下面我试图写的观察者模式的须藤代码时，观察者要观察不同的项目。
忽略语法错误。 我想知道这是否是实现这一正确的方法。 如果没有，请建议更好的方法。
// Used by the subject for keeping a track of what items the observer wants to observe
typedef struct observerListStruct
{
bool getTemperatureUpdate;
bool getHumidityUpdate;
bool getPressureUpdate;
observer's-function pointer's address;
};
// Subject's class
class weatherData
{
public:
// Observers will call this function to register themselves. The function pointer will point to the function which will get called when updates are available.
void registerObservers (observer obj, observer's-FunctionPointer)
{
// This observer's function returns which items to observe.
char* f = obj.returnItemsToObserve ();
if f[0] = `1`
observerListStruct.getTemperatureUpdate = true;
}
void unregisterObservers (observer obj) {}
private:
vector <observerListStruct> observerList;
float temperature;
float humidity;
float pressure;
void notifyObservers () {}
float getTemperature () {}
float getHumidity () {}
float getPressure () {}
} weatherDataObject;
// Base class for observers containing common functions
class observers
{
char ItemsToObserve [3] = {1, 2, 3};
// This observer's function returns which items to observe. Default - return all items
virtual char* returnItemsToObserve ()
{
return ItemsToObserve;
}
};
class observerDisplayElementCurrentConditions : public observers
{
char ItemsToObserve [3] = {1, 2};
char* returnItemsToObserve ()
{
return ItemsToObserve;
}
// this function will be used as a function pointer for getting updates
void getUpdatesAndDisplayWeatherData (float, float) {}
};
Answer 1:
更图案定向的溶液（但没有函数指针）可以是以下内容。 你可以参数化的WeatherObserver级只拿到了价值，你想要的。
#include <list>
#include <iostream>
class Observable; //forward declaration
//Base class for all observers
class Observer {
friend class Observable; //allow access to observedSubject
protected:
Observable *observedSubject;
public:
virtual void update(){};
};
//Base class for all observables
class Observable {
private:
std::list<Observer * const> m_registeredObservers;
public:
~Observable()
{
//delete the observers
std::list<Observer * const>::iterator it = m_registeredObservers.begin();
while (it != m_registeredObservers.end())
{
delete *it;
it = m_registeredObservers.erase(it);
}
}
void addObserver(Observer * const _pObserver)
{
_pObserver->observedSubject = this;
m_registeredObservers.push_back(_pObserver);
}
void removeObserver(Observer * const _pObserver)
{
m_registeredObservers.remove(_pObserver);
delete _pObserver;
}
void notifyObservers()
{
std::list<Observer * const>::iterator it = m_registeredObservers.begin();
while (it != m_registeredObservers.end())
{
(*it)->update();
it++;
}
}
};
//Concrete Observable
class WeatherData : public Observable {
private:
float temperature;
float humidity;
float pressure;
public:
WeatherData(): temperature(0), humidity(0), pressure(0)
{};
float getTemperature () const
{
return temperature;
}
float getHumidity () const
{
return humidity;
}
float getPressure () const
{
return pressure;
}
void setTemperature(float _temperature)
{
if (temperature != _temperature)
{
temperature = _temperature;
notifyObservers();
}
}
void setHumidity(float _humidity)
{
if (humidity != _humidity)
{
humidity = _humidity;
notifyObservers();
}
}
void setPressure(float _pressure)
{
if (pressure != _pressure)
{
pressure = _pressure;
notifyObservers();
}
}
};
//Concrete implementation of an weather observer
class WeatherObserver : public Observer
{
public:
WeatherObserver():Observer(){};
void update()
{
WeatherData* pWeatherPtr = static_cast<WeatherData*>(observedSubject);
if (pWeatherPtr != 0)
{
float actHumidity = pWeatherPtr->getHumidity();
float actPressure = pWeatherPtr->getPressure();
float actTemperature = pWeatherPtr->getTemperature();
//do something with the data
std::cout << "WeatherObserver update" << std::endl;
std::cout << "Temperature : " << actTemperature << std::endl;
std::cout << "Humidity : " << actHumidity << std::endl;
std::cout << "Pressure : " << actPressure << std::endl;
}
}
};
int main()
{
WeatherData weatherData;
Observer * pObserver = new WeatherObserver();
weatherData.addObserver(pObserver);
weatherData.setHumidity(100);
weatherData.setTemperature(100);
}
Answer 2:
我认为这是更容易，更可扩展，定义一组，每个观察者可以听的事件类型。 然后您注册观察者听那个特定的事件类型。 所观察到的，然后保持每个事件注册的观察者的名单，并通知他们，如果和事件发生时。 使用的组合std::function ， std::bind （或boost当量），很容易进行注册，以便一个给定事件类型的回调。 你可以把回调在地图事件类型的回调。
例如，沿着这些线的东西（几乎伪代码中，还没有被测试）
class Publisher {
public :
void subscribe(const std::string& event,
std::function<void(double)> callback) {
m_subscribers[s].push_back(callback);
}
void publish(const std::string& event) const {
for (auto& f : m_subscribers[event]) f( some double );}
void event(const std::string& event) const { publish(event);}
private:
// map of event types (here simply strings) to list of callbacks
std::map<std::string&,
std::list<std::function<void(const std::string&)>>> m_subscribers;
};
struct Foo {
void foo(double x) {
std::cout << "Foo received message: " << x << "\n";
}
};
struct Bar {
void bar(double x) {
std::cout << "Bar received message: " << x << "\n";
}
};
int main() {
Publisher pub;
Foo f0;
Foo f1;
Bar bar0;
pub.subscribe("RED", std::bind(&Foo::foo, &foo0, _1));
pub.subscribe("GREEN", std::bind(&Foo::foo, &foo1, _1));
pub.subscribe("WHITE", std::bind(&Foo::foo, &foo1, _1));
pub.subscribe("RED", std::bind(&Bar::bar, &bar0, _1));
pub.subscribe("BLUE", std::bind(&Bar::bar, &bar0, _1));
pub.subscribe("MAGENTA", std::bind(&Bar::bar, &bar0, _1));
// trigger a "GREEN" event
pub.event("GREEN");
}
在这里，观察者（或用户）注册到一些事件，通过串这里表示，当这个事件发生时他们注册的回调被调用。 在上面的例子中我手动触发事件来说明的机制。
此事件回调机制允许去耦回调动作的实际项目。 所观察到的（或发布者）知道什么参数来传递回调对于给定的事件，并且该回调调用，所以观察者不依赖于所观察到的物体的内部数据。
Answer 3:
我写了很多的C ++代码，并创造我工作的一些游戏组件观察员需要。 我需要的东西来分发，“用户输入”等“帧的开始”，因为在比赛中向有关方面事件。
我在可能被处理的事件，也希望更多的粒度。 我有很多的小东西，熄灭......我并不需要有一个有兴趣重新下一帧担心在用户输入一个变化的部分。
我也希望它是直C ++，不依赖于平台或特定技术（如升压，Qt的，等等），因为我经常建立和重复使用的组件（及其背后的想法）在不同的项目。
这里是什么，我想出了一个解决方案的草图：
- 观察者的钥匙单身（枚举值，而不是字符串，这是一个速度的权衡，因为密钥是不搜索散列，但它意味着不容易的“串”的名字，你必须预先定义它们）为主体进行注册在兴趣，因为它是一个单，它始终存在。
- 每个受试者是从一个共同的基类派生的。 基类有一个抽象的虚拟功能通知（...），其必须在派生类来实现，并且析构函数，从该观察（它总是可以达到）除去它时，它被删除。
- 观察者本身内部，如果拆离（...）被调用而通知（...）正在进行中，任何分离的主题最终名单。
- 当通知（...）被调用的观察，它创建的主题列表中的临时副本。 由于它遍历它，它比较它的最近分离。 如果目标不就行了，通知（...）被称为目标。 否则，将被跳过。
- 通知（...）的观察员也保持深度的跟踪处理级联呼叫的（A通知B，C，d和D.Notify（...）触发Notify（...）调用E，等等。）
这是接口告终什么看起来像：
/*
The Notifier is a singleton implementation of the Subject/Observer design
pattern. Any class/instance which wishes to participate as an observer
of an event can derive from the Notified base class and register itself
with the Notiifer for enumerated events.
Notifier derived classes MUST implement the notify function, which has
a prototype of:
void Notify(const NOTIFIED_EVENT_TYPE_T& event)
This is a data object passed from the Notifier class. The structure
passed has a void* in it. There is no illusion of type safety here
and it is the responsibility of the user to ensure it is cast properly.
In most cases, it will be "NULL".
Classes derived from Notified do not need to deregister (though it may
be a good idea to do so) as the base class destructor will attempt to
remove itself from the Notifier system automatically.
The event type is an enumeration and not a string as it is in many
"generic" notification systems. In practical use, this is for a closed
application where the messages will be known at compile time. This allows
us to increase the speed of the delivery by NOT having a
dictionary keyed lookup mechanism. Some loss of generality is implied
by this.
This class/system is NOT thread safe, but could be made so with some
mutex wrappers. It is safe to call Attach/Detach as a consequence
of calling Notify(...).
*/
class Notified;
class Notifier : public SingletonDynamic<Notifier>
{
public:
typedef enum
{
NE_MIN = 0,
NE_DEBUG_BUTTON_PRESSED = NE_MIN,
NE_DEBUG_LINE_DRAW_ADD_LINE_PIXELS,
NE_DEBUG_TOGGLE_VISIBILITY,
NE_DEBUG_MESSAGE,
NE_RESET_DRAW_CYCLE,
NE_VIEWPORT_CHANGED,
NE_MAX,
} NOTIFIED_EVENT_TYPE_T;
private:
typedef vector<NOTIFIED_EVENT_TYPE_T> NOTIFIED_EVENT_TYPE_VECTOR_T;
typedef map<Notified*,NOTIFIED_EVENT_TYPE_VECTOR_T> NOTIFIED_MAP_T;
typedef map<Notified*,NOTIFIED_EVENT_TYPE_VECTOR_T>::iterator NOTIFIED_MAP_ITER_T;
typedef vector<Notified*> NOTIFIED_VECTOR_T;
typedef vector<NOTIFIED_VECTOR_T> NOTIFIED_VECTOR_VECTOR_T;
NOTIFIED_MAP_T _notifiedMap;
NOTIFIED_VECTOR_VECTOR_T _notifiedVector;
NOTIFIED_MAP_ITER_T _mapIter;
// This vector keeps a temporary list of observers that have completely
// detached since the current "Notify(...)" operation began. This is
// to handle the problem where a Notified instance has called Detach(...)
// because of a Notify(...) call. The removed instance could be a dead
// pointer, so don't try to talk to it.
vector<Notified*> _detached;
int32 _notifyDepth;
void RemoveEvent(NOTIFIED_EVENT_TYPE_VECTOR_T& orgEventTypes, NOTIFIED_EVENT_TYPE_T eventType);
void RemoveNotified(NOTIFIED_VECTOR_T& orgNotified, Notified* observer);
public:
virtual void Reset();
virtual bool Init() { Reset(); return true; }
virtual void Shutdown() { Reset(); }
void Attach(Notified* observer, NOTIFIED_EVENT_TYPE_T eventType);
// Detach for a specific event
void Detach(Notified* observer, NOTIFIED_EVENT_TYPE_T eventType);
// Detach for ALL events
void Detach(Notified* observer);
/* The design of this interface is very specific. I could
* create a class to hold all the event data and then the
* method would just have take that object. But then I would
* have to search for every place in the code that created an
* object to be used and make sure it updated the passed in
* object when a member is added to it. This way, a break
* occurs at compile time that must be addressed.
*/
void Notify(NOTIFIED_EVENT_TYPE_T, const void* eventData = NULL);
/* Used for CPPUnit. Could create a Mock...maybe...but this seems
* like it will get the job done with minimal fuss. For now.
*/
// Return all events that this object is registered for.
vector<NOTIFIED_EVENT_TYPE_T> GetEvents(Notified* observer);
// Return all objects registered for this event.
vector<Notified*> GetNotified(NOTIFIED_EVENT_TYPE_T event);
};
/* This is the base class for anything that can receive notifications.
*/
class Notified
{
public:
virtual void Notify(Notifier::NOTIFIED_EVENT_TYPE_T eventType, const void* eventData) = 0;
virtual ~Notified();
};
typedef Notifier::NOTIFIED_EVENT_TYPE_T NOTIFIED_EVENT_TYPE_T;
注：本通报类有一个单一的功能，通知（......）在这里。 因为void *的不是类型安全的，我创建的其他版本，其中相同的通知长相：
virtual void Notify(Notifier::NOTIFIED_EVENT_TYPE_T eventType, int value);
virtual void Notify(Notifier::NOTIFIED_EVENT_TYPE_T eventType, const string& str);
相应的通知（...）方法添加到通知本身。 所有这些使用单个函数来获取“目标清单”，然后呼吁的目标适当的功能。 这种运作良好，将接收器不必做丑陋的转换。
这似乎运作良好。 该解决方案在网络上张贴在这里的源代码一起。 这是一个相对较新的设计，让任何反馈是极大的赞赏。
Answer 4:
#include <algorithm>
#include <vector>
class WeatherFlags
{
public:
WeatherFlags()
: mask_(0)
{}
union {
struct {
unsigned int temperature_ : 1;
unsigned int humidity_ : 1;
unsigned int pressure_ : 1;
};
unsigned int mask_;
};
};
class WeatherData;
class WeatherEvent
{
public:
WeatherEvent(WeatherData* data, WeatherFlags const& flags)
: data_(data)
, flags_(flags)
{}
double getTemperature() const;
WeatherData* data_;
WeatherFlags flags_;
};
class WeatherListener
{
public:
virtual ~WeatherListener() = 0;
virtual void onWeatherUpdate(WeatherEvent& e) = 0;
};
inline WeatherListener::~WeatherListener() {}
class WeatherListenerEntry
{
public:
WeatherListenerEntry()
: listener_(0)
{}
WeatherListenerEntry(WeatherListener* listener, WeatherFlags const& flags)
: listener_(listener)
, flags_(flags)
{}
WeatherListener* listener_;
WeatherFlags flags_;
};
class WeatherData
{
public:
WeatherData();
void addListener(WeatherListener* listener, WeatherFlags const& flags);
void removeListener(WeatherListener* listener);
void notify(WeatherFlags const& flags);
double getTemperature() const { return temperature_; }
private:
typedef std::vector<WeatherListenerEntry> Listeners;
Listeners listeners_;
double temperature_;
};
WeatherData::WeatherData()
: temperature_(0)
{}
void WeatherData::addListener(WeatherListener* listener, WeatherFlags const& flags)
{
// TODO Could maybe check for the addition of duplicates here...
listeners_.push_back(WeatherListenerEntry(listener, flags));
}
void WeatherData::removeListener(WeatherListener* listener)
{
struct ListenerEquals {
WeatherListener* listener_;
ListenerEquals(WeatherListener* listener)
: listener_(listener)
{}
bool operator()(WeatherListenerEntry const& e) const {
return (e.listener_ == listener_);
}
};
listeners_.erase(
std::remove_if(listeners_.begin(), listeners_.end(), ListenerEquals(listener)),
listeners_.end());
}
void WeatherData::notify(WeatherFlags const& flags)
{
WeatherEvent evt(this, flags);
for (Listeners::iterator i = listeners_.begin(); i != listeners_.end(); ++i)
{
if (0 != (i->flags_.mask_ & flags.mask_)) {
i->listener_->onWeatherUpdate(evt);
}
}
}
double
WeatherEvent::getTemperature() const
{
return data_->getTemperature();
}
#include <iostream>
class WeatherObserverStdout : public WeatherListener
{
public:
void observe(WeatherData& data) {
WeatherFlags flags;
flags.temperature_ = true; // interested in temperature only.
data.addListener(this, flags);
}
virtual void onWeatherUpdate(WeatherEvent& e);
};
void
WeatherObserverStdout::onWeatherUpdate(WeatherEvent& e)
{
double temp = e.getTemperature();
std::cout << "Temperatrure: " << temp << std::endl;
}
int _tmain(int argc, _TCHAR* argv[])
{
WeatherData wdata;
WeatherObserverStdout obs;
obs.observe(wdata);
WeatherFlags flags;
wdata.notify(flags);
flags.temperature_ = true;
wdata.notify(flags);
return 0;
}
Answer 5:
我的两分钱...
经典（四人帮）实现观察者模式的通知对这个问题的任何属性更改的观察员。 在你的问题，你想注册观测到的特定属性，而不是一个主题作为一个整体。 您可以在一个水平向下移动观察者模式，并采取属性，具体科目和定义他们的观察员（每财产），但有解决这个问题的一个更好的方式。
在C＃观察者模式是通过事件和委托实施。 代表们表示事件处理程序 - 功能当事件被触发时应该执行。 代表可以添加从事件（注册）或去除（未注册的）。
在C ++中， 仿函数作为代表-他们可以将所有必要的信息，调用一些全局函数或类的方法在不同的上下文。 事件是（注册）函子集，并在引发事件（调用）它基本上经过该名单，并呼吁所有仿函数（见Publisher::publish在juanchopanza的解决方法）。
我试图实现事件和委托的C ++版本，并可能在你的情况下应用改进的观察模式中使用它们。 这是我想出了：
#include <list>
#include <iostream>
#include <algorithm>
// use base class to resolve the problem of how to put into collection objects of different types
template <typename TPropertyType>
struct PropertyChangedDelegateBase
{
virtual ~PropertyChangedDelegateBase(){};
virtual void operator()(const TPropertyType& t) = 0;
};
template <typename THandlerOwner, typename TPropertyType>
struct PropertyChangedDelegate : public PropertyChangedDelegateBase<TPropertyType>
{
THandlerOwner* pHandlerOwner_;
typedef void (THandlerOwner::*TPropertyChangeHandler)(const TPropertyType&);
TPropertyChangeHandler handler_;
public:
PropertyChangedDelegate(THandlerOwner* pHandlerOwner, TPropertyChangeHandler handler) :
pHandlerOwner_(pHandlerOwner), handler_(handler){}
void operator()(const TPropertyType& t)
{
(pHandlerOwner_->*handler_)(t);
}
};
template<typename TPropertyType>
class PropertyChangedEvent
{
public:
virtual ~PropertyChangedEvent(){};
void add(PropertyChangedDelegateBase<TPropertyType>* const d)
{
std::list<PropertyChangedDelegateBase<TPropertyType>* const>::const_iterator it = std::find(observers_.begin(), observers_.end(), d);
if(it != observers_.end())
throw std::runtime_error("Observer already registered");
observers_.push_back(d);
}
void remove(PropertyChangedDelegateBase<TPropertyType>* const d)
{
std::list<PropertyChangedDelegateBase<TPropertyType>* const>::const_iterator it = std::find(observers_.begin(), observers_.end(), d);
if(it != observers_.end())
observers_.remove(d);
}
// notify
void operator()(const TPropertyType& newValue)
{
std::list<PropertyChangedDelegateBase<TPropertyType>* const>::const_iterator it = observers_.begin();
for(; it != observers_.end(); ++it)
{
(*it)->operator()(newValue);
}
}
protected:
std::list<PropertyChangedDelegateBase<TPropertyType>* const> observers_;
};
// class that owns concrete subjects
class PropertyOwner1
{
int property1_;
float property2_;
public:
PropertyChangedEvent<int> property1ChangedEvent;
PropertyChangedEvent<float> property2ChangedEvent;
PropertyOwner1() :
property1_(0),
property2_(0.0f)
{}
int property1() const {return property1_;}
void property1(int n)
{
if(property1_ != n)
{
property1_ = n;
std::cout << "PropertyOwner1::property1(): property1_ set to " << property1_ << std::endl;
property1ChangedEvent(property1_);
}
}
float property2() const {return property2_;}
void property2(float n)
{
if(property2_ != n)
{
property2_ = n;
std::cout << "PropertyOwner1::property2(): property2_ set to " << property2_ << std::endl;
property2ChangedEvent(property2_);
}
}
};
// class that owns concrete subjects
class PropertyOwner2
{
bool property1_;
double property2_;
public:
PropertyChangedEvent<bool> property1ChangedEvent;
PropertyChangedEvent<double> property2ChangedEvent;
PropertyOwner2() :
property1_(false),
property2_(0.0)
{}
bool property1() const {return property1_;}
void property1(bool n)
{
if(property1_ != n)
{
property1_ = n;
std::cout << "PropertyOwner2::property1(): property1_ set to " << property1_ << std::endl;
property1ChangedEvent(property1_);
}
}
double property2() const {return property2_;}
void property2(double n)
{
if(property2_ != n)
{
property2_ = n;
std::cout << "PropertyOwner2::property2(): property2_ set to " << property2_ << std::endl;
property2ChangedEvent(property2_);
}
}
};
// class that observes changes in property1 of PropertyOwner1 and property1 of PropertyOwner2
struct PropertyObserver1
{
void OnPropertyOwner1Property1Changed(const int& newValue)
{
std::cout << "\tPropertyObserver1::OnPropertyOwner1Property1Changed(): \n\tnew value is: " << newValue << std::endl;
}
void OnPropertyOwner2Property1Changed(const bool& newValue)
{
std::cout << "\tPropertyObserver1::OnPropertyOwner2Property1Changed(): \n\tnew value is: " << newValue << std::endl;
}
};
// class that observes changes in property2 of PropertyOwner1 and property2 of PropertyOwner2
struct PropertyObserver2
{
void OnPropertyOwner1Property2Changed(const float& newValue)
{
std::cout << "\tPropertyObserver2::OnPropertyOwner1Property2Changed(): \n\tnew value is: " << newValue << std::endl;
}
void OnPropertyOwner2Property2Changed(const double& newValue)
{
std::cout << "\tPropertyObserver2::OnPropertyOwner2Property2Changed(): \n\tnew value is: " << newValue << std::endl;
}
};
int main(int argc, char** argv)
{
PropertyOwner1 propertyOwner1;
PropertyOwner2 propertyOwner2;
PropertyObserver1 propertyObserver1;
PropertyObserver2 propertyObserver2;
// register observers
PropertyChangedDelegate<PropertyObserver1, int> delegate1(&propertyObserver1, &PropertyObserver1::OnPropertyOwner1Property1Changed);
propertyOwner1.property1ChangedEvent.add(&delegate1);
PropertyChangedDelegate<PropertyObserver2, float> delegate2(&propertyObserver2, &PropertyObserver2::OnPropertyOwner1Property2Changed);
propertyOwner1.property2ChangedEvent.add(&delegate2);
PropertyChangedDelegate<PropertyObserver1, bool> delegate3(&propertyObserver1, &PropertyObserver1::OnPropertyOwner2Property1Changed);
propertyOwner2.property1ChangedEvent.add(&delegate3);
PropertyChangedDelegate<PropertyObserver2, double> delegate4(&propertyObserver2, &PropertyObserver2::OnPropertyOwner2Property2Changed);
propertyOwner2.property2ChangedEvent.add(&delegate4);
propertyOwner1.property1(1);
propertyOwner1.property2(1.2f);
propertyOwner2.property1(true);
propertyOwner2.property2(3.4);
// unregister PropertyObserver1
propertyOwner1.property1ChangedEvent.remove(&delegate1);
propertyOwner2.property1ChangedEvent.remove(&delegate3);
propertyOwner1.property1(2);
propertyOwner1.property2(4.5f);
}
输出：
PropertyOwner1::property1(): property1_ set to 1 PropertyObserver1::OnPropertyOwner1Property1Changed(): new value is: 1 PropertyOwner1::property2(): property2_ set to 1.2 PropertyObserver2::OnPropertyOwner1Property2Changed(): new value is: 1.2 PropertyOwner2::property1(): property1_ set to 1 PropertyObserver1::OnPropertyOwner2Property1Changed(): new value is: 1 PropertyOwner2::property2(): property2_ set to 3.4 PropertyObserver2::OnPropertyOwner2Property2Changed(): new value is: 3.4 PropertyOwner1::property1(): property1_ set to 2 PropertyOwner1::property2(): property2_ set to 4.5 PropertyObserver2::OnPropertyOwner1Property2Changed(): new value is: 4.5
每个观察者与特定财产登记和通知时，每一个观看确切地知道谁是财产的所有者，什么是属性的新值。
文章来源: Implementing Observer pattern when observers wish to observe different items
