public class MyInteraction : Interaction
{
    public override RequestCode OnStart(InteractionContext oContext)
    {
        return RequestCode.Point;
    }

    public override RequestCode OnPoint(Position oPosition)
    {
        m_arrPoints[m_iPoints] = oPosition.FinalPosition;
        ++m_iPoints;
        if (m_iPoints == 2)
        {
            return RequestCode.Success;
        }
        return RequestCode.Point;
    }

    public override void OnSuccess(InteractionContext oContext)
    {
        Line oLine = new Line();
        oLine.Create(Page, m_arrPoints[0], m_arrPoints[1]);
    }

    private int m_iPoints = 0;
    private PointD[] m_arrPoints = new PointD[2];
}

string strAction = "XGedStartInteractionAction";

ActionManager oActionManager = new ActionManager();
Action oAction = oActionManager.FindAction(strAction);
if (oAction != null)
{
    ActionCallingContext oContext = new ActionCallingContext();
    oContext.AddParameter("Name", "MyInteraction");
    oAction.Execute(oContext);
}