I have a Windows Form that has a WebBrowser control names formWebBrowser. I am creating a new non-UI thread with another instance of WebBrowser named newThreadBrowser. Reference WebBrowser Control in a new thread
When documentcompleted event is fired I am able to write the url to a textbox using the approach mentioned in C# - Updating GUI using non-main Thread
Now, I am trying to update the html of "formWebBrowser" from the html of "newThreadBrowser". It is causing exception saying Specified cast is not valid.
In WebBrowser control: "Specified cast is not valid.", accepted answer says -
WebBrowser is a COM component under the hood. An apartment threaded one, COM takes care of calling its methods in a thread-safe way. Your Navigate() call works for that reason, it is actually executed on the UI thread. What doesn't work is the DocumentText property, it is implemented in the .NET wrapper and they somewhat fumbled the code. It bombs when the COM interop support in the CLR notices that a thread in the MTA tries to access a property of a component that lives on an STA.
QUESTION
What should I do in-order to render the html from newThreadBrowser in formWebBrowser? I am not sure how Control.Invoke() can resolve this.
Note: This application is not performance critical. So it is okay even if it take some time to execute.
Reference
- How to change webBrowser DocumentText?
- How do I extract info from a webpage?
- http://htmlagilitypack.codeplex.com/
From WebBrowser.DocumentText Property
Use this property when you want to manipulate the contents of an HTML page displayed in the WebBrowser control using string processing tools. You can use this property, for example, to load pages from a database or to analyze pages using regular expressions. When you set this property, the WebBrowser control automatically navigates to the about:blank URL before loading the specified text. This means that the Navigating, Navigated, and DocumentCompleted events occur when you set this property, and the value of the Url property is no longer meaningful.
CODE
public partial class Form1 : Form
{
public void WriteToTextBoxEvent(object sender, WebBrowserDocumentCompletedEventArgs e)
{
#region Textbox
if (this.textBox1.InvokeRequired)
{
//BeginInvoke is Asynchronus
this.textBox1.BeginInvoke(new Action(() => WriteToTextBoxEvent(sender, e)));
}
else
{
textBox1.Text = e.Url.ToString();
}
#endregion
#region WebBrowser
if (this.formWebBrowser.InvokeRequired)
{
//BeginInvoke is Asynchronus
this.textBox1.BeginInvoke(new Action(() => WriteToTextBoxEvent(sender, e)));
}
else
{
var newThreadBrowser = sender as WebBrowser;
if (sender != null)
{
//The function evaluation requires all threads to run
formWebBrowser.DocumentText = newThreadBrowser.DocumentText;
}
}
#endregion
}
System.Windows.Forms.TextBox textBox1 = new TextBox();
System.Windows.Forms.WebBrowser formWebBrowser = new WebBrowser();
public Form1()
{
WriteLogFunction("App Satrt");
// Web Browser
#region Web Browser
formWebBrowser.Location = new Point(10, 20);
formWebBrowser.Size = new Size(1200, 900);
this.Controls.Add(formWebBrowser);
textBox1.Location = new Point(0, 0);
textBox1.Size = new Size(800, 10);
this.Controls.Add(textBox1);
var th = new Thread(() =>
{
var newThreadBrowser = new WebBrowser();
//To Process the DOM.
newThreadBrowser.DocumentCompleted += browser_DocumentCompleted;
//To update URL textbox
newThreadBrowser.DocumentCompleted += WriteToTextBoxEvent;
newThreadBrowser.ScriptErrorsSuppressed = true;
newThreadBrowser.Navigate(GetHomoePageUrl());
Application.Run();
});
th.SetApartmentState(ApartmentState.STA);
th.Start();
#endregion
// Form1
this.Text = "B2B Crawler";
this.Size = new Size(950, 950);
}
List<string> visitedUrls = new List<string>();
List<string> visitedProducts = new List<string>();
private void ExerciseApp(object sender, WebBrowserDocumentCompletedEventArgs e)
{
var wbReceived = sender as WebBrowser;
int catalogElementIterationCounter = 0;
var elementsToConsider = wbReceived.Document.All;
string productUrl = String.Empty;
bool isClicked = false;
foreach (HtmlElement e1 in elementsToConsider)
{
catalogElementIterationCounter++;
string x = e1.TagName;
String idStr = e1.GetAttribute("id");
if (!String.IsNullOrWhiteSpace(idStr))
{
//Each Product Navigation
if (idStr.Contains("catalogEntry_img"))
{
productUrl = e1.GetAttribute("href");
if (!visitedProducts.Contains(productUrl))
{
WriteLogFunction("productUrl -- " + productUrl);
visitedProducts.Add(productUrl);
isClicked = true;
e1.InvokeMember("Click");
//nextNavigationUrl = productUrl;
break;
}
}
}
}
if (visitedProducts.Count == 4)
{
visitedProducts = new List<string>();
isClicked = true;
HomoePageNavigate(wbReceived);
}
if (!isClicked)
{
HomoePageNavigate(wbReceived);
}
}
void browser_DocumentCompleted(object sender, WebBrowserDocumentCompletedEventArgs e)
{
ExerciseApp(sender, e);
}
private string GetHomoePageUrl()
{
return @"C:\Samples_L\MyTableTest.html";
}
private void HomoePageNavigate(WebBrowser bw)
{
WriteLogFunction("HomoePageNavigate");
bw.Navigate(GetHomoePageUrl());
}
private void WriteLogFunction(string strMessage)
{
using (StreamWriter w = File.AppendText("log.txt"))
{
w.WriteLine("\r\n{0} ..... {1} ", DateTime.Now.ToLongTimeString(), strMessage);
}
}
}
MyTableTest.html
<html>
<head>
<style type="text/css">
table {
border: 2px solid blue;
}
td {
border: 1px solid teal;
}
</style>
</head>
<body>
<table id="four-grid">
<tr>
<td>
<a href="https://www.wikipedia.org/" id="catalogEntry_img63666">
<img src="ssss"
alt="B" width="70" />
</a>
</td>
<td>
<a href="http://www.keralatourism.org/" id="catalogEntry_img63667">
<img src="ssss"
alt="A" width="70" />
</a>
</td>
</tr>
<tr>
<td>
<a href="https://stackoverflow.com/users/696627/lijo" id="catalogEntry_img63664">
<img src="ssss"
alt="G" width="70" />
</a>
</td>
<td>
<a href="http://msdn.microsoft.com/en-US/#fbid=zgGLygxrE84" id="catalogEntry_img63665">
<img src="ssss"
alt="Y" width="70" />
</a>
</td>
</tr>
</table>
</body>
</html>
