RequiredFieldValidator To Validate ListBox In ASP.NET

This blog will show you, how you can validate a list box, using RequiredFieldValidator control in ASP.NET. Thus, for this blog, we will create ASP.NET Application, add a listbox and a RequiredFieldValidator control. 

<asp:ListBox ID = "ListBox1" runat = "server" Width="200" Height="150" SelectionMode = "Multiple">
       <asp:ListItem Value="1">Item 1</asp:ListItem>
       <asp:ListItem Value="2">Item  2</asp:ListItem>
       <asp:ListItem Value="3">Item  3</asp:ListItem>
       <asp:ListItem Value="4">Item 4</asp:ListItem>
       <asp:ListItem Value="5">Item  5</asp:ListItem>
       <asp:ListItem Value="6">Item 6</asp:ListItem>
       <asp:ListItem Value="7">Item  7</asp:ListItem>
       <asp:ListItem Value="8">Item  8</asp:ListItem>
   </asp:ListBox>

   <asp:RequiredFieldValidator ID = "RequiredFieldValidator1" ControlToValidate ="ListBox1" InitialValue = ""  runat="server" ErrorMessage = "Please select some items" ForeColor="Red"></asp:RequiredFieldValidator>
   <br />
   <hr />
   <asp:Button ID="Button1" runat="server" Text="Submit" />

In the code, mentioned above, I specified the control to validate. In validation, it will display the error message. Now, we will run the Application to check the output.