<p>In a workflow, to call the external method, you need the following ready.</p>
        <li>The workflow need a interface marked with ExternalDataExchange. In the callExternalMethodActivity node, you need to configure the InterfaceType, MethodName, MethodInvoking, and what value to be used as passed-in parameter.

        In workflow host, you need to config the workflow runtime to service the ExternalService. When a workflow instance execute an callExternalMethodActivity, it will ask the workflow runtime to supply a service.

        <pre data-sub="prettyprint:_">
        //workflow definition
        public interface ICustomerService
        void SendCustomerData(string customerName);

        //host enviroment code
        public class CustomerService : ICustomerService

        public void SendCustomerData(string customerName)

        ExternalDataExchangeService xchangeSvc = new ExternalDataExchangeService();
        CustomerService custSvc = new CustomerService();