概述
描述
运用共享技术有效地支持大量细粒度对象的复用。系统只使用少量的对象，而这些对象都很相似，状态变化很小，可以实现对象的多次复用。
由于享元模式要求能够共享的对象必须是细粒度对象，因此它又称为轻量级模式，它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共享部分。-
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，其实例称为享元对象。 -
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”键值对的集合（可以结合工厂模式设计）。其作用就在于：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，那么则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
- 这将耗尽目标设备的所有内存
- 对象中包含可抽取且能在多个对象间共享的重复状态。
- 示例
- 游戏场景中的植被、子弹等重复的物体，贴图或是网格一样，Transform不一样
- 注意与对象池（也叫资源池，如连接池、线程池）的区别，对象池可重复使用，每次使用都是独占使用；享元是共享使用；对象池可以看作是享元模式的升级版
优缺点
- 优点
- 享元模式的优点在于它可以极大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。
- 享元模式的外部状态相对独立，而且不会影响其内部状态，从而使得享元对象可以在不同的环境中被共享。
- 缺点
- 享元模式使得系统更加复杂，需要分离出内部状态和外部状态，这使得程序的逻辑复杂化。
- 为了使对象可以共享，享元模式需要将享元对象的状态外部化，而读取外部状态使得运行时间变长。
UE4 实践
做个打地鼠雏形，过程中假设只提供地鼠和炸弹两种物品。避免高频率创建和销毁，提高重复利用，此时可以用享元模式，
-
创建享元抽象类、具体类
// 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;
}; // 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();
} }; // 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<AMole>(FVector::ZeroVector, FRotator::ZeroRotator);
m_pMolePool.Add(mole->GetName(), mole); ABomb* bomb = GetWorld()->SpawnActor<ABomb>(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<FString,AMole*>& 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<FString, ABomb*>& 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<FString,AMole*> m_pMolePool; // 存储的炸弹对象池
UPROPERTY()
TMap<FString,ABomb*> m_pBombPool;
}; -
调用测试
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>(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();
} } } -
调式输出
- 可以看出每次都是调用空闲的实例
- 生命周期结束或者被击中后，实例都会归为空闲状态
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.