Design Patterns: Solidify Your C# Application Architecture with Design Patterns中文版(尾篇二)
作者：Samir Bajaj
译者：荣耀
【译序：C#进阶文章。译者对Samir提供的C#例子进行了简单整理（作者提供的某些代码在译者的环境中无法通过编译），并编写了对应的C++示例，一并置于译注中，以便读者比对。译文中所有C#、C++程序调试环境均为Microsoft Visual Studio.NET 7.0 Beta2】
C++示例：【译注：由于此例代码相对复杂，故把类的声明和定义分离开J】
state.h
#include "stdafx.h";
class State;
class VendingMachine;
class Start;
class Five;
class Ten;
class Fiftee;
class Twenty;
class State
{
public:
virtual void AddNickel(VendingMachine* vm) { }
virtual void AddDime(VendingMachine* vm) { }
virtual void AddQuarter(VendingMachine* vm) { }
protected:
virtual void ChangeState(VendingMachine* vm, State* s);
};
class VendingMachine
{
private:
State* state;
public:
VendingMachine();
void ChangeState(State* to);
void Vend();
void AddNickel();
void AddDime();
void AddQuarter();
};
class Start : public State
{
private:
static State* state;
public:
static State* Instance();
void AddNickel(VendingMachine* vm);
void AddDime(VendingMachine* vm);
void AddQuarter(VendingMachine* vm);
};
class Five : public State
{
private:
static State* state;
public:
static State* Instance();
void AddNickel(VendingMachine* vm);
void AddDime(VendingMachine* vm);
void AddQuarter(VendingMachine* vm);
};
class Ten : public State
{
private:
static State* state;
public:
static State* Instance();
void AddNickel(VendingMachine* vm);
void AddDime(VendingMachine* vm);
void AddQuarter(VendingMachine* vm);
};
class Fifteen : public State
{
private:
static State* state;
public:
static State* Instance();
void AddNickel(VendingMachine* vm);
void AddDime(VendingMachine* vm);
void AddQuarter(VendingMachine* vm);
};
class Twenty : public State
{
private:
static State* state;
public:
static State* Instance();
void AddNickel(VendingMachine* vm);
void AddDime(VendingMachine* vm);
void AddQuarter(VendingMachine* vm);
state.cpp
#include "stdafx.h";
#include "test.h";
#include <iostream>
using namespace std;
void State::ChangeState(VendingMachine* vm, State* s)
{
vm->ChangeState(s);
}
VendingMachine::VendingMachine()
{
cout<<"The Vending Machine is now online: product costs 25c"<<endl;
state = Start::Instance();
}
void VendingMachine::ChangeState(State* to)
{
state = to;
}
void VendingMachine::Vend()
{
//发饮料
cout<<"Dispensing product...Thank you!"<<endl;
}
void VendingMachine::AddNickel()
{
state->AddNickel(this);
}
void VendingMachine::AddDime()
{
state->AddDime(this);
}
void VendingMachine::AddQuarter()
{
state->AddQuarter(this);
}
State* Start::state = new Start();
State* Start::Instance()
{
// singleton 逻辑
cout<<"Credit: 0c"<<endl;
return state;
}
void Start::AddNickel(VendingMachine* vm)
{
ChangeState(vm, Five::Instance());
}
void Start::AddDime(VendingMachine* vm)
{
ChangeState(vm, Ten::Instance());
}
void Start::AddQuarter(VendingMachine* vm)
{
vm->Vend();
}
State* Five::state = new Five();
State* Five::Instance()
{
// singleton逻辑
cout<<"Credit: 5c"<<endl;
return state;
}
void Five::AddNickel(VendingMachine* vm)
{
ChangeState(vm, Ten::Instance());
}
void Five::AddDime(VendingMachine* vm)
{
ChangeState(vm, Fifteen::Instance());
}
void Five::AddQuarter(VendingMachine* vm)
{
vm->Vend();
ChangeState(vm, Start::Instance()); // no change returned :-)
}
State* Ten::state = new Ten();
State* Ten::Instance()
{
// singleton 逻辑
cout<<"Credit: 10c"<<endl;
return state;
}
void Ten::AddNickel(VendingMachine* vm)
{
ChangeState(vm, Fifteen::Instance());
}
void Ten::AddDime(VendingMachine* vm)
{
ChangeState(vm, Twenty::Instance());
}
void Ten::AddQuarter(VendingMachine* vm)
{
vm->Vend();
ChangeState(vm, Start::Instance()); // no change returned :-)
}
State* Fifteen::state = new Fifteen();
State* Fifteen::Instance()
{
// singleton 逻辑
cout<<"Credit: 15c"<<endl;
return state;
}
void Fifteen::AddNickel(VendingMachine* vm)
{
ChangeState(vm, Twenty::Instance());
}
void Fifteen::AddDime(VendingMachine* vm)
{
vm->Vend();
ChangeState(vm, Start::Instance());
}
void Fifteen::AddQuarter(VendingMachine* vm)
{
vm->Vend();
ChangeState(vm, Start::Instance()); // no change returned :-)
}
State* Twenty::state = new Twenty();
State* Twenty::Instance()
{
// singleton 逻辑
cout<<"Credit: 20c"<<endl;
return state;
}
void Twenty::AddNickel(VendingMachine* vm)
{
vm->Vend();
ChangeState(vm, Start::Instance());
}
void Twenty::AddDime(VendingMachine* vm)
{
vm->Vend();
ChangeState(vm, Start::Instance());
}
void Twenty::AddQuarter(VendingMachine* vm)
{
vm->Vend();
ChangeState(vm, Start::Instance()); // no change returned :-)
}
int _tmain(int argc, _TCHAR* argv[])
{
int coin = 0;
VendingMachine* vm = new VendingMachine();
int i = 0;
while (i < 10) //【译注：对应的C#代码是while(true)，为避免内存泄漏问题，改为如此。否则，永远都不会执行后面四行@代码】
{
cout<<"Insert a coin (5, 10, 25): ";
cin>>coin;
switch (coin)
{
case 5:
vm->AddNickel();
break;
case 10:
vm->AddDime();
break;
case 25:
vm->AddQuarter();
break;
default:
break;
}
i++;
}
delete Start::Instance();//@
delete Five::Instance();//@
delete Ten::Instance();//@
delete Fifteen::Instance();//@
return 0;
}
/*以下是某次运行时输出结果：
The Vending Machine is now online: product costs 25c
Credit: 0c
Insert a coin <5, 10, 25>: 5
Credit: 5c
Insert a coin <5, 10, 25>: 10
Credit: 15c
Insert a coin <5, 10, 25>: 5
Credit: 20c
Insert a coin <5, 10, 25>: 5
Dispensing product...Thank you!
*/
】
结论
设计模式吸取了在面向对象软件设计中常见问题的解决方案的多年经验之精华。不管项目规模如何，它们为大多数软件开发人员碰到的问题提供了答案。C#提高了程序员的生产力，它加入了可以促进面向对象设计的特性，并减少了开发人员手工劳动负担。二者结合，无往不利。