如何异步调用asp.net中的函数？或任何其他解决方案来达到目标​​？

Question

该函数的目标是填写from（来自第3方网站）并单击提交按钮并获取提交结果页面的html源。此任务需要在 asp.net 中按钮的单击事件上完成。如果函数返回 true，则在最后执行一些 sql 任务。我读到了有关 asp.net 中的异步处理程序的内容，但确实是初学者，不确定在 asp.net 中模拟此类任务的最佳解决方案是什么。

Protected Sub lbtnSave_Click(ByVal sender As Object, ByVal e As System.Web.UI.ImageClickEventArgs) Handles lbtnSave.Click
             If  CrawlWebSite() then
                'Save
             End If
         End Sub

Private Function CrawlWebSite() As Boolean
            Dim objBrowser = CreateObject("InternetExplorer.Application")
            Dim url As String = "https://test.com/Search.do?subAction=reset&searchType=ind"
            With objBrowser
                .navigate(url)
                System.Threading.Thread.Sleep(1000)

                Dim StartTime As DateTime
                Dim ElapsedTime As TimeSpan
                Dim bLong As Boolean = False
                StartTime = Now
                Do While .busy = True
                    ElapsedTime = Now().Subtract(StartTime)
                    If (ElapsedTime.TotalSeconds Mod 60) >= 55 Then
                        bLong = True
                        Exit Do
                    End If
                    System.Threading.Thread.Sleep(1000)
                Loop

                If bLong = True Then
                    PageName.Alert(Page, "There is a delay retrieving the website for checking NPI. Please try again.")
                    Return False
                End If

                .document.getElementById("lastname").Value = txtLastName.Text.Trim
                .document.getElementById("searchNpi").Value = txtUPIN.Text.Trim
                .document.getElementsByTagName("input").item(7).click()

                System.Threading.Thread.Sleep(1000)

                bLong = False
                StartTime = Now
                Do While .busy = True
                    'There is a delay retrieving the website. Continue ?
                    ElapsedTime = Now().Subtract(StartTime)
                    If (ElapsedTime.TotalSeconds Mod 60) >= 50 Then
                        bLong = True
                        Exit Do
                    End If
                    System.Threading.Thread.Sleep(1000)
                Loop

                If bLong = True Then
                    PageName.Alert(Page, "There is a delay retrieving the website. Please try again.")
                    Return False
                End If

                If .document.getElementById("lastname") Is Nothing Then
                    'We have result
                    Return True
                Else
                    PageName.Alert(Page, "Attention: No matching records found.")
                    Return False
                End If

            End With

        End Function

Answer 1

以下是使用 HttpHandler 实现长轮询时使用的一些类。我使用此解决方案来处理需要很长时间才能完成的操作。基本上有6个类（见下文）。其中一些课程可能最终对于您的目的来说是不需要的，但它们对我来说是有意义的。这些已“大部分”为您进行了消毒。

1. 控制器：处理创建有效响应所需的操作（数据库操作等）
2. 处理器：管理与网页（本身）的异步通信
3. IAsynchProcessor ：服务处理实现此接口的实例
4. Service：处理实现 IAsynchProcessor 的请求对象
5. Request：包含您的响应（对象）的 IAsynchProcessor 包装器
6. 响应：包含自定义对象或字段

如果您需要有关 JavaScript 或 HTML 插件的帮助，请在下面的评论中...我将为您写一些内容。

HTTP 处理程序：

using System;
using System.Configuration;
using System.Web;
using System.Web.Script.Serialization;
using System.Web.Services;
using System.Web.SessionState;

namespace Concept.LongPolling.Handlers
{
    /// <summary>
    /// Summary description for Controller
    /// </summary>
    public class Controller : IHttpHandler, IReadOnlySessionState
    {
        #region CONSTRUCTORS
        #endregion

        #region PROPERTIES

        /// <summary>Gets a Boolean value indicating that another request can use the current instance of the DefaultHttpHandler class.</summary>
        /// <remarks>Returning true makes the same AsyncHttpHandler object be used for all requests.</remarks>
        /// <remarks>Returning false here makes ASP.Net create object per request.</remarks>
        public bool IsReusable { get { return true; } }

        #endregion

        #region METHODS

        /// <summary>Enables synchronous processing of HTTP Web requests</summary>
        /// <param name="context">An HttpContext object that provides references to the intrinsic server objects</param>
        /// /// <remarks>This is where you would send commands to the controller that would affect processing in some manner.</remarks>
        public void ProcessRequest(HttpContext context)
        {
            throw new NotImplementedException();
        }

        /// <summary>Creates the response object which is serialized back to the client</summary>
        /// <param name="response"></param>
        public static Response CreateResponse(Response response)
        {
            try
            {
                response.Generate();
            }
            catch (System.Exception ex)
            {
                response.SessionValid = false;
            }

            return response;
        }

        #endregion
    }
}

using System;
using System.Configuration;
using System.Web;
using System.Web.Script.Serialization;
using System.Web.Services;
using System.Web.SessionState;
using Concept.LongPolling.LongPolling;

namespace Concept.LongPolling.Handlers
{
    /// <summary>
    /// Summary description for Processor
    /// </summary>
    public class Processor : IHttpHandler, IHttpAsyncHandler, IReadOnlySessionState
    {
        #region CONSTRUCTORS
        #endregion

        #region PROPERTIES

        /// <summary>Gets a Boolean value indicating that another request can use the current instance of the DefaultHttpHandler class.</summary>
        /// <remarks>Returning true makes the same AsyncHttpHandler object be used for all requests.</remarks>
        /// <remarks>Returning false here makes ASP.Net create object per request.</remarks>
        public bool IsReusable { get { return false; } }

        #endregion

        #region METHODS

        /// <summary>Enables synchronous processing of HTTP Web requests</summary>
        /// <param name="context">An HttpContext object that provides references to the intrinsic server objects</param>
        public void ProcessRequest(HttpContext context)
        {
            throw new NotImplementedException();
        }

        #region IHttpAsyncHandler Members

        /// <summary>Enables asynchronous processing of HTTP Web requests</summary>
        /// <param name="context">An HttpContext object that provides references to the intrinsic server objects</param>
        /// <param name="cb">The method to call when the asynchronous method call is complete. If callback is null, the delegate is not called.</param>
        /// <param name="extraData"></param>
        /// <returns>Any state data that is needed to process the request.</returns>
        public IAsyncResult BeginProcessRequest(HttpContext context, AsyncCallback cb, object extraData)
        {
            Int32 someValueYouLikeToSendInYourClass = Convert.ToInt32(context.Request["Number"]);

            Request request = new Request(cb, context);
            request.Response.Number = someValueYouLikeToSendInYourClass;

            Service.Singleton.AddRequest(request);

            return request;
        }

        /// <summary>Provides an end method for an asynchronous process.</summary>
        /// <param name="result">An object that contains information about the status of the process.</param>
        public void EndProcessRequest(IAsyncResult result)
        {
            Request request = result as Request;
            JavaScriptSerializer serializer = new JavaScriptSerializer();

            request.HttpContext.Response.ContentType = "text/json";
            request.HttpContext.Response.Write(serializer.Serialize(request.Response));
            request.HttpContext.Response.End();
        }

        #endregion

        #endregion
    }
}

支持类：

using System;
using System.Runtime.InteropServices;

namespace Concept.LongPolling.LongPolling
{
    /// <summary>Represents the executable instance of an asynchronous operation.</summary>
    [ComVisible(true)]
    public interface IAsynchProcessor : IAsyncResult
    {
        /// <summary>
        /// Gets a value that indicates whether the operation completed sucessfully.
        /// </summary>
        /// <returns>true if the operation completed sucessfully; otherwise, false.</returns>
        bool ProcessRequest();
    }
}


using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Threading;

namespace Concept.LongPolling.LongPolling
{
    public sealed class Service
    {
        #region CONSTRUCTORS

        private Service()
        {
            requests = new List<IAsynchProcessor>();
            backgroundThread = new Thread(new ThreadStart(MainLoop));
            backgroundThread.IsBackground = true;
            backgroundThread.Start();
        }

        #endregion

        #region PROPERTIES

        private static Service singleton;
        private Thread backgroundThread;
        private List<IAsynchProcessor> requests;
        static readonly object padlock = new object();

        public static Service Singleton
        {
            get
            {
                if (_singleton == null)
                    lock (_padlock)
                    {
                        if (_singleton == null)
                            _singleton = new Service();
                    }

                return _singleton;
            }
        }

        #endregion

        #region METHODS

        private void MainLoop()
        {
            while (true)
            {
                foreach (IAsynchProcessor request in requests.ToArray())
                {
                    if (request.ProcessRequest())
                        requests.Remove(request);
                }
                Thread.Sleep(500);
            }
        }

        public void AddRequest(IAsynchProcessor request)
        {
            lock (padlock)
            {
                requests.Add(request);
            }
        }

        #endregion
    }
}

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using Concept.LongPolling.Business;
using System.Data;

namespace Concept.LongPolling.Handlers
{
    public class Response
    {
        #region CONSTRUCTORS

        public Response()
        {
            SessionValid = true;
            Exception = String.Empty;
        }

        #endregion

        #region PROPERTIES

        public const int TimeOffset = 120;

        public Int32 Number { get; set; }
        public bool SessionValid { get; set; }
        public String Exception { get; set; }

        #endregion

        #region METHODS

        public void Generate()
        {
            // do some desired operation
            Number += 1;
        }

        #endregion
    }
}

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using Concept.LongPolling.LongPolling;

namespace Concept.LongPolling.Handlers
{
    public class Request : IAsynchProcessor
    {
        #region CONSTRUCTORS

        public Request(AsyncCallback callback, HttpContext context)
        {
            asyncCallback = callback;
            httpContext = context;
            createdTime = DateTime.Now;

            Response = new Response();
        }

        #endregion

        #region PROPERTIES

        public const int TimeoutSeconds = 15;

        private AsyncCallback asyncCallback;
        private HttpContext httpContext;
        private DateTime createdTime;

        public bool TimedOut
        {
            get
            {
                return ((DateTime.Now - createdTime).TotalSeconds >= TimeoutSeconds);
            }
        }

        public Response Response { get; set; }

        #region IAsyncResult Members

        public HttpContext HttpContext
        {
            get
            {
                return httpContext;
            }
        }
        public object AsyncState { get; set; }

        System.Threading.WaitHandle IAsyncResult.AsyncWaitHandle
        {
            get { throw new NotImplementedException(); }
        }

        bool IAsyncResult.CompletedSynchronously
        {
            get { return false; }
        }

        public bool IsCompleted
        {
            get { return isCompleted; }
            set
            {
                if (!value) return;

                this.isCompleted = true;
                asyncCallback(this);
            }
        }
        bool isCompleted = false;

        #endregion

        #endregion

        #region METHODS

        public bool ProcessRequest()
        {
            this.Response = Controller.CreateResponse(this.Response);
            this.IsCompleted = true;

            return this.IsCompleted;
        }

        #endregion
    }
}

Answer 2

看一下这篇文章，它描述了如何异步执行方法，并使用在异步方法调用完成时触发的事件处理程序。

http://www.csharp-examples.net/create-asynchronous-method/

以下是如何将本文内容应用到您的情况的草稿。我还没有测试过代码，所以它可能不完美，但应该很接近。

您需要导入以下命名空间：

using System.Threading;
using System.ComponentModel;
using System.Runtime.Remoting.Messaging;

这是粗略的实现：

//boolean flag which indicates whether the async task is running
private bool crawling = false;

private delegate bool CrawlWebsiteDelegate();

private bool CrawlWebsite()
{
    //crawl the website

    return false;
}

protected void Button1_Click(object sender, EventArgs e)
{
    CrawlWebsiteDelegate worker = new CrawlWebsiteDelegate(CrawlWebsite);
    AsyncCallback completedCallback = new AsyncCallback(CrawlWebsiteCompletedCallback);

    if (!crawling)
    {
        worker.BeginInvoke(completedCallback, AsyncOperationManager.CreateOperation(null));
        crawling = true;
    }
}

private void CrawlWebsiteCompletedCallback(IAsyncResult ar)
{
    //get the original worker delegate and the AsyncOperation instance
    CrawlWebsiteDelegate worker = (CrawlWebsiteDelegate)((AsyncResult)ar).AsyncDelegate;

    //finish the asynchronous operation
    bool success = worker.EndInvoke(ar);
    crawling = false;

    if (success)
    {
        //perform sql tasks now that crawl has completed
    }
}

编辑：这是 VB.NET 中的代码 - 并不肯定所有语法都正确

Private crawling As Boolean = False    
Private Delegate Function CrawlWebsiteDelegate() As Boolean

Private Function CrawlWebsite() As Boolean
    Return False    
End Function

Protected Sub Button1_Click(sender As Object, e As EventArgs)
    Dim worker As New CrawlWebsiteDelegate(AddressOf CrawlWebsite)
    Dim completedCallback As New AsyncCallback(AddressOf CrawlWebsiteCompletedCallback) 
    If Not crawling Then
        worker.BeginInvoke(completedCallback, AsyncOperationManager.CreateOperation(Nothing))
        crawling = True
    End If  
End Sub

Private Sub CrawlWebsiteCompletedCallback(ar As IAsyncResult)
    Dim worker As CrawlWebsiteDelegate = DirectCast(DirectCast(ar, AsyncResult).AsyncDelegate, CrawlWebsiteDelegate)
    Dim success As Boolean = worker.EndInvoke(ar)
    crawling = False        
    If success Then
        DoSomeSqlTasks()
    End If
End Sub