新线程中的 WebBrowser 控件

我有一个 Uri 的列表，我想“点击”实现这一点，我正在尝试创建一个新的网络浏览器控件每 Uri。我为每个 Uri 创建一个新线程。我遇到的问题是在文档完全加载之前线程结束，所以我从来没有使用过 DocumentComplete 事件。我怎样才能克服这个问题呢？

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);
}
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小开

From my experience in the past the webbrowser does not like operating outside of the main application thread.

Try using httpwebrequests instead, you can set them as asynchronous and create a handler for the response to know when it is succesfull:

how-to-use-httpwebrequest-net-asynchronously

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最佳答案

You have to create an STA thread that pumps a message loop. That's the only hospitable environment for an ActiveX component like WebBrowser. You won't get the DocumentCompleted event otherwise. Some sample code:

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
}
}
小开

Here is how to organize a message loop on a non-UI thread, to run asynchronous tasks like WebBrowser automation. It uses async/await to provide the convenient linear code flow and loads a set of web pages in a loop. The code is a ready-to-run console app which is partially based on this excellent post.

Related answers:

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();
}
}
}
}
小开

A simple solution at which the simultaneous operation of several WebBrowsers occurs

  1. Create a new Windows Forms application
  2. Place the button named button1
  3. Place the text box named textBox1
  4. Set properties of text field: Multiline true and ScrollBars Both

  5. Write the following button1 click handler:

    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);

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