How To Create a DCOM Client/Server Application

MORE INFORMATION

This sample was not intended to address multiple user scenarios. If you are attempting to create a DCOM server that will handle multiple users, process callbacks, raise events, or use security then please see the following article in the Microsoft Knowledge Base:

This is an advanced DCOM demonstration using Visual Basic 5.0. If you are using Visual Basic 6, please see the following articles in the Microsoft Knowledge Base: For additional information on how to set up security or for help with troubleshooting DCOM issues, click the article numbers below to view the articles in the Microsoft Knowledge Base:

System Requirements

The following operating systems may be used for DCOM applications:

   Operating System          Server           Client
   ----------------          ------           ------
   Windows 2000 Server        YES              YES
   Windows 2000 Professional  YES              YES
   WinNT 4.0 Server           YES              YES
   WinNT 4.0 Workstation      YES              YES
   Windows 98                 YES*             YES
   Windows Me                 YES*             YES
   Windows 95                 YES*             YES:

                                               with DCOM for Win95 files

   * For more information about using Windows 95/98/Me for a DCOM Server.
     Please see the following article in the Microsoft Knowledge Base:
				

Prepare the Computer

(While this step is not required, it keeps your project in order.)

Create the following directories on your computer:

   C:\DCOMDemo
   C:\DCOMDemo\Server
   C:\DCOMDemo\Server\Setup
   C:\DCOMDemo\Client
   C:\DCOMDemo\Client\Setup
				

Create the Server

1. Start a new Visual Basic Project. In the New Project dialog box, select ActiveX EXE and click Open.
2. Set the following properties:

      Control             Name        Property         Value
      ------------------------------------------------------------------
      Class Module        Class1      (Name)           clsDCOMDemoServer
                                       Instancing       5 - MultiUse
   					

3. Copy the following code to the Class Module clsDCOMDemoServer:

         Option Explicit
   
         Public Function ServerTime()
              'Retrieves the time from the server.
              ServerTime = Time
         End Function
   
         Public Function AddNumbers(x As Integer, y As Integer) As Integer
              'Receives two integers and adds them together.
              AddNumbers = x + y
         End Function
   
         Public Function SubtractNumbers(x As Integer, y As Integer) _
              As Integer
              'Receives two integers and subtracts the second from the first.
              SubtractNumbers = x - y
         End Function
   					

4. On the Project menu, click Project1 Properties.
   
   NOTE: If you saved the project previously or have another project open, the menu item may not be called "Project1." Select the menu item for Properties.
5. Click the General tab and set the following properties:

      Project Type:             ActiveX EXE       (Create out-of-process
                                                   ActiveX component)
   
      Startup Object:           (None)            (None required)
   
      Project Name:             proDCOMDemoServer (Will be used in client
                                                   code to define the project
                                                   to be used)
      Help File Name:           <Blank>
      Project Help Context ID:  0
      Project Description:      DCOM Demo Project - Server
      Unattended Execution:     <Unchecked>
      Upgrade ActiveX Controls: <Checked>          (Enables upgrading of
                                                    ActiveX controls)
   					

6. Click the Make tab and set the following properties:

      Auto Increment:                     <Checked> (Useful for version
                                                     comparison.)
   
      Application Title:                  proDCOMDemoServer (Name of the EXE
                                                             that will be
                                                             compiled.)
      Version Information:                <As desired>
      Command Line Arguments:             <Blank>
      Conditional Compilation Arguments:  <Blank>
   					

7. Click the Compile tab and set the following properties:
   

      Compile to P-Code:       <Selected>
      Compile to Native Code:  <Not Selected>
   						

   The rest of the options should be unavailable.
8. Click the Component tab and set the following options:
   

      Start Mode:             ActiveX Component
      Remote Server Files:    <Checked> (Creates TLB and VBR files)
      Version Compatibility:  Project Compatibility (Keeps GUIDs updated)
   						

   Click OK.
9. On the File menu, click Save Project As. Save the following files as described:

      Directory             File           Filename              Extension
      ---------------------------------------------------------------------
      C:\DCOMDemo\Server    Class Module   clsDCOMDemoServer     .cls
                            Project        proDCOMDemoServer     .vbp
   					

10. Select File from the menu, and choose Make proDCOMDemoServer.exe.
11. In the Make Project dialog box, save the executable to the \DCOMDemo\Server directory.
12. Select Project from the menu and choose proDCOMDemoServer Properties.
13. Click the Component tab and confirm that Version Compatibility is still set to Project Compatibility.
14. The file proDCOMDemo.exe appears in the text box at the bottom of the Version Compatibility group. In the Compatible ActiveX Component dialog box, select the file that you just compiled (C:\DCOMDemo\Server\proDCOMDemoServer.exe).
    
    If it is not there, click on the button with the three ellipses (...) and go to step 15. If the file is already in the text box, proceed to step 16.
15. Click OK to close the proDCOMDemoServer - Project Properties dialog box.
16. Open a new project (select New Project on the File menu) and save the changes in the server project.

Create the Client

1. In the New Project dialog box, select Standard EXE and click OK.
2. On the Project menu, click References.
3. Scroll down in the Available References text box until you see DCOM Project - Server. Select the box on the left and click OK. Note that the component automatically appears in the Available References text box. In Remote OLE Automation, you have to double-click the server executable to register it. In DCOM, the server component is automatically registered.
4. Insert a Module. Place two CommandButtons, two text boxes, and three labels on Form1. Set the following properties:
   

      Control         Name              Property         Value
      ------------------------------------------------------------------
      Module          Module1           Name             modDCOMDemoClient
   
      Form            Form1             Name             frmDCOMDemoClient
                                        Caption          DCOM Demo - Client
   
      CommandButton  Command1           Name             cmdServerTime
                                        Caption          &Get Server Time
   
                     Command2           Name             cmdComputeNumbers
                                        Caption          &Compute Numbers
   
      Text Box        Text1             Name             txtX
                                        TabStop          True
                                        TabIndex         0
   
                      Text2             Name             txtY
                                        TabStop          True
                                        TabIndex         1
   
      Label           Label1            Name             lblAnswerAdd
                      Label2            Name             lblAnswerSubtract
                      Label3            Name             lblServerTime
   
   						

   You may want to add additional labels to the form to serve as captions for these labels.
5. Copy the following code to the Module:

         Option Explicit
   
         Public oServer As New proDCOMDemoServer.clsDCOMDemoServer
   
   					

6. Copy the following code to the frmDCOMDemoClient code window:

         Option Explicit
   
         Private Sub Form_Load()
              'Set initial values for text boxes.
               txtX.Text = "1"
               txtY.Text = "2"
         End Sub
   
         Private Sub txtX_GotFocus()
               'Select all the text when the text box gets focus.
               'This makes it easier to change the values.
               txtX.SelStart = 0
               txtX.SelLength = Len(txtX.Text)
         End Sub
   
         Private Sub txtY_GotFocus()
               'Select all the text when the text box gets focus.
               'This makes it easier to change the values.
               txtY.SelStart = 0
               txtY.SelLength = Len(txtY.Text)
           End Sub
   
         Private Sub cmdServerTime_Click()
              'Get the time from the server and put it in the
              'lblServerTime label.
              lblServerTime.Caption = oServer.ServerTime
         End Sub
   
         Private Sub cmdComputeNumbers_Click()
               'Passes the integers to the server and puts the answers in the
               'appropriate labels. The "CInt" is to ensure that you are
               'passing integers, which is what the server is expecting.
               lblAnswerAdd.Caption = oServer.AddNumbers _
                   (CInt(txtX.Text), CInt(txtY.Text))
               lblAnswerSubtract.Caption = oServer.SubtractNumbers _
                   (CInt(txtX.Text), CInt(txtY.Text))
         End Sub
   
         Private Sub Form_QueryUnload(Cancel As Integer, UnloadMode As _
                   Integer)
        'Closes the object when the form unloads.
               Set oServer = Nothing
         End Sub
   
   					

7. On the Project menu, click Project1 Properties.
   
   NOTE: If you saved the project previously or have another project open, the menu item may not be called "Project1." Select the menu item for Properties.
8. Click the General tab and set the following properties:

      Project Type:             Standard EXE       (Client is a Standalone
                                                   executable)
   
      Startup Object:           frmDCOMDemoClient  (frmDCOMDemoClient and
                                                   the code behind
                                                   the form run upon
                                                   execution)
   
      Project Name:             proDCOMDemoClient  (Will be the name of the
                                                   client executable)
      Help File Name:           <Blank>
      Project Help Context ID:  0
      Project Description:      DCOM Demo Project - Client
      Unattended Execution:     <Disabled>
      Upgrade ActiveX Controls: <Checked>          (Enables upgrading of
                                                   ActiveX controls)
   
   					

9. Click the Make tab and set the following properties:

      Auto Increment:                     <Checked> (Useful for Version
                                                    checking)
   
      Application Title:                  proDCOMDemoClient
      Version Information:                <As desired>
      Command Line Arguments:             <Blank>
      Conditional Compilation Arguments:  <Blank>
   
   					

10. Click the Compile tab and set the following properties:
    

       Compile to P-Code:       <Selected>
       Compile to Native Code:  <Not Selected>
    
    						

    The rest of the options should be unavailable.
11. Click the Component tab and ensure that all options are disabled. Click OK.
12. On the File menu, click Save Project As. Save the following files as described:

       Directory           File         Filename              Extension
       ----------------------------------------------------------------
       C:\DCOMDemo\Client  Module       modDCOMDemoClient     .bas
                           Form1        frmDCOMDemoClient     .frm
                           Project      proDCOMDemoClient     .vbp
    
    					

13. Test the client by clicking Run or pressing the F5 key. When you click Get Server Time, the current system time appears in the label. When you click Compute Numbers, the sum and the difference between the numbers appear in the appropriate labels. Stop the project.
14. On the File menu, click Make proDCOMDemoClient.exe.
15. In the Make Project dialog box, save the executable to the C:\DCOMDemo\Client directory.
16. Close your project, and save the changes.

Distribute the Server

You can use the same computer that you developed the application on as your server. However, if you want to distribute your server to another computer, follow these instructions:

1. Start the Application Setup Wizard by clicking Start, Programs, Visual Basic 5.0, Application Setup Wizard. (If the Introduction dialog box appears, click Next.)
2. In the Select Project and Options dialog box, click Browse. In the Locate VB application's .VBP file dialog box, select C:\DCOMDemo\Server\proDCOMDemoServer.VBP.
3. Click Open and set the following options:
   

      Rebuild the Project:  <Unchecked>
      Options:              Create a Setup Program
   
   						

   Click Next.
4. In the Distribution Method dialog box, select Single Directory and click Next.
5. In the Single Directory dialog box, select the C:\DCOMDemo\Server\Setup directory. Click Next.
6. In the ActiveX Components dialog box, click Next. (Do not select any components. They are not needed for this project.)
7. In the Confirm Dependencies dialog box, make sure that the Stdole2.tlb file is listed. (If it is not listed, you will have to add it later. It is located in your \Windows\System directory.) Click Next.
8. In the Shared ActiveX Application dialog box, select Install as a shared component and No since we are installing this as a DCOM application. Click Next.
9. In the File Summary dialog box, the Setup Wizard processes your files. When it is finished you will see a list of files that will be included in your project. If the Stdole2.tlb file is not listed, click Add. In the Add Files dialog box, select the file from your system directory. Click Next.
10. Save the template if desired, and then click Finish.
11. Connect to the distribution directory from your server and run the Setup.exe file that the Setup Wizard generated.
12. After the server setup is complete, start the Dcom Configuration application by clicking Start then Run and type Dcomcnfg.exe in the Run dialog box.
    
    If you do not configure the server class that was just installed, the default configuration is used. For this example, select proDCOMDemoServer.clsDCOMDemoServer and click Properties.
13. Click the General tab. This tab lists the following information about the application, its name, type, and where it is stored:

       Application Name:  proDCOMDemoServer.clsDCOMDemoServer
       Application Type:  Local Server
       Local Path:        C:\WINNT\system32\proDCOMDemoServer.exe
    
    					

14. Click the Location tab to choose where you want the application to run from. Set the following properties:

     
       Run application on the computer where the data is located  <Unchecked>
       Run application on this computer                           <Checked>
       Run application on the following computer                  <Unchecked>
    
    					

15. Click the Security tab to set application security. You set Access, Launch, and Configuration permissions from this tab.
16. Select Use custom access permissions. Click Edit, which just became available. In the Registry Value Permissions dialog box, click Add.
17. In the Add Users and Groups dialog box, select Everyone, and then click Add. The Add Users and Groups dialog box enables you to allow or deny access to the class to certain individuals or groups.
18. In Type of Access box, select Allow Access and click OK. The Registry Value Permissions dialog box now reflects that you are allowing access to this class to Everyone. Click OK.
19. On the Security tab, select Use custom launch permissions. Click Edit which just became available. In the Registry Value Permissions dialog box, click Add.
20. In the Add Users and Groups dialog box, select Everyone and then click Add. The Add Users and Groups dialog box enables you to allow or deny certain individuals or groups to launch the class.
21. In the Type of Access box, select Allow Launch and click OK. The Registry Value Permissions dialog box now reflects that you are allowing Everyone to launch this class. Click OK.
22. Close Configure Permissions in the Custom selection.
23. Click the Identity tab to set the user account that you want to use to run the application. Set the following properties:

       The Interactive User  <Unselected>
       The Launching User    <Selected>
       This User             <Unselected>
    
    					

24. Click OK. When you get back to Distributed COM Configuration Properties, click OK. The following message should appear: "The operation completed successfully." Click OK.

Distribute the Client

1. Start the Application Setup Wizard by clicking Start, Programs, Visual Basic 5.0, Application Setup Wizard. (If the Introduction dialog box appears, click Next.)
2. In the Select Project and Options dialog box, click Browse. In the Locate VB application's .VBP file dialog box, select C:\DCOMDemo\Client\proDCOMDemoClient.VBP.
3. Click Open and set the following options:
   

      Rebuild the Project:  <Unchecked>
      Options:              Create a Setup Program
   
   						

   Click Next.
4. In the Missing Dependencies dialog box, click Next. Dependency files are not required for this project. In the Confirm Missing Dependencies dialog box, click Yes.
5. In the Distribution Method dialog box, select Single Directory and then click Next.
6. In the Single Directory dialog box, select the C:\DCOMDemo\Client\Setup directory. Click Next.
7. In the ActiveX Components dialog box, deselect proDCOMDemoServer.exe. You do not need to distribute it with the client.
8. Click Add Remote. In the Add ActiveX Components dialog box, select C:\DCOMDemo\Server\proDCOMDemoServer.VBR. This file was created when you compiled the server executable. It was created because you checked the Remote Server Files option on the Server's Properties Component tab.
9. Click Open. The Remote Connection Details dialog box appears. Set the following options:
   

      Remote Transport:   Distributed COM (DCOM)
      Network Address:    <The name of the computer the server will be
                          installed on. Do not include backslashes>
   
   						

   Click OK. Click Next.
10. In the Confirm Dependencies dialog box, make sure that the Stdole2.tlb file is listed. (If it is not listed, you will have to add it later. It is located in your \Windows\System directory.) Click Next.
11. The File Summary dialog box appears and the Setup Wizard processes your files. When it is finished you will see a list of files that will be included in your project. If the Stdole2.tlb file is not listed, click Add. In the Add Files dialog box, select the file from your system directory. Click Next.
12. Save the template if desired, and then click Finish.
13. Connect to the distribution directory from your client and run the Setup.exe file that the Setup Wizard generated.

When you run the application from the client, it returns the time of the computer that the server component is on. When you click Compute Numbers, the result of the addition and subtraction of the numbers appears in the text boxes. Try changing the numbers to confirm that everything works, but don't use a very large number because you told that class that you are passing integers.