1 类图

前面对World和Level的关系和源码进行了简单分析，这里介绍WorldContext，同样首先给出类图。

2 WorldContext

在上一篇文章中对World概念及类型做出了简单的分析。那么World不止有一个，类型也不止有一个，UE中是使用什么对World进行管理呢？就是WorldContext。

首先卡看WorldContext代码：

/** FWorldContext
 *	A context for dealing with UWorlds at the engine level. As the engine brings up and destroys world, we need a way to keep straight
 *	what world belongs to what.
 *
 *	WorldContexts can be thought of as a track. By default we have 1 track that we load and unload levels on. Adding a second context is adding
 *	a second track; another track of progression for worlds to live on. 
 *
 *	For the GameEngine, there will be one WorldContext until we decide to support multiple simultaneous worlds.
 *	For the EditorEngine, there may be one WorldContext for the EditorWorld and one for the PIE World.
 *
 *	FWorldContext provides both a way to manage 'the current PIE UWorld*' as well as state that goes along with connecting/travelling to 
 *  new worlds.
 *
 *	FWorldContext should remain internal to the UEngine classes. Outside code should not keep pointers or try to manage FWorldContexts directly.
 *	Outside code can still deal with UWorld*, and pass UWorld*s into Engine level functions. The Engine code can look up the relevant context 
 *	for a given UWorld*.
 *
 *  For convenience, FWorldContext can maintain outside pointers to UWorld*s. For example, PIE can tie UWorld* UEditorEngine::PlayWorld to the PIE
 *	world context. If the PIE UWorld changes, the UEditorEngine::PlayWorld pointer will be automatically updated. This is done with AddRef() and
 *  SetCurrentWorld().
 *
 */
USTRUCT()
struct FWorldContext
{
	GENERATED_USTRUCT_BODY()

	/**************************************************************/
	
	TEnumAsByte<EWorldType::Type>	WorldType;

	FSeamlessTravelHandler SeamlessTravelHandler;

	FName ContextHandle;

	/** URL to travel to for pending client connect */
	FString TravelURL;

	/** TravelType for pending client connects */
	uint8 TravelType;

	/** URL the last time we traveled */
	UPROPERTY()
	struct FURL LastURL;

	/** last server we connected to (for "reconnect" command) */
	UPROPERTY()
	struct FURL LastRemoteURL;

	UPROPERTY()
	UPendingNetGame * PendingNetGame;

	/** A list of tag/array pairs that is used at LoadMap time to fully load packages that may be needed for the map/game with DLC, but we can't use DynamicLoadObject to load from the packages */
	UPROPERTY()
	TArray<struct FFullyLoadedPackagesInfo> PackagesToFullyLoad;

	/**
	 * Array of package/ level names that need to be loaded for the pending map change. First level in that array is
	 * going to be made a fake persistent one by using ULevelStreamingPersistent.
	 */
	TArray<FName> LevelsToLoadForPendingMapChange;

	/** Array of already loaded levels. The ordering is arbitrary and depends on what is already loaded and such.	*/
	UPROPERTY()
	TArray<class ULevel*> LoadedLevelsForPendingMapChange;

	/** Human readable error string for any failure during a map change request. Empty if there were no failures.	*/
	FString PendingMapChangeFailureDescription;

	/** If true, commit map change the next frame.																	*/
	uint32 bShouldCommitPendingMapChange:1;

	/** Handles to object references; used by the engine to e.g. the prevent objects from being garbage collected.	*/
	UPROPERTY()
	TArray<class UObjectReferencer*> ObjectReferencers;

	UPROPERTY()
	TArray<struct FLevelStreamingStatus> PendingLevelStreamingStatusUpdates;

	UPROPERTY()
	class UGameViewportClient* GameViewport;

	UPROPERTY()
	class UGameInstance* OwningGameInstance;

	/** A list of active net drivers */
	UPROPERTY(transient)
	TArray<FNamedNetDriver> ActiveNetDrivers;

	/** The PIE instance of this world, -1 is default */
	int32	PIEInstance;

	/** The Prefix in front of PIE level names, empty is default */
	FString	PIEPrefix;

	/** The feature level that PIE world should use */
	ERHIFeatureLevel::Type PIEWorldFeatureLevel;

	/** Is this running as a dedicated server */
	bool	RunAsDedicated;

	/** Is this world context waiting for an online login to complete (for PIE) */
	bool	bWaitingOnOnlineSubsystem;

	/** Handle to this world context's audio device.*/
	uint32 AudioDeviceID;

	/** Custom description to be display in blueprint debugger UI */
	FString CustomDescription;

	// If > 0, tick this world at a fixed rate in PIE
	float PIEFixedTickSeconds  = 0.f;
	float PIEAccumulatedTickSeconds = 0.f;

	/**************************************************************/

	/** Outside pointers to CurrentWorld that should be kept in sync if current world changes  */
	TArray<UWorld**> ExternalReferences;

	/** Adds an external reference */
	void AddRef(UWorld*& WorldPtr)
	{
		WorldPtr = ThisCurrentWorld;
		ExternalReferences.AddUnique(&WorldPtr);
	}

	/** Removes an external reference */
	void RemoveRef(UWorld*& WorldPtr)
	{
		ExternalReferences.Remove(&WorldPtr);
		WorldPtr = nullptr;
	}

	/** Set CurrentWorld and update external reference pointers to reflect this*/
	ENGINE_API void SetCurrentWorld(UWorld *World);

	/** Collect FWorldContext references for garbage collection */
	void AddReferencedObjects(FReferenceCollector& Collector, const UObject* ReferencingObject);

	FORCEINLINE UWorld* World() const
	{
		return ThisCurrentWorld;
	}

	FWorldContext()
		: WorldType(EWorldType::None)
		, ContextHandle(NAME_None)
		, TravelURL()
		, TravelType(0)
		, PendingNetGame(nullptr)
		, bShouldCommitPendingMapChange(0)
		, GameViewport(nullptr)
		, OwningGameInstance(nullptr)
		, PIEInstance(INDEX_NONE)
		, PIEWorldFeatureLevel(ERHIFeatureLevel::Num)
		, RunAsDedicated(false)
		, bWaitingOnOnlineSubsystem(false)
		, AudioDeviceID(INDEX_NONE)
		, ThisCurrentWorld(nullptr)
	{ }

private:

	UWorld*	ThisCurrentWorld;
};

标签：UPROPERTY,World,PIE,FWorldContext,WorldContext,UWorld,UE,world
来源： https://www.cnblogs.com/hxhspace/p/16139977.html