drichardson · May 21, 2021 17:42 · drichardson · May 21, 2021
diff --git a/WorldSingleton.h b/WorldSingleton.h
 #pragma once

 #include "CoreMinimal.h"

 #include "Engine/World.h"
 #include "EngineUtils.h"

 DECLARE_LOG_CATEGORY_EXTERN(LogWorldSingleton, Log, All);

 /*
 * TWorldSingleton is a weak pointer to a actor in a level, which is only a
 * singleton by convention of only one actor of that type being in a UWorld.
 * Unlike code based singletons, it is therefore okay to have multiple
 * TWorldSingleton's pointing to the same actor, thought this is typically
 * unnecessary and less performant since each instance of TWorldSingleton must
 * do an actor search the first time it is used.
 *
 * Example Use Case
 * If you have an single inventory catalog actor in your level that all other
 * actors should be able to find, you can use TWorldSingleton to access it.
 */
 template <typename ActorType>
 class TWorldSingleton
 {
 private:
 	TWeakObjectPtr<ActorType> Singleton;
 	TWeakObjectPtr<UWorld> SingletonWorld;

 public:
 	// Get the actor instance in this world, if any, logging errors if there is more than one.
 	// This function should only be called after all actors are loaded. You wouldn't want to use it,
 	// for example, in a constructor.
 	ActorType* Get(UWorld* World)
 	{
 		if (!World)
 		{
 			// Although Singleton.Get() could be returned here, don't. Rather,
 			// error out on null World now, so that anyone passing in a null
 			// world know about it immediately. Otherwise, if another call site is correctly called
 			// Get() with a valid world before the incorrect call, the incorrect call would succeed
 			// (in spite of the null world), making the bug hard to track down.
 			return nullptr;
 		}

 		if (SingletonWorld.Get() != World && World && SingletonWorld.IsValid() &&
 			Singleton.IsValid())
 		{
 			// Both SingletonWorld and World are non-null and different. Log a warning
 			// here since this is probably not what the caller wants. That said, this class handles
 			// this situation, but it isn't as performant since the singleton will be looked up
 			// whenever this happens. This situation is common in PIE since there are multiple
 			// worlds created for each player.
 			UE_CLOG(
 				!World->IsPlayInEditor(),
 				LogWorldSingleton,
 				Warning,
 				TEXT("Cached singleton %s (%p) is in valid world %s (%p), but caller is trying to "
 					 "get a singleton in world %s (%p)."),
 				*GetNameSafe(Singleton.Get()),
 				Singleton.Get(),
 				*GetNameSafe(SingletonWorld.Get()),
 				SingletonWorld.Get(),
 				*GetNameSafe(World),
 				World);

 			Singleton = nullptr;
 			SingletonWorld = nullptr;
 		}

 		if (!Singleton.IsValid())
 		{
 			for (TActorIterator<ActorType> It(World); It; ++It)
 			{
 				if (!Singleton.IsValid())
 				{
 					Singleton = *It;
 					SingletonWorld = World;
 				}
 				else
 				{
 					UE_LOG(
 						LogWorldSingleton,
 						Error,
 						TEXT("TWorldSingleton::Get found another actor of class %s named %s. The "
 							 "actor being used as the singleton is %s. To fix, delete all but one "
 							 "of the actors."),
 						*GetNameSafe(ActorType::StaticClass()),
 						*GetNameSafe(*It),
 						*GetNameSafe(Singleton.Get()));
 				}
 			}
 		}

 		return Singleton.Get();
 	}
 };
	#pragma once

	#include "CoreMinimal.h"

	#include "Engine/World.h"
	#include "EngineUtils.h"

	DECLARE_LOG_CATEGORY_EXTERN(LogWorldSingleton, Log, All);

	/*
	* TWorldSingleton is a weak pointer to a actor in a level, which is only a
	* singleton by convention of only one actor of that type being in a UWorld.
	* Unlike code based singletons, it is therefore okay to have multiple
	* TWorldSingleton's pointing to the same actor, thought this is typically
	* unnecessary and less performant since each instance of TWorldSingleton must
	* do an actor search the first time it is used.
	*
	* Example Use Case
	* If you have an single inventory catalog actor in your level that all other
	* actors should be able to find, you can use TWorldSingleton to access it.
	*/
	template <typename ActorType>
	class TWorldSingleton
	{
	private:
	TWeakObjectPtr<ActorType> Singleton;
	TWeakObjectPtr<UWorld> SingletonWorld;

	public:
	// Get the actor instance in this world, if any, logging errors if there is more than one.
	// This function should only be called after all actors are loaded. You wouldn't want to use it,
	// for example, in a constructor.
	ActorType* Get(UWorld* World)
	{
	if (!World)
	{
	// Although Singleton.Get() could be returned here, don't. Rather,
	// error out on null World now, so that anyone passing in a null
	// world know about it immediately. Otherwise, if another call site is correctly called
	// Get() with a valid world before the incorrect call, the incorrect call would succeed
	// (in spite of the null world), making the bug hard to track down.
	return nullptr;
	}

	if (SingletonWorld.Get() != World && World && SingletonWorld.IsValid() &&
	Singleton.IsValid())
	{
	// Both SingletonWorld and World are non-null and different. Log a warning
	// here since this is probably not what the caller wants. That said, this class handles
	// this situation, but it isn't as performant since the singleton will be looked up
	// whenever this happens. This situation is common in PIE since there are multiple
	// worlds created for each player.
	UE_CLOG(
	!World->IsPlayInEditor(),
	LogWorldSingleton,
	Warning,
	TEXT("Cached singleton %s (%p) is in valid world %s (%p), but caller is trying to "
	"get a singleton in world %s (%p)."),
	*GetNameSafe(Singleton.Get()),
	Singleton.Get(),
	*GetNameSafe(SingletonWorld.Get()),
	SingletonWorld.Get(),
	*GetNameSafe(World),
	World);

	Singleton = nullptr;
	SingletonWorld = nullptr;
	}

	if (!Singleton.IsValid())
	{
	for (TActorIterator<ActorType> It(World); It; ++It)
	{
	if (!Singleton.IsValid())
	{
	Singleton = *It;
	SingletonWorld = World;
	}
	else
	{
	UE_LOG(
	LogWorldSingleton,
	Error,
	TEXT("TWorldSingleton::Get found another actor of class %s named %s. The "
	"actor being used as the singleton is %s. To fix, delete all but one "
	"of the actors."),
	*GetNameSafe(ActorType::StaticClass()),
	GetNameSafe(It),
	*GetNameSafe(Singleton.Get()));
	}
	}
	}

	return Singleton.Get();
	}
	};