带参数的.NET vb6包装器属性

Question

i need to write ac# wrapper for a vb6 application. I always get error 450 ( Wrong number of arguments or property assignment was not valid.) This is my VB Code

Dim DBEngine As New DBEngineNet

Set mDbEProp = DBEngine.Properties("Version") ' <-- ERROR

This code is working, so the problem is the parameter of the property

Dim DBEngine As New DBEngineNet
Set mDbEProps = DBEngine.Properties
Set mDbEProp = mDbEProps("Version")  '<-- Working. Results 1.0

Here is my COM-Visible C#-Code. It uses the Interop-Interfaces of the old VB6-MotorApp.

[ComVisible(true)]
public class DBEngineNet : VB6MotorApp.DBEngine
{
    public VB6MotorApp.Properties Properties
    {
        // [return: MarshalAs(UnmanagedType.SafeArray, SafeArraySubType = VarEnum.VT_SAFEARRAY)] Maybe something like this???
        get
        {
            return new PropertiesNet
                {
                    new PropertyNet{Name="Version", Value="1.0"}
                };
        }
    }

Here is the Properties-Object:

[ComVisible(true)]
public class PropertiesNet : VB6MotorApp.Properties, IList<PropertyNet>
{
    List<PropertyNet> _properties = new List<PropertyNet>();

    public VB6MotorApp.Property this[object Item]
    {
        get
        {
            return _properties.FirstOrDefault(p => p.Name == Item.ToString());
        }
    }
}

Any ideas?

Answer 1

The basic diagnostic tool you need here is OleView.exe, run it from the Visual Studio Command Prompt. Use its File + View typelib command to look at the type libraries and compare them. First on your original VB6 implementation so you have a base-line, next on the type library for your .NET version.

There are inevitably going to be major difference the way you are doing it now, you are exposing too many details of the class implementation. All of the System.Object methods as well as the IList<> implementation methods are going to be visible. Boilerplate is to declare a [ComVisible(true)] interface (VB6 likes their name to start with an _underscore) and hide the class implementation by giving it the [ClassInterface(ClassInterfaceType.None)] attribute. You already have the interface so only the attribute should be necessary.

What you want to look for first in the OleView.exe output is the [dispid] attribute for the DBEngineNet.Properties property. It doesn't act like the default property which is why you have to obtain the property value explicitly in your VB6 code. The default property has dispid(0). You force the value in .NET code by giving it the [DispId(0)] attribute.

You also want to look at the original type library, "VB6MotorApp.Properties" looks wrong. That's a coclass name, not an interface name. Non-zero odds that you should be using VB6MotorApp._Properties. Same for VB6MotorApp._DBEngine.

And look at which interfaces in the coclasses have the [default] attribute. It should be the VB6 interfaces. Probably not an issue if your VB6 snippets work as posted.