Using UGameInstance for ID storage

Development Programming & Scripting C++
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1

What is wrong

I am trying to use a UGameInstance to store ID’s of items. These ID’s are stored in a helper class that is a child of UObject. However, when I try to use the UGameInstance class, I get a duplicate symbols error.

What I am doing

I used Rama’s tutorial, “Game Instance, Custom Game Instance For Inter-Level Persistent Data Storage”, which is very informative on setting up the UGameInstance class, but less so on using it.

My Relevant classes consist of:

UOncomingGameInstance.h

#pragma once

#include "Engine/GameInstance.h"
#include "ItemRegistry.h"
#include "OncomingGameInstance.generated.h"

/**
 * 
 */
UCLASS()
class ONCOMINGPREALPHA_API UOncomingGameInstance : public UGameInstance
{
	GENERATED_UCLASS_BODY()
	
public:
    UOncomingGameInstance();
    
    UItemRegistry* ItemRegistry;
	
};

UOncomingGameInstance.cpp

// Fill out your copyright notice in the Description page of Project Settings.

#include "OncomingPreAlpha.h"
#include "Item/NULLItem.h"
#include "OncomingGameInstance.h"

UItemRegistry* ItemRegistry = NewObject<UItemRegistry>();

UOncomingGameInstance::UOncomingGameInstance(const FObjectInitializer& ObjInit) : Super(ObjInit) {
    UWorld* world = GetWorld();
    if (world) {
        AItem* Item = Cast<AItem>(world->SpawnActor(ANULLItem::StaticClass()));
        
        ItemRegistry->AddToRegistry(Item, "NULL");
    }
}

ItemRegistry.h

// Fill out your copyright notice in the Description page of Project Settings.

#pragma once

#include "Object.h"
#include "ItemRegistry.generated.h"

/**
 * 
 */
UCLASS()
class ONCOMINGPREALPHA_API UItemRegistry : public UObject
{
	GENERATED_BODY()
	
public:
    
    bool AddToRegistry(class AItem* Item, FString ID);
    AItem* GetID(FString ID);
    
    TMap<FString, class AItem*> Registry;
	
	
};

ItemRegistry.cpp

// Fill out your copyright notice in the Description page of Project Settings.

#include "OncomingPreAlpha.h"
#include "ItemRegistry.h"


bool UItemRegistry::AddToRegistry(class AItem* Item, FString ID) {
    if(Registry.Contains(ID)) {
        return false;
    }
    
    Registry.Add(ID, Item);
    
    return true;
}

AItem* UItemRegistry::GetID(FString ID) {
    if (Registry.Contains(ID)) return Registry[ID];
    else return Registry["NULL"];
}

What I have tried

Firstly, I looked into using singletons, eventually coming to the conclusion that they weren’t the best choice. I searched around for a while and found the UGameInstance class. I decided that it would be the best thing to use, I tried researching how to use it. Rama’s tutorial was the best (And only I could find).

After no success trying to get it working, I have come to post a question. I am probably trying to implement this in a stupid way, so I am open to suggestions on a different method.

I get the Duplicate Symbols error when I write the following:

#include UOncomingGameInstance.h

...

void AActorChild::BeginPlay() {
    Super::BeginPlay();
    
    UOncomingGameInstance* inst = Cast<UOncomingGameInstance>(GetGameInstance());
    if(inst) {
        GEngine->AddOnScreenDebugMessage(-1, 20, FColor::Blue, inst->ItemRegistry->GetID("NULL")->GetName());
    
    }
}

Thanks for taking the time to read and reply. Sorry for the code dump.

2

Bump. I’m desperate for an answer.

3

Not sure whether this will help with what you want to do, but here is the way I use GameInstance to store stuff…

MyGameInstance.h:

UCLASS()
class MyGame_API UMyGameInstance : public UGameInstance
{
	GENERATED_BODY()
	UMyGameInstance(const class FObjectInitializer& PCIP);

public:
	static uint8 AReallyImportantInteger;
};

My GameInstance.cpp:

// Fill out your copyright notice in the Description page of Project Settings.

#include "MyGame.h"
#include "MyGameInstance.h"

uint8 MyGameInstance::AReallyImportantInteger = 255;

Then to access from whatever .cpp file needs to:

UMyGameInstance* VGI = Cast<UMyGameInstance>(GetGameInstance());
if (!VGI) {
//freak out here
   return;
}
VGI->AReallyImportantInteger = 0;

Hope that is of help.

4

Paste the logs here, maybe I can help…

5

answer has fixed my problem. Thanks for taking the time to read my question.

6

Thanks for the answer! Turns out I was forgetting to declare my initialiser in the header correctly.