Editable ComboBox History

<window x:class="WpfApplication3.MainWindow" xmlns:x="#unknown">
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Title="Window1" Height="300" Width="300">
    <grid>
        <stackpanel>
            <combobox x:name="tbHostname" width="120" iseditable="True" />
            <button x:name="btDisableSC" content="  Test1 " verticalalignment="Top" click="btDisableSC_Click" height="20" grid.columnspan="2" />
        </stackpanel>
    </grid>
</window>

using System;
using System.IO;
using System.Collections;
using System.Collections.Generic;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;

namespace WpfApplication3
{
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {
        string strXMLDataSourceFLDR = Environment.GetEnvironmentVariable("APPDATA") + "\\MyApplicationFLDR";
        string strSourceHostsTXT = Environment.GetEnvironmentVariable("APPDATA") + "\\MyApplicationFLDR\\Hosts.TXT";
        string strHostName;
        ArrayList alHosts = new ArrayList();

        public MainWindow()
        {
            funcCheckHostDataSource();
            funcReadHostsFile();
            InitializeComponent();
            funcPopulatetbHostname();
        }

        public void funcCheckHostDataSource()
        {
            if (!Directory.Exists(strXMLDataSourceFLDR))
            {
                Directory.CreateDirectory(strXMLDataSourceFLDR);
            }

            if (!File.Exists(strSourceHostsTXT))
            {
                using (StreamWriter objSWFile = File.CreateText(strSourceHostsTXT))
                {
                    objSWFile.Close();
                }
            }
        }

        public void funcReadHostsFile()
        {
            using (StreamReader objSRFile = File.OpenText(strSourceHostsTXT))
            {
                string strReadLine = "";
                while ((strReadLine = objSRFile.ReadLine()) != null)
                {
                    alHosts.Add(strReadLine.ToLower());
                }
                objSRFile.Close();
            }
        }

        public void funcPopulatetbHostname()
        {
            tbHostname.ItemsSource = alHosts;
        }

        private void btDisableSC_Click(object sender, RoutedEventArgs e)
        {
            if (this.tbHostname.Text == String.Empty)
            {
                MessageBox.Show("Please fill in the Hostname of the target System!");
            }
            else
            {
                strHostName = tbHostname.Text.Replace("\\", "");
                funcUpdateCombobox1(strHostName);
            }
        } 

        public void funcUpdateCombobox1(string strNewHostName)
        {
            ArrayList alHostsNew = new ArrayList();
            alHostsNew.Add(strNewHostName.ToLower());
            foreach (string item in alHosts)
            {
                int alHostsNewCount = alHostsNew.Count;
                if (alHostsNewCount <= 14)
                {
                    if (strNewHostName != item)
                    {
                        alHostsNew.Add(item);
                    }
                }
            }

            using (StreamWriter objSWFile = File.CreateText(strSourceHostsTXT))
            {
                foreach (string item in alHostsNew)
                {
                    objSWFile.WriteLine(item);
                }
                objSWFile.Close();
            }

            alHosts = alHostsNew;
            tbHostname.ItemsSource = alHostsNew;
        }
    }
}