using System.Net;
using System.IO;
private void button1_Click(object sender, EventArgs e)
{
  string URL=textBox1.Text;
  try
  {
  this.Text=URL+"......下载中";
  client.DownloadFile(URL, textBox3.Text);
  MessageBox.Show("下载成功......","成功");
  this.Text="D/U Loader";
  }
  catch(WebException exp)
  {
  MessageBox.Show(exp.Message,"错误");
  }
  FileStream filestr = new FileStream(textBox3.Text, FileMode.OpenOrCreate, FileAccess.Write);
  filestr.Close();
  MessageBox.Show("下载结束....", "成功");
}
private void button3_Click(object sender, EventArgs e)
{
  saveFileDialog1.InitialDirectory = "C:\\";//默认路径
  saveFileDialog1.Filter = "Html(*.html)|*.html|All Files (*.*)|*.*";
  saveFileDialog1.FilterIndex = 1;
  if (saveFileDialog1.ShowDialog() == DialogResult.OK)
  {
  textBox3.Text = saveFileDialog1.FileName;
  }
}