Why I am not able to download multiple files in WPF C# (pause and resume not working properly)?

See more:

C#

.NET

XAML

WPF

I am developing a Download Manager. It works fine for one single file but, for multiple files it is not working properly: what is wrong?

When I enter first url, it works fine, but when I click on pause and try a second url after clicking on download, the first file's progress bar starts from 0, and the first file starts downloading automatically without clicking on resume.

When I click on pause, both files pause, when I click on resume both files start downloading. Why this is happening? When I click pause on first url downloading window, I want only the first file to pause, and when I click on resume, only that file should be resumed.

ViewModel:

namespace DownloadManager
{
    public class ViewModel : INotifyPropertyChanged
    {
        public ICommand _Download { get; set; }
        public ICommand Pause { get; set; }

        public ICommand Resume { get; set; }
        public ViewModel()
        {
            _Download = new Command(Start, canExecuteMethod);
            Pause = new Command(Pause_Download, canExecuteMethod);
            Resume = new Command(Resume_Download, canExecuteMethod);
        }
        private bool canExecuteMethod(object parameter)
        {
            return true;
        }
        private void Start(object parameter) //Download Method
        {
            new Add_URL().Button_Click_1(link);
        }
        private void Pause_Download(object parameter) //Pause Download
        {
            new Add_URL().Pause();
        }
        private void Resume_Download(object parameter) //Resume Download
        { 
            new Add_URL().Resume();
        }
        
        public event PropertyChangedEventHandler? PropertyChanged;
        
        private string link;
        public string Link
        {
            get { return link; }
            set { link = value; OnPropertyChanged(Link); }
        }
        
        private void OnPropertyChanged(string property)
        {
            if(PropertyChanged != null)
            {
                PropertyChanged(this, new PropertyChangedEventArgs(property));
            }
        }
    }
}

Model:

<pre>public static bool CheckForInternetConnection()
{
    try
    {
        using (var client = new WebClient())
        using (var stream = client.OpenRead("http://www.google.com"))
        {
            return true;
        }
    }
    catch
    {
        return false;
    }
}

 Download fw;
static int row = 0;

public void Button_Click_1(string link)
{
    Uri uri = null;
    if (CheckForInternetConnection())
    {
        {
            uri = new Uri(link);
            if (!uri.IsFile)
            {
                WarningUrl.Content = "File Found";
                file = true;
            }
        }
    }
    else
    {
        WarningUrl.Content = "No Internet";
    }
    if (file)
    {
        String name = link;
        Add_URL a = new Add_URL();
        String FileName = System.IO.Path.GetFileName(uri.AbsolutePath);
        MainWindow mainwindow = new MainWindow();
        string check = mainwindow.Check(FileName);
               
        MainWindow m = Application.Current.MainWindow as MainWindow;
        //Extension
        string extension = System.IO.Path.GetExtension(FileName);
        var s = GetFileSize(uri);
        int x = Int32.Parse(s); //size in KB
        var fileSizeInMegaByte = Math.Round(Convert.ToDouble(s) / 1024.0 / 1024.0, 2).ToString();
        String size = fileSizeInMegaByte + " MB";  // For addgin in list (MB)

        String time = DateTime.Now.ToString("g");
        Download download = new Download();
        // var method2 = new Action(() => { download.pb.Value = 90; });
        var method2 = new Action<int>(i =>
        {
            download.pb.Value = i;

            MainWindow m = Application.Current.MainWindow as MainWindow;
            if (i< 100)
            {
                m.change(download, i.ToString(), row, FileName);
            }

            download.FileName1.Content = FileName;
        });
        
        var method3 = new Action(() =>
        {
            download.pb.Value = 100;
            string a = "100";
            m.change(download, a, row, FileName);
            row++;
            download.Status.Content = "Completed";
            download.Close();
        });

        fw = new Download(name, path + @"\" + FileName, x);

        CancellationTokenSource tokenSource = new CancellationTokenSource();
        CancellationToken token = tokenSource.Token;
        mre.Set();
        new Thread(() =>
        {
            while (!fw.Done)
            {
                mre.WaitOne();

                double receive = double.Parse(fw.BytesWritten.ToString());

                double Filesize = x;
                double Percentage = receive / Filesize * 100;
                int per = int.Parse(Math.Truncate(Percentage).ToString());

                try
                {
                    Thread.Sleep(300);
                    this.Dispatcher.Invoke(() =>
                    {
                        method2(per);
                        if (fw.Done)
                        {
                            method3();
                        }
                    });
                }
                catch (Exception ex) 
                {
                    MessageBox.Show(ex.Message);
                }
            }
        }).Start();
        fw.Start();       ---> throws exception here
        download.Show();
        m.AddItem(a, FileName, extension, time, size);
        Close();
    }            
}

public void Pause()
{
    fw.Pause1();
}

public void Resume() 
{
    fw.Start();
}

What I have tried:

Check out this image :-- https://i.stack.imgur.com/e6hZB.png[^]



I have tried above things but didn't work properly.

What can I do?

Please help!!