Question

if this possible to write a com control or activex in C# and use it in MFC ?

Answer 1

Yes. First, you need to create COM object. Below is a very simple example.

[Guid("123565C4-C5FA-4512-A560-1D47F9FDFA20")]
public interface IDoSomething
{
    [DispId(1)]
    string Name { get; }

    [DispId(2)]
    int DoSomething();
}

[ComVisible(true)]
[Guid("12AC8095-BD27-4de8-A30B-991940666927")]
[ClassInterface(ClassInterfaceType.None)]
public sealed class DoSomething: IDoSomething
{
    public DoSomething()
    {
    }

    public string Name
    {
        get { return ""; }
    }

    public int DoSomething()
    {
        return 4; //random number
    }
}

After that you need to regasm your assembly. The regasm tool will add the necessary registry COM entries:

regasm.exe /tlb component.dll

/tlb is necessary to generate the type library to be imported in your MFC application.

Once your assembly is registered, you can call DoSomething in your MFC application like any other COM objects.

Check this link for more information.