添加“无"到数据绑定下拉列表 [英] add "None " to databound dropdown list

问题描述

我有一个下拉列表，绑定到后面代码中的数据.
我希望默认值是-无-在列表的顶部.
如果用户选择列表的顶部，即无"，则应提示，如pl z从列表中选择，
如果用户选择-无"以外的其他选项，则应继续执行该过程

我已将顶部列表添加为

Hi,

I have a dropdownlist that is bound to data in the code behind.
i want the default to be -- None -- at the top of the list.
if the user select the top of list i.e --None-- it should prompt as pl z select from the list ,
if user select the other than --None-- then it should continue the process

i have added the top list as

drop down.Items.Insert(0, new ListItem("-- None--", "")) 

如何验证

在此先感谢

how to validate

thanks in advance

推荐答案

使用此功能.

use this one.

drop down.Items.Insert(0, new ListItem("-- None--", "-- None--"));

dropdownlist1.Items.Insert(0, new ListItem("None", "0"));

用于验证，您可以使用javascript例如

for validating you can use javascript for example

try
{
  if(dropdownlist1.SelectedValue == "0")
  {
     throw new Exception("<script language="javascript">" + "alert('Please select something');" + "");
  }
}

catch (Exception ex)
{
   label1.Text = ex.Message;
}</script>

function validateDropDown(){
       if(document.getElementById(<%=ddl.ClientID%>).value=='0')
       {
           alert('please select valid item.');
           return false;
       }
   }

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