设计模式---行为类型---职责链

来源：互联网发布：网络安利是什么意思编辑：程序博客网时间：2024/05/16 23:55

1、意图

使多个对象都有机会处理请求，从而避免请求的发送者和接受者之间的耦合关系。将这些对象连成一条链，并沿着这条链传递该请求，直到有一个对象处理它为止。

2、适用性

在以下条件下使用Responsibility链：

1）有多个的对象可以处理一个请求，哪个对象处理该请求运行时刻自动确定。

2）你想在不明确指定接受者的情况下，向多个对象中的一个提交一个请求。

3）可处理一个请求的对象集合应被动态指定。

3、C++实例

// Test.cpp : 定义控制台应用程序的入口点。//#include "stdafx.h"#include <iostream>using namespace std;typedef int Topic;const Topic NO_HELP_TOPIC      = -1;const Topic PRINT_TOPIC        = 1;const Topic PAPER_ORIENTATION  = 2;const Topic APPLICATIOIN_TOPIC = 3;// 基类class HelpHandler{public:HelpHandler(HelpHandler * = 0, Topic = NO_HELP_TOPIC );virtual bool HasHelp();virtual void SetHandler( HelpHandler *, Topic );virtual void HandleHelp();private:HelpHandler *_successor;Topic _topic;};HelpHandler::HelpHandler( HelpHandler  *h, Topic t ):_successor(h),_topic(t){}bool HelpHandler::HasHelp(){return _topic != NO_HELP_TOPIC;}void HelpHandler::HandleHelp(){if ( 0 != _successor ){_successor->HandleHelp();}}void HelpHandler::SetHandler( HelpHandler *h, Topic t){_successor = h;_topic = t;}class Widget:public HelpHandler{protected:Widget( Widget *parent, Topic t = NO_HELP_TOPIC );private:Widget *_parent;};Widget::Widget( Widget *w, Topic t /*= NO_HELP_TOPIC */ ):HelpHandler(w,t){_parent = w;}class Button:public Widget{public:Button(Widget *d, Topic t = NO_HELP_TOPIC );virtual void HandleHelp();};Button::Button( Widget *h, Topic t /*= NO_HELP_TOPIC */ ):Widget( h, t){}void Button::HandleHelp(){if ( HasHelp() ){cout<<"Button::HandleHelp"<<endl;}else{HelpHandler::HandleHelp();}}class Dialog:public Widget{public:Dialog(HelpHandler *d, Topic t = NO_HELP_TOPIC );virtual void HandleHelp();};Dialog::Dialog( HelpHandler *h, Topic t /*= NO_HELP_TOPIC */ ):Widget( 0 ){SetHandler( h, t );}void Dialog::HandleHelp(){if ( HasHelp() ){cout<<"Dialog::HandleHelp"<<endl;}else{HelpHandler::HandleHelp();}}class Application:public HelpHandler{public:Application( Topic t ):HelpHandler( 0, t ){}virtual void HandleHelp();};void Application::HandleHelp(){cout<<"Application::HandleHelp"<<endl;}int _tmain(int argc, _TCHAR* argv[]){Application *application = new Application( APPLICATIOIN_TOPIC );Dialog *dialog = new Dialog( application, PRINT_TOPIC );Button *button = new Button( dialog, PAPER_ORIENTATION );button->HandleHelp();button->SetHandler( dialog, NO_HELP_TOPIC );button->HandleHelp();delete button;delete dialog;delete application;return 0;}

0 0