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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. 
  1. <asp:ListBox ID = "ListBox1" runat = "server" Width="200" Height="150" SelectionMode = "Multiple">  
  2.        <asp:ListItem Value="1">Item 1</asp:ListItem>  
  3.        <asp:ListItem Value="2">Item  2</asp:ListItem>  
  4.        <asp:ListItem Value="3">Item  3</asp:ListItem>  
  5.        <asp:ListItem Value="4">Item 4</asp:ListItem>  
  6.        <asp:ListItem Value="5">Item  5</asp:ListItem>  
  7.        <asp:ListItem Value="6">Item 6</asp:ListItem>  
  8.        <asp:ListItem Value="7">Item  7</asp:ListItem>  
  9.        <asp:ListItem Value="8">Item  8</asp:ListItem> 
  10.    </asp:ListBox>   
  11.   
  12.    <asp:RequiredFieldValidator ID = "RequiredFieldValidator1" ControlToValidate ="ListBox1" InitialValue = ""  runat="server" ErrorMessage = "Please select some items" ForeColor="Red"></asp:RequiredFieldValidator>  
  13.    <br />  
  14.    <hr />  
  15.    <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.
 
output