C# Async, Await and using statements

Async, Await 是基於 .NEt 4.5架構的， 用於處理異步，防止死鎖的方法的開始和結束, 提升程序的響應能力。好比：

Application area           Supporting APIs that contain async methods

 Web access                    HttpClient , SyndicationClient

 Working with files           StorageFile, StreamWriter, StreamReader, XmlReader

 Working with images       MediaCapture, BitmapEncoder, BitmapDecoder

 WCF programming          Synchronous and Asynchronous Operations

 

Async, Await 不會產生新的線程。 可是Task.Run 方法就是多線程的。 Asynchronous code is code that returns upon completion. By Task.Run, we can make is a multithreaded.

Take files as an example I encountered today:

        public async Task SendFallMail(string path){
            try
            {
                mail.Subject = subjectFall;
                mail.Body = "Fall down!";

                using (MailMessage ms = mail) {
                    ms.Attachments.Add(new Attachment(path));
                    using (SmtpClient sc = SmtpServer)
                    {
                        Task t = Task.Factory.StartNew(() =>
                        { 
                            sc.Send(ms); 
                        });
                        await t;
                    }
                }
                File.Delete(path);
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.ToString());
            }

It should wait t which is sending an e-mail wihich attached an picture in path.

Then delete the pic in path, wihch is working properly after I use the using statement...

Without using the using statement, it shows IO exception said: 

Process Cannot Access the file 「\Path」 because it is being used by some other process