Question

I am trying to write a small c# application to test a COM interface (also written in c#). The interface contains a method which accepts a single string as a parameter.

I’ve included a couple code samples below. I use the following to perform the invocation:

public class CreateObject
{
    private Type comType;
    public object comObject;

    public CreateObject(string ProgID)
    {
        comType = Type.GetTypeFromProgID(ProgID);
        comObject = Activator.CreateInstance(comType);
    }
    public void Execute(string Method, params object[] Parameters)
    {
        comType.InvokeMember(Method, BindingFlags.InvokeMethod, null, comObject, Parameters);
    }
}

Which I then execute using:

String sParam = "test";
CreateObject obj = new CreateObject("Namespace.Class");          
obj.Execute("Method", sParam );

Inside the COM, interface looks like this:

[InterfaceType(ComInterfaceType.InterfaceIsDual), Guid("xxxxxx-xxxx-xxxx-xxxx-xxxxxx")]
public interface Interface
{
    void Method(String sParam);
}

Simplified implementation of Method(String):

[ClassInterface(ClassInterfaceType.None), Guid("xxxxxx-xxxx-xxxx-xxxx-xxxxxxxxx"), ProgId("Namespace.Class")]
public class Class: Interface
{
    public void Method(String sParam)
    {
        XmlDocument xml = new XmlDocument();
        xml.LoadXml(sParam);
        XmlWriter writer = XmlWriter.Create("result.xml");

        *** other code used to create the xml ***
    }
}

Even though there are no errors returned, the COM doesn’t actually seem to execute. However when I take out the string parameter from both the test app and the COM, I do get the correct output (the COM interface creates an XML file on disc). Can anyone see a fault in my use of the parameter?

Answer 1

I’ve found out that class libraries don’t use app.config, which means my COM had no access to any of its settings (connection strings, etc.) and threw errors I couldn’t see until I returned them as part of the try/catch.

So the answer is that use of parameters in this case was correct.