Automation Error when instantiating a .Net COM visible class

Question

I created a COM-interop .dll with this simple class:

using System.Runtime.InteropServices;

namespace ClassLibrary1
{
    [ComVisible(true)]
    [Guid("795ECFD8-20BB-4C34-A7BE-DF268AAD3955")]
    public interface IComWeightedScore
    {
        int Score { get; set; }
        int Weight { get; set; }
}

[ClassInterface(ClassInterfaceType.None)]
[Guid("9E62446D-207D-4653-B60B-E624EFA85ED5")]
public class ComWeightedScore : IComWeightedScore
{

    private int _score;

    public int Score
    {
        get { return _score; }
        set { _score = value; }
    }
    private int _weight;

    public int Weight
    {
        get { return _weight; }
        set { _weight = value; }
    }

    public ComWeightedScore()
    {
        _score = 0;
        _weight = 1;
    }
  }

} I registered it using: C:\WINDOWS\Microsoft.NET\Framework\v4.0.30319\regasm C:\ComClasses\Classlibrary1.dll /tlb: Classlibrary1.tlb

Finally I succesfully added a reference to the .dll after which VB6 gave me intellisense on the object.

Private Sub Form_Load()
    Dim score1 As ComWeightedScore

    Set score1 = New ComWeightedScore
    score1.Score = 500

End Sub

On the line Set score1=new ComWeightedScore the exception Automation Error is raised.

It can hardly be any simpler than this... Where is the error?!

And why do you say the error is in assigning int or long? what fails is the constructor call. Does it still fail if you remove the assignments from the body of the constructor? Also, provide more info and details on the error you get. — Davide Piras

Hans Passant Hans Passant · Accepted Answer · 2011-08-29T00:15:22

You forgot the /codebase option in the Regasm.exe command line.

Without it, you'll have to strong-name the assembly and put it in the GAC with gacutil.exe. Good idea on the client machine, just not on yours.

Automation Error when instantiating a .Net COM visible class

3 Answers