c# - SMTP 发送邮件已取消

Question

尝试发送邮件，但任务被取消。知道为什么吗？

public static Task SendAsync(this SmtpClient client, MailMessage message)
{
    TaskCompletionSource<object> tcs = new TaskCompletionSource<object>();
    Guid sendGuid = Guid.NewGuid();

    SendCompletedEventHandler handler = null;
    handler = (o, ea) =>
    {
        if (ea.UserState is Guid && ((Guid)ea.UserState) == sendGuid)
        {
            client.SendCompleted -= handler;
            if (ea.Cancelled)
            {
                tcs.SetCanceled(); // TASK CANCELLED: Why?
            }
            else if (ea.Error != null)
            {
                tcs.SetException(ea.Error);
            }
            else
            {
                tcs.SetResult(null);
            }
        }
    };

    client.SendCompleted += handler;
    client.SendAsync(message, sendGuid);
    return tcs.Task;
}

调用者:

using( SmtpClient smtpClient = new SmtpClient() )
{
    return smtpClient.SendAsync(msg);
}

预先感谢您的帮助!杰拉德

Answer 1

一个using语句将调用一个对象 Dispose完成执行 block 时的方法。调用smtpClient.SendAsync不使用await异步方法上将导致执行 block 结束并且 Dispose将被调用SmtpClient ，尽管SendAsync方法仍在执行，这解释了为什么一些邮件完成，因为有些可能会在处理对象之前完成，而另一些则不会。

这样做:

using (SmtpClient smtpClient = new SmtpClient())
{
    await smtpClient.SendAsync(msg);
}