ue4-uobject-gc.cpp

UCLASS()
class FORTHEDAYSANDBOX_API UMyObject : public UObject
{
	GENERATED_BODY()

public:
	virtual void BeginDestroy() override;
};
//------------------------------------------------------------------------------

UCLASS()
class FORTHEDAYSANDBOX_API AMyActor : public AActor
{
	GENERATED_BODY()
	
public:	
	virtual ~AMyActor();

private:
	UPROPERTY()
	UMyObject *m_pMyObject1;			// UPROPERTY
	UMyObject *m_pMyObject2;			// RAW PTR, UNSAFE, BAD USAGE
	TSharedPtr<UMyObject> m_spMyObject3;// BAD USAGE, TSharedPtr is for FSomethings.

protected:
	virtual void BeginPlay() override;
};

//------------------------------------------------------------------------------
// UMyObject
//------------------------------------------------------------------------------
void UMyObject::BeginDestroy()
{
	LOGW("UMyObject::BeginDestroy() %s", *GetFName().GetPlainNameString());
	Super::BeginDestroy();
}

//------------------------------------------------------------------------------
// AMyActor
//------------------------------------------------------------------------------
AMyActor::~AMyActor()
{
	LOGW("MyObjs: %p, %p", m_pMyObject1, m_pMyObject2);
	// m_pMyObject2 is dangling ptr.
}

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

	UClass *pMyObjectClass = UMyObject::StaticClass();

	// case1
	{
		m_pMyObject1 = NewObject<UMyObject>(GetTransientPackage(), pMyObjectClass, TEXT("Obj1")); // property
		m_pMyObject2 = NewObject<UMyObject>(GetTransientPackage(), pMyObjectClass, TEXT("Obj2")); // raw ptr
		m_pMyObject1 = nullptr;
		GetWorld()->ForceGarbageCollection(true);
		// Obj1, Obj2 Destroy
	}
	// case2
	{
		m_pMyObject1 = NewObject<UMyObject>(GetTransientPackage(), pMyObjectClass, TEXT("Obj1")); // property
		m_pMyObject2 = NewObject<UMyObject>(GetTransientPackage(), pMyObjectClass, TEXT("Obj2")); // raw ptr
		GetWorld()->ForceGarbageCollection(true);
		// Obj2 Destroy
	}
}