multiselect checkbox inside DropDownList in asp.net

by using RadComboBox its easy to develop checkbox inside dropdownlist
<%@ Register Assembly="Telerik.Web.UI" Namespace="Telerik.Web.UI" TagPrefix="telerik" %>

<tr>
                <td>
                    Country Name
                </td>
                <td>
                    <asp:ScriptManager ID="ScriptManager1" runat="server">
                    </asp:ScriptManager>
                    <telerik:RadComboBox ID="rcbMyList1" runat="server" DataTextField="country_Name"
                        DataValueField="country_Id" Width="200px" Height="200px" AutoPostBack="true">
                        <ItemTemplate>
                            <asp:CheckBox ID="CheckBox1" runat="server" ToolTip='<%# Eval("country_Id") %>' Text='<%# Eval("country_Name") %>' />
                        </ItemTemplate>
                        <CollapseAnimation Type="OutQuint" Duration="200"></CollapseAnimation>
                    </telerik:RadComboBox>
                </td>
            </tr>

code behind:

protected void Page_Load(object sender, EventArgs e)
   {
       if (!IsPostBack)
       {
           DataTable dt = new DataTable();
           dt = CountryHandler.GetAll_Country();
           rcbMyList1.DataTextField = "country_Name";
           rcbMyList1.DataValueField = "country_Id";
           rcbMyList1.DataSource = dt;
           rcbMyList1.DataBind();

       }
   }

A Multiple Selection DropDownList (a CheckBoxList Inside a DropDownList)[^] could help you as well.

Check this link.

DropDownList with checkboxes[^]