I am very close to having a C# program work as an ActiveX control with 
Xbase++.
I have added many types of controls in the C# toolbox and can manipulate 
them in the Xbase++ program with no problem
by calling their properties and methods.

I can publish events in the C# program and react to those events in the 
Xbase++ program (thanks to Till Warweg).
When I am completed with this project, I will share the C# and Xbase++ code 
with everyone and will write a detailed white paper on how to do this.

Example of C# code that accomplishes this:

[Guid("7BD20046-DF8C-44A6-8F6B-687FAA26FA71"),
InterfaceType(ComInterfaceType.InterfaceIsIDispatch)]
public interface UserControl1Events
  {
    [DispId(4)]
   void DateChanged( int n, object o, DateRangeEventArgs e, string c1, 
string c2 );
  }
public delegate void DateChangedDelegate( int n, object o, 
DateRangeEventArgs e, string start, string end );
public event DateChangedDelegate DateChanged;
private void monthCalendar1_DateChanged(object sender, DateRangeEventArgs e)
  {
     DateChanged(1, this.monthCalendar1, e, e.Start.ToShortDateString(), 
e.End.ToShortDateString());
  }

* -----------------------------

On the Xbase++ side:

oControl:DateChanged := {|n,o1,o2,c1,c2|DateChanged(oControl,n,o1,o2,c1,c2)}

FUNCTION DateChanged( oControl, n, oCalendar, oDateRangeEventArgs, c1, c2 )

oControl:label1:text := 'You chose ' + c1

RETURN nil

* --------------------------------------

What I haven't figured out however, is how to use an Automation Object that 
has been passed as an argument via the event handler.   For Example, I would 
have expected the below code to work, but it gives an Automation error.  If 
I could figure out how to make this work, then it would simplify the code in 
the C# program and I could control the reaction to events in the Xbase++ 
program.  Any ideas?

FUNCTION DateChanged( oControl, n, oCalendar, oDateRangeEventArgs, c1, c2 )

oControl:label1:text := oDateRangeEventArgs:Start:ToShortDateString()

RETURN nil