[CrmWorkflowActivity("My Demo workflow")]
    public partial class MyDemo : Activity
	{
        public MyDemo()
        {

        }

        protected override ActivityExecutionStatus Execute(ActivityExecutionContext executionContext)
        {

            try
            {
                //Debugger.Break();
                IContextService contextService = (IContextService)executionContext.GetService(typeof(IContextService));
                IWorkflowContext context = contextService.Context;

                // Create the CRM service
                ICrmService crmService = context.CreateCrmService();

                //get all contacts
                //            QueryExpression query = new QueryExpression();
                using (FileStream fileStream = new FileStream(@"C:\inetpub\wwwroot\cwf.log", FileMode.Append))
                {
                    byte[] data = System.Text.Encoding.UTF8.GetBytes(DateTime.Now.ToString());
                    fileStream.Write(data,0,data.Length);
                }
            }
            catch (Exception exc)
            {
                throw;
            }

            return ActivityExecutionStatus.Closed;
        }
	}