chain.c

design_patterns code设计模式书中的源码 对学习设计模式的人很有帮助的

/*
*/
#ifdef Implementation1
/*
*/
class HelpHandler {
public:
    HelpHandler(HelpHandler* s) : _successor(s) { }
    virtual void HandleHelp();
private:
    HelpHandler* _successor;
};
/*
*/
void HelpHandler::HandleHelp () {
    if (_successor) {
        _successor->HandleHelp();
    }
}
/*
*/
class Request {
  public:
    int GetKind();
};
class HelpRequest : public Request {
};

class PrintRequest : public Request {
};


class Handler {
  public:
    virtual void HandleRequest(Request* theRequest);
    void HandleHelp(HelpRequest*);
    void HandlePrint(PrintRequest*);
};

const int Help = 1;
const int Print = 2;
const int Preview = 2;
/*
*/
void Handler::HandleRequest (Request* theRequest) {
    switch (theRequest->GetKind()) {
    case Help:
        // cast argument to appropriate type
        HandleHelp((HelpRequest*) theRequest);
        break;
/*
*/
    case Print:
        HandlePrint((PrintRequest*) theRequest);
        // ...
        break;
/*
*/
    default:
        // ...
        break;
    }
}
/*
*/
class ExtendedHandler : public Handler {
public:
    virtual void HandleRequest(Request* theRequest);
    // ...
};
/*
*/
void ExtendedHandler::HandleRequest (Request* theRequest) {
    switch (theRequest->GetKind()) {
    case Preview:
        // handle the Preview request
        break;
/*
*/
    default:
        // let Handler handle other requests
        Handler::HandleRequest(theRequest);
    }
}
/*
*/
#endif
/*
*/
#ifdef SampleCode
#include"defs.H"
class Application;
class Dialog;
class HelpHandler;
/*
*/
typedef int Topic;
const Topic NO_HELP_TOPIC = -1;

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 (_successor != 0) {
        _successor->HandleHelp();
    }
}
/*
*/
class Widget : public HelpHandler {
protected:
    Widget(Widget* parent, Topic t = NO_HELP_TOPIC);
private:
    Widget* _parent;
};
/*
*/
Widget::Widget (Widget* w, Topic t) : HelpHandler(w, t) {
    _parent = w;
}
/*
*/
class Button : public Widget {
public:
    Button(Widget* d, Topic t = NO_HELP_TOPIC);

    virtual void HandleHelp();
    // Widget operations that Button overrides...
};
/*
*/
Button::Button (Widget* h, Topic t) : Widget(h, t) { }

void Button::HandleHelp () {
    if (HasHelp()) {
        // offer help on the button
    } else {
        HelpHandler::HandleHelp();
    }
}
/*
*/
class Dialog : public Widget {
public:
    Dialog(HelpHandler* h, Topic t = NO_HELP_TOPIC);
    virtual void HandleHelp();

    // Widget operations that Dialog overrides...
    // ...
};
/*
*/
Dialog::Dialog (HelpHandler* h,  Topic t) : Widget(0) {
    SetHandler(h, t);
}
/*
*/
void Dialog::HandleHelp () {
    if (HasHelp()) {
        // offer help on the dialog
    } else {
        HelpHandler::HandleHelp();
    }
}
/*
*/
class Application : public HelpHandler {
public:
    Application(Topic t) : HelpHandler(0, t) { }

    virtual void HandleHelp();
    // application-specific operations...
};
/*
*/
void Application::HandleHelp () {
    // show a list of help topics
}
/*
*/
void dummy () {
/*
*/
const Topic PRINT_TOPIC = 1;
const Topic PAPER_ORIENTATION_TOPIC = 2;
const Topic APPLICATION_TOPIC = 3;

Application* application = new Application(APPLICATION_TOPIC);
Dialog* dialog = new Dialog(application, PRINT_TOPIC);
Button* button = new Button(dialog, PAPER_ORIENTATION_TOPIC);
/*
*/
button->HandleHelp();
/*
*/
}
#endif
/*
*/