1

我的应用程序经常使用 WebRequest 从网页中获取数据，但是在获取时无法单击按钮等。我知道我必须使用线程/后台工作者，但我无法让它正常工作；它不会使 GUI 更具响应性。

我想应用某种线程的代码，以便它停止使我的应用程序无响应：

public string SQLGet(string query)
{
    string post = "q=" + query;
    WebRequest request = WebRequest.Create("http://test.com");
    request.Timeout = 20000;
    request.Method = "POST";
    byte[] bytes = Encoding.UTF8.GetBytes(post);
    request.ContentType = "application/x-www-form-urlencoded";
    request.ContentLength = bytes.Length;

    Stream requestStream = request.GetRequestStream();
    requestStream.Write(bytes, 0, bytes.Length);
    requestStream.Close();

    WebResponse response = request.GetResponse();
    requestStream = response.GetResponseStream();
    StreamReader reader = new StreamReader(requestStream);
    string ret = reader.ReadToEnd();

    reader.Close();
    requestStream.Close();
    response.Close();

    return ret;
}

编辑：谢谢你，lc，我试过类似的东西。但是我这样使用后台工作人员的问题是；如何将 queryResult 返回到调用（在我的情况下为 SQLGet，在你的情况下）StartQuery 的函数？

在我的示例中，返回的字符串将用作 void 中的局部变量，该字符串在内部被调用。

并且可能同时有很多查询，所以我不想冒险将它分配给全局变量。

4

3 回答 3

5

这是一个简单的示例，说明如何将BackgroundWorker应用于您的代码：

private void StartQuery(string query)
{
    BackgroundWorker backgroundWorker1 = new BackgroundWorker();
    backgroundWorker1.DoWork += new DoWorkEventHandler(backgroundWorker1_DoWork);
    backgroundWorker1.RunWorkerCompleted += new RunWorkerCompletedEventHandler(backgroundWorker1_RunWorkerCompleted);
    backgroundWorker1.RunWorkerAsync(query);
}

private void backgroundWorker1_DoWork(object sender, DoWorkEventArgs e)
{   
    e.Result = SQLGet((string)e.Argument);
}

private void backgroundWorker1_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
{
    queryResult = (string)e.Result;
}

您可能还希望允许取消、提供错误详细信息或在获取数据时提供可靠的反馈。查看MSDN 页面上的示例以获取更多详细信息。

您的查询结果将在BackgroundWorker.RunWorkerCompleted事件中显示为e.Result（在这种情况下，我将其存储为实例变量）。如果您要同时运行其中的许多，您将需要一种方法来区分哪个查询是哪个。因此，您应该向该方法传递的不仅仅是一个字符串。举个例子：

private int NextID = 0;

private struct QueryArguments
{
    public QueryArguments()
    {
    }

    public QueryArguments(int QueryID, string Query)
        : this()
    {
        this.QueryID = QueryID;
        this.Query = Query;
    }

    public int QueryID { get; set; }
    public string Query { get; set; }
    public string Result { get; set; }
}

private int StartQuery(string query)
{
    QueryArguments args = new QueryArguments(NextID++, query);

    BackgroundWorker backgroundWorker1 = new BackgroundWorker();
    backgroundWorker1.DoWork += new DoWorkEventHandler(backgroundWorker1_DoWork);
    backgroundWorker1.RunWorkerCompleted += new RunWorkerCompletedEventHandler(backgroundWorker1_RunWorkerCompleted);
    backgroundWorker1.RunWorkerAsync(args);

    return args.QueryID;
}

private void backgroundWorker1_DoWork(object sender, DoWorkEventArgs e)
{   
    QueryArguments args = (QueryArguments)e.Argument;
    args.Result = SQLGet(args.Query);
    e.Result = args;
}

private void backgroundWorker1_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
{
    QueryArguments args = (QueryArguments)e.Result;
    //args.Result contains the result

    //do something
}
于 2009-07-09T03:54:26.793 回答
3

BackgroundWorker 是一个很好的解决方案，对取消和进度有一些内置支持。您也可以只使用 HttpWebRequest.BeginGetResponse 而不是 GetResponse 来启动异步 Web 请求操作。这最终变得非常简单，您可以设置进度回调。

有关您尝试执行的操作的确切示例，请参阅：

使用 HttpWebRequest 进行异步下载

于 2009-07-09T12:33:11.107 回答
2

这是一个快速的解决方案，应该很容易从中获取您需要的东西。

using System;
using System.ComponentModel;
using System.IO;
using System.Net;
using System.Text;

namespace ConsoleApplication5
{
    class Program
    {
        static void Main(string[] args)
        {
            BackgroundWorker b = new BackgroundWorker();
            b.DoWork += new DoWorkEventHandler(b_DoWork);
            b.RunWorkerCompleted += new RunWorkerCompletedEventHandler(b_RunWorkerCompleted);
            b.RunWorkerAsync("My Query");

            while(b.IsBusy)
            {

            }
            Console.ReadLine();
        }

        static void b_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
        {
            if(e.Result is string)
            {
                Console.WriteLine((string)e.Result);
            }
        }

        static void b_DoWork(object sender, DoWorkEventArgs e)
        {
            if (e.Argument is string)
            {
                string post = "q=" + (string) e.Argument;
                WebRequest request = WebRequest.Create("http://test.com");
                request.Timeout = 20000;
                request.Method = "POST";
                byte[] bytes = Encoding.UTF8.GetBytes(post);
                request.ContentType = "application/x-www-form-urlencoded";
                request.ContentLength = bytes.Length;
                Stream requestStream = request.GetRequestStream();
                requestStream.Write(bytes, 0, bytes.Length);
                requestStream.Close();
                WebResponse response = request.GetResponse();
                requestStream = response.GetResponseStream();
                StreamReader reader = new StreamReader(requestStream);
                string ret = reader.ReadToEnd();
                reader.Close();
                requestStream.Close();
                response.Close();
                e.Result = ret;
            }
        }
    }
}
于 2009-07-09T03:58:56.987 回答