Add the sample code for the double click event to the ListBox

 
<!-- To create a JS call button the click The event --> 
<script type="text/javascript"> 
function JsListChangeItem() { 

document.getElementById("buttonShow").click(); 
} 
</script> 
<!-- Create a hidden button To create a double-click event ---> 
<asp:Button ID="buttonShow" runat="server" onclick="buttonShow_Click" Text="Button" style="display:none"/> 

<!-- double-click listbox--> 
<asp:ListBox ID="listBox1" runat="server"Height="226px" Width="211px" AutoPostBack="True"></asp:ListBox> 

 
protected void Page_Load(object sender, EventArgs e) 
{ 
listBox1.Attributes.Add("ondblclick", "JsListChangeItem()");//Add a double-click event to listBox1.
}