BUG: Error "438" When Implementing Base Class in ActiveX Exe

• Microsoft Visual Basic Learning, Professional, and Enterprise Editions for Windows, version 6.0
• Microsoft Visual Basic Control Creation, Learning, Professional, and Enterprise Editions for Windows, version 5.0

SYMPTOMS

If you late-bind to an ActiveX EXE that contains a derived class that implements a base class, you receive the following error when trying to use a method or property of that base class:

Run Time Error "438"
Object Doesn't Support This Property Or Method

RESOLUTION

Use early binding or put the base and derived classes into an ActiveX DLL.

STATUS

Microsoft has confirmed this to be a bug in the Microsoft products listed at the beginning of this article. We are researching this bug and will post new information here in the Microsoft Knowledge Base as it becomes available.

MORE INFORMATION

Steps To Reproduce

Part 1

1. Start a new ActiveX EXE Project in Visual Basic. Form1 is created by default.



2. On the Project menu, click Project1 Properties, and change the name of the ActiveX EXE project to "OutProcServer."



3. Add two additional class modules to the Project. Name the existing three class modules as follows:
   
   clsBase
   clsDerived
   clsStarter



4. Paste the following code into the clsBase module:

   
         Property Get MyFirstProperty() As String
         End Property
    




5. Paste the following code into the clsDerived module:

   
         Implements clsBase
   
         Private Property Get clsBase_MyFirstProperty() As String
            clsBase_MyFirstProperty = "Hello from MyFirstProperty!"
         End Property
    




6. Paste the following code into the clsStarter module :

   
         Public Function CreateDerivedClass() As clsBase
             Set CreateDerivedClass = New clsDerived
         End Function
    




7. Save the ActiveX EXE project, and then compile it.

Part 2

1. Create a new Standard EXE project. Form1 is created by default.



2. On the Project menu, click References, then select "OutProcServer," which is the server that was just compiled step 7 of Part 1 above.



3. Add two Command Buttons to Form1 (Command1 and Command2).



4. Paste the following code into the code module of Form1:

   
         ' Early bound object references.
         Dim oEarlyStarterClass As OutProcServer.clsStarter
         Dim oEarlyDerivedClass As OutProcServer.clsBase
   
         ' Late bound object references.
         Dim oLateStarterClass As Object
         Dim oLateDerivedClass As Object
   
         Private Sub Command1_Click()
   
            ' Create an instance of the out-proc server starter class object.
            Set oEarlyStarterClass = New clsStarter
   
            ' Now that there is a reference to the starter class object; use
            ' this object to return an instance of the derived class, which
            ' implements the base class declared in the out-proc server.
            Set oEarlyDerivedClass = oEarlyStarterClass.CreateDerivedClass
   
            ' Show the object type of the newly created object returned
            ' from the starter class object; it will be the derived class.
            MsgBox "oEarlyDerivedClass Is Of Type : " & _
                    TypeName(oEarlyDerivedClass)
   
            ' To prove that an instance of the derived class was successfully
            ' created, call the base class's interface, which the derived
            ' class implemented.
            MsgBox oEarlyDerivedClass.MyFirstProperty
   
            ' Destroy our objects.
            Set oEarlyDerivedClass = Nothing
            Set oEarlyStarterClass = Nothing
   
         End Sub
   
         Private Sub Command2_Click()
   
            ' Create an instance of the out-proc server starter class object
            ' late-bound.
            Set oLateStarterClass = CreateObject("OutProcServer.clsStarter")
   
            ' Create a late-bound instance of the derived class.
            Set oLateDerivedClass = oLateStarterClass.CreateDerivedClass
   
            ' The first test is to show the type of the object that was just
            ' created through the starter class object. The MsgBox will show
            ' the correct value; which is the derived class, and not the base
            ' class.
            MsgBox "oLateDerivedClass Is Of Type : " & _
               TypeName(oLateDerivedClass)
   
            ' Finally, try to call the property that the derived class
            ' has implemented. This will fail!
            MsgBox oLateDerivedClass.MyFirstProperty
   
         End Sub
    




5. Press the F5 key to run the project.



6. Click the Command1 button; this creates an instance of the "Starter Class." The Starter Class is used to create an instance of the derived Class. The Starter Class then checks to make sure that the proper class is being returned, and then calls the base class's property. This test uses early binding.



7. Click the Command2 button; similar to the Command1 button, the Command2 button creates an instance of the "Starter Class." This class then returns an instance of the derived class, then checks that that the proper object type is returned. Calling the base class property results in the 438 error. This second test uses late binding, and fails when it should succeed.

Additional query words: kbVBp500bug kbVBp600bug kbdss kbDSupport kbVBp kbActiveX

Keywords : kbGrpVB
Version :
Platform : WINDOWS
Issue type : kbbug