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Lesson - 4 : Documents and Views
4.1 : Understanding the Document Class
When you generate your source code with AppWizard, you get an application featuring all the bells and whistles of a commercial 32-bit Windows application, including a toolbar, a status bar, ToolTips, menus, and even an About dialog box. However, in spite of all those features, the application really doesn’t do anything useful. In order to create an application that does more than look pretty on your desktop, you need to modify the code that AppWizard generates. This task can be easy or complex, depending on how you want your application to look and act. Probably the most important set of modifications are those related to the document—the information the user can save from your application and restore later—and to the view—the way that information is presented to the user. MFC’s document/view architecture separates an application’s data from the way the user actually views and manipulates that data. Simply, the document object is responsible for storing, loading, and saving the data, whereas the view object (which is just another type of window) enables the user to see the data onscreen and to edit that data in a way that is appropriate to the application. In this Unit, you learn the basics of how MFC’s document/view architecture works. SDI and MDI applications created with AppWizard are document/view applications. That means that AppWizard generates a class for you derived from CDocument, and delegates certain tasks to this new document class. It also creates a view class derived from CView and delegates other tasks to your new view class. Let’s look through an AppWizard starter application and see what you get. Choose File, New, and select the Projects tab. Fill in the project name as App1 and fill in an appropriate directory for the project files. Make sure that MFC AppWizard (exe) is selected. Click OK. Move through the AppWizard dialog boxes, changing the settings to match those in the following table, and then click Next to continue: Step 1: Multiple documents Step 2: Don’t change the defaults presented by AppWizard Step 3: Don’t change the defaults presented by AppWizard Step 4: Deselect all check boxes except Printing and Print Preview Step 5: Don’t change the defaults presented by AppWizard Step 6: Don’t change the defaults presented by AppWizard After you click Finish on the last step, the New project information box summarizes your work. Click OK to create the project. Expand the App1 classes in ClassView, and you see that six classes have been created: CAboutDlg, CApp1App, CApp1Doc, CApp1View, CChildFrame, and CMainframe. CApp1Doc represents a document; it holds the application’s document data. You add storage for the document by adding data members to the CApp1Doc class. To see how this works, look at Listing 4.1, which shows the header file AppWizard creates for the CApp1Doc class. Listing 4.1 APP1DOC.H—The Header File for the CApp1Doc Class // App1Doc.h : interface of the CApp1Doc class ///////////////////////////// #if !defined(AFX_APP1DOC_H__43BB481D_64AE _11D0_9AF3_0080C81A397C__INCLUDED_) #define AFX_APP1DOC_H__43BB481D_64AE _11D0_9AF3_0080C81A397C__INCLUDED_ #if _MSC_VER > 1000 #pragma once #endif // _MSC_VER > 1000 class CApp1Doc : public CDocument { protected: // create from serialization only CApp1Doc(); DECLARE_DYNCREATE(CApp1Doc) // Attributes public: // Operations public: // Overrides // ClassWizard generated virtual function overrides //{{AFX_VIRTUAL(CApp1Doc) public: virtual BOOL OnNewDocument(); virtual void Serialize(CArchive& ar); //}}AFX_VIRTUAL // Implementation public: virtual ~CApp1Doc(); #ifdef _DEBUG virtual void AssertValid() const; virtual void Dump(CDumpContext& dc) const; #endif protected: // Generated message map functions protected: //{{AFX_MSG(CApp1Doc) // 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() }; ///////////////////////////// //{{AFX_INSERT_LOCATION}} // Microsoft Visual C++ will insert additional declarations // immediately before the previous line. #endif // !defined(AFX_APP1DOC_H__43BB481D _64AE_11D0_9AF3 [ccc] _0080C81A397C__INCLUDED_) Near the top of the listing, you can see the class declaration’s Attributes section, which is followed by the public keyword. This is where you declare the data members that will hold your application’s data. In the program that you create a little later in this Unit, the application must store an array of CPoint objects as the application’s data. That array is declared as a member of the document class like this: // Attributes public: CPoint points[100]; CPoint is an MFC class that encapsulates the information relevant to a point on the screen, most importantly the x and y coordinates of the point. Notice also in the class’s header file that the CApp1Doc class includes two virtual member functions called OnNewDocument() and Serialize(). MFC calls the OnNewDocument() function whenever the user selects the File, New command (or its toolbar equivalent, if a New button has been implemented in the application). You can use this function to perform whatever initialization must be performed on your document’s data. In an SDI application, which has only a single document open at any time, the open document is closed and a new blank document is loaded into the same object; in an MDI application, which can have multiple documents open, a blank document is opened in addition to the documents that are already open. The Serialize() member function is where the document class loads and saves its data.

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