C# 异步编程

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.IO;
using System.Security.Cryptography;

namespace Crypto
{
    class Hash
    {
        //需要返回值的异步方法使用Task作为方法的返回值类型
        public static Task<string> GetSHA1Async(string fileName)
        {
            //使用Task.Run(Action)创建线程池线程
            return Task.Run(() =>
            {
                string sha1str = "";
                if (File.Exists(fileName))
                {
                    FileStream file = new FileStream(fileName, FileMode.Open);
                    byte[] sha1 = SHA1.Create().ComputeHash(file);  //计算文件的sha1
                    file.Close();
                    //先用BitConverter将sha1字节数组转换为16进制表示的字符串,默认每个字节用"-"分割
                    //再将字符串中的分隔符"-"去掉(替换为空字符串"")
                    sha1str = BitConverter.ToString(sha1).Replace("-", "");
                }
                return sha1str;
            });
        }
    }
}
//在一个按钮控件的click事件中调用此异步方法
private async void buttonSHA1JiShuan_Click(object sender, RoutedEventArgs e)
        {
            textboxSHA1JiShuan.Text = "";
            groupboxSHA1.IsEnabled = false;
            string sha1 = await Crypto.Hash.GetSHA1Async(textboxFileName.Text);
            textboxSHA1JiShuan.Text = sha1;
            groupboxSHA1.IsEnabled = true;
        }