWorld,
	UClass* TheBP,
	const FVector& Loc,
	const FRotator& Rot,
	const bool bNoCollisionFail = true,
	AActor* Owner = NULL,
	APawn* Instigator = NULL
	){
	if (!TheWorld) return NULL;
	if (!TheBP) return NULL;
	//~~

	FActorSpawnParameters SpawnInfo;
	SpawnInfo.bNoCollisionFail = bNoCollisionFail;
	SpawnInfo.Owner = Owner;
	SpawnInfo.Instigator = Instigator;
	SpawnInfo.bDeferConstruction = false;

	return TheWorld->SpawnActor<ObjectType>(TheBP, Loc, Rot, SpawnInfo);
}

Credits to rama: A new, community-hosted Unreal Engine Wiki - Announcements - Epic Developer Community Forums
and the guys over here: Spawn Blueprint from C++ - Editor Scripting - Epic Developer Community Forums

Then you can create the cube like this:
(I just used my gamemode constructor)

#include "BP_Libs.h"

ASomeProjectGameMode::ASomeProjectGameMode(const class FPostConstructInitializeProperties& PCIP)
	: Super(PCIP)
{
	FVector Position = FVector(0, 0, 0);
	FRotator Rotation = FRotator(0);
	SpawnBP<ACubeActor>(GetWorld(), GetCubeBP(), Position, Rotation);
}

I also added the full source here, if you want to pick through it: