c# - 发送附件时无法访问已关闭的流

Question

我正在尝试使用 C# 发送带附件的电子邮件。这是我的方法:

public void SendEmail(string from, string to, SmtpClient client)
    {
        MailMessage mm = new MailMessage(from, to, "Otrzymałeś nowe zamówienie od "+from , "Przesyłam nowe zamówienie na sprzęt");
        mm.BodyEncoding = UTF8Encoding.UTF8;
        mm.DeliveryNotificationOptions = DeliveryNotificationOptions.OnFailure;
        // Adding attachment:

        System.IO.MemoryStream ms = new System.IO.MemoryStream();
        System.IO.StreamWriter writer = new System.IO.StreamWriter(ms);
        writer.Write("Hello its my sample file");
        writer.Flush();
        writer.Dispose();

        System.Net.Mime.ContentType ct = new System.Net.Mime.ContentType(System.Net.Mime.MediaTypeNames.Text.Plain);
        System.Net.Mail.Attachment attach = new System.Net.Mail.Attachment(ms, ct);
        attach.ContentDisposition.FileName = "myFile.txt";

        mm.Attachments.Add(attach);
        try
        {
            client.Send(mm);
        }
        catch(SmtpException e)
        {
            Console.WriteLine(e.ToString());
        }
        ms.Close();
    }

堆栈跟踪指向这一行:

client.Send(mm);

问题是由这一行引起的:

writer.Dispose();

为什么我不能在使用它写入MemoryStream后立即处理这个元素？此元素以后不会在代码中使用。

Answer 1

在编写器上调用 Dispose 也会处理底层流。发送电子邮件后，您必须同时处理作者和流。您可以通过将代码包装在两个 using 语句中来实现这一点。

    using(var ms = new System.IO.MemoryStream())
    {
      using(var writer = new System.IO.StreamWriter(ms))
      {
         writer.Write("Hello its my sample file");
         writer.Flush();

         System.Net.Mime.ContentType ct = new System.Net.Mime.ContentType(System.Net.Mime.MediaTypeNames.Text.Plain);
         System.Net.Mail.Attachment attach = new System.Net.Mail.Attachment(ms, ct);
         attach.ContentDisposition.FileName = "myFile.txt";

         mm.Attachments.Add(attach);
         try
         {
             client.Send(mm);
         }
         catch(SmtpException e)
         {
            Console.WriteLine(e.ToString());
         }
       }
    }