设计模式C++描述----16.状态(State)模式 (一)

一. 举例

一般汽车发动机工作时有四种状态，吸气、压缩、做功和排气。

在运行时，不同的状态会有不同的行为，当前的状态机在适当的时候会过渡到下一状态。

其实用户在使用时根本不知道当前的状态，也无需知道当前的状态。用户只需要给发动机一个初始状态，最后得到一个停止状态就行了。

结构图如下：

代码如下：
[cpp]//状态
class State
{
public:
virtual void Operation(Work *work) {}
};

//工作
class Work
{
private:
State *m_state; //目前状态
int m_step; //步骤

public:
Work(State *state): m_state(state), m_step(0)
{}

~Work()
{
delete m_state;
}

int GetStep()
{
return m_step;
}

void SetStep(int step)
{
m_step = step;
}

void SetState(State *state)
{
delete m_state;
m_state = state;
}

void Operation()
{
m_state->Operation(this);
}
};

//排气状态
class ExhaustState: public State
{
public:
void Operation(Work *work) //排气操作
{
if(work->GetStep() == 4)
{
cout<<"Step : "<GetStep()<<"排气操作"< }
}
};

//做功状态
class ActState: public State
{
public:
void Operation(Work *work) //做功操作
{
if(work->GetStep() == 3)
{
cout<<"Step : "<GetStep()<<"做功操作"< }
else
{
work->SetState(new ExhaustState());
work->Operation();
}
}
};

//压缩状态
class CompressState: public State
{
public:
void Operation(Work *work) //压缩操作
{
if(work->GetStep() == 2)
{
cout<<"Step : "<GetStep()<<"压缩操作"< }
else
{
work->SetState(new ActState());
work->Operation();
}
}
};

//吸气状态
class InhaleState: public State
{
public:
void Operation(Work *work) //吸气操作
{
if(work->GetStep() == 1)
{
cout<<"Step : "<GetStep()<<"吸气操作"< }
else
{
State *p = new CompressState();
work->SetState(p);
work->Operation();
}
}
};


//测试代码
int main()
{
State* st = new InhaleState(); //初始状态

Work *work = new Work(st);

for(int i = 1; i < 5; ++i)
{
work->SetStep(i);

work->Operation(); //操作
}

delete work;

return 0;
}
//状态 www.2cto.com
class State
{
public:
virtual void Operation(Work *work) {}
};

//工作
class Work
{
private:
State *m_state; //目前状态
int m_step; //步骤

public:
Work(State *state): m_state(state), m_step(0)
{}

~Work()
{
delete m_state;
}

int GetStep()
{
return m_step;
}

void SetStep(int step)
{
m_step = step;
}

void SetState(State *state)
{
delete m_state;
m_state = state;
}

void Operation()
{
m_state->Operation(this);
}
};

//排气状态
class ExhaustState: public State
{
public:
void Operation(Work *work) //排气操作
{
if(work->GetStep() == 4)
{
cout<<"Step : "<GetStep()<<"排气操作"< }
}
};

//做功状态
class ActState: public State
{
public:
void Operation(Work *work) //做功操作
{
if(work->GetStep() == 3)
{
cout<<"Step : "<GetStep()<<"做功操作"< }
else
{
work->SetState(new ExhaustState());
work->Operation();
}
}
};

//压缩状态
class CompressState: public State
{
public:
void Operation(Work *work) //压缩操作
{
if(work->GetStep() == 2)
{
cout<<"Step : "<GetStep()<<"压缩操作"< }
else
{