Unreal Engine, from C++ spawn Blueprint inherited from C++ class, very small example

Prepare Project

Create Project

• Games / Blank
  • C++
  • Desktop
  • Maximum
  • Starter Content: no
  • Raytracing: no
  • Location: your choice
  • Project Name: ShowActor
• Create

Change Map to Basic

When the UE-Editor is open:

• File / New Level / Basic / Create
• File / Save Current Level as ... / Basic01
• Edit / Project Settings / Maps & Modes / Editor Startup Map: Basic01
• Edit / Project Settings / Maps & Modes / Editor Game Default Map: Basic01

Create Classes

Actor

This is the class from which we will create a blueprint which we will then spawn.

• Tools / New C++ Class
  • Parent Class: Actor
  • Name: MiniActor
  • Create Class

Header File: MiniActor.h

#pragma once

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

UCLASS(Blueprintable)
class SHOWACTOR_API AMiniActor : public AActor
{
  GENERATED_BODY()
	
public:	

	AMiniActor();

protected:

  virtual void BeginPlay() override;

  UPROPERTY(EditAnywhere, Category = "Structure", meta = (DisplayName = "Mesh"))
  UStaticMesh* m_pMesh;

  UPROPERTY(EditAnywhere, Category = "Structure", meta = (DisplayName = "Scene Component Root"))
  USceneComponent* m_pScRoot;

  UPROPERTY(EditAnywhere, Category = "Structure", meta = (DisplayName = "Static Mesh Component of Root"))
  UStaticMeshComponent* m_pSmcRoot;
};

Source File: MiniActor.cpp

#include "MiniActor.h"

AMiniActor::AMiniActor()
{
  m_pScRoot = CreateDefaultSubobject<USceneComponent>("Root");
  RootComponent = m_pScRoot;

  m_pSmcRoot = CreateDefaultSubobject<UStaticMeshComponent>("SmcRoot");

  FAttachmentTransformRules transformRule = FAttachmentTransformRules::SnapToTargetIncludingScale;
  m_pSmcRoot->AttachToComponent(RootComponent, transformRule);

  PrimaryActorTick.bCanEverTick = false;
}

void AMiniActor::BeginPlay()
{
  Super::BeginPlay();

  if (m_pMesh != nullptr)
  {
    m_pSmcRoot->SetStaticMesh(m_pMesh);
  }
}

Build

Now build the project. Nothing works so don't even try to test it in the UE-Editor, but the code should compile and link. This is a class that is complete as it is.

Nagtc

We need "something" to tell UE what blueprint we want to spawn and how many. There are many places where you can do it. This is just an example.

• Nagtc: (N)ot (a) (g)lobal (t)rash (c)an

• Tools / New C++ Class
  • Parent Class: Actor
  • Name: Nagtc
  • Create Class

Header File: Nagtc.h

#pragma once

#include "CoreMinimal.h"
#include "GameFramework/Actor.h"
#include "MiniActor.h"
#include "Nagtc.generated.h"

UCLASS()
class SHOWACTOR_API ANagtc : public AActor
{
  GENERATED_BODY()
	
public:

  UPROPERTY(BlueprintReadWrite, EditAnywhere, Category = "Generating Test Data", Meta = (DisplayName = "Number of Test objects"))
  int32	m_nNumberOfTestObjects;

  UPROPERTY(BlueprintReadWrite, EditAnywhere, Category = "Generating Test Data", Meta = (DisplayName = "MiniActor Blueprint Class for Test 1"))
  TSubclassOf<AMiniActor> m_MiniActorTest1;

  static void test1(UWorld* pWorld);

protected:

  static ANagtc* getInstanceFromWorld(UWorld* pWorld);

  void test1();
};

Source File: Nagtc.cpp

#include "Nagtc.h"
#include "Engine/World.h"
#include "Kismet/GameplayStatics.h"

///  static
void 
ANagtc::test1(UWorld* pWorld)
{
  ANagtc* pNagtc = getInstanceFromWorld(pWorld);
  if (pNagtc)
  {
    pNagtc->test1();
  }
}

void
ANagtc::test1()
{
  if (m_nNumberOfTestObjects > 0 && m_MiniActorTest1.Get() != nullptr)
  {
    double fX = 0;
    double fY = 0;
    double fZ = 0;
    for (int n = 0; n < m_nNumberOfTestObjects; ++n)
    {
      FVector locator(fX, fY, fZ);
      AActor* pActor = GetWorld()->SpawnActor(m_MiniActorTest1, &locator);

      fY += 100;
      fZ += 50;
    }
  }
}

ANagtc*
ANagtc::getInstanceFromWorld(UWorld* pWorld)
{
  TArray<AActor*> arrActorsToFind;
  UGameplayStatics::GetAllActorsOfClass(pWorld, ANagtc::StaticClass(), arrActorsToFind);

  if (arrActorsToFind.Num() == 1)
  {
    ANagtc* pNagtc = Cast<ANagtc>(arrActorsToFind[0]);
    return pNagtc;
  }

  return nullptr;
}