// The control needs to be XU_Employee
form.DoctorID.LoadDataSource(XU_EmployeeSource.Create());

// Handle it
 form.DoctorID.OnButtonClick += (s, e) =>
{
    XF_EmployeeFinder.F_ShowLekar((doctID) =>
    {
        ((XU_Employee)s).EditValue = doctID;
    });
};