异步多线程解决界面卡顿问题

 点击button下载一个网页，并将网页的长度显示在textbox中。

注意是将网页的长度显示在textbox中，而不是将下载的网页字符显示在textbox中，因为太大的字符串在textbox上显示本身就会卡界面。

using System;
using System.Net;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace WindowsFormsApp6
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        //private void button1_Click(object sender, EventArgs e)
        //{
        //    textBox1.Text = "";//每次点击按钮清空
        //    //第一个例子，卡界面
        //    WebClient webClient = new WebClient();
        //    string html = webClient.DownloadString("https://www.163.com");
        //    this.textBox1.Text = html.Length.ToString();
        //}

        //private void button1_Click(object sender, EventArgs e)
        //{
        //    textBox1.Text = "";//每次点击按钮清空
        //    //第二个例子，通过多线程解决不卡界面
        //    WebClient webClient = new WebClient();
        //    Task.Run(() =>
        //    {
        //        string html = webClient.DownloadString("https://www.163.com");
        //        this.Invoke(new Action(() =>
        //        {
        //            this.textBox1.Text = html.Length.ToString();
        //        }));
        //    });
        //}

        //private async void button1_Click(object sender, EventArgs e)
        //{
        //    textBox1.Text = "";//每次点击按钮清空
        //    //第三个例子，使用HttpClient的异步多线程，不卡界面
        //    HttpClient Client = new HttpClient();
        //    string html = await Client.GetStringAsync("https://www.163.com");
        //    this.textBox1.Text = html.Length.ToString();
        //}

        //private async void button1_Click(object sender, EventArgs e)
        //{
        //    textBox1.Text = "";//每次点击按钮清空
        //    //第四个例子，将WebClient改造成异步，实现不卡界面
        //    WebClient webClient = new WebClient();
        //    string html = await Task.Run(() =>
        //    {
        //        return webClient.DownloadString("https://www.163.com");               
        //    });
        //    this.textBox1.Text = html.Length.ToString();
        //}

        //private async void button1_Click(object sender, EventArgs e)
        //{
        //    textBox1.Text = "";//每次点击按钮清空
        //    //第四个例子的变形，写一个WebClient的异步方法，实现不卡界面
        //    string html = await getDownloadAsync("https://www.163.com");
        //    this.textBox1.Text = html.Length.ToString();
        //}

        //private Task<string> getDownloadAsync(string url)
        //{
        //    WebClient webClient = new WebClient();
        //    return Task.Run(() =>
        //    {
        //        return webClient.DownloadString(url);
        //    });
        //}

        private async void button1_Click(object sender, EventArgs e)
        {
            textBox1.Text = "";//每次点击按钮清空
            //第四个例子的变形，写一个WebClient的异步方法，实现不卡界面
            Task<string> t = getDownloadAsync("https://www.163.com");
            string html = await t;
            this.textBox1.Text = html.Length.ToString();
        }

        private Task<string> getDownloadAsync(string url)
        {
            WebClient webClient = new WebClient();
            return Task.Run(() =>
            {
                return webClient.DownloadString(url);
            });
        }
    }
}