新线程中的WebBrowser控件

Question

我有一个列表Uri，我想“单击”以实现此目的，我正在尝试为每个Uri创建一个新的Web浏览器控件。我为每个Uri创建一个新线程。我遇到的问题是文档之前的线程结尾已完全加载，所以我再也无法利用DocumentComplete事件了，我该如何克服呢？

var item = new ParameterizedThreadStart(ClicIt.Click); 
var thread = new Thread(item) {Name = "ClickThread"}; 
thread.Start(uriItem);

public static void Click(object o)
{
    var url = ((UriItem)o);
    Console.WriteLine(@"Clicking: " + url.Link);
    var clicker = new WebBrowser { ScriptErrorsSuppressed = true };
    clicker.DocumentCompleted += BrowseComplete;
    if (String.IsNullOrEmpty(url.Link)) return;
    if (url.Link.Equals("about:blank")) return;
    if (!url.Link.StartsWith("http://") && !url.Link.StartsWith("https://"))
        url.Link = "http://" + url.Link;
    clicker.Navigate(url.Link);
}

Answer 1

您必须创建一个STA线程来泵送消息循环。 对于像WebBrowser这样的ActiveX组件，这是唯一的好客环境。 否则，您将不会获得DocumentCompleted事件。 一些示例代码：

private void runBrowserThread(Uri url) {
    var th = new Thread(() => {
        var br = new WebBrowser();
        br.DocumentCompleted += browser_DocumentCompleted;
        br.Navigate(url);
        Application.Run();
    });
    th.SetApartmentState(ApartmentState.STA);
    th.Start();
}

void browser_DocumentCompleted(object sender, WebBrowserDocumentCompletedEventArgs e) {
    var br = sender as WebBrowser;
    if (br.Url == e.Url) {
        Console.WriteLine("Natigated to {0}", e.Url);
        Application.ExitThread();   // Stops the thread
    }
}

Answer 2

这是在非UI线程上组织消息循环，运行异步任务（如WebBrowser自动化）的方法。 它使用async/await提供便利的线性代码流，并在循环中加载一组网页。 该代码是一个随时可以运行的控制台应用程序，部分基于此出色的文章 。

相关答案：

• https://stackoverflow.com/a/22262976/1768303
• https://stackoverflow.com/a/21775343/1768303

using System;
using System.Threading;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace ConsoleApplicationWebBrowser
{
    // by Noseratio - https://stackoverflow.com/users/1768303/noseratio
    class Program
    {
        // Entry Point of the console app
        static void Main(string[] args)
        {
            try
            {
                // download each page and dump the content
                var task = MessageLoopWorker.Run(DoWorkAsync,
                    "http://www.example.com", "http://www.example.net", "http://www.example.org");
                task.Wait();
                Console.WriteLine("DoWorkAsync completed.");
            }
            catch (Exception ex)
            {
                Console.WriteLine("DoWorkAsync failed: " + ex.Message);
            }

            Console.WriteLine("Press Enter to exit.");
            Console.ReadLine();
        }

        // navigate WebBrowser to the list of urls in a loop
        static async Task<object> DoWorkAsync(object[] args)
        {
            Console.WriteLine("Start working.");

            using (var wb = new WebBrowser())
            {
                wb.ScriptErrorsSuppressed = true;

                TaskCompletionSource<bool> tcs = null;
                WebBrowserDocumentCompletedEventHandler documentCompletedHandler = (s, e) =>
                    tcs.TrySetResult(true);

                // navigate to each URL in the list
                foreach (var url in args)
                {
                    tcs = new TaskCompletionSource<bool>();
                    wb.DocumentCompleted += documentCompletedHandler;
                    try
                    {
                        wb.Navigate(url.ToString());
                        // await for DocumentCompleted
                        await tcs.Task;
                    }
                    finally
                    {
                        wb.DocumentCompleted -= documentCompletedHandler;
                    }
                    // the DOM is ready
                    Console.WriteLine(url.ToString());
                    Console.WriteLine(wb.Document.Body.OuterHtml);
                }
            }

            Console.WriteLine("End working.");
            return null;
        }

    }

    // a helper class to start the message loop and execute an asynchronous task
    public static class MessageLoopWorker
    {
        public static async Task<object> Run(Func<object[], Task<object>> worker, params object[] args)
        {
            var tcs = new TaskCompletionSource<object>();

            var thread = new Thread(() =>
            {
                EventHandler idleHandler = null;

                idleHandler = async (s, e) =>
                {
                    // handle Application.Idle just once
                    Application.Idle -= idleHandler;

                    // return to the message loop
                    await Task.Yield();

                    // and continue asynchronously
                    // propogate the result or exception
                    try
                    {
                        var result = await worker(args);
                        tcs.SetResult(result);
                    }
                    catch (Exception ex)
                    {
                        tcs.SetException(ex);
                    }

                    // signal to exit the message loop
                    // Application.Run will exit at this point
                    Application.ExitThread();
                };

                // handle Application.Idle just once
                // to make sure we're inside the message loop
                // and SynchronizationContext has been correctly installed
                Application.Idle += idleHandler;
                Application.Run();
            });

            // set STA model for the new thread
            thread.SetApartmentState(ApartmentState.STA);

            // start the thread and await for the task
            thread.Start();
            try
            {
                return await tcs.Task;
            }
            finally
            {
                thread.Join();
            }
        }
    }
}

Answer 3

根据我过去的经验，Web浏览器不喜欢在主应用程序线程之外进行操作。

尝试使用httpwebrequests代替，您可以将它们设置为异步，并为响应创建处理程序以知道响应何时成功：

如何异步使用httpwebrequest-net

Answer 4

一个简单的解决方案，可以同时运行多个WebBrowsers

1. 创建一个新的Windows窗体应用程序
2. 放置名为button1的按钮
3. 放置名为textBox1的文本框
4. 设置文本字段的属性：多行true和ScrollBars两者

5. 编写以下button1单击处理程序：

    textBox1.Clear(); textBox1.AppendText(DateTime.Now.ToString() + Environment.NewLine); int completed_count = 0; int count = 10; for (int i = 0; i < count; i++) { int tmp = i; this.BeginInvoke(new Action(() => { var wb = new WebBrowser(); wb.ScriptErrorsSuppressed = true; wb.DocumentCompleted += (cur_sender, cur_e) => { var cur_wb = cur_sender as WebBrowser; if (cur_wb.Url == cur_e.Url) { textBox1.AppendText("Task " + tmp + ", navigated to " + cur_e.Url + Environment.NewLine); completed_count++; } }; wb.Navigate("https://stackoverflow.com/questions/4269800/webbrowser-control-in-a-new-thread"); } )); } while (completed_count != count) { Application.DoEvents(); Thread.Sleep(10); } textBox1.AppendText("All completed" + Environment.NewLine);