PRB: Unsupported Automation Type Compile Error Using ActiveX Server's Method

• Microsoft Visual Basic Learning, Professional, and Enterprise Editions for Windows, versions 5.0, 6.0

SYMPTOMS

When you use an ATL ActiveX DLL server in Microsoft Visual Basic, if one of the server's methods uses parameters with type UINT, then calling this method generates the compile error message:

Function or interface marked as restricted, or the function uses an Automation type not supported in Visual Basic.

CAUSE

As indicated in the error message, the server is using an Automation type not supported in Visual Basic. Check the MSDN document "Type not supported in Visual Basic" for more information.

RESOLUTION

If you are at the design or early development stage for your server, you are encouraged to change the interface prototypes so that only types supported by Visual Basic are used.

If you already released your product or you are using third-party servers, you can work around the problem most of the time with late binding in your Visual Basic code. The reason why late binding works is that Visual Basic does not check the type at the compile time for late binding objects and Visual Basic uses IDispatch->Invoke at run time for late binding objects.

STATUS

This behavior is by design.

MORE INFORMATION

You can follow the steps below to reproduce the behavior.

Steps to Create an ATL Server

1. Open Visual C++ 6.0.



2. Under the File menu, click New and choose ATL COM AppWizard from the project type list. Type ATLUINT in the Project Name text box. Click OK and then click Finish. Click OK to close the New Project Information dialog box.



3. In Class View, right-click ATLUINT classes and choose New ATL Object from the pop-up menu. Click Next and then type ATLObj in the Short Name text box. Click OK and a new ATL object is created.



4. In Class View, right-click on IATLObj and choose Add Method from the pop-up menu. Type Hello in the Method Name text box and type [in] UINT n in the Parameters text box.



5. Build the project and the DLL is automatically registered.

Steps to Create the Visual Basic Client

1. Create a new Visual Basic standard EXE project. Form1 is created by default.



2. Under Project, select References and select ATLUINT 1.0 type library from the list. Click OK.



3. Put the following code to the code window of Form1:




Private Sub Form_Click()
    Dim obj As ATLUINTLib.ATLObj
    Set obj = New ATLUINTLib.ATLObj
    obj.Hello 5
End Sub 

4. Press the CTRL+F5 key combination to run with full Compile. Note that you see the error message:




Function or interface marked as restricted, or the function uses an Automation type not supported in Visual Basic.

5. Change the line:




    Dim obj As ATLUINTLib.ATLObj 

to be:

    Dim obj As Object 

6. Press the CTRL+F5 key combination to run with full Compile. Now you do not see the error message.


NOTE: Although you can work around the compile-time error message with late binding, you still need to make sure that the information passed in can be interpreted by the server correctly; otherwise, you might get a run-time error or get incorrect results.

NOTE: You only need to use late binding when you try to access the methods that have parameter types unsupported by Visual Basic.

REFERENCES

MSDN topic "Type not supported in Visual Basic"

For additional information on an alternative to using late binding, click the article number below to view the article in the Microsoft Knowledge Base:

Q189133 HOWTO: Make C DLL More Accessible to VB with a Type Library

Additional query words:

Keywords : kbActiveX kbATL kbDLL kbVBp kbVBp500 kbVBp600 kbGrpVB kbDSupport
Version : WINDOWS:5.0,6.0
Platform : WINDOWS
Issue type : kbprb