The functions in Listing 32.3 use some basic ADO code to interact with the VcBank database. Each of these functions calls SetAbort or SetComplete, depending on the function's success or failure. This is especially useful when performing a money transfer. The transfer of money consists of two operations:

• The removal of money from the first account
• The addition of money to the second account

If the first operation succeeds but the second fails, SetAbort is called, causing the first operation to be rolled back. This type of mechanism is especially useful when a transaction consists of operations performed by multiple components. If any component calls SetAbort, the entire transaction rolls back.

Registering the VcBank COM+ Application

Open the COM+ MMC snap-in and select the COM+ applications node. Create a new COM+ application by following these steps:

1. Right-click on the COM+ applications node; then choose New, Application from the context menu. The COM Application Install Wizard appears.
2. Click Next to move past the welcome page.
3. Click the icon to create an empty application.
4. For the application name, enter Visual C++ Bank. Leave the application type set to the default value of Server application, and click Next.
5. Leave the application identity set to the default value of the interactive user. Click Next.
6. Click Finish to complete the application creation procedure.

The next step is to add the VcBank component to the COM+ application. Expand the tree node associated with the Visual C++ Bank and the component by following these steps:

1. Right-click on the Components node; then choose New, Component from the context menu. The COM Component Install Wizard appears.
2. Click Next to move past the welcome page.
3. Click the icon to install a new component. A File Open dialog box appears.
4. Navigate to the directory that contains VcBankApp.dll, select the file, and click Open.
5. The VcBank component is listed as a component found in the DLL. Click Next to continue.
6. Click Finish to complete the component installation.

The component now is registered in the COM+ catalog. Some changes must be made to the component before you use it in this example, however. Finish configuring the component by following these steps:

1. Right-click on the VcBank component, and choose Properties from the context menu.
2. Select the Transactions tab, and click the Transactions Required radio button.
3. Select the Activation tab, and enable object pooling.
4. Click OK to complete the configuration changes.

The Visual C++ Bank COM+ application now is registered and ready to use. The next several sections create a client application that will use the component.

A Client Application for VcBank

You can access a COM+ application in a number of ways. Visual Basic, the Windows Scripting Host (WSH), and Active Server Pages (ASP) are three of the more popular ways to use COM+ applications. Because this is a Visual C++ book, this chapter creates an MFC application that serves as a client to the VcBank component.

Begin by using MFC AppWizard to create a dialog-based application named BankClient. Accept all the default properties for a dialog box–based application.

Adding Dialog Boxes to the BankClient Project

The BankClient project consists of several dialog boxes. In addition to the dialog boxes created by AppWizard, you must add three new dialog boxes to the BankClient project:

• A dialog box to handle withdrawals from an account
• A dialog box to handle deposits to an account
• A dialog box to handle money transfers between accounts

Begin by adding three new dialog box resources to the BankClient project:

1. Open the project workspace Resources tab.
2. Right-click on the dialog box icon, and choose Insert Dialog from the context menu.
3. Repeat Step 2 twice to create three dialog boxes.

Use the information in Table 32.6 to set the properties for each dialog box.

Table 32.6. New Dialog Boxes for the BankClient Project

Figure 32.23 shows the IDD_DEPOSIT dialog box. Add two edit controls and two static text labels to the dialog box.

Figure 32.23 The BankClient Deposit dialog box.

Use the values from Table 32.7 to define the properties for the new controls.

Table 32.7. Control Properties for the Deposit Dialog Box

In addition to the properties listed in Table 32.7, the IDC_ACCOUNT edit control has the read-only property.

Use the ClassWizard to associate a new class with the dialog box. Open ClassWizard by pressing Ctrl+W. As the ClassWizard opens, you are asked whether a new class should be created or an existing class reused. Select the default option, which is to create a new class to manage the dialog box, and click OK. The New Class dialog box appears.

Use the values in Table 32.8 to fill in the New Class dialog box.

Table 32.8. New Class Dialog Box Properties for the Deposit Dialog Box

Click OK to add the CDlgDeposit class to the project, and then use the values in Table 32.9 to associate two CDlgDeposit member variables with dialog box controls.

Table 32.9. New Class Dialog Box Properties for the Deposit Dialog Box

Click OK to dismiss the ClassWizard, and add the new member variables to the project.

The IDD_WITHDRAW dialog box is similar to the IDD_DEPOSIT dialog box (see Figure 32.24). Add two edit controls and two static text labels to the dialog box.

Figure 32.24 The BankClient Withdraw dialog box.

Use the values in Table 32.10 to define the properties for the new controls.

Table 32.10. Control Properties for the Withdraw Dialog Box

In addition to the properties listed in Table 32.10, the IDC_ACCOUNT edit control has the read-only property.

Use the ClassWizard to associate a new class with the Withdraw dialog box. Open the ClassWizard by pressing Ctrl+W, and elect to create a new class to manage the dialog box. The New Class dialog box appears.

Use the values in Table 32.11 to fill in the New Class dialog box.

Table 32.11. New Class Dialog Box Properties for the Withdraw Dialog Box

Click OK to add the CDlgWithdraw class to the project, and then use the values in Table 32.12 to associate two CDlgWithdraw member variables with dialog box controls.

Table 32.12. New Class Dialog Box Properties for the Withdraw Dialog Box

Click OK to dismiss the ClassWizard and add the new member variables to the project.

Figure 32.25 shows the IDD_TRANSFER dialog box. Add three edit controls and three static text labels to the dialog box.

Figure 32.25 The BankClient Transfer dialog box.

Use the values in Table 32.13 to define the properties for the new controls.

Table 32.13. New Dialog Boxes for the BankClient Project

In addition to the properties listed in Table 32.13, the IDC_ACCOUNT edit control has the read-only property.

As with the previous dialog boxes, use the ClassWizard to associate a new class with the dialog box. Use the values from Table32.14 to fill in the New Class dialog box.

Table 32.14. New Class Dialog Box Properties for the Transfer Dialog Box

Click OK to add the CDlgTransfer class to the project, and then use the values in Table 32.15 to associate three CDlgTransfer member variables with dialog box controls.

Table 32.15. New Class Dialog Box Properties for the Transfer Dialog Box

Click OK to dismiss the ClassWizard and add the new member variables to the project.

Modifying the Main Dialog Box for BankClient

Figure 32.26 shows the main dialog box for the BankClient application. Add one edit control, three static text labels, and four pushbutton controls to the dialog box. The IDC_BALANCE_LABEL static control is located directly under the edit control, but isn't shown in the figure because it has no caption.

Figure 32.26 The main dialog box for BankClient.

Use the values in Table 32.16 to define the properties for the new controls.

Table 32.16. Control Properties for the Withdraw Dialog Box

Use the values in Table 32.17 to associate a CBankClientDlg member variable with the dialog box control.

Table 32.17. Control Properties for the Main Dialog Box

Use the values in Table 32.18 to add four message-handling functions to the CBankClientDlg class. These functions will handle messages generated when the pushbuttons in the main dialog box are clicked.

Table 32.18. Message-Handling Functions for the Main Dialog Box

Click OK to dismiss the ClassWizard.

Accessing the COM+ Application

For maximum efficiency, COM+ clients typically acquire references to COM+ objects as early as possible and release them as late as possible. The BankClient application will hold on to a single IVcBank interface pointer for as long as the application is running. The COM+ application will use just-in-time activation and object pooling to make the application as efficient as possible.

To include definitions for the symbols used in the VcBankApp module, copy the VcBankApp.h and VcBankApp_i.c files from the VcBankApp project directory to the BankClient project directory.

Add the following #include directive to the StdAfx.h header file after the existing #include directives.

#include "vcbankapp.h"

Add the following #include directive to the BankClientDlg.cpp source file. This file contains definitions for the CLSID and other symbols from VcBankApp.

#include "vcbankapp_i.c"

Add a new member variable to the CBankClientDlg class. The new member variable is an ATL smart pointer that will store a pointer to the IVcBank interface. In Listing 32.4, the modification to the CBankClientDlg class is shown in bold, with most existing lines in the class removed to conserve space.

Example 32.4. Modifications (in bold) to the CBankClientDlg Declaration

class CBankClientDlg : public CDialog
{


// Implementation
protected:
    HICON m_hIcon;
    CComQIPtr<IVcBank> m_pBank;



};

The m_pBank interface pointer is set when the dialog box is initialized. The initialization code is provided in Listing 32.5 and is located in the CBankClientDlg::OnInitDialog function. As with the preceding listing, the new code is shown in bold, and many existing lines have been removed for clarity and to conserve space.

Example 32.5. Modifications (in bold) to the CBankClientDlg::OnInitDialog Function

BOOL CBankClientDlg::OnInitDialog()
{



    // TODO: Add extra initialization here
    CoInitializeEx(NULL, COINIT_MULTITHREADED);

       HRESULT hr =  m_pBank.CoCreateInstance(CLSID_VcBank);

       if(FAILED(hr))

       {

           ErrorHandling(hr);

       }
    return TRUE;
}

#include "atlbase.h"

#define _WIN32_WINNT 0x0400

void CBankClientDlg::OnBalance()
{
    long nBalance = 0;
    BOOL fValid = FALSE;
    int nAccount = GetDlgItemInt(IDC_ACCOUNT, &fValid);
    if(!fValid)
    {
        AfxMessageBox("Please enter an account number");
        return;
    }
    ASSERT(m_pBank);
    HRESULT hr = m_pBank->Balance(nAccount, &nBalance);
    if(SUCCEEDED(hr))
        SetDlgItemInt(IDC_BALANCE_LABEL, nBalance);
}

void CBankClientDlg::OnDeposit()
{
    CDlgDeposit dlg;

    BOOL fValid = FALSE;
    int nAccount = GetDlgItemInt(IDC_ACCOUNT, &fValid);
    if(!fValid)
    {
        AfxMessageBox("Please enter an account number");
        return;
    }

    dlg.m_nAccount = nAccount;

    if(!dlg.DoModal())
    {
        return;
    }
    ASSERT(m_pBank);
    HRESULT hr = m_pBank->Deposit(nAccount, dlg.m_nAmount);
    if(FAILED(hr))
        AfxMessageBox("Could not deposit to account");

    long nBalance = 0;
    hr = m_pBank->Balance(nAccount, &nBalance);
    if(SUCCEEDED(hr))
        SetDlgItemInt(IDC_BALANCE_LABEL, nBalance);
}

#include "dlgdeposit.h"

void CBankClientDlg::OnWithdraw()
{
    CDlgWithdraw dlg;

    BOOL fValid = FALSE;
    int nAccount = GetDlgItemInt(IDC_ACCOUNT, &fValid);
    if(!fValid)
    {
        AfxMessageBox("Please enter an account number");
        return;
    }

    dlg.m_nAccount = nAccount;
    if(!dlg.DoModal())
    {
        // User cancelled dialog box.
        return;
    }

    ASSERT(m_pBank);
    HRESULT hr = m_pBank->Withdraw(nAccount, dlg.m_nAmount);
    if(FAILED(hr))
        AfxMessageBox("Could not withdraw from account");

    long nBalance = 0;
    hr = m_pBank->Balance(nAccount, &nBalance);
    if(SUCCEEDED(hr))
        SetDlgItemInt(IDC_BALANCE_LABEL, nBalance);
}

#include "dlgwithdraw.h"

void CBankClientDlg::OnTransfer()
{
    CDlgTransfer dlg;

    BOOL fValid = FALSE;
    int nAccount = GetDlgItemInt(IDC_ACCOUNT, &fValid);
    if(!fValid)
    {
        AfxMessageBox("Please enter an account number");
        return;
    }


    dlg.m_nAccount = nAccount;
    if(!dlg.DoModal())
    {
        // User cancelled dialog box.
        return;
    }

    ASSERT(m_pBank);
    HRESULT hr = m_pBank->Transfer(nAccount, dlg.m_nDestination, dlg.m_nAmount);
    if(FAILED(hr))
        AfxMessageBox("Could not transfer from account");

    long nBalance = 0;
    hr = m_pBank->Balance(nAccount, &nBalance);
    if(SUCCEEDED(hr))
        SetDlgItemInt(IDC_BALANCE_LABEL, nBalance);
}

#include "dlgtransfer.h"