1:webClient client=new WebClient();

client.Downloadstring(地址)

client.Downloadfile(地址，保存路径)

2：后台线程dowork

3：声明委托

//江县城写道主界面（控件）

private void Meg()

{

messageBox.Show("下载成功")！

}

Action action=new Action(Meg);//这就是委托，就是将方法给

this.invoke()

一下是个具体事例：

public partial class Form1 : Form

    {

        public Form1()

        {

InitializeComponent();

        }

        private void button1_Click(object sender, EventArgs e)

        {

            this.backgroundWorker1.RunWorkerAsync();

        }

        private void button2_Click(object sender, EventArgs e)

        {

            MessageBox.Show("各种Info快来下载吧!");

        }

        private void backgroundWorker1_DoWork(object sender, DoWorkEventArgs e)

        {

            for (int i = 3010; i < 3050; i++)

            {

                WebClient client = new WebClient();

                try

                {

                    client.DownloadFile(@"" + i + "/", @"d:\" + i + ".html");

                }

                catch { }

            }

            //Action是委托

            Action action = new Action(msg);

            this.Invoke(action);

        }

        private void msg()

        {

            MessageBox.Show("下载完成!");

        }

    }