Wpf Backgroundworker

<Window x:Class="WpfApp53.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:local="clr-namespace:WpfApp53"
        mc:Ignorable="d"
        Title="MainWindow" Height="450" Width="800">
    <Grid>
        <Grid.RowDefinitions>
            <RowDefinition Height="*"/>
            <RowDefinition Height="Auto"/>
            <RowDefinition Height="Auto"/>
            <RowDefinition Height="Auto"/>
        </Grid.RowDefinitions>
        <ListBox Grid.Row="0" x:Name="listBox1"/>
        <ProgressBar Grid.Row="1" x:Name="progressBar1" Height="20" Margin="5"/>
        <StackPanel Grid.Row="2" Orientation="Horizontal" Margin="5">
            <TextBlock Text="Status: "/>
            <TextBlock x:Name="statusTextBox"/>
        </StackPanel>
        <Grid Grid.Row="3" Margin="10">
            <Grid.ColumnDefinitions>
                <ColumnDefinition Width="*"/>
                <ColumnDefinition Width="*"/>
            </Grid.ColumnDefinitions>
            <Button Grid.Column="0" x:Name="startBtn" Content="Start" Click="StartBtn_Click"/>
            <Button Grid.Column="1" x:Name="cancelBtn" Content="Cancel" Click="CancelBtn_Click"/>
        </Grid>
    </Grid>
</Window>

 using System;
 using System.Collections.Generic;
 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;

 namespace WpfApp53
 {
     /// <summary>
     /// Interaction logic for MainWindow.xaml
     /// </summary>
     public partial class MainWindow : Window
     {
         BackgroundWorker bgWorker;
         public MainWindow()
         {
             InitializeComponent();
             cancelBtn.IsEnabled = false;
         }

         private void StartBtn_Click(object sender, RoutedEventArgs e)
         {
             listBox1.Items.Clear();
             startBtn.IsEnabled = false;
             cancelBtn.IsEnabled = true;
             bgWorker = new BackgroundWorker();
             bgWorker.DoWork += BgWorker_DoWork;
             bgWorker.ProgressChanged += BgWorker_ProgressChanged;
             bgWorker.RunWorkerCompleted += BgWorker_RunWorkerCompleted;
             bgWorker.WorkerReportsProgress = true;
             bgWorker.WorkerSupportsCancellation = true;

             int maxItems = ;
             progressBar1.Minimum = ;
             progressBar1.Maximum = ;

             statusTextBox.Text = "Starting...";
             bgWorker.RunWorkerAsync(maxItems);
         }

         private void BgWorker_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
         {
              if(e.Cancelled)
             {
                 statusTextBox.Text = "Cancelled";
             }
             else
             {
                 statusTextBox.Text = "Completed";
             }
             statusTextBox.IsEnabled = true;
             cancelBtn.IsEnabled = false;
         }

         private void BgWorker_ProgressChanged(object sender, ProgressChangedEventArgs e)
         {
             double percent = (e.ProgressPercentage * ) / ;
             progressBar1.Value = Math.Round(percent, );
             listBox1.Items.Add(new ListBoxItem { Content = e.ProgressPercentage + " item added" });
             statusTextBox.Text = Math.Round(percent, ) + "% percent completed";
         }

         private void BgWorker_DoWork(object sender, DoWorkEventArgs e)
         {
             int? maxItems = e.Argument as int?;
             for(int i=;i<=maxItems.GetValueOrDefault();i++)
             {
                 if(bgWorker.CancellationPending)
                 {
                     e.Cancel = true;
                     break;
                 }
                 Thread.Sleep();
                 bgWorker.ReportProgress(i);
             }
         }

         private void CancelBtn_Click(object sender, RoutedEventArgs e)
         {
             bgWorker.CancelAsync();
             startBtn.IsEnabled = true;
         }
     }
 }