How to give alert for user for select at least any one radio button?

Question

<asp:RadioButtonList ID="rlist" runat="server"          
  style="z-index: 1; left: 194px; top: 69px; position: absolute;
  height: 21px; width: 110px" 
  RepeatDirection="Horizontal" Font-Bold="True" ForeColor="Black">
       <asp:ListItem Value="True">Yes</asp:ListItem>
       <asp:ListItem Value="False">No</asp:ListItem>
</asp:RadioButtonList>

This is my coding if user has not selected any one radio button means it will show alert in JavaScript.

Answer 1

Use Validators

   <asp:RequiredFieldValidator   
        ID="ReqiredFieldValidator1"  
        runat="server"  
        ControlToValidate="RadioButtonList1"  
        ErrorMessage="Select your choice!"  
        >  
    </asp:RequiredFieldValidator>  

Answer 2

You can use JQuery to validate this.

The statement $('#RadioButtonList1 input:checked').val() will give you the text of selected item otherwise null.

Answer 3

<form id="Form1" method="post" runat="server">
 <asp:RadioButtonList id="RadioButtonList1" runat="server" RepeatDirection="Horizontal">
  <asp:ListItem Text="Excellent" Value="1" />
  <asp:ListItem Text="Good" Value="2" />
  <asp:ListItem Text="Average" Value="3" />
  <asp:ListItem Text="Poor" Value="4" />
  <asp:ListItem Text="Very Poor" Value="5" />
 </asp:RadioButtonList>
 <input type="button" onclick="onButtonClick();" value="Validate">
</form>

<script type="text/javascript">
<!--
function onButtonClick()
{
 return validateRadioButtonList('<%= RadioButtonList1.ClientID %>');
}
function validateRadioButtonList(radioButtonListId)
{
 var listItemArray = document.getElementsByName(radioButtonListId);
 var isItemChecked = false;

 for (var i=0; i<listItemArray.length; i++)
 {
  var listItem = listItemArray[i];

  if ( listItem.checked )
  {
   //alert(listItem.value);
   isItemChecked = true;
  }
 }

 if ( isItemChecked == false )
 {
  alert('Nothing is checked!');

  return false;
 }

 return true;
}
// -->
</script>

<asp:Button ID="btnSubmit" runat="server" Text="Submit" OnClientClick="return onButtonClick() ;" onclick="btnSubmit_Click" />