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【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

image

  • 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

    // 原文链接 https://www.cnblogs.com/shiroe/p/14819721.html
// 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
    // 原文链接 https://www.cnblogs.com/shiroe/p/14819721.html
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

    // 原文链接 https://www.cnblogs.com/shiroe/p/14819721.html
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;	
};

    // 原文链接 https://www.cnblogs.com/shiroe/p/14819721.html
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;
}

    image

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

    // 原文链接 https://www.cnblogs.com/shiroe/p/14819721.html
/**
 * 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

    image

    image

其他用法

  • 支持Tick， 需继承 FTickableGameObject，参考 UAutoDestroySubsystem 写法

    // 原文链接 https://www.cnblogs.com/shiroe/p/14819721.html
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

    // 原文链接 https://www.cnblogs.com/shiroe/p/14819721.html
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();
};

    // 原文链接 https://www.cnblogs.com/shiroe/p/14819721.html
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;
}

    image

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

    // 原文链接 https://www.cnblogs.com/shiroe/p/14819721.html
#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;

};

    image

系统自带 Subsystem 使用蓝图示例

Asset Editor Subsystem

image

Asset Tag Subsystem

image

Editor Utility Subsystem

image

Layer Subsystem

image

Import Subsystem

image

Editor Validator Subsystem

  • 检查、验证资产

  • 从 EditorUtilityBlueprint 中选择父类 EditorValidatorBase

    image

    image

    image

参考

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);
}
posted @ 2021-05-27 20:48  砥才人  阅读(8499)  评论(0)  编辑  收藏  举报