Why my progress bar is not updating? Wpf

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows;
using System.IO;
using System.Windows.Controls.Primitives;
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.Shapes;
using System.ComponentModel;
using System.Windows;
using System.Net;
using System.Threading;
using System.Reflection;

namespace DownloadManager
{
    /// <summary>
    /// Interaction logic for Download.xaml
    /// </summary>
    public partial class Download : Window,INotifyPropertyChanged
    {
        public Download()
        {
            InitializeComponent();
           //this.Loaded += OnLoad;


        }


        private int m_Progress;

        public int Progress
        {
            get { return m_Progress; }
            set
            {
                if (value == m_Progress) return;
                m_Progress = value;


                OnPropertyChanged("Progressb");
            }
        }
        public event PropertyChangedEventHandler PropertyChanged;
        private void OnPropertyChanged(string propertyname)
        {
            var handler = PropertyChanged;
            if (handler != null) handler(this, new PropertyChangedEventArgs("Progressb"));


    Application.Current.Dispatcher.Invoke(() => {
                PropertyChanged?.Invoke(this, new PropertyChangedEventArgs("Progressb"));
            }, System.Windows.Threading.DispatcherPriority.Background);
            if (PropertyChanged != null)
            {
                PropertyChanged(this, new PropertyChangedEventArgs("Progressb"));
            }
        }
        Uri uri;
        static WebClient client = new WebClient();


       static int row = 0;
        public void download(string link, string path)
        {
            uri = new Uri(link);
            String FileName = System.IO.Path.GetFileName(uri.AbsolutePath);
            client.DownloadFileAsync(uri, path +@"\" + FileName);
            client.DownloadProgressChanged += downloadprogress;
            FileName1.Content = FileName;


        }

        double Percentage;
        public void downloadprogress(object sender, DownloadProgressChangedEventArgs e)
        {
            pb.Minimum = 0;
            double receive = double.Parse(e.BytesReceived.ToString());
            double Filesize = double.Parse(e.TotalBytesToReceive.ToString());
            Percentage = receive / Filesize * 100;
            // a1 = int.Parse(Math.Truncate(Percentage).ToString());
            pb.Value = int.Parse(Math.Truncate(Percentage).ToString());
            //pb1.Value = pb.Value;
            Download download = new Download();
            int p = (int) Percentage;
            MainWindow m = Application.Current.MainWindow as MainWindow;
            m.change(download,p.ToString(),row);

                Status.Content = "Downloading.";
                Status.Content = "Downloading..";
                Status.Content = "Downloading...";

            if (pb.Value == 100)
            {
                row++;
                Status.Content = "Completed";
                Close();


            }

        }

        private void Button_Click(object sender, RoutedEventArgs e)
        {
        }



        private volatile bool _allowedToRun;
        private string _source;
        private string _destination;
        private int _chunkSize;
        Download d1;
        private IProgress<double> _progress;


        private Lazy<int> _contentLength;

        public int BytesWritten { get; private set; }
        public int ContentLength { get { return _contentLength.Value; } }

        public bool Done { get { return ContentLength == BytesWritten; } }

        public Download(string source, string destination, int chunkSize, IProgress<double> progress = null)
        {
            _allowedToRun = true;

            _source = source;
            _destination = destination;
            _chunkSize = chunkSize;
            _contentLength = new Lazy<int>(() => Convert.ToInt32(GetContentLength()));
            _progress = progress;

            BytesWritten = 0;
        }

        private long GetContentLength()
        {
            var request = (HttpWebRequest)WebRequest.Create(_source);
            request.Method = "HEAD";

            using (var response = request.GetResponse())
                return response.ContentLength;
        }

        static public int p9;
        private async Task Start(int range)
        {

            if (!_allowedToRun)
                throw new InvalidOperationException();

            var request = (HttpWebRequest)WebRequest.Create(_source);
            request.Method = "GET";
            request.UserAgent = "Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.2; .NET CLR 1.0.3705;)";
            request.AddRange(range);


            using (var response = await request.GetResponseAsync())
            {
                using (var responseStream = response.GetResponseStream())
                {
                    using (var fs = new FileStream(_destination, FileMode.Append, FileAccess.Write, FileShare.ReadWrite))
                    {
                        while (_allowedToRun)
                        {
                            var buffer = new byte[_chunkSize];
                            var bytesRead = await responseStream.ReadAsync(buffer, 0, buffer.Length);

                            if (bytesRead == 0) break;

                            await fs.WriteAsync(buffer, 0, bytesRead);
                            BytesWritten += bytesRead;
                            double receive = double.Parse(BytesWritten.ToString());

                            double Filesize = 5761048;
                            double Percentage = receive / Filesize * 100;

                            // a1 = int.Parse(Math.Truncate(Percentage).ToString());
                            //pb.Value = int.Parse(Math.Truncate(Percentage).ToString());
                            //progress(int.Parse(Math.Truncate(Percentage).ToString()));
                            // MessageBox.Show(int.Parse(Math.Truncate(Percentage).ToString()) + "Done");
                            int per = int.Parse(Math.Truncate(Percentage).ToString());
                            Progress = per;
                            await Task.Delay(20);

                        }
                        await fs.FlushAsync();
                    }
                }


            }

        }

        public Task Start()
        {
            _allowedToRun = true;

            return Start(BytesWritten);
        }

        public void Pause1()
        {
            _allowedToRun = false;
        }




        void MakeButton2()
        {
            Button b2 = new Button();
            //  b2.AddHandler(Button.ClickEvent, new RoutedEventHandler(Onb2Click2));
            // MessageBox.Show("HI");
        // b2.Click += new RoutedEventHandler(Onb2Click2);
           // b2.AddHandler(Button.ClickEvent, new RoutedEventHandler(Onb2Click2));
           // Onb2Click2(null, RoutedEventArgs.Empty);
           // Onb2Click2(this, new RoutedEventArgs());

           //Onb2Click2(new object(), new RoutedEventArgs());

        }

         object sender;


        public void Onb2Click2(object sender, RoutedEventArgs e)
        {

           //    Button b = b2(sender);
           // MessageBox.Show("Hi");
          // ProgressBar pb= e.Source as ProgressBar;
          //  pb.Value = p;

           // MessageBox.Show(p + "");
        }
        void OnLoad(object sender, RoutedEventArgs e)
        {

           // pb.Value = p;


        }


        private void Pause_Click(object sender, RoutedEventArgs e)
        {

            //change();
            //pb.Value = p;
            int m=0;


                    //Onb2Click2(sender, e);
                   //    Thread.Sleep(5000);

               // m = perc();
                   }


    }


}