Question

尝试发送带有附件的电子邮件。但是我收到一个错误：

“无法从 'System.Threading.Tasks.Task'到 'System.Net.Mail.Attachment'

我的错误发生在Attachments.Add(GetAttachment(attachmentFileName));行

我尝试了各种转换（请参阅代码），但我不太清楚问题出在哪里。我知道解决方案就在我眼前，但我看不到。

public class NonFERosterEmail : BaseNotificationEmail<OfferViewModel>
{
    public NonFERosterEmail(OfferViewModel vm, string emailList, string attachmentFileName) : base(vm)
    {
        To.AddRange(GetTo(emailList));
        Body = GetBody();
        Subject = GetSubject();
        //Attachments.Add(new Attachment(GetAttachment(attachmentFileName)));
        Attachments.Add(GetAttachment(attachmentFileName));
        From = new MailAddress(ConfigurationManager.AppSettings["RedirectEmailTo"]);
    }

    //public async Task<List<Attachment>> GetAttachment(string attachmentFileName)
    public async Task<Attachment> GetAttachment(string attachmentFileName)
    {
        //var ret = new List<Attachment>();

        CloudStorageAccount storageAccount = CloudStorageAccount.Parse(ConfigurationManager.AppSettings["azureStorageAccount"]); 
        CloudBlobClient blobClient = storageAccount.CreateCloudBlobClient();
        CloudBlobContainer container = blobClient.GetContainerReference("attachments");
        CloudBlockBlob blob = container.GetBlockBlobReference(attachmentFileName);

        var contentType = MimeMapping.GetMimeMapping(attachmentFileName);
        Stream target = new MemoryStream();
        await blob.DownloadToStreamAsync(target);
        target.Position = 0;
        //ret.Add(new Attachment(target, attachmentFileName, contentType));

        Attachment ret = new Attachment(target, attachmentFileName, contentType);

        return ret;
    }

//remainder of code left out for brevity
}

我希望GetAttachment返回正确的附件对象，该对象将被添加到邮件对象并成功发送。

Answer 1

要从Task<T>获取值，必须使方法async和await成为任务。

Answer 2

在返回await的调用方法时，您需要Task，所以要代替

Attachments.Add(GetAttachment(attachmentFileName));

使用：

Attachments.Add(await GetAttachment(attachmentFileName));

或

Attachments.Add(GetAttachment(attachmentFileName).GetAwaiter().GetResult());

Answer 3

我认为@SLaks和@Roman Marusyk的答案是正确的，但是看起来您正在从构造器中调用GetAttachment，这不是异步的。因此，如果不使用await方法，将无法使用async。尝试使用GetAttachment的result属性，如下所示。

Attachments.Add(GetAttachment(attachmentFileName).Result);

一个更好的解决方案是使用.GetAwaiter().GetResult()，正如@Roman Marusyk指出并在this post中显示的那样，如果该方法失败，它将直接抛出异常，而不是抛出{{1} }。

更好的解决方案是使用以下内容

AggregateException

将文件附加到System.Net.Mail时出错。如何解决此错误？

3 个答案: