NPOI 添加下拉框

             XSSFDataValidationHelper helper = new XSSFDataValidationHelper((XSSFSheet)sheet);//获得一个数据验证Helper  
            var namelist = new string[] { "张三", "李四", "王五" };//创建一个数组作为数据源
            CellRangeAddressList regions = new CellRangeAddressList(4, 50, 1, 50);
            IDataValidation validation = helper.CreateValidation(helper.CreateExplicitListConstraint(namelist), regions);//创建约束
            validation.CreateErrorBox("错误", "请按右侧下拉箭头选择!");//不符合约束时的提示  
            validation.ShowErrorBox = true;//显示上面提示 = True  
            sheet.AddValidationData(validation);//添加进去