private async void btnBackUp_Click(object sender, EventArgs e)
    {
      string sourceDirectory = txtSource.Text;
      string targetDirectory = txtTarget.Text;
      if (sourceDirectory.ToLower() == targetDirectory.ToLower())
      {
        Console.WriteLine("源目錄和備份目錄不能是同一目錄！");
        MessageBox.Show("源目錄和備份目錄不能是同一目錄！", "提示", MessageBoxButtons.OK, MessageBoxIcon.Warning);
        return;
      }
      DirectoryInfo diSource = new DirectoryInfo(sourceDirectory);  // 源目錄
      DirectoryInfo diTarget = new DirectoryInfo(targetDirectory);  // 備份目錄
      if (diTarget.Name != diSource.Name)
        diTarget = new DirectoryInfo(Path.Combine(diTarget.FullName, diSource.Name));  // 創(chuàng)建同名目錄
      if (!diTarget.Exists) diTarget.Create();  // 如果該目錄已存在，則此方法不執(zhí)行任何操作
      btnBackUp.Enabled = false;
      txtSource.Enabled = false;
      txtTarget.Enabled = false;
      lblWork.Text = "備份開始！";
      if (await CopyAllAsync(diSource, diTarget))
      {
        lblWork.Text = "備份完成！";
        MessageBox.Show("備份完畢！", "提示", MessageBoxButtons.OK, MessageBoxIcon.Information);
      }
      else lblWork.Text = "出現(xiàn)錯誤！";
      btnBackUp.Enabled = true;
      txtSource.Enabled = true;
      txtTarget.Enabled = true;
      btnBackUp.Focus();
    }

    public async Task<bool> CopyAllAsync(DirectoryInfo source, DirectoryInfo target)
    {
      try
      {
        foreach (FileInfo fi in source.GetFiles())  // 復(fù)制最新文件
        {
          Console.WriteLine(@"準(zhǔn)備復(fù)制文件 {0}\{1}", target.FullName, fi.Name);  // Name不含路徑，僅文件名
          FileInfo newfi = new FileInfo(Path.Combine(target.FullName, fi.Name));
          if (!newfi.Exists || (newfi.Exists && fi.LastWriteTime > newfi.LastWriteTime))
          {
            Console.WriteLine("正在復(fù)制文件 {0}", newfi.FullName);
            lblWork.Text = string.Format("正在復(fù)制文件 {0}", newfi.FullName);
            if (newfi.Exists && newfi.IsReadOnly) newfi.IsReadOnly = false;
            // 覆蓋或刪除只讀文件會產(chǎn)生異常：對路徑“XXX”的訪問被拒絕
            fi.CopyTo(newfi.FullName, true);  // Copy each file into it's new directory
          }
        }

        foreach (FileInfo fi2 in target.GetFiles())  // 刪除源目錄沒有而目標(biāo)目錄中有的文件
        {
          FileInfo newfi2 = new FileInfo(Path.Combine(source.FullName, fi2.Name));
          if (!newfi2.Exists)
          {
            Console.WriteLine("正在刪除文件 {0}", fi2.FullName);
            lblWork.Text = string.Format("正在刪除文件 {0}", fi2.FullName);
            if (fi2.IsReadOnly) fi2.IsReadOnly = false;
            fi2.Delete();  // 沒有權(quán)限(如系統(tǒng)盤需管理員權(quán)限)會產(chǎn)生異常，文件不存在不會產(chǎn)生異常
          }
        }

        foreach (DirectoryInfo di in source.GetDirectories())  // 復(fù)制目錄(實(shí)際上是創(chuàng)建同名目錄，和源目錄的屬性不同步)
        {
          Console.WriteLine(" {0} {1}", di.FullName, di.Name);  // Name不含路徑，僅本級目錄名
          Console.WriteLine(@"準(zhǔn)備創(chuàng)建目錄 {0}\{1}", target.FullName, di.Name);
          DirectoryInfo newdi = new DirectoryInfo(Path.Combine(target.FullName, di.Name));
          if (!newdi.Exists)  // 如果CopyAllAsync放在if里的bug: 只要存在同名目錄，則不會進(jìn)行子目錄和子文件的檢查和更新
          {
            Console.WriteLine("正在創(chuàng)建目錄 {0}", newdi.FullName);
            lblWork.Text = string.Format("正在復(fù)制目錄 {0}", newdi.FullName);
            DirectoryInfo diTargetSubDir = target.CreateSubdirectory(di.Name);  // 創(chuàng)建目錄
            Console.WriteLine("完成創(chuàng)建目錄 {0}", diTargetSubDir.FullName);
          }
          if (await CopyAllAsync(di, newdi) == false) return false; ;  // Copy each subdirectory using recursion
        }

        foreach (DirectoryInfo di2 in target.GetDirectories())  // 刪除源目錄沒有而目標(biāo)目錄中有的目錄(及其子目錄和文件)
        {
          DirectoryInfo newdi2 = new DirectoryInfo(Path.Combine(source.FullName, di2.Name));
          if (!newdi2.Exists)
          {
            Console.WriteLine("正在刪除目錄 {0}", di2.FullName);
            lblWork.Text = string.Format("正在刪除目錄 {0}", di2.FullName);
            di2.Delete(true);  // 只讀的目錄和文件也能刪除，如不使用參數(shù)則異常"目錄不是空的"
          }
        }
        return true;
      }
      catch (Exception e)
      {
        Console.WriteLine(e.Message);
        MessageBox.Show(e.Message, "提示", MessageBoxButtons.OK, MessageBoxIcon.Error);
        return false;
      }
    }

lblWork.Text = "備份開始！"; bool result = await Task.Run(() => CopyAllAsync(diSource, diTarget));   // 這兒是關(guān)鍵
if (result)  // if (await CopyAllAsync(diSource, diTarget)) 開始后界面會卡{
  lblWork.Text = "備份完成！";
  MessageBox.Show("備份完畢！", "提示", MessageBoxButtons.OK, MessageBoxIcon.Information);
}
else lblWork.Text = "出現(xiàn)錯誤！";