在C/S架构中，不管是传统的winform还是wpf都可能会遇到进行异步操作文件的时候。文件小还好说，直接写操作代码。

如果是大文件很多时候做成异步的操作。在界面上显示一个进度条什么的，后台使用一个backgroundworker来做。在这里告诉大家在.NET Framework4.5中支持异步IO的操作。大大简化之前些的异步方法代码。

使用backgroundworker代码

private void Button_Click_3(object sender, RoutedEventArgs e)
        {
            System.ComponentModel.BackgroundWorker bak = new System.ComponentModel.BackgroundWorker();
            bak.DoWork += bak_DoWork;
            bak.RunWorkerCompleted += bak_RunWorkerCompleted;
            bak.RunWorkerAsync();         
        }

        void bak_DoWork(object sender, System.ComponentModel.DoWorkEventArgs e)
        {
            string sourceDir = @\"E:\\\";
            string endDir = @\"F:\\\";
            foreach (string filename in Directory.EnumerateFiles(sourceDir))
            {
                using (FileStream SourceStream = File.Open(filename, FileMode.Open))
                {
                    using (FileStream DestinationStream = File.Create(endDir + filename.Substring(filename.LastIndexOf(\'\\\\\'))))
                    {
                        SourceStream.CopyTo(DestinationStream);
                    }
                }
            }
        }

        void bak_RunWorkerCompleted(object sender, System.ComponentModel.RunWorkerCompletedEventArgs e)
        {
            MessageBox.Show(\"ok\");
        }