Working with Assets and Blueprint-Defined Data from C++
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When working with C++ code and hybrid mods, you may encounter situations where you need to reference and operate on assets. This poses a complication, as assets and their fields don’t 'exist' yet when writing C++ code, only in the blueprint code.
Generally, if you need to access a class/field in C++, have the parent class defined on the C++ side that define the fields you want to work with in C++, then populate them in a blueprint child version of the class. TODO example, TODO move this to a section?
There are many solutions to this problem, each with their own tradeoffs. We have listed them in order of what we suggest below:
Approach 0: Hybrid Mod
Does the operation you’re performing need to happen on the C++ side? If you can work with the data on the blueprint code side instead, you can avoid this problem.
Consider if the performance gains from doing the operation in C++ are worth the added complexity of this problem.
TODO example
Approach 1: Data Asset
Create a subclass of UDataAsset on the cpp side
Define fields for values you want to pass across to the C++ side.
Add UPROPERTY(EditAnywhere, BlueprintReadWrite) or BlueprintReadOnly to the properties you want to access
Create a field on your Game Instance Module that holds a reference to your Data Asset Create the data asset on the BP side + populate its fields there + populate the field in your game instance module with it
To access the data, get your instance module, get data class, get field.
TODO mircea mentioned static getter?
TODO example
#pragma once
#include "CoreMinimal.h"
#include "Resources/FGItemDescriptor.h"
#include "Buildables/FGBuildablePowerStorage.h"
#include "ApBlueprintDataBridge.generated.h"
/**
* Data asset definition to allow passing assets from blueprint to the C++ side without having to LoadObject hard code them
*/
UCLASS(NotBlueprintable, BlueprintType)
class UApBlueprintDataBridge : public UDataAsset {
GENERATED_BODY()
public:
// Power Storage building asset for UI modifications
UPROPERTY(EditAnywhere, BlueprintReadWrite)
TSubclassOf<AFGBuildablePowerStorage> PowerStorageBuilding;
// Item to use as the Archipelago Blocker
UPROPERTY(EditAnywhere, BlueprintReadWrite)
TSubclassOf<UFGItemDescriptor> BlockerItem;
// Item to use as the replacement for Somersloops
UPROPERTY(EditAnywhere, BlueprintReadWrite)
TSubclassOf<UFGItemDescriptor> ExplorationPickupItem_Somersloop;
// Item to use as the replacement for Mercer Spheres
UPROPERTY(EditAnywhere, BlueprintReadWrite)
TSubclassOf<UFGItemDescriptor> ExplorationPickupItem_Mercer;
};Approach 2: Field on Game Instance Module
Similar to Approach 1, putting
This can get messy pretty fast because you’re adding a lot of fields to your game instance module.
It also causes stuff to preload sooner than it probably needs to → hitches?
TODO example
Approach 3: Find Object and Load Object
Generally don’t use this with hardcoded strings because it’s very brittle, if you move the asset it will no longer point to something and Unreal can’t notice to auto-fix it up for you.
The only approach that can find assets with a location determined at runtime.
Okayish for base-game stuff that Should™ never move.
Example from ContentLib:
UClass* Class = FindObject<UClass>(FindPackage(nullptr, TEXT("/Game/")), TEXT("BP_UnlockInfoOnly_C"), false);
if (!Class) {
Class = LoadObject<UClass>(nullptr, TEXT("/Game/FactoryGame/Unlocks/BP_UnlockInfoOnly.BP_UnlockInfoOnly_C"));
if (!Class) {
UE_LOG(LogContentLib, Fatal, TEXT("CL: Couldn't find BP_UnlockInfoOnly_C wanting to Add to %s"), *Schematic->GetName())
}
}