職責鏈模式(Chain of Responsibility):使多個對象都有機會處理請求,從而避免請求的發送者和接收者之間的耦合關係。將這個對象連城一條鏈,並沿着這條鏈傳遞該請求,直到有一個對象處理它爲止。【DP】
// ResponsbilityChain.cpp : 定義控制檯應用程序的入口點。
//
#include "stdafx.h"
#include <iostream>
using namespace std;
class Handler
{
protected:
Handler *successor;
public:
virtual ~Handler(){}
void SetSuccessor(Handler *successor)
{
this->successor = successor;
}
public:
virtual void HandleRequest(int request) = 0;
};
class ConcreteHandler1 : public Handler
{
public:
void HandleRequest(int request)
{
if (request >= 0 && request < 10)
{
cout << "ConcreteHandler1" << "處理請求" << request << endl;
}
else if (successor != 0)
{
successor->HandleRequest(request);
}
}
};
class ConcreteHandler2 : public Handler
{
public:
void HandleRequest(int request)
{
if (request >= 10 && request < 20)
{
cout << "ConcreteHandler2" << "處理請求" << request << endl;
}
else if (successor != 0)
{
successor->HandleRequest(request);
}
else if (successor != 0)
{
successor->HandleRequest(request);
}
}
};
class ConcreteHandler3 : public Handler
{
public:
void HandleRequest(int request)
{
if (request >= 20 && request < 30)
{
cout << "ConcreteHandler2" << "處理請求" << request << endl;
}
else if (successor != 0)
{
successor->HandleRequest(request);
}
}
};
int _tmain(int argc, _TCHAR* argv[])
{
Handler *h1 = new ConcreteHandler1;
Handler *h2 = new ConcreteHandler2;
Handler *h3 = new ConcreteHandler3;
h1->SetSuccessor(h2);//設置鏈條
h2->SetSuccessor(h3);
int requests[] = { 2, 5, 14, 22, 18, 3, 27, 20 };
for (int i = 0; i < sizeof(requests) / sizeof(int); ++i)
{
h1->HandleRequest(requests[i]);
}
return 0;
}
優點:
1.當客戶提交一個請求時,請求是沿着鏈傳遞直到有一個ConcreteHandler對象處理它。【DP】
2.接收者和發送者都沒有對方的明確信息,且鏈中的對象自己也不知道鏈的結構。結果是職責鏈可簡化對象的相互連接,它們僅需保持一個指向其後繼者的引用,而不需要保持它所有的候選接受者的引用。【DP】
3.隨時地增加或修改處理一個請求的結構。增強了給對象指派職責的靈活性【DP】
缺點:一個請求極有可能到了鏈的末端都得不到處理,或者因爲沒有正確配置而得不到處理,這就很糟糕了,需要事先考慮周全。