Is there a cleaner method of making COM visible applications?

Question

Given a specific class:

public class Klass
{
    public int value;
    public void doSomething(){
        return;
    }
}

To make said class COM visible, as far as I know, one needs to do a few things:

1. Import System.Runtime.InteropServices
2. Create an interface for the class.
3. Extend the interface created.
4. Create 2 unique GUIDs, one for the Interface and another for the class.
5. Add Dispatch IDs to the interface.

Producing something like:

[Guid("EAA4976A-45C3-4BC5-BC0B-E474F4C3C83F")]
public interface IKlass
{
    [DispId(0)]
    public int value;
    [DispId(1)]
    public void doSomething();
}

[Guid("0D53A3E8-E51A-49C7-944E-E72A2064F938"),
    ClassInterface(ClassInterfaceType.None)]
public class Klass : IKlass
{
    public int value;
    public void doSomething(){
        return;
    }
}

The resulting code looks utterly gross in my opinion... The question is, is there a simple cleaner method of creating these COM interfaces? I can imagine modifying the build process myself to give a interop feature. E.G.

public interop class Klass
{
    public interop int value;
    //...
}

However, this is non-standard, which has it's issues as well. Is there anything built-in to Visual Studio / C# that I can use to make building COM interfaces easier/cleaner?

Answer 1

As suggested by Zohar Peled the best way is to use RegAsm.exe:

1. Create some C# class library "TestProject":

---

using System.Windows.Forms;
namespace TestProject
{
    // Note. Only public classes are exported to COM!
    public class Test
    {
        // Note. Only public methods are exported to COM!
        public void testIt() {
            MessageBox.Show("Yellow world");
        }
    }
}

---

IMPORTANT: Only public classes are exported to COM. And only public methods of these classes are available via a COM object instance.

---

2. Sign the project.

3. In AssemblyInfo.cs set [assembly: ComVisible(false)] to [assembly: ComVisible(true)]. Note: You can also use attribute [ComVisible(true)] before each class you want to expose to COM. This just sets the default to true making it easier to work with if building an API

4. Build the project.

5. Run regasm. Remember to use the correct version of Regasm (32-bit/64-bit) and the version for your .NET framework:

---

# .NET v4.5 64-bit
"C:\Windows\Microsoft.NET\Framework64\v4.0.30319\RegAsm.exe" -tlb -codebase "C:\Users\sancarn\Desktop\tbd\TestProject\TestProject\bin\Debug\TestProject.dll" -verbose

# .NET v4.5 32-bit
"C:\Windows\Microsoft.NET\Framework\v4.0.30319\RegAsm.exe" -tlb -codebase "C:\Users\sancarn\Desktop\tbd\TestProject\TestProject\bin\Debug\TestProject.dll" -verbose

...

---

Regasm should output something like this:

Microsoft .NET Framework Assembly Registration Utility version 4.7.3056.0
for Microsoft .NET Framework version 4.7.3056.0
Copyright (C) Microsoft Corporation.  All rights reserved.

Types registered successfully
Type 'TestProject.Test' exported.
Assembly exported to 'C:\Users\sancarn\Desktop\tbd\TestProject\TestProject\bin\Debug\TestProject.tlb', and the type library was registered successfully

---

Now you can test the file in VBScript for example:

Dim o As Object
Set o = CreateObject("TestProject.Test")
Call o.testIt

Answer 2

Sancarn answers your question, but note that this makes ALL COM-compatible classes in your project COM-visible as well, which you might not want (see here and here). If you do not explicitly set the UUIDs you are opening yourself up to problems when you deploy if you access the classes with early-bound clients like VB or VBA (not VBScript, which is late-bound).

Yes it's not "clean" but neither is COM, especially when you want to expose it to late-binding clients live VBScript.

I would also change your public field to a property, which is more standard for public members:

    [Guid("EAA4976A-45C3-4BC5-BC0B-E474F4C3C83F")]
    public interface IKlass
    {
        [DispId(0)]
        public int value {get; set;}
        [DispId(1)]
        public void doSomething();
    }