目录

描述

套路

使用场景

优缺点

UE4实践

创建享元抽象类

创建具体享元类-地鼠

创建具体享元类-炸弹

创建享元工厂类

---

描述

• 运用共享技术有效的支持大量细粒度对象的复用，系统只使用少量对象，而这些对象都很相似，状态变换很小，可以实现对象的多次复用
• 由于向元模式要求能够共享的对象必须是细粒度对象，因此又称为轻量级模式，是一种对象结构型模式
• 享元类可以有多个对象，单例类只有一个对象
• 内部状态
  • 享元对象内部不随外界环境改变而改变的公共部分
• 外部状态
  • 享元对象内部随环境的改变而改变，不能够共享的状态就是外部状态

套路

• Flyweight（抽象享元类）
  • 一个接口或者抽象类，声明了具体享元类的公共方法
• ConcreteFlyweight（具体享元类）
  • 实现了抽象享元类，实例为享元对象
• UnsharedConcreteFlyweight（非共享具体享元类）
  • 并不是所有的抽象享元类的子类都需要被共享，不能被共享的子类可设计为非共享具体享元类
• FlyweightFactory（享元工厂类）
  • 用于创建并管理享元对象，一般设计为一个存储“Key-Value”键值对的组合，可结合工厂模式设计
  • 提供一个用于存储享元对象的享元池，当用户需要对象时，首先从享元池中获取，如果享元池中不存在，那么创建一个新的享元对象返回给用户，并在享元池中保存该新增对象

使用场景

• 程序需要生成数量巨大的相似对象
• 对象中包含可抽取且能在多个对象之间共享的重复状态
• 示例：
  • 游戏场景中的植被、子弹等重复物体，贴图或者是网格，Transform不一样
  • 与对象池的区别：对象池是可以重复使用，每次使用都是独占使用；享元是共享使用，对象池可以看做享元模式的升级版

优缺点

• 优点
  • 可以极大地减少内存中对象的数量，使得相同对象或相似对象在内存中只保存一份
  • 外部状态相对独立，而且不会影响其内部状态，从而使得享元对象可以再不同的环境中被共享
• 缺点
  • 使系统变得复杂，需要分离出内部状态和外部状态，使得程序逻辑复杂化
  • 为了使对象可以共享，享元模式需要将对线的状态外部化，而读取外部状态使得运行时间变长

UE4实践

打地鼠，中间有炸弹。

避免高频率创建和销毁，提高重复利用，此时可以使用享元模式

创建享元抽象类

// 抽象享元类 
UCLASS(Abstract)
class DESIGNPATTERNS_API AFlyweightObject : public AActor
{
	GENERATED_BODY()
public:
	// 用于每次重新调用时，初始化各个参数
	virtual void Init(FVector pInitPos) {
		bIsLiving = true;
		UE_LOG(LogTemp, Warning, TEXT("----------------------------------"));
		UE_LOG(LogTemp, Warning, TEXT(__FUNCTION__" %s is used. Pos%s"),
			*this->GetName(),
			*UKismetStringLibrary::Conv_VectorToString(pInitPos));
 
		GetWorld()->GetTimerManager().SetTimer(m_pTimerHandle, this, &AFlyweightObject::End, 1.0f, false);
 
	}
 
	// 自定义销毁程序，不是真正的销毁实例
	virtual void End() {
		if (bIsLiving)
		{
			UE_LOG(LogTemp, Warning, TEXT(__FUNCTION__" ******** %s is destroyed."), *this->GetName());
			bIsLiving = false;
			GetWorld()->GetTimerManager().ClearTimer(m_pTimerHandle);
		}
	}
 
	// 击中
	virtual void Hit() PURE_VIRTUAL(AFlyweightObject::IsValid, );
 
	// 用于判断是否已经在使用、空闲状态
	bool IsLiving() {
		return bIsLiving;
	}
 
protected:
	bool bIsLiving;
	FTimerHandle m_pTimerHandle;
};

创建具体享元类-地鼠

// 具体享元类 —— 地鼠
UCLASS()
class DESIGNPATTERNS_API AMole : public AFlyweightObject
{
	GENERATED_BODY()
public:
	virtual void Hit() {	
		UE_LOG(LogTemp, Warning, TEXT(__FUNCTION__" %s is hit. Add 10 score"), *this->GetName());
		End();
	}
 
};

创建具体享元类-炸弹

// 具体享元类 —— 炸弹
UCLASS()
class DESIGNPATTERNS_API ABomb : public AFlyweightObject
{
	GENERATED_BODY()
public:
	virtual void Hit() {		
		UE_LOG(LogTemp, Warning, TEXT(__FUNCTION__" %s is hit. Add -5 score"), *this->GetName());
		End();
	}
};

创建享元工厂类

内部可使用享元池存储多个享元对象

// 享元工厂类 
UCLASS()
class DESIGNPATTERNS_API AFlyweightFactory : public AActor
{
	GENERATED_BODY()
public:
	// 初始化多个地鼠和炸弹实例以供使用
	void Init() {
		for (int32 i = 0; i < 3; i++)
		{
			AMole* mole = GetWorld()->SpawnActor(FVector::ZeroVector, FRotator::ZeroRotator);
			m_pMolePool.Add(mole->GetName(), mole);			
		
			ABomb* bomb = GetWorld()->SpawnActor(FVector::ZeroVector, FRotator::ZeroRotator);
			m_pBombPool.Add(bomb->GetName(), bomb);
		}
	}
 
	// 获取未被使用的地鼠实例
	AMole* GetMole() {
		for (TTuple& item : m_pMolePool)
		{
			if (!(item.Value)->IsLiving())
			{
				return item.Value;
			}			
		}
		return nullptr;
	}
 
	// 获取未被使用的炸弹实例
	ABomb* GetBomb() {
		for (TTuple& item : m_pBombPool)
		{
			if (!(item.Value)->IsLiving())
			{
				return item.Value;
			}			
		}
		return nullptr;
	}
 
	// 随机获取未被使用的地鼠或炸弹实例
	AFlyweightObject* GetRandomElement() {
		if (UKismetMathLibrary::RandomFloat() < 0.7f)
		{
			return GetMole();
		}
		else 
		{
			return GetBomb();
		}
		
	}
 
private:
	// 存储的地鼠对象池
	UPROPERTY()
	TMap m_pMolePool;
	
	// 存储的炸弹对象池
	UPROPERTY()
	TMap m_pBombPool;
};

 

测试

UCLASS()
class DESIGNPATTERNS_API AFlyweightTestActor : public AActor
{
	GENERATED_BODY()
	
public:	
	// Sets default values for this actor's properties
	AFlyweightTestActor();
	// Called every frame
	virtual void Tick(float DeltaTime) override;
 
protected:
	// Called when the game starts or when spawned
	virtual void BeginPlay() override;
 
public:	
	UPROPERTY()
	AFlyweightFactory* m_pFlyweightFactory;
 
	UPROPERTY()
	FTimerHandle TimerHandle;
 
	// 定时生成地鼠或炸弹
	UFUNCTION()
	void AutoSpawner();
 
	
};

 

// Called when the game starts or when spawned
void AFlyweightTestActor::BeginPlay()
{
	Super::BeginPlay();
 
	// 享元工厂实例
	m_pFlyweightFactory = GetWorld()->SpawnActor(AFlyweightFactory::StaticClass());
	m_pFlyweightFactory->Init();
 
	// 定时器
	GetWorld()->GetTimerManager().SetTimer(TimerHandle, this, &AFlyweightTestActor::AutoSpawner, 0.4f, true);
}
 
void AFlyweightTestActor::AutoSpawner()
{
	// 随机位置
	int32 RandomInt = UKismetMathLibrary::RandomInteger(16);
	FVector RandomPos = FVector::ZeroVector + FVector(1, 0, 0) * (RandomInt / 4) + FVector(0, 1, 0) * (RandomInt % 4);
	// 获取随机空闲的地鼠或炸弹
	AFlyweightObject* FlyweightObj = m_pFlyweightFactory->GetRandomElement();
	if (FlyweightObj)
	{
		// 初始化享元对象
		FlyweightObj->Init(RandomPos);
 
		// 假定一定概率击中
		if (UKismetMathLibrary::RandomFloat()<0.2)
		{
			FLatentActionInfo LatentActionInfo;
			UKismetSystemLibrary::Delay(GetWorld(), 0.1, LatentActionInfo);
			FlyweightObj->Hit();
		}				
 
	}
 
}

 

LogTemp: Warning: ----------------------------------
LogTemp: Warning: AFlyweightObject::Init Mole_0 is used. PosX=3.000 Y=1.000 Z=0.000
LogTemp: Warning: ----------------------------------
LogTemp: Warning: AFlyweightObject::Init Mole_1 is used. PosX=2.000 Y=3.000 Z=0.000
LogTemp: Warning: ----------------------------------
LogTemp: Warning: AFlyweightObject::Init Mole_2 is used. PosX=1.000 Y=1.000 Z=0.000
LogTemp: Warning: AMole::Hit Mole_2 is hit. Add 10 score
LogTemp: Warning: AFlyweightObject::End ******** Mole_2 is destroyed.
LogTemp: Warning: AFlyweightObject::End ******** Mole_0 is destroyed.
LogTemp: Warning: ----------------------------------
LogTemp: Warning: AFlyweightObject::Init Mole_0 is used. PosX=3.000 Y=3.000 Z=0.000
LogTemp: Warning: AFlyweightObject::End ******** Mole_1 is destroyed.
LogTemp: Warning: ----------------------------------
LogTemp: Warning: AFlyweightObject::Init Mole_1 is used. PosX=3.000 Y=2.000 Z=0.000
LogTemp: Warning: ----------------------------------
LogTemp: Warning: AFlyweightObject::Init Bomb_0 is used. PosX=3.000 Y=1.000 Z=0.000
LogTemp: Warning: AFlyweightObject::End ******** Mole_0 is destroyed.
LogTemp: Warning: ----------------------------------
LogTemp: Warning: AFlyweightObject::Init Bomb_1 is used. PosX=3.000 Y=2.000 Z=0.000
LogTemp: Warning: ABomb::Hit Bomb_1 is hit. Add -5 score
LogTemp: Warning: AFlyweightObject::End ******** Bomb_1 is destroyed.
LogTemp: Warning: AFlyweightObject::End ******** Mole_1 is destroyed.
LogTemp: Warning: ----------------------------------
LogTemp: Warning: AFlyweightObject::Init Bomb_1 is used. PosX=2.000 Y=2.000 Z=0.000
LogTemp: Warning: AFlyweightObject::End ******** Bomb_0 is destroyed.
LogTemp: Warning: ----------------------------------
LogTemp: Warning: AFlyweightObject::Init Bomb_0 is used. PosX=2.000 Y=2.000 Z=0.000
LogTemp: Warning: ----------------------------------
LogTemp: Warning: AFlyweightObject::Init Bomb_2 is used. PosX=0.000 Y=3.000 Z=0.000
LogTemp: Warning: AFlyweightObject::End ******** Bomb_1 is destroyed.
LogTemp: Warning: ----------------------------------
LogTemp: Warning: AFlyweightObject::Init Bomb_1 is used. PosX=1.000 Y=2.000 Z=0.000
LogTemp: Warning: ABomb::Hit Bomb_1 is hit. Add -5 score
LogTemp: Warning: AFlyweightObject::End ******** Bomb_1 is destroyed.
LogTemp: Warning: AFlyweightObject::End ******** Bomb_0 is destroyed.
LogTemp: Warning: ----------------------------------
LogTemp: Warning: AFlyweightObject::Init Mole_0 is used. PosX=1.000 Y=2.000 Z=0.000
LogTemp: Warning: AMole::Hit Mole_0 is hit. Add 10 score
LogTemp: Warning: AFlyweightObject::End ******** Mole_0 is destroyed.
LogTemp: Warning: AFlyweightObject::End ******** Bomb_2 is destroyed.
LogTemp: Warning: ----------------------------------
LogTemp: Warning: AFlyweightObject::Init Mole_0 is used. PosX=2.000 Y=3.000 Z=0.000
LogTemp: Warning: ----------------------------------
LogTemp: Warning: AFlyweightObject::Init Mole_1 is used. PosX=1.000 Y=0.000 Z=0.000
LogTemp: Warning: ----------------------------------
LogTemp: Warning: AFlyweightObject::Init Bomb_0 is used. PosX=3.000 Y=3.000 Z=0.000
LogTemp: Warning: ABomb::Hit Bomb_0 is hit. Add -5 score
LogTemp: Warning: AFlyweightObject::End ******** Bomb_0 is destroyed.
LogTemp: Warning: AFlyweightObject::End ******** Mole_0 is destroyed.