使用WebClient类对网页下载源码,对文件下载保存及异步下载并报告下载进度

private void button1_Click(object sender, EventArgs e)
        {
            WebClient webclient = new WebClient();
            webclient.Proxy = null;
            webclient.Encoding = Encoding.UTF8;
            richTextBox1.AppendText(webclient.DownloadString(textBox1.Text.Trim()));
            webclient.Dispose();
        }

        private void button2_Click(object sender, EventArgs e)
        {
            WebClient webclient = new WebClient();
            webclient.Proxy = null;
            webclient.DownloadFile(textBox2.Text, textBox3.Text);
            MessageBox.Show("成功！");
            webclient.Dispose();

        }

        private void button3_Click(object sender, EventArgs e)
        {
            WebClient webclient = new WebClient();
            webclient.Proxy = null;
            webclient.DownloadProgressChanged += webclient_DownloadProgressChanged;
            webclient.DownloadDataCompleted += webclient_DownloadDataCompleted;
            webclient.DownloadFileAsync(new Uri(textBox2.Text), textBox3.Text);
            webclient.Dispose();
        }

        void webclient_DownloadDataCompleted(object sender, DownloadDataCompletedEventArgs e)
        {
            MessageBox.Show("成功");
        }

        void webclient_DownloadProgressChanged(object sender, DownloadProgressChangedEventArgs e)
        {
            progressBar1.Value = e.ProgressPercentage;
        }