행위패턴-State

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[State]
의도:
객체 자신의 내부 상태에 따라 행위를 변경하도록 한다. 객체가 클래스를 바꾸는 것처럼 보일
수 있다.

다른 이름:
Object for State

설명:
FSM(Finite State Machine)를 구현함에 있어서 State패턴을 이용한다.
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/////////////////////////////////////////////////////////////////////////////
//
// A Behavioral part of GoF's Design Patterns
//
// - State
//
/////////////////////////////////////////////////////////////////////////////

#include <windows.h>
#include <tchar.h>

#include <iostream>

/////////////////////////////////////////////////////////////////////////////
//
// State
//
/////////////////////////////////////////////////////////////////////////////
class Context;

class State
{
public:
 virtual ~State() {}
public:
 virtual void Handle      (Context*) {}
protected:
 virtual void ChangeState (Context*, State*);
};

//// ------------------------------------------------------------------------

class ConcreteStateA : public State
{
public:
 virtual void Handle(Context* c);
};

class ConcreteStateB : public State
{
public:
 virtual void Handle(Context* c);
};

class ConcreteStateC : public State
{
public:
 virtual void Handle(Context* c);
};

void ConcreteStateA::Handle(Context* c)
{
 std::cout << "ConcreteStateA::Handle()" << std::endl;
 ChangeState (c, new ConcreteStateB());
}

void ConcreteStateB::Handle(Context* c)
{
 std::cout << "ConcreteStateB::Handle()" << std::endl;
 ChangeState (c, new ConcreteStateC());
}

void ConcreteStateC::Handle(Context* c)
{
 std::cout << "ConcreteStateC::Handle()" << std::endl;
 ChangeState (c, new ConcreteStateA());
}

//// ------------------------------------------------------------------------

class Context
{
public:
 friend class State;
public:
 Context () : State_(0)
 {
  State_ = new ConcreteStateA();
 }

 virtual ~Context ()
 {
  if (State_)
   delete State_;
 }

public:
 void Request (void)
 {
  if (State_)
  {
   State_->Handle(this);
  }
 }

protected:
 void ChangeState (State *s)
 {
  if (State_)
  {
   delete State_;
  }

  State_ = s;
 }

private:
 State *State_;
};

//// ------------------------------------------------------------------------

void State::ChangeState (Context* c, State* s)
{
 c->ChangeState (s);
}

/////////////////////////////////////////////////////////////////////////////
//
// Startup
//
//
/////////////////////////////////////////////////////////////////////////////
int _tmain(int argc, _TCHAR* argv[])
{
 Context context;

 context.Request();
 context.Request();
 context.Request();

 context.Request();
 context.Request();
 context.Request();

 return 0;
}
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ConcreteStateA::Handle()
ConcreteStateB::Handle()
ConcreteStateC::Handle()
ConcreteStateA::Handle()
ConcreteStateB::Handle()
ConcreteStateC::Handle()