你可以使用 RequiredFieldValidator 。



参考 - / =http：// www。 c-sharpcorner.com/Blogs/5385/Asp-Net-dropdownlist-validation-using-required-field-validat.aspx\"target =_ blanktitle =New Window> ^ ]。



否则，在某些按钮单击服务器事件中，检查 SelectedValue $ c> DropDownLists 并相应地显示消息。

除了Tadit的解决方案，下拉列表的验证也可以在javascript中完成。

试试这个：

 <   asp：dropdownlist     id   =  DropDownList1    runat   =  服务器 >  
 <   / asp：dropdownlist  >  

Javascript：

< script language =   javascript type =   text / javascript> 

 function  Validate（）{

 if  （ document  .getElementById（' <％= DropDownList1。 ClientID％>'）。value ==  选择）{
 alert（ 请选择DropDownList1！）; 
 document  .getElementById（' <％ = DropDownList1.ClientID％>'）。focus（）; 
 return   false ; 
} 
} 
< / script> 

提交按钮：

 <   asp：按钮    id   =  Button1    runat   =  server    text   = 按钮    onclientclick   =  return Validate（）;  /  >  

位于 Tadit Dash 解决方案。



你可以在 Javascript 还...

示例：

 <   html     xmlns   =  http://www.w3.org/ 1999 / xhtml >  
<   head     runat   =  服务器 >  
 <   script     src   =  jquery-1.10.2.js    type   =  text / javascript >  <   / script  >  
<   script     type   =  text / javascript  >  

 var Check = function（）{
 var ddls = ['<％ = DropDownList1。 ClientID ％> '，'<％ = DropDownList2.ClientID ％&GT; 跨度>']; 
 for（var i = 0; i <     ddls.length;     i ++）    {  
  
                                  var     ddl     =   document.getElementById（ddls [i]）; 
  
                                 如果   （ddl.value     =   =  '-----选择---'）    {n>  
  
                                          ddl.focus（）;   
  
                                          alert（'some            详细信息       不   找到'）;   
  
                                         return     false;   
  
                                 }   
  
  
  
                         }   
  
                          return     true;   
  
                 }   
  
  
  
  
  
         < / script  >  
<   / head  >  
<   body  >  
<  表格    id   =  form1    runat   =  server >  
<   div  >  
<   asp：按钮    ID   =  Button1    runat   =  server    OnClientClick   =  return Check（）;    OnClick   =  Button1_Click  
  
                         文字  = 添加到网格    /   >  
<   br     /  >  
 <   asp：DropDownList     ID   =  DropDownList1    runat   = 服务器 >  
<   asp：ListItem    文本  =  -----选择---    /  >  
<   asp：ListItem    文本  =  Item1    /  >  
<   asp： ListItem    文本  =  Item1    /  >  
<   / asp：DropDownList  >  
<   asp：DropDownList     ID   =  DropDownList2    runat   =  server >  
<   asp：ListItem    文字  =pan>  -----选择---    /  >  
<   asp：ListItem    文本  =  Item1    /  >  
<   asp：ListItem    文本  =  Item1    /  >  
<   / asp：DropD ownList  >  
<   br     /  >  
<   / div  >  
<   / form  &gt ;  
<   / body  >  
<   / html  &GT; 跨度> 

i have list of 8 dropdownlist as follows

Student id Dropdownlist1
Course Dropdownlist2
Rank Dropdownlist3
Faculty id Dropdownlist4
Faculty name Dropdownlist5
Rate for faculty Dropdownlist6
Practicals Dropdownlist7
Booking for course Dropdownlist8

i want to validate if any of the one Dropdownlist is not selected. i want to show the message "some of the details are not found".

for that how can i validate in asp.net using c#.


Regards,
Narasiman P.

You can use RequiredFieldValidator.

Refer - asp.net dropdownlist validation using Required Field Validation[^].

Otherwise, in some Button Click Server Event, check the SelectedValue of the DropDownLists and show message accordingly.

In addition to Tadit's Solution, Validation for dropdownlist can be done in javascript also.
Try this:

<asp:dropdownlist id="DropDownList1" runat="server">
                 </asp:dropdownlist> 

Javascript:

<script language="javascript" type="text/javascript">

         function  Validate() {

             if (document.getElementById('<%= DropDownList1.ClientID%>').value == "Select") {
                 alert("Please Select DropDownList1!");
                 document.getElementById('<%= DropDownList1.ClientID%>').focus();
                 return false;
             }  
         }     
    </script>

Submit Button:

<asp:button id="Button1" runat="server" text="Button" onclientclick="return Validate();"/>

on top of Tadit Dash Solution.

you can try this in Javascript also...
Sample:

<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
    <script src="jquery-1.10.2.js" type="text/javascript"></script>
    <script type="text/javascript">

        var Check = function () {
            var ddls = ['<%= DropDownList1.ClientID %>', '<%= DropDownList2.ClientID %>'];
            for (var i = 0; i < ddls.length; i++) {

                var ddl = document.getElementById(ddls[i]);

                if (ddl.value == '-----Select---') {

                    ddl.focus();

                    alert('some of the details are not found');

                    return false;

                }



            }

            return true;

        }





    </script>
</head>
<body>
    <form id="form1" runat="server">
    <div>
        <asp:Button ID="Button1" runat="server" OnClientClick="return Check();" OnClick="Button1_Click"

            Text="Add to Grid" />
        <br />
        <asp:DropDownList ID="DropDownList1" runat="server">
            <asp:ListItem Text="-----Select---" />
            <asp:ListItem Text="Item1" />
            <asp:ListItem Text="Item1" />
        </asp:DropDownList>
        <asp:DropDownList ID="DropDownList2" runat="server">
            <asp:ListItem Text="-----Select---" />
            <asp:ListItem Text="Item1" />
            <asp:ListItem Text="Item1" />
        </asp:DropDownList>
        <br />
    </div>
    </form>
</body>
</html>