PRB: Can't Use Late Binding When Server Method Uses UDT

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

SYMPTOMS

When you have an ActiveX server that you created with Visual Basic version 6.0, you receive an error when accessing a method or property that accepts and/or returns a user-defined type (UDT).

You receive one of the following errors when accessing a method that returns a UDT or accepts a UDT as an argument:

Run-time Error '429':
ActiveX component can't create object

-or-

Compile error:
Only user-defined types defined in public object modules can be coerced
to or from a variant or passed to late-bound functions.

CAUSE

A method that returns or accepts a user-defined type (UDT) cannot be called when using late binding.

   Dim oMyObject as Object
   Dim MyUDT as Object
   Set oMyObject = CreateObject("MyProject.MyClass")
   MyUDT = oMyObject.MyMethod    '<-- This line generates a run-time error
                                 '    if MyMethod returns a UDT. 

RESOLUTION

To correct this problem, you can use either of the following two solutions:

• Use early binding instead of late binding.



• Modify the server so that the method returns an object of another class rather than a UDT.

STATUS

This behavior is by design.

MORE INFORMATION

Steps to Reproduce Behavior

1. Create a new ActiveX EXE project.



2. On the Project menu, click Properties. Change the Project Name to "TestServer" and click OK.



3. Add the following code to Class1:

   
         Public Type MyUDT
            x as Long
            y as Long
         End Type
   
         Public Function MyMethod() as MyUDT
            MyMethod.x = 1
            MyMethod.y = 2
         End Function
    




4. On the File menu, click Make TestServer.EXE.



5. Close this project and start a new Standard EXE project.



6. Add two command buttons to Form1.



7. Add the following code to Form1:

   
         Private Type MyUDT
            x as Long
            y as Long
         End Type
   
         Private Sub Command1_Click()
            Dim obj1 as Object
            Dim obj2 as Object
            Set obj1 = CreateObject("TestServer.Class1")
            obj2 = obj1.MyMethod           '<== Generates run-time error #429.
         End Sub
   
         Private Sub Command2_Click()
            Dim obj1 as Object
            Dim mu as MyUDT
            Set obj1 = CreateObject("TestServer.Class1")
            mu = obj1.MyMethod             '<== Generates compile error.
         End Sub
    




8. Run the project by pressing F5 and click Command1. You receive the run-time error #429. Click End to end the program.



9. Run the project once more and click Command2. You receive the compile error described at the beginning of this article.

REFERENCES

For information about binding ActiveX components in your project, refer to the "Declaring an Object Variable" and "How Binding Affects ActiveX Component Performance" topics in the Visual Basic product documentation.

For information about creating your own collection classes, refer to the "Using Properties and Collections to Create Object Models" topic in the Visual Basic product documentation.

Additional query words: kbVBp kbdsd kbDSupport kbVBp600 kbActiveX kbDSupport kbDSD

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