bootstrap multiselect dropdown code example
Example 1: asp multi select dropdown
<asp:ListBox runat="server" SelectionMode="Multiple" >
<asp:ListItem Text="test1"></asp:ListItem>
<asp:ListItem Text="test2"></asp:ListItem>
<asp:ListItem Text="test3"></asp:ListItem>
</asp:ListBox>
Example 2: multiple select dropdown in bootstrap
$('select').selectpicker();
Example 3: bootstrap multiselect dropdown with search stackoverflow
<link rel="stylesheet" href="https://stackpath.bootstrapcdn.com/bootstrap/4.1.1/css/bootstrap.min.css">
<link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/bootstrap-select/1.13.1/css/bootstrap-select.css" />
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<script src="https://stackpath.bootstrapcdn.com/bootstrap/4.1.1/js/bootstrap.bundle.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/bootstrap-select/1.13.1/js/bootstrap-select.min.js"></script>
<select class="selectpicker" multiple data-live-search="true">
<option>Mustard</option>
<option>Ketchup</option>
<option>Relish</option>
</select>