如何对电子邮件执行异步 IMAP 操作

使用 ImapClient 的异步操作

使用 Aspose.Email 可以异步处理消息 ImapClient。本文展示了如何异步检索邮箱中的消息。本文还展示了如何通过提供搜索条件使用 MailQuery。将单独展示如何使用基于任务的异步模式（TAP）方法。

异步检索邮件

以下代码片段展示了如何异步检索邮件。

使用 MailQuery 异步列出消息

该 MailQuery 该类可用于指定搜索条件，以异步检索指定的邮件列表，如下代码示例所示。

异步发送消息

异步发送电子邮件非常方便，因为该过程不会阻塞程序或线程的执行。程序无需等待邮件发送完成即可继续执行其他任务，而邮件在后台发送时程序可以继续运行。

以下功能将帮助您在项目中实现异步发送：

• IAsyncImapClient - 允许应用程序使用 Internet Message Access Protocol（IMAP）访问和操作消息。

• ImapClient.CreateAsync - 创建 Aspose.Email.Clients.Imap.ImapClient 类的新实例

下面的代码示例演示了如何在后台列出消息：

// Authenticate the client to obtain necessary permissions
static readonly string tenantId = "YOU_TENANT_ID";
static readonly string clientId = "YOU_CLIENT_ID";
static readonly string redirectUri = "http://localhost";
static readonly string username = "username";
static readonly string[] scopes = { "https://outlook.office.com/IMAP.AccessAsUser.All" };

// Use the ImapAsync method for asynchronous operations
static async Task Main(string[] args)
{
    await ImapAsync();
    Console.ReadLine();
}

// Establish the connection with the server
// Create an instance of the ImapClient asynchronously using the CreateAsync method
// Select the Inbox folder using SelectFolderAsync method to complete and fetch the list of email messages asynchronously using the ListMessagesAsync method.
static async Task ImapAsync()
{
    var tokenProvider = new TokenProvider(clientId, tenantId, redirectUri, scopes);
    var client = ImapClient.CreateAsync("outlook.office365.com", username, tokenProvider, 993).GetAwaiter().GetResult();
    await client.SelectFolderAsync(ImapFolderInfo.InBox);
    var messages = await client.ListMessagesAsync();
    Console.WriteLine("Messages :" + messages.Count);
}

// Token provider implementation
public class TokenProvider : IAsyncTokenProvider
{
    private readonly PublicClientApplicationOptions _pcaOptions;
    private readonly string[] _scopes;

    public TokenProvider(string clientId, string tenantId, string redirectUri, string[] scopes)
    {
        _pcaOptions = new PublicClientApplicationOptions
        {
            ClientId = clientId,
            TenantId = tenantId,
            RedirectUri = redirectUri
        };

        _scopes = scopes;
    }

    public async Task<OAuthToken> GetAccessTokenAsync(bool ignoreExistingToken = false, CancellationToken cancellationToken = default)
    {

        var pca = PublicClientApplicationBuilder
            .CreateWithApplicationOptions(_pcaOptions).Build();

        try
        {
            var result = await pca.AcquireTokenInteractive(_scopes)
                .WithUseEmbeddedWebView(false)
                .ExecuteAsync(cancellationToken);

            return new OAuthToken(result.AccessToken);
        }
        catch (MsalException ex)
        {
            Console.WriteLine($"Error acquiring access token: {ex}");
        }
        catch (Exception ex)
        {
            Console.WriteLine($"Error: {ex}");
        }

        return null;
    }

    public void Dispose()
    {

    }
}

管理异步操作

中断 TAP 方法

从 .NET Framework 4.5 开始，您可以使用符合 TAP 模型实现的异步方法。下面的代码片段展示了如何使用名为 AppendMessagesAsync 然后在一段时间后中断此过程。

// For complete examples and data files, please go to https://github.com/aspose-email/Aspose.Email-for-.NET

List<MailMessage> mailMessages = new List<MailMessage>();

// create mail messages
for (int i = 0; i < 100; i++)
    mailMessages.Add(new MailMessage(senderEmail, receiverEmail, $"Message #{i}", "Text"));

using (ImapClient client = new ImapClient(host, 993, senderEmail, password, SecurityOptions.SSLImplicit))
{
    CancellationTokenSource cancellationTokenSource = new CancellationTokenSource();
    AutoResetEvent autoResetEvent = new AutoResetEvent(false);
    Exception exception = null;

    ThreadPool.QueueUserWorkItem(delegate
    {
        try
        {
            // start uploading the messages
            var task = client.AppendMessagesAsync(mailMessages, cancellationTokenSource.Token);
            AppendMessagesResult appendMessagesResult = task.GetAwaiter().GetResult();
            Console.WriteLine("All messages have been appended.");
        }
        catch (Exception e)
        {
            exception = e;
        }
        finally
        {
            autoResetEvent.Set();
        }
    });

    Thread.Sleep(5000);

    // stop uploading the messages
    cancellationTokenSource.Cancel();
    autoResetEvent.WaitOne();

    foreach (MailMessage mailMessage in mailMessages)
        mailMessage.Dispose();

    if (exception is OperationCanceledException)
        Console.WriteLine("Operation has been interrupted: " + exception.Message);
}

取消异步操作

有时您可能需要停止异步操作。为此，我们的库通过使用 CancellationToken 参数提供了对异步操作的取消功能。调用支持取消的异步方法时，您可以将 CancellationToken 实例作为参数传入。CancellationToken 用于发出信号并控制操作的取消。

要启用取消，首先需要创建一个提供 CancellationToken 的 CancellationTokenSource 实例。然后，将 CancellationToken 传递给异步方法，使其在执行期间能够检查取消请求。

下面的示例演示了使用 CancellationToken 进行取消：

CancellationTokenSource tokenSource = new CancellationTokenSource();
AppendMessagesResult appendMessagesResult = null;
AutoResetEvent autoResetEvent = new AutoResetEvent(false);
ThreadPool.QueueUserWorkItem(delegate(object state)
    {
        try
        {
            appendMessagesResult = imapClient.AppendMessagesAsync(mmList, tokenSource.Token).GetAwaiter().GetResult();
        }
        catch (Exception ex)
        {

        }
        finally
        {
            autoResetEvent.Set();
        }
    });

tokenSource.Cancel();
autoResetEvent.WaitOne();