PRB: Version Compatibility of OLE Servers

MORE INFORMATION

Prior to following this example, make sure you have built the OLE server and OLE client. For additional information on building OLE clients and servers, please see the following article in the Microsoft Knowledge Base:

Phase One - Modify the Client

You will have to make the following modifications to the OLE client project:

1. Change the code in the Form1_Click event procedure to:

         Dim MyObj As New Project1.Class1
         Print MyObj.MyString
         Print MyObj.MyFunction
   
   						

2. Delete the code from the Form1_Load event procedure.
3. From the Tools menu, select Options. In the Project tab set the Project Name to Client.
4. Add a reference to the OLE server by selecting Tools-Reference from the menu and marking the checkbox which references the OLE server(Project1) in order to successfully compile the OLE client.
5. Make an executable file. Save the OLE client executable file as CLIENT.EXE. Also save the OLE client project.

Phase Two - Modify the Server

Modify the server to make a version compatible but not version identical server. This will involve changing the OLE interface by simply adding a method to the class module.

1. Open the OLE server project previously created.
2. In the Class Module insert the following code in the general declarations section:

         Private Function MyFunction2() as Integer
   
         End Function
   
   						

3. From the Tools menu, choose Options. In the Project tab place the name of the previously created OLE server in the "Compatible OLE Server" editbox.
4. From the File menu, select Make EXE File. Select Options from the file dialog and change the version number to 1.
5. Start the program by choosing Start from the Run menu or by pressing the F5 key to register the OLE server.
6. Save the project. Exit Visual Basic.

Phase Three - Test the OLE Client

1. Run the OLE client executable file.
2. Click Form1. You'll see the following error message:

         Run-time error '-2147319765 (8002802b)':
           Ole Automation error
           Element not found.
   
   						

Phase Four - Fix the OLE Client

In order to make the OLE client execute properly again it will have to be recompiled referencing the updated OLE server.

1. Open the OLE client project.
2. Make a new executable file.
3. Run the executable file. Click Form1. You will see this output:
   
   Life is like a box of chocolates.
   You never know what you're gonna get.