Singleton pattern in c++

Development Programming & Scripting Blueprint
, , , , , ,
4

Header:

UCLASS()
class YOURGAME_API UYourGameInstance : public UGameInstance
{
	GENERATED_BODY()
	
	
public:
	// Accessor for C++ & BP. Should be self-explanatory
	UFUNCTION(
		BlueprintPure,
		Category = "Persistence",
		meta = (
			DisplayName = "Get Savegame Manager",
			Keywords = "SavegameManager"))
	USavegameManager *SavegameManager();


protected:
	// This is where we will clean up, as the game is shut down
	virtual void Shutdown() override;


private:
// Needs to be an UPROPERTY(), so the GC does its thing
// Transient, so it doesn't get serialized itself. Will be nulled when the
// game starts. Initialization happens later by hand.
	UPROPERTY(
		Transient)
	USavegameManager *SavegameManagerInstance;
};

Source:

// Singleton-like accessor. I only use this as a workaround for PIE
// The GameInstance lifecycle is different in PIE
// In proper builds, this wouldn't be necessary (I'll explain this further down)
USavegameManager *UYourGameInstance::SavegameManager()
{
	return
		IsValid(SavegameManagerInstance) ?
		SavegameManagerInstance :
		SavegameManagerInstance = NewObject<USavegameManager>(
			this,
			FName("SavegameManager"));
}

// Cleanup. This acts as a quasi-destructor
void UYourGameInstance::Shutdown()
{
	// Important, if you overwrite functionality in UE4.
	// Omitting this, may cause errors (depending on the class).
	Super::Shutdown();

	// PIE may cause this to be invalid. During the game, it will always be valid
	if (IsValid(SavegameManagerInstance))
	{
		SavegameManagerInstance->ClearStoredActors();
		SavegameManagerInstance->ClearLevelStorage();
		ClearPlayerInventoryCache();
	}
}
2 Likes