Programming Microsoft vc++学习（1）

The MessageMap

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When the user presses the left mouse button in a view window, Windows sends a message—specifically WM_LBUTTONDOWN—to that window. If your program needs to take action in responseto WM_LBUTTONDOWN, your view class must have a member function that looks likethis:

void CMyView::OnLButtonDown(UINT nFlags, CPoint point)

{

    // event processing code here

}

Your class header filemust also have the corresponding prototype:

afx_msg void OnLButtonDown(UINT nFlags, CPoint point);

Theafx_msgnotation is a "no-op" that alerts you that this is a prototype for amessage map function. Next, your code file needs a message map macro thatconnects yourOnLButtonDown function to the application framework:

BEGIN_MESSAGE_MAP(CMyView, CView)

    ON_WM_LBUTTONDOWN() // entry specifically for OnLButtonDown

    // other message map entries

END_MESSAGE_MAP()

Finally, your classheader file needs the statement

DECLARE_MESSAGE_MAP()

You can manually code the message-handling functions—indeed, that is still necessary for certain messages. Fortunately, Visual C++ provides a tool, ClassWizard, that automa tes the coding of most message map functions.