【UE4 C++】编程子系统 Subsystem

概述

定义

• Subsystems 是一套可以定义、自动实例化和释放的类的框架。可以将其理解为 GamePlay 级别的 Component
• 不支持网络赋值
• 4.22开始引入，4.24完善。（可以移植源码到更早之前的版本使用。源码在手，为所欲为）

五类 Subsystems 及其生命周期

• UEngineSubsystem（继承自 UDynamicSubsystem，UDynamicSubsystem继承自 USubsystem）

  UEngine* GEngine
  
  代表引擎，数量1。 Editor或Runtime模式都是全局唯一，从进程启动开始创建，进程退出时销毁。

  UEngine::Init()

• UEditorSubsystem（继承自 UDynamicSubsystem，UDynamicSubsystem继承自 USubsystem）

  UEditorEngine* GEditor
  
  代表编辑器，数量1。 顾名思义，只在编辑器下存在且全局唯一，从编辑器启动开始创建，到编辑器退出时销毁。

• UGameInstanceSubsystem （继承自 USubsystem）

  UGameInstance* GameInstance
  
  代表一场游戏，数量1。 从游戏的启动开始创建，游戏退出时销毁。这里的一场游戏指的是Runtime或PIE模式的运行的都算，一场游戏里可能会创建多个World切换。

• UWorldSubsystem （继承自 USubsystem）

  UWorld* World
  
  代表一个世界，数量可能>1。其生命周期，跟GameMode是一起的。(EWorldType:Game，Editor，PIE，EditorPreview，GamePreview等 )

• ULocalPlayerSubsystem （继承自 USubsystem）

  ULocalPlayer* LocalPlayer：代表本地玩家，数量可能>1。
  
  UE支持本地分屏多玩家类型的游戏，但往往最常见的是就只有一个。LocalPlayer虽然往往跟PlayerController一起访问，但是其生命周期其实是跟UGameInstance一起的(默认一开始的时候就创建好一定数量的本地玩家)，或者更准确的说是跟LocalPlayer的具体数量挂钩（当然你也可以运行时动态调用AddLocalPlayer)。

为什么要使用 Subsystems

• 更适用的生命周期
  • 引擎只支持一个 GameInstance ，运行周期是整个引擎的生命周期
  • 自定义 ManagerActor，生命周期一般为当前 level 的生命周期
  • Subsystems 的生命周期可以依存于Engine，Editor，World，LocalPlayer
• 更简
  • GameInstance 或者自定义 ManagerActor，需要手动维控制创建、释放
  • Subsystems 自动创建、释放，提供 Initialize()、Deinitialize()，并且可重载
• 更模块化、更优雅、更封装、更易于维护、移植复用
  • GameInstance 中将任务系统，计分系统，经济系统、对话系统等多个Manager 写在一起，会变得臃肿
    • 模块间的数据访问封装不够良好，容易污染
    • 不利于业务逻辑模块的复用，特别是需要进行移植的时候，以及多个插件同时都有自己的 GameInstance
  • Subsystems 可以为不同的 Manager 创建对应的Subsystems
    • 如 Manager 划分，
      • 任务系统Subsystem : UGameInstanceSubsystem
      • 计分系统Subsystem : UGameInstanceSubsystem
      • 经济系统Subsystem : UGameInstanceSubsystem
      • 对话系统Subsystem : UGameInstanceSubsystem
    • 更模块化，代码显得优雅
    • 解耦性高，易于维护、分工协作；易于移植复用
    • 模块间的数据访问具有更好的封装性
• 更友好的访问接口
  • Subsystem 更像以全局变量的形式来访问
  • 提供了 Python 脚本的访问，用于编写编辑器脚本或编写测试代码
• Subsystem 无需覆盖引擎类。

---

Subsystems 的使用

• 创建过程，涉及 FSubsystemCollectionBase

  FSubsystemCollectionBase::Initialize()
  FSubsystemCollectionBase::AddAndInitializeSubsystem()
  FSubsystemCollectionBase::Deinitialize()
  

  参考附录源码 或者 EngineDir\Engine\Source\Runtime\Engine\Private\Subsystems\SubsystemCollection.cpp

• 默认重载函数

  • ShouldCreateSubsystem
  • Initialize()
  • Deinitialize()

• C++ 访问

  // UMyEngineSubsystem 获取
  UMyEngineSubsystem* MyEngineSubsystem = GEngine->GetEngineSubsystem<UMyEngineSubsystem>();
  // UMyEditorSubsystem 获取
  UMyEditorSubsystem* MyEditorSubsystem = GEditor->GetEditorSubsystem<UMyEditorSubsystem>();
  // UMyGameInstanceSubsystem 获取
  //UGameInstance* GameInstance = GetWorld()->GetGameInstance();
  UGameInstance* GameInstance = UGameplayStatics::GetGameInstance();
  UMyGameInstanceSubsystem* MyGameInstanceSubsystem = GameInstance->GetSubsystem<UMyGameInstanceSubsystem>();
  // UMyWorldSubsystem 获取
  UMyWorldSubsystem* MyWorldSubsystem = GetWorld()->GetSubsystem<UMyWorldSubsystem>();
  // UMyLocalPlayerSubsystem 获取
  ULocalPlayer* LocalPlayer = UGameplayStatics::GetPlayerController()->GetLocalPlayer();
  UMyLocalPlayerSubsystem* MyLocalPlayerSubsystem = LocalPlayer->GetSubsystem<UMyLocalPlayerSubsystem>();
  

  • 引擎自带 USubsystemBlueprintLibrary 访问方法

  UCLASS()
  class ENGINE_API USubsystemBlueprintLibrary : public UBlueprintFunctionLibrary
  {
  	GENERATED_BODY()
  public:
  	/** Get a Game Instance Subsystem from the Game Instance associated with the provided context */
  	UFUNCTION(BlueprintPure, Category = "Engine Subsystems", meta = (BlueprintInternalUseOnly = "true"))
  	static UEngineSubsystem* GetEngineSubsystem(TSubclassOf<UEngineSubsystem> Class);
  	/** Get a Game Instance Subsystem from the Game Instance associated with the provided context */
  	UFUNCTION(BlueprintPure, Category = "GameInstance Subsystems", meta = (WorldContext = "ContextObject", BlueprintInternalUseOnly = "true"))
  	static UGameInstanceSubsystem* GetGameInstanceSubsystem(UObject* ContextObject, TSubclassOf<UGameInstanceSubsystem> Class);
  	/** Get a Local Player Subsystem from the Local Player associated with the provided context */
  	UFUNCTION(BlueprintPure, Category = "LocalPlayer Subsystems", meta = (WorldContext = "ContextObject", BlueprintInternalUseOnly = "true"))
  	static ULocalPlayerSubsystem* GetLocalPlayerSubsystem(UObject* ContextObject, TSubclassOf<ULocalPlayerSubsystem> Class);
  	/** Get a World Subsystem from the World associated with the provided context */
  	UFUNCTION(BlueprintPure, Category = "GameInstance Subsystems", meta = (WorldContext = "ContextObject", BlueprintInternalUseOnly = "true"))
  	static UWorldSubsystem* GetWorldSubsystem(UObject* ContextObject, TSubclassOf<UWorldSubsystem> Class);
  	/**
  	 * Get a Local Player Subsystem from the LocalPlayer associated with the provided context
  	 * If the player controller isn't associated to a LocalPlayer nullptr is returned
  	 */
  	UFUNCTION(BlueprintPure, Category = "LocalPlayer Subsystems", meta = (BlueprintInternalUseOnly = "true"))
  	static ULocalPlayerSubsystem* GetLocalPlayerSubSystemFromPlayerController(APlayerController* PlayerController, TSubclassOf<ULocalPlayerSubsystem> Class);
  private:
  	static UWorld* GetWorldFrom(UObject* ContextObject);
  };
  

UGameInstanceSubsystem

用法一

• 支持委托

• 支持普通变量和函数

• 支持蓝图调用

  UCLASS()
  class DESIGNPATTERNS_API UScoreGameInsSubsystem : public UGameInstanceSubsystem
  {
  	GENERATED_BODY()
  public:
  	// 是否允许被创建
  	virtual bool ShouldCreateSubsystem(UObject* Outer) const override { return true; }
  	// 初始化
  	virtual void Initialize(FSubsystemCollectionBase& Collection) override;
  	// 释放
  	virtual void Deinitialize() override;
  	// 声明委托
  	DECLARE_DYNAMIC_MULTICAST_DELEGATE_OneParam(FScoreChanged, int32, CurrentScore);
  	UPROPERTY(BlueprintAssignable)
  	FScoreChanged ScoreChange;
  	UFUNCTION(BlueprintCallable, Category = "MySubsystem | ScoreGameInsSubsystem")
  		int32 AddScore(int32 BaseScore);
  private:
  	int32 Score;
  };
  

  void UScoreGameInsSubsystem::Initialize(FSubsystemCollectionBase& Collection)
  {
  	Super::Initialize(Collection);
  	UE_LOG(LogTemp, Warning, TEXT(__FUNCTION__""));
  }
  void UScoreGameInsSubsystem::Deinitialize()
  {
  	Super::Deinitialize();
  	UE_LOG(LogTemp, Warning, TEXT(__FUNCTION__""));
  }
  int32 UScoreGameInsSubsystem::AddScore(int32 BaseScore)
  {
  	Score = UKismetMathLibrary::Max(0, Score + BaseScore);
  	// 调用委托
  	ScoreChange.Broadcast(Score);
  	return Score;
  }
  

  

用法二

• 支持创建抽象类，多个派生类，支持蓝图继承，支持遍历访问

  • 注意UCLASS(Type)
    • 父类为 Abstract抽象类，防止实例化
    • Blueprintable 蓝图继承
    • BlueprintType 可定义蓝图变量
  • 注意每种类型的 Subsystem 只能创建一个实例

• C++访问

  • 访问单个 GetWorld()->GetGameInstance()->GetSubsystem<T>()
  • 访问多个 GetWorld()->GetGameInstance()->GetSubsystemArray<T>()

• 使用示例

  /**
   * 抽象类 USourceControlSubsystem
   */
  UCLASS(Abstract, Blueprintable, BlueprintType)
  class DESIGNPATTERNS_API USourceControlSubsystem : public UGameInstanceSubsystem
  {
  	GENERATED_BODY()
  public:
  	// ShouldCreateSubsystem 默认返回 True
  	// 可重载
  	UFUNCTION(BlueprintCallable, BlueprintNativeEvent, Category = "MySubsystem | SourceControl")
  		FString GetPlatformName();
  };
  /**
   * 派生类 UGitSubsystem
   */
  UCLASS()
  class DESIGNPATTERNS_API UGitSubsystem : public USourceControlSubsystem
  {
  	GENERATED_BODY()
  public:
   	// 初始化
   	virtual void Initialize(FSubsystemCollectionBase& Collection) override {
   		Super::Initialize(Collection);
   		UE_LOG(LogTemp, Warning, TEXT(__FUNCTION__"【%s】"),*GetName());
   	}
   	// 释放
   	virtual void Deinitialize() override {
   		Super::Deinitialize();
   		UE_LOG(LogTemp, Warning, TEXT(__FUNCTION__"【%s】"),*GetName());
   	}
  	virtual  FString GetPlatformName_Implementation()override {
  		UE_LOG(LogTemp, Warning, TEXT(__FUNCTION__"【Git】"));
  		return TEXT("Git");
  	}
  	void Help() {
  		UE_LOG(LogTemp, Warning, TEXT(__FUNCTION__" Help Command"));
  	}
  };
  /**
   * 派生类 USVNSubsystem
   */
  UCLASS()
  class DESIGNPATTERNS_API USVNSubsystem : public USourceControlSubsystem
  {
  	GENERATED_BODY()
  public:
  	 	// 初始化
  	 	virtual void Initialize(FSubsystemCollectionBase& Collection) override {
  	 		Super::Initialize(Collection);
  	 		UE_LOG(LogTemp, Warning, TEXT(__FUNCTION__"【%s】"), *GetName());
  	 	}
  	 	// 释放
  	 	virtual void Deinitialize() override {
  	 		Super::Deinitialize();
  	 		UE_LOG(LogTemp, Warning, TEXT(__FUNCTION__"【%s】"), *GetName());
  	 	}
  		virtual  FString GetPlatformName_Implementation()override {
  			UE_LOG(LogTemp, Warning, TEXT(__FUNCTION__"【SVN】"));
  			return TEXT("SVN");
  		}
  };
  /**
   *  用于测试 ASourceControlActor
   */
  UCLASS(Blueprintable, BlueprintType)
  class DESIGNPATTERNS_API ASourceControlActor : public AActor
  {
  	GENERATED_BODY()
  public:
  	ASourceControlActor(){}
  	virtual void BeginPlay()override {
  		Super::BeginPlay();
  		// 获取单个 Subsystem
  		UGitSubsystem* GitSubsystem = GetWorld()->GetGameInstance()->GetSubsystem<UGitSubsystem>();
  		GitSubsystem->Help();
  		// 获取多个 Subsystem，继承自同个抽象类
  		const TArray<USourceControlSubsystem*> SourceControlSubsystems = GetWorld()->GetGameInstance()->GetSubsystemArray<USourceControlSubsystem>();
  		UE_LOG(LogTemp, Warning, TEXT(__FUNCTION__"********************* 遍历USourceControlSubsystem ********************"));
  		for (USourceControlSubsystem* ItemSubSystem : SourceControlSubsystems)
  		{
  			ItemSubSystem->GetPlatformName();
  		}
  	}
  };
  

• 蓝图调用

  

  

其他用法

• 支持Tick， 需继承 FTickableGameObject，参考 UAutoDestroySubsystem 写法

  UCLASS()
  class DESIGNPATTERNS_API UScoreGameInsSubsystem : public UGameInstanceSubsystem, public FTickableGameObject
  {
  	GENERATED_BODY()
  public:
  	virtual void Tick(float DeltaTime)override{ UE_LOG(LogTemp, Warning, TEXT(__FUNCTION__"Ping Pong"));}
  	virtual bool IsTickable()const override { return !IsTemplate(); } //判断是否是 CDO，避免执行两次 Tick
  	virtual TStatId GetStatId() const override { RETURN_QUICK_DECLARE_CYCLE_STAT(UMyScoreSubsystem, STATGROUP_Tickables); }
  };
  

• 支持 Subsystem 之间的访问

• 支持多个Subsystem定义依赖顺序，再初始化时调用 Collection.InitializeDependency(UScoreGameInsSubsystem::StaticClass());

---

UWorldSubsystem

• 可以再编辑器 和 运行时 使用

  UCLASS()
  class DESIGNPATTERNS_API UMyWorldSubsystem : public UWorldSubsystem
  {
  	GENERATED_BODY()
  public:
  	// 是否允许被创建
  	virtual bool ShouldCreateSubsystem(UObject* Outer) const override { return true; }
  	// 初始化
  	virtual void Initialize(FSubsystemCollectionBase& Collection) override;
  	// 释放
  	virtual void Deinitialize() override;
  	FString GetWorldType();
  };
  

  void UMyWorldSubsystem::Initialize(FSubsystemCollectionBase& Collection)
  {
  	UE_LOG(LogTemp, Warning, TEXT(__FUNCTION__" [World] %-20s\t[Type] %s\t"), *GetWorld()->GetName(), *GetWorldType());
  }
  void UMyWorldSubsystem::Deinitialize()
  {
  	UE_LOG(LogTemp, Warning, TEXT(__FUNCTION__" [World] %-20s\t[Type] %s\t"), *GetWorld()->GetName(), *GetWorldType());
  }
  FString UMyWorldSubsystem::GetWorldType()
  {
  	FString WorldTypeName;
  	switch (GetWorld()->WorldType) {
  	case EWorldType::None: {WorldTypeName = TEXT("None"); }break;
  	case EWorldType::Game: {WorldTypeName = TEXT("Game"); }break;
  	case EWorldType::Editor: {WorldTypeName = TEXT("Editor"); }break;
  	case EWorldType::PIE: {WorldTypeName = TEXT("PIE"); }break;
  	case EWorldType::EditorPreview: {WorldTypeName = TEXT("EditorPreview"); }break;
  	case EWorldType::GamePreview: {WorldTypeName = TEXT("GamePreview"); }break;
  	case EWorldType::GameRPC: {WorldTypeName = TEXT("GameRPC"); }break;
  	case EWorldType::Inactive: {WorldTypeName = TEXT("Inactive"); }break;
  	default: WorldTypeName = TEXT("default");
  	};
  	return WorldTypeName;
  }
  

  

UEditorSubsystem

• 需要再 .build.cs 添加 EditorSubsystem 模块

  if (Target.bBuildEditor)
  {
  	PublicDependencyModuleNames.AddRange(new string[] { "EditorSubsystem" });
  }
  

• 需要添加头文件

• 编译模式记得选Editor 模式

  #include "EditorSubsystem.h"
  UCLASS()
  class DESIGNPATTERNS_API UMyEditorSubsystem : public UEditorSubsystem
  {
  	GENERATED_BODY()
  public:
  	// 是否允许被创建
  	virtual bool ShouldCreateSubsystem(UObject* Outer) const override { return true; }
  	// 初始化
  	virtual void Initialize(FSubsystemCollectionBase& Collection) override;
  	// 释放
  	virtual void Deinitialize() override;
  };
  

  

系统自带 Subsystem 使用蓝图示例

Asset Editor Subsystem

Asset Tag Subsystem

Editor Utility Subsystem

Layer Subsystem

Import Subsystem

Editor Validator Subsystem

• 检查、验证资产

• 从 EditorUtilityBlueprint 中选择父类 EditorValidatorBase

  

  

  

---

参考

• 编程子系统
• 【B站】[英文直播]Programming Subsystems(真实字幕组)
• 《InsideUE4》GamePlay架构（十一）Subsystems
• 【PPT】猫でも分かるUE4.22から入ったSubsystem
• Does 'Data Validation' not work for Blueprints?

---

附录

• SubsystemCollection.cpp

  • FSubsystemCollectionBase::Initialize()
  • FSubsystemCollectionBase::AddAndInitializeSubsystem()
  • FSubsystemCollectionBase::Deinitialize()

  void FSubsystemCollectionBase::Initialize(UObject* NewOuter)
  {
  	if (Outer != nullptr)
  	{
  		// already initialized
  		return;
  	}
  	Outer = NewOuter;
  	check(Outer);
  	if (ensure(BaseType) && ensureMsgf(SubsystemMap.Num() == 0, TEXT("Currently don't support repopulation of Subsystem Collections.")))
  	{
  		check(!bPopulating); //Populating collections on multiple threads?
  		if (SubsystemCollections.Num() == 0)
  		{
  			FSubsystemModuleWatcher::InitializeModuleWatcher();
  		}
  		TGuardValue<bool> PopulatingGuard(bPopulating, true);
  		if (BaseType->IsChildOf(UDynamicSubsystem::StaticClass())) // 判断是否是 UDynamicSubsystem 的子类
  		{
  			for (const TPair<FName, TArray<TSubclassOf<UDynamicSubsystem>>>& SubsystemClasses : DynamicSystemModuleMap)
  			{
  				for (const TSubclassOf<UDynamicSubsystem>& SubsystemClass : SubsystemClasses.Value)
  				{
  					if (SubsystemClass->IsChildOf(BaseType))
  					{
  						AddAndInitializeSubsystem(SubsystemClass);
  					}
  				}
  			}
  		}
  		else // 不是 UDynamicSubsystem 的子类
  		{
  			TArray<UClass*> SubsystemClasses;
  			GetDerivedClasses(BaseType, SubsystemClasses, true);
  			for (UClass* SubsystemClass : SubsystemClasses)
  			{
  				AddAndInitializeSubsystem(SubsystemClass);
  			}
  		}
  		// Statically track collections
  		SubsystemCollections.Add(this);
  	}
  }
  void FSubsystemCollectionBase::Deinitialize()
  {
  	// Remove static tracking
  	SubsystemCollections.Remove(this);
  	if (SubsystemCollections.Num() == 0)
  	{
  		FSubsystemModuleWatcher::DeinitializeModuleWatcher();
  	}
  	// Deinit and clean up existing systems
  	SubsystemArrayMap.Empty();
  	for (auto Iter = SubsystemMap.CreateIterator(); Iter; ++Iter) // 遍历 SubsystemMap
  	{
  		UClass* KeyClass = Iter.Key();
  		USubsystem* Subsystem = Iter.Value();
  		if (Subsystem->GetClass() == KeyClass)
  		{
  			Subsystem->Deinitialize(); // 清理、释放
  			Subsystem->InternalOwningSubsystem = nullptr;
  		}
  	}
  	SubsystemMap.Empty();
  	Outer = nullptr;
  }
  USubsystem* FSubsystemCollectionBase::AddAndInitializeSubsystem(UClass* SubsystemClass)
  {
  	if (!SubsystemMap.Contains(SubsystemClass))
  	{
  		// Only add instances for non abstract Subsystems
  		if (SubsystemClass && !SubsystemClass->HasAllClassFlags(CLASS_Abstract))
  		{
  			// Catch any attempt to add a subsystem of the wrong type
  			checkf(SubsystemClass->IsChildOf(BaseType), TEXT("ClassType (%s) must be a subclass of BaseType(%s)."), *SubsystemClass->GetName(), *BaseType->GetName());
  			// Do not create instances of classes aren't authoritative
  			if (SubsystemClass->GetAuthoritativeClass() != SubsystemClass)
  			{
  				return nullptr;
  			}
  			const USubsystem* CDO = SubsystemClass->GetDefaultObject<USubsystem>();
  			if (CDO->ShouldCreateSubsystem(Outer)) // 从CDO调用ShouldCreateSubsystem来判断是否要创建
  			{
  				USubsystem* Subsystem = NewObject<USubsystem>(Outer, SubsystemClass); //创建
  				SubsystemMap.Add(SubsystemClass,Subsystem); // 添加到 SubsystemMap
  				Subsystem->InternalOwningSubsystem = this;
  				Subsystem->Initialize(*this); //调用Initialize
  				return Subsystem;
  			}
  		}
  		return nullptr;
  	}
  	return SubsystemMap.FindRef(SubsystemClass);
  }