sharepoint工作流代码item.update()错误

C# code

            bool approval = Convert.ToBoolean(this.TaskProperties1.ExtendedProperties["approval"]);            //获取到任务表单中的comments字段            string comments = "" + this.TaskProperties1.ExtendedProperties["comments"];            SPModerationStatusType approvalState = approval ? SPModerationStatusType.Approved : SPModerationStatusType.Denied;            SPListItem item = this.workflowProperties.Item;            item["_ModerationStatus"] = (int)approvalState; //设置内容审批状态            item["_ModerationComments"] = comments;     //设置内容审批批注                        item.Update();

item.Update();执行的时候报错：说文档没有签出，不能修改应该怎么解决啊，请各位大侠指教

[解决办法]
1. check out:

C# code

            bool approval = Convert.ToBoolean(this.TaskProperties1.ExtendedProperties["approval"]);            //获取到任务表单中的comments字段            string comments = "" + this.TaskProperties1.ExtendedProperties["comments"];            SPModerationStatusType approvalState = approval ? SPModerationStatusType.Approved : SPModerationStatusType.Denied;            SPListItem item = this.workflowProperties.Item;            item.CheckOut();            item["_ModerationStatus"] = (int)approvalState; //设置内容审批状态            item["_ModerationComments"] = comments;     //设置内容审批批注                        item.Update();            item.CheckIn();
[解决办法]
探讨

1. check out:

C# codebool approval= Convert.ToBoolean(this.TaskProperties1.ExtendedProperties["approval"]);//获取到任务表单中的comments字段string comments=""+this.TaskProperties1.ExtendedProperties["comments"];

            SPModerationStatusType approvalState= approval? SPModerationStatusType.Approved : SPModerationStatusType.Denied;

            SPListItem item=this.workflowProperties.Item;
            item.CheckOut();

            item["_ModerationStatus"]= (int)approvalState;//设置内容审批状态
            item["_ModerationComments"]= comments;//设置内容审批批注
            
            item.Update();
            item.CheckIn();

2. 提升权限：
C# codeSPSecurity.RunWithElevatedPrivileges(delegate()
{// implementation details omitted});