Catch 22 situation with FObjectFinder and constructor

Development Programming & Scripting
1

I’m porting a non-UE game to UE and I have a class “Building”. Usually, I’d pass the BuildingType (an enum, let’s say) to the constructor and in the constructor I could specify the static mesh in code.

However, UE doesn’t allow arguments in constructors.

So, from what I gather I have to do something like this:

ABuilding* building = GetWorld()->Spawn<ABuilding>(...)
building->SetBuilding(EBuildingType) // Set the static mesh after construction.

Unfortunately, I can’t use ConstructorHelpers::FObjectFinder in that SetBuilding method to choose the static mesh because the construction phase has already passed at that point. Hence the Catch-22 situation.

At the moment I’m spawning the buildings from a Blueprint that has a pre-made TMap that I pick the building from.

Is there a way I can get the BuildingType into the constructor beforehand?

This is hard to explain, so apologies in advance if this isn’t clear.

2

So I think you can declare a class variable in the constructor, so in your header you want to set

UStaticMeshComponent* BuildingStaticMesh;

Then in your constructor you call FObjectFinder

static ConstructorHelpers::FObjectFinder<UStaticMesh>MeshAsset(TEXT("StaticMesh'/Game/Sphere.Sphere'"));
UStaticMesh* Asset = MeshAsset.Object;

Then in any function in your class you can call

BuildingStaticMesh->SetStaticMesh(Asset);

You can preload as many meshes as you want this way, and then set them outside of the constructor as you please.

3

Hi there, thanks for replying.

Sadly, It’s not the usage or understanding of FObjectFinder that’s the problem. **I need to pass an argument into the constructor so that the right mesh is selected. **

e,g,

ABuilding::ABuilding(BuildingType bt /* <-- CAN'T DO THIS */) {
	if(bt == House) {
		static ConstructorHelpers::FObjectFinder<UStaticMesh>MeshAsset(TEXT("StaticMesh'/Game/Meshes/House.House'"));
		// set mesh...
	}
	else if(bt == Castle) {
		static ConstructorHelpers::FObjectFinder<UStaticMesh>MeshAsset(TEXT("StaticMesh'/Game/Meshes/Castle.Castle'"));
		// set mesh...
	}
	else if(bt == Port) {
		static ConstructorHelpers::FObjectFinder<UStaticMesh>MeshAsset(TEXT("StaticMesh'/Game/Meshes/Port.Port'"));
		// set mesh...
	}
	// etc.
}

I’m thinking of maybe just having a separate static global class or function library that pre-loads all the meshes in its constructor with FObjectFinder and then can hand them over, e.g., UStaticMesh* mesh = MeshLibrary::GetBuildingMesh(BuildingType).

4

Aha! I did some more research and it turns out I don’t need to use ConstructorHelpers::FObjectFinder at all.

It seems that from anywhere you can use StaticLoadObject

There was another AnswerHub query with a similar problem:
Load Static Mesh With Path in c++

I switched the code to this and now it works fine!

UStaticMesh* newMesh = nullptr;

if(building == Hovel)
	newMesh = Cast<UStaticMesh>(StaticLoadObject(UStaticMesh::StaticClass(), nullptr, TEXT("StaticMesh'/Game/Meshes/Hovel.Hovel'")));
else if(building == Castle)
	newMesh = Cast<UStaticMesh>(StaticLoadObject(UStaticMesh::StaticClass(), nullptr, TEXT("StaticMesh'/Game/Meshes/Castle.Castle'")));
else if(building == Port)
	newMesh = Cast<UStaticMesh>(StaticLoadObject(UStaticMesh::StaticClass(), nullptr, TEXT("StaticMesh'/Game/Meshes/Port.Port'")));
5

Yeah, you’re supposed to be able to pass variables prior to construction using deferred actor spawning, but that hasn’t seemed to work so far for me.