使用：
 private string roleName;
        public  string RoleName
        {
            get
            {
                return roleName;
            }
            set
            {
                roleName=value;
                WebWorkflowRole _webWorkflowRole=new WebWorkflowRole(roleName);
                POInitiators.Add(_webWorkflowRole);
            }
        }
        private WorkflowRoleCollection poInitiatorsValue = new WorkflowRoleCollection();

        public WorkflowRoleCollection POInitiators
        {
            get
            {
                return poInitiatorsValue;
            }
        }