WebClient是C# System.Net下的常用类，用于请求URI标识的资源，如http、https、ftp、file等，常用方法有OpenWrite、UploadData、UploadFile、UploadValues、DownloadData、DownloadFile、OpenRead等。
本文利用WebClient做了一个实例，用来查看网页源码：

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.IO;
using System.Linq;
using System.Net;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace WindowsFormsApp3
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void btnGet_Click(object sender, EventArgs e)
        {
            string url = this.textUrl.Text.Trim();
            if (string.IsNullOrEmpty(url))
                MessageBox.Show("要获取的URL地址不能为空！");
            else
            {
                if (!url.ToLower().StartsWith("http://") && !url.ToLower().StartsWith("https://"))
                    url = "http://" + url;
                WebClient webClient = new WebClient();
                Uri uri = new Uri(url);
                Stream data = webClient.OpenRead(uri);
                StreamReader streamReader;
                if (radioButton1.Checked)
                    streamReader = new StreamReader(data, Encoding.UTF8);
                else
                    streamReader = new StreamReader(data, Encoding.Default);
                this.txtContent.Text = streamReader.ReadToEnd();
                
            }
        }
    }
}

C#使用WebClient查看网页源码_.net