In this Unit you pull together the concepts demonstrated in previous units to create an application that really does something. You add a menu, a menu item, a dialog box, and persistence to an application that draws output based on user settings. In subsequent Units this application serves as a base for more advanced work.

The sample application you will build is very much like the traditional "Hello, world!" of C programming. It simply displays a text string in the main window. The document (what you save in a file) contains the string and a few settings. There is a new menu item to bring up a dialog box to change the string and the settings, which control the string’s appearance. This is a deliberately simple application so that the concepts of adding menu items and adding dialogs are not obscured by trying to understand the actual brains of the application. So, bring up Developer Studio and follow along.

First, use AppWizard to create the starter application. Choose File, New and the Project tab. Select an MFC AppWizard (exe) application, name the project ShowString so that your classnames will match those shown throughout this Unit, and click OK.

In Step 1 of AppWizard, it doesn’t matter much whether you choose SDI or MDI, but MDI will enable you to see for yourself how little effort is required to have multiple documents open at once. So, choose MDI. Choose U.S. English, and then click Next.

The ShowString application needs no database support and no compound document support, so click Next on Step 2 and Step 3 without changing anything.

FIG. 6.1 AppWizard summarizes the design choices for ShowString.

In AppWizard’s Step 4 dialog box, select a docking toolbar, initial status bar, printing and print preview, context-sensitive help, and 3D controls, and then click Next. Choose source file comments and shared DLL, and then click Next. The classnames and filenames are all fine, so click Finish. Figure 6.1 shows the final confirmation dialog box. Click OK.

The ShowString application displays a string that will be kept in the document. You need to add a member variable to the document class, CShowStringDoc, and add loading and saving code to the Serialize() function. You can initialize the string by adding code to OnNewDocument() for the document and, in order to actually display it, override OnDraw() for the view.

Member Variable and Serialization Add a private variable to the document and a public function to get the value by adding these lines to ShowStringDoc.h:

The inline function gives other parts of your application a copy of the string to use whenever necessary but makes it impossible for other parts to change the string.

Next, change the skeleton CShowStringDoc::Serialize() function provided by AppWizard to look like Listing 6.1. (Expand CShowStringDoc in ClassView and double-click Serialize() to edit the code.) Because you used the MFC CString class, the archive has operators << and >> already defined, so this is a simple function to write. It fills the archive from the string when you are saving the document and fills the string from the archive when you are loading the document from a file.

Initializing the String Whenever a new document is created, you want your application to initialize string to "Hello, world!". A new document is created when the user chooses File, New. This message is caught by CShowStringApp (the message map is shown in Listing 6.2, you can see it yourself by scrolling toward the top of ShowString.cpp) and handled by CWinApp::OnFileNew(). Starter applications generated by AppWizard call OnFileNew() to create a blank document when they run. OnFileNew() calls the document’s OnNewDocument(), which actually initializes the member variables of the document.

AppWizard gives you the simple OnNewDocument() shown in Listing 6.3. To see yours in the editor, double-click OnNewDocument() in ClassView—you may have to expand CshowStringDoc first.

Take away the comments and add this line in their place:

(What else could it say, after all?) Leave the call to CDocument::OnNewDocument() because that will handle all other work involved in making a new document.

Getting the String Onscreen A view’s OnDraw() function is called whenever that view needs to be drawn, such as when your application is first started, resized, or restored or when a window that had been covering it is taken away. AppWizard has provided a skeleton, shown in Listing 6.4. To edit this function, expand CShowStringView in ClassView and then double-click OnDraw().

OnDraw() takes a pointer to a device context . The device context class, CDC, has a member function called DrawText() that draws text onscreen. It is declared like this:

The CString to be passed to this function is going to be the string from the document class, which can be accessed as pDoc->GetString(). The lpRect is the client rectangle of the view, returned by GetClientRect(). Finally, nFormat is the way the string should display; for example, DT_CENTER means that the text should be centered from left to right within the view. DT_VCENTER means that the text should be centered up and down, but this works only for single lines of text that are identified with DT_SINGLELINE. Multiple format flags can be combined with |, so DT_CENTER|DT_VCENTER|DT_SINGLELINE is the nFormat that you want. The drawing code to be added to CShowStringView::OnDraw() looks like this:

This sets up a CRect and passes its address to GetClientRect(), which sets the CRect to the client area of the view. DrawText() draws the document’s string in the rectangle, centered vertically and horizontally.

At this point, the application should display the string properly. Build and execute it, and you will see something like Figure 6.2. You have a lot of functionality—menus, toolbars, status bar, and so on—but nothing that any other Windows application doesn’t have, yet. Starting with the next section, that changes.

FIG. 6.2 ShowString starts simply, with the usual greeting.