Modifying ShowDib's Resources

Now that you have the basic ShowDib application created, you can use Visual C++'s tools to modify the application to fit your needs. The following steps describe how to modify the ShowDib application's resources:

1. Click the ResourceView tab. Visual C++ displays the ResourceView window.

2. In the ResourceView window, double-click ShowDib Resources, double-click the Menu resource, and then double-click the IDR_MAINFRAME menu ID. Visual C++'s menu editor appears.

3. Click on ShowDib's Edit menu (not Visual C++'s Edit menu), and then press your keyboard's Delete key to delete the E dit menu. When you do, a dialog box asks for verification of the delete command. Click the OK button.

4. Click on ShowDib's File menu (not Visual C++'s File menu). The File menu appears, showing its various commands. Using your mouse and your keyboard's Delete key, delete all the File menu's commands except Open and Exit. When you're done.

5. Close the menu editor, and then double-click the Accelerator resource in the browser window. Double-click the IDR_MAINFRAME accelerator ID to bring up the accelerator editor.

6. Using your keyboard's arrow and Delete keys, delete all accelerators except ID_FILE_OPEN.

7. Close the accelerator editor and then double-click the Dialog resource in the browser window. Double-click the IDD_ABOUTBOX dialog box ID to bring up the dialog box editor.

8. Close the dialog box editor. Then select the Build, Build command to compile the modified application.

When you run the newly compiled application, you see the application's main window. If you select the File menu's Open command, the File Open dialog box appears, from which you can select a file. When you select a file, its name appears in the window in place of the "Untitled" string. If you select the Help menu's About ShowDib command, you see the About dialog box, which you modified in the dialog box editor.

Adding Code to ShowDib

After you've edited the application's resources, ShowDib's user interface is complete. However, the program is still incapable of loading and displaying DIBs. Even when you use the Open command to select a DIB file, nothing happens (except that the DIB's file name appears in the window's title bar). The next step, then, is to add the code needed to make ShowDib do what you want it to do. The following steps describe how to add this code to the application.

1. Load the MainFrm.cpp file, and then add the following lines to the PreCreateWindow() function, right before the function's return statement:

cs.cx = 640;

cs.cy = 480;

2. Copy the cdib.cpp and cdib.h files into ShowDib's project directory.

3. Select the Project, Add to Project, Files command. The Insert Files Into Project dialog box appears. In the file window, double-click the cdib.cpp file to add it to the project.

4. Load the ShowDibDoc.h file, and then add the following line to the top of the source code, right before the declaration of the CShowDibDoc class:

#include "cdib.h"

This line includes the CDib class's declaration into the ShowDib application's document header file so that you can use the CDib class in the document class.

5. In ShowDibDoc.h, add the following line to the Attributes section of the CShowDibDoc class's declaration, right after the public keyword:

CDib* m_pDib;

This line declares a pointer to a CDib object as a data member of the CShowDibDoc class. The CDib object represents whatever DIB the application is currently displaying.

6. Load the ShowDibDoc.cpp file, and then add the following line to the class's constructor, after the

// TODO: add one-time construction code here comment:

m_pDib = 0;

This line ensures that the CDib pointer starts off as NULL.

7. Select the View, ClassWizard command. The MFC ClassWizard dialog box appears.

8. In the Class Name box, select the CShowDibDoc class. Then click ID_FILE_OPEN in the Object IDs box, and double-click COMMAND in the Messages box. The Add Member Function dialog box appears.

9. Click the OK button to add the OnFileOpen() function to the class. Click the Edit Code button to open the source code window to this new function.

10. Add the code shown in Listing 11.13 to the new OnFileOpen() function, after the

// TODO: Add your command handler code here comment.

Listing 11.13 Code for the OnFileOpen() Function

// Construct an Open dialog-box object.

CFileDialog fileDialog(TRUE, "bmp", "*.bmp");

// Display the Open dialog box.

int result = fileDialog.DoModal();

// If the user exited the dialog box

// via the OK button...

if (result == IDOK)

{ // Get the selected path and file name.

CString string = fileDialog.GetPathName();

// Construct a new CDib object.

m_pDib = new CDib(string);

// Check that the CDib object was created okay.

// If there was an error, the pBmInfo pointer

// will be 0.

LPBITMAPINFO pBmInfo = m_pDib->GetDibInfoPtr();

// If the CDib object was not constructed

// properly, delete it.

if (!pBmInfo)

DeleteContents();

// Otherwise, set the document's title to

// the DIB's path and file name.

else

SetTitle(string);

}

// Notify the view object that it has new data to display.

UpdateAllViews(0);

The OnFileOpen() function will now respond to the File menu's Open command, not only by enabling the user to select a file, but also by creating a new CDib object from the selected DIB. This function is discussed in detail later in this chapter, in the section "Examining the OnFileOpen() Function."

11. Select the View, ClassWizard command. When the MFC ClassWizard dialog box appears, select the CShowDibDoc class in the Class Name box; click CShowDibDoc in the Object IDs box, and double-click DeleteContents in the Messages box to add the virtual DeleteContents() function.

12. Click the Edit Code button to jump to the DeleteContents() function and then add the code shown in Listing 17.14 to the function, after the // TODO: Add your specialized code here and/or call the base class comment.

Listing 17.14 LST17_14.CPP Code for the DeleteContents() Function

// If there's a valid CDib object, delete it.

if (m_pDib)

{

delete m_pDib;

m_pDib = 0;

}

The DeleteContents() function overrides the CDocument base class's DeleteContents() function. MFC calls this function whenever the application needs to delete the current document's data. Because DeleteContents() is also called when a new document is created (to ensure that the new document is empty), you must check that m_pDib is not 0 before you delete it.

13. Open the ShowDibView.cpp file, and then add the code shown in Listing 11.15 to the OnDraw() function, right after the // TODO: add draw code for native data here comment.

Listing 11.15 LST3_15.CPP Code for the OnDraw() Function

// Get a pointer to the current CDib object.

CDib* pDib = pDoc->m_pDib;

// If the CDib object is valid, display it.

if (pDib)

{

// Get a pointer to the DIB's image data.

BYTE* pBmBits = pDib->GetDibBitsPtr();

// Get a pointer to the DIB's info structure.

LPBITMAPINFO pBmInfo = pDib->GetDibInfoPtr();

// Get the DIB's width and height.

UINT bmWidth = pDib->GetDibWidth();

UINT bmHeight = pDib->GetDibHeight();

// Display the DIB.

StretchDIBits(pDC->m_hDC,

10, 10, bmWidth, bmHeight,

0, 0, bmWidth, bmHeight,

pBmBits, pBmInfo, DIB_RGB_COLORS, SRCCOPY);

}

MFC calls the OnDraw() function whenever the application's main window must be redrawn. The code in Listing 3.15, which is described in detail later in the section "Examining the OnDraw() Function," displays the currently loaded DIB.

14. Select the Build, Build command to compile and link the new version of the ShowDib application.

Version of ShowDib is now complete. Before you run the application, however, read the following sections, which explain how the OnFileOpen() and OnDraw() functions work.