Design Pattern learning-chain of responsiblity)

Intention: give multiple objects the opportunity to process requests, so as to avoid coupling between the request sender and receiver. connect these objects into a chain and pass requests along the chain until an object processes it.

Applicability:

Multiple objects can process one request, which is automatically determined when processing the request

You want to submit a request to one of multiple objects without specifying the recipient.

The object set that can process a request should be dynamically specified

Example:

ExampleCode:

Class Chandler
{
Public:
Chandler (Chandler *
Nexthandler );
Public:
~ Chandler (void );
Public:
Void
Handlerequest (crequest req)
{

If (ismatch (req. getrequesttype ()))
{

_ Handlerequest (req );
}
Else
{

If (m_nexthandler)
{

M_nexthandler-> handlerequest (req );
}

Else
{
_ Tprintf (_ T ("unhandler
Message/N "));
}
}

}
Protected:
Virtual void _ handlerequest (crequest req) = 0;

Virtual bool ismatch (crequest: requesttype reqtype) = 0;
PRIVATE:

Chandler * m_nexthandler;
};

// Message Processing
Class cmessagehandler: Public Chandler
{
Public:

Cmessagehandler (Chandler * pnexthandler)
: Chandler (pnexthandler)

{

}
Public:
~ Cmessagehandler ()
{

}
Public:
Virtual bool ismatch (crequest: requesttype
Reqtype)
{
If (reqtype = crequest: emessage)

{
Return true;
}
Return false;

}
Virtual void _ handlerequest (crequest req)
{

_ Tprintf (_ T ("message handled/N "));
}
};

// Keyboard processing class processes keyboard messages
Class ckeyhandler: Public
Cmessagehandler
{
Public:
Ckeyhandler (Chandler *
Pnexthandler)
: Cmessagehandler (pnexthandler)
{

}
Public:
~ Ckeyhandler ()
{
}
Public:

Virtual bool ismatch (crequest: requesttype reqtype)
{

If (reqtype = crequest: EKEY)
{
Return
True;
}
Return false;
}
Virtual void
_ Handlerequest (crequest req)
{
_ Tprintf (_ T ("key message
Handled/N "));
}
};

// Process the request

Class crequest
{
Public:
Enum requesttype
{

Emessage,
EKEY,
Emouse,
};
Public:

Crequest (crequest: requesttype reqtype );
Public:

~ Crequest (void );

Public:
Crequest: requesttype
Getrequesttype ()
{
Return m_reqtype;
}
PRIVATE:

Crequest: requesttype m_reqtype;
};

 

// Call

Ckeyhandler keyhandler (null );
Cmessagehandler
Messagehandler (& keyhandler );
Crequest keyreq (crequest: EKEY );

Crequest msgreq (crequest: emessage );
Crequest
Mousereq (crequest: emouse );
Messagehandler. handlerequest (keyreq );

Messagehandler. handlerequest (msgreq );

Messagehandler. handlerequest (mousereq );

Result