SELEC2 4.0 with multi select in ASP.Net: How to get and set selected items?

I am trying to use SELECT2 in ASP.Net in combination with a dropdown list.

This is my .aspx

<%@ Page Language="C#" AutoEventWireup="true" CodeBehind="default.aspx.cs" Inherits="ASPNet_SELECT2_1._default" %>

<!DOCTYPE html>

<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
<meta http-equiv="Content-Type" content="text/html; charset=utf-8"/>
    <title>a SELECT2 implementation in ASP.NET</title>
    <script src="scripts/js/jquery-1.12.0.js"></script>
    <script src="scripts/js/select2/select2.js"></script>
    <link rel="stylesheet" href="css/select2.css" />

    <script>
            $(document).ready(function () {
                $("#" + "<%=dd.ClientID%>").select2({
                placeholder: "Select a Subject",
                allowClear: true
            });
        });
    </script>
</head>
<body>
    <form id="form1" runat="server">
        <div>
            <asp:DropDownList ID="dd" runat="server" ClientIDMode="Static" Width="300px" multiple="multiple"></asp:DropDownList>
        </div>
        <asp:Button ID="btnGetSelected" runat="server" Text="Get selected items" OnClick="btnGetSelected_Click" />&nbsp;<asp:Button ID="btnSetSelected" runat="server" Text="Set selected items" OnClick="btnSetSelected_Click" />
        <br />
        <asp:Literal ID="lit" runat="server"></asp:Literal>
    </form>
</body>
</html>

This is my code behind

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;

namespace ASPNet_SELECT2_1
{
    public partial class _default : System.Web.UI.Page
    {
        protected void Page_Load(object sender, EventArgs e)
        {
            if (!Page.IsPostBack)
            {
                for (int i = 0; i < 10; i++)
                {
                    ListItem l = new ListItem("Item " + i.ToString());
                    dd.Items.Add(l);
                }
            }
        }

        protected void btnGetSelected_Click(object sender, EventArgs e)
        {
            lit.Text = dd.Text;
        }

        protected void btnSetSelected_Click(object sender, EventArgs e)
        {

        }
    }
}

The binding of the SELECT2 control with my dropdown list works fine. I also have set the "multiple" attribute for the dropdown list to have the multi select functionality. But i am not able to get the selected items. And also am i not able to set these items.

When i select multiple elements and do a postback (for example on button click), then after the postback only one item is selected. And i always get the selected first item.

How can get all selected items and also set multiple selected items on postback and also via code?

I have solved it by using a HTML Select Tag with runat="server" instead of using the DropDownList cause i think the Postback functionality etc. is implemented in the control by default and cannot changed with less effort.

This is my JS

$(document).ready(function () {
    $("#select1").select2({
        placeholder: "Select a Subject",
        allowClear: true
    });
});

This is my .aspx

<select id="select1" name="select1" runat="server" multiple="true" style="width:300px"></select>

This is my codebehind in C# to fill the items in select

for (int i = 0; i < 10; i++)
{
    ListItem l = new ListItem("Item " + i.ToString(), i.ToString());
    select1.Items.Add(l);
}

and this is the way to get and set the selected items

// GET SELECTED ITEMS
for (int i = 0; i <= select1.Items.Count - 1; i++)
{
    if (select1.Items[i].Selected)
        lit.Text += "<br /> &nbsp;&nbsp; - " + select1.Items[i].Text + " | " + select1.Items[i].Value;
}

// SET SELECTED ITEMS
select1.Items[2].Selected = true;
select1.Items[4].Selected = true;

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