Dewsoft Frontpage Tutorials

Lesson - 4:Documents and Views
4.2 - Understanding the View Class
As mentioned previously, the view class displays the data stored in the document object and enables the user to modify this data. The view object keeps a pointer to the document object, which it uses to access the document’s member variables in order to display or modify them. Listing 4.2 is the header file for Capp1View, as generated by AppWizard. Listing 4.2 APP1VIEW.H—The Header File for the CApp1View Class // App1View.h : interface of the CApp1View class // ////////////////////////////////////////// #if !defined(AFX_APP1VIEW_H__43BB481F_64AE_11D0_9AF3 [ccc]_0080C81A397C__INCLUDED_) #define AFX_APP1VIEW_H__43BB481F _64AE_11D0_9AF3_0080C81A397C__INCLUDED_ #if _MSC_VER > 1000 #pragma once #endif // _MSC_VER > 1000 class CApp1View : public CView { protected: // create from serialization only CApp1View(); DECLARE_DYNCREATE(CApp1View) // Attributes public: CApp1Doc* GetDocument(); // Operations public: // Overrides // ClassWizard generated virtual function overrides //{{AFX_VIRTUAL(CApp1View) public: virtual void OnDraw(CDC* pDC); // overridden to draw this view virtual BOOL PreCreateWindow(CREATESTRUCT& cs); protected: virtual BOOL OnPreparePrinting(CPrintInfo* pInfo); virtual void OnBeginPrinting(CDC* pDC, CPrintInfo* pInfo); virtual void OnEndPrinting(CDC* pDC, CPrintInfo* pInfo); //}}AFX_VIRTUAL // Implementation public: virtual ~CApp1View(); #ifdef _DEBUG virtual void AssertValid() const; virtual void Dump(CDumpContext& dc) const; #endif protected: // Generated message map functions protected: //{{AFX_MSG(CApp1View) // NOTE - the ClassWizard will add and remove member functions here. // DO NOT EDIT what you see in these blocks of generated code ! //}}AFX_MSG DECLARE_MESSAGE_MAP() }; #ifndef _DEBUG // debug version in App1View.cpp inline CApp1Doc* CApp1View::GetDocument() { return (CApp1Doc)m_pDocument; } #endif ////////////////////////////////////////// //{{AFX_INSERT_LOCATION}} // Microsoft Visual C++ will insert additional declarations // immediately before the previous line. #endif // !defined(AFX_APP1VIEW_H__ 43BB481F_64AE_11D0_9AF3 [ccc] _0080C81A397C__INCLUDED_) Near the top of the listing, you can see the class’s public attributes, where it declares the GetDocument() function as returning a pointer to a CApp1Doc object. Anywhere in the view class that you need to access the document’s data, you can call GetDocument() to obtain a pointer to the document. For example, to add a CPoint object to the aforementioned array of CPoint objects stored as the document’s data, you might use the following line: GetDocument()->m_points[x] = point; You also can do this a little differently, of course, by storing the pointer returned by GetDocument() in a local pointer variable and then using that pointer variable to access the document’s data, like this: pDoc = GetDocument(); pDoc->m_points[x] = point; The second version is more convenient when you need to use the document pointer in several places in the function, or if using the less clear GetDocument()->variable version makes the code hard to understand. Notice that the view class, like the document class, overrides a number of virtual functions from its base class. As you’ll soon see, the OnDraw() function, which is the most important of these virtual functions, is where you paint your window’s display. As for the other functions, MFC calls PreCreateWindow() before the window element (that is, the actual Windows window) is created and attached to the MFC window class, giving you a chance to modify the window’s attributes (such as size and position). These two functions are discussed in more detail in next Unit, "Drawing on the Screen." OnPreparePrinting() is used to modify the Print dialog box before it displays for the user; the OnBeginPrinting() function gives you a chance to create GDI objects like pens and brushes that you need to handle the print job; and OnEndPrinting() is where you can destroy any objects you might have created in OnBeginPrinting(). NOTE:* When you first start using an application framework like MFC, it’s easy to get confused about the difference between an object instantiated from an MFC class and the Windows element it represents. For example, when you create an MFC frame-window object, you’re actually creating two things: the MFC object that has member functions and member variables, and a Windows window that you can manipulate using the functions of the MFC object. The window element is associated with the MFC class, but is also an entity unto itself.

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