LstBox Selected Item with Checkbox Problem - C#

using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.ComponentModel;
using System.Linq;
using System.Text;
using System.Threading;
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;
using System.Windows.Threading;
using MahApps.Metro.Controls;

namespace Outlook_Add_In_Test
{
    /// <summary>
    /// Interaction logic for WPFDistroList.xaml
    /// </summary>
    public partial class WPFDistroList : MetroWindow
    {
        DispatcherTimer dispatcherTimer = new DispatcherTimer();
        public static Dictionary<string, userInits> returnedResults { get; set; }
        public bool selectionchanged { get; set; }
        WPFNewEventv2 mainWindow;
        private ObservableCollection<SelectableItem> Items { get; set; }

        public WPFDistroList(WPFNewEventv2 oldWindow)
        {
            InitializeComponent();

            selectionchanged = false;

            mainWindow = oldWindow;

            //Set the Tick Method
            dispatcherTimer.Tick += new EventHandler(dispatcherTimer_Tick);
            //Set timer interval in seconds ( (0, 0, 1) = 1 second)
            dispatcherTimer.Interval = new TimeSpan(0, 0, 1);

            LoadingRing.IsActive = true;
            BtnOk.Background = Brushes.DarkGray;
            BtnOk.IsEnabled = false;
            Thread th = new Thread(searchThread);
            th.Start();
        }

        private void searchThread()
        {
            //Connect to database and get a List of all the users Initials
            Database connect = new Database();
            returnedResults = connect.ExecGetUserInits();

            //Stop the previous search/Timer before starting it again
            dispatcherTimer.Stop();
            //Start search timer
            dispatcherTimer.Start();
        }

        private void dispatcherTimer_Tick(object sender, EventArgs e)
        {
            int counter = 0;
            LstDistro.Items.Clear();

            foreach (var eventReturned in returnedResults)
            {
                userInits er = new userInits();
                er = eventReturned.Value;

                string LstBackground;

                //Set background to green for every even index in list
                if ((counter % 2) == 0)
                    LstBackground = "#99FFFFFF";
                else
                    LstBackground = "#99E8E8E8";

                var listVar = new
                {
                    LBackground = LstBackground,
                    LInits = er.userInit,
                    LFullName = er.userFullName
                };

                ComboBoxItem newItem = new ComboBoxItem();
                newItem.Content = er.userInit;
                LstDistro.Items.Add(listVar);
                counter = counter + 1;
            }

            var bc = new BrushConverter();
            BtnOk.Background = (Brush)bc.ConvertFrom("#FF333333");
            BtnOk.IsEnabled = true;
            LoadingRing.IsActive = false;

            if (mainWindow.LblDistro.Content != "")
            {
                string searchValue = mainWindow.LblDistro.Content as string;
                string[] searchArray = searchValue.Split(',');

                foreach (var searchItem in searchArray)
                {
                    foreach (var item in LstDistro.Items)
                    {
                        if (item.ToString().Contains(searchItem.Remove(searchItem.Length - 1)))
                        {
                            LstDistro.SelectedItems.Add(item);
                            selectionchanged = false;
                        }
                    }
                }
            }
            dispatcherTimer.Stop();
        }

        private void BtnOk_Click(object sender, RoutedEventArgs e)
        {
            if (selectionchanged == true)
            {
                foreach (var item in LstDistro.SelectedItems)
                {
                    var curItem = item.ToString();
                    //Trim selected value string to give just the event and subject string
                    int evNameIndex = curItem.IndexOf("LFullName = ");
                    string evNameString = curItem.Substring(evNameIndex + 12);
                    int commaIndex = evNameString.IndexOf('}');
                    evNameString = evNameString.Substring(0, commaIndex);

                    //Check to see if a comma should be added before the string addition
                    if (mainWindow.LblDistro.Content == "")
                    {
                        mainWindow.LblDistro.Content = evNameString;
                    }
                    else
                    {
                        //Check to see if Name is already on label. If so dont re add it.
                        if ((mainWindow.LblDistro.Content as string).Contains(evNameString))
                        {
                            //Do nothing
                        }
                        else
                        {
                            mainWindow.LblDistro.Content = mainWindow.LblDistro.Content + " , " + evNameString;
                        }
                    }
                }
            }
            this.Close();
        }

        private void CheckBox_Checked(object sender, RoutedEventArgs e)
        {
            ////Select the Item using the DataContext of the Button
            //object clicked = (e.OriginalSource as FrameworkElement).DataContext;
            //var lbi = LstDistro.ItemContainerGenerator.ContainerFromItem(clicked) as ListBoxItem;
            //lbi.IsSelected = true;
        }

        private void LstDistro_SelectionChanged(object sender, SelectionChangedEventArgs e)
        {
           selectionchanged = true;
        }

        public class SelectableItem : INotifyPropertyChanged
        {
            private bool _isSelected;
            public bool IsSelected
            {
                get { return _isSelected; }
                set
                {
                    _isSelected = value;
                    OnPropertyChanged("IsSelected");
                }
            }

            public string DisplayName { get; set; }

            public event PropertyChangedEventHandler PropertyChanged;

            protected virtual void OnPropertyChanged(string propertyName)
            {
                PropertyChangedEventHandler handler = PropertyChanged;
                if (handler != null) handler(this, new PropertyChangedEventArgs(propertyName));
            }
        }
    }
}