Design Patterns: Solidify Your C# Application Architecture with Design Patterns中文版(尾篇二)<?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" />
作者：Samir Bajaj
譯者：榮耀
【譯序：C#進階文章。譯者對Samir提供的C#例子進行了簡單整理（作者提供的某些代碼在譯者的環境中無法通過編譯），並編寫了對應的C++示例，一併置於譯註中，以便讀者比對。譯文中所有C#、C++程序調試環境均爲Microsoft Visual Studio.NET 7.0 Beta2】
C++示例：【譯註：由於此例代碼相對複雜，故把類的聲明和定義分離開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()
{
//發飲料
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 邏輯
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邏輯
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 邏輯
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 邏輯
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 邏輯
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) //【譯註：對應的C#代碼是while(true)，爲避免內存泄漏問題，改爲如此。否則，永遠都不會執行後面四行@代碼】
{
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;
}
/*以下是某次運行時輸出結果：
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!
*/
】
結論
設計模式吸取了在面向對象軟件設計中常見問題的解決方案的多年經驗之精華。不管項目規模如何，它們爲大多數軟件開發人員碰到的問題提供了答案。C#提高了程序員的生產力，它加入了可以促進面向對象設計的特性，並減少了開發人員手工勞動負擔。二者結合，無往不利。