ตัวอย่างโค๊ดที่ให้ ควรแก้ยังไงแล้วสร้างปุ่มอะไรมาใช้
private void Completed(object sender, AsyncCompletedEventArgs e)
        {
            MessageBox.Show("Download completed!");
        }
    private void ProgressChanged(object sender, DownloadProgressChangedEventArgs e)
        {
            progressBar1.Value = e.ProgressPercentage;
        }
        
        public void downloadFile(string url,string filename)
        {
            WebClient webClient = new WebClient();
            webClient.DownloadFileCompleted += new AsyncCompletedEventHandler(Completed);
            webClient.DownloadProgressChanged += new DownloadProgressChangedEventHandler(ProgressChanged);
            webClient.DownloadFileAsync(new Uri(url), @filename);
        }