How to shift a value from one listbox to another listbox?

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ListBox

I have a webpage in which i want to move value from one listbox to another.I am successful to moving value from one listbox to another but the problem is when i run the code then listbox is empty.My previous value is not shown in the listbox.
Please suggest something where i have done mistake.
My code is:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Data;
using System.Data.SqlClient;
using System.Configuration;

public partial class Move_value_from_one_listbox_to_another_listbox : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
        { }
    }
    protected void button1_Click(object sender, EventArgs e)
    {
        if (Textbox1.Text == "")
        {
            return;
        
        }
        ListItem item = new ListItem();
        item.Value = Textbox1.Text;
        item.Text = Textbox1.Text;
        listbox1.Items.Add(item);
        Textbox1.Text = "";
    }
    protected void Buttonfrom_Click(object sender, EventArgs e)
    {
        //if (Listboxto.SelectedIndex == -1)
        //{
        //    return;
        //}
        ListItem item = new ListItem();
        item.Value = Listboxto.SelectedItem.Value;
        item.Text = Listboxto.SelectedItem.Text;
        listbox1.Items.Add(item);
        Listboxto.Items.Remove(item);

    }
    protected void buttonto_Click(object sender, EventArgs e)
    {
        if (listbox1.SelectedIndex == -1)
        {
            return;
        }
        ListItem item = new ListItem();
        item.Value = listbox1.SelectedItem.Value;
        item.Text = listbox1.SelectedItem.Text;
        Listboxto.Items.Add(item);
        listbox1.Items.Remove(item);
    }
}

Thanks!!