如何用mshtml获得Javascript中function的返回值[mshtml]
今天琢磨了一下如何用mshtml获得Javascript中function的返回值。我们以前都是用没mshtml.IHTMLWindow2接口的execScript方法来执行HTML文档中的javascript代码段，如
//awbMain为AxSHDocVw.AxWebBrowser控件mshtml.IHTMLDocument2 doc = this.awbMain.Document; private mshtml.IHTMLWindow2 win = doc.parentWindow;string strScript = "alert('OK');";win.execScript(strScript, "javascript");
智能提示显示execScript方法的返回值类型是object，但是其实其返回值永远是null（当然，我们不应该相信COM的智能提示，很多参数、返回值等都是object类型，无法得到更详细的信息），即使该方法执行的是一个有返回值javascript函数。
那么，这个问题如何解决呢？Google一下吧。简体中文的页面中没有这个问题的答案，看看英文的文档吧（这里说一句，很多人因为懒或者不会使用google等搜索引擎而错过了学习一些东西的机会。多用一下搜索引擎，考虑怎样使用关键词，并不断提高关键字的质量，相信很容易找到相应的资料）。输入“"javascript return value" +mshtml +c#”作为关键字，搜索结果只有一篇文档，要的就是它。这篇文档详细描述了如何在.NET应用程序中控制Internet Explorer，示例既有C#也有VB.NET，既有1.0也有2.0，非常棒（附在随笔的最后）。
文档中给出了这个问题的解决方法，不过是.NET 2.0中的解决方法。.NET 2.0中的解决方法是利用HtmlDocument类的InvokeScript方法来实现：
string strRetVal = "";//awbMain为System.Windows.Forms.WebBrowser控件HtmlDocument doc = this.awbMain.Document;//jsFunction为HTML文档中javascript函数的函数名strRetVal = (string)doc.InvokeScript("jsFunction");System.Windows.Forms.MessageBox.Show(strRetVal);
要注意的是，HTML文档中的javascript函数名后要加空括号（没有参数的情况下），而在C# 2.0中调用之则不用加空括号。
在C# 1.x中使用mshtml如何解决这个问题呢，这里介绍一个变通的方法（这些变通的方法在以前的随笔中也用到过）：
1、在Form中定义变量用于存储javascript函数的返回值；
2、使用.NET 1.x中的InteropServices把应用程序的Form对象传入到HTML DOM中；
3、在javascript函数中为1中的变量赋值（赋和javascript函数返回值一样的值），这样javascript函数甚至不需要有返回值了。
步骤2的代码如下：
private System.Runtime.InteropServices.Expando.IExpando iex;private mshtml.IHTMLDocument2 doc = null;//awbMain为AxSHDocVw.AxWebBrowser控件，wendang加载完毕后执行的代码private void awbMain_DocumentComplete(object sender, AxSHDocVw.DWebBrowserEvents2_DocumentCompleteEvent e)
{
this.doc = (mshtml.IHTMLDocument2)this.awbMain.Document; ex = (System.Runtime.InteropServices.Expando.IExpando)doc; System.Reflection.PropertyInfo piform = ex.AddProperty("MainForm"); piform.SetValue(doc, this, null);
}
这样在步骤3的HTML文档的javascript函数中就可以用document.MainForm来指代Windows应用程序中的Form了。
附：
Using Internet Explorer from .NET
5.0 Introduction
Earlier in this book we have looked at how to read HTML from websites, and how to navigate through websites using GET and POST requests. These techniques certainly offer high performance, but with many websites using cryptic POST data, complex cookie data, and JavaScript rendered text, it might be useful to know that you can always call on the assistance of Internet Explorer browsing engine to help you get the data you need.
It must be stated though, that using Internet Explorer to data mine web pages creates a much larger memory footprint, and is not as fast as scanning using HTTP requests alone. But it does come into its own when a data mining process requires a degree of human interaction. A good example of this would be if you wanted to create an automated test of your website, and needed to allow a non-technical user the ability to follow a sequence of steps, and select data to extract and compare, based on the familiar Internet Explorer interface.
This chapter is divided into two main sections. The first deals with how to use the Internet Explorer object to interact with all the various types of web page controls. The second section deals with how Internet explorer can detect and respond to a user interacting with web page elements.
5.1 Web page navigation
The procedure for including the Internet Explorer object in your application differs depending on which version of Visual Studio .NET you are using. After starting a new windows forms project, users of Visual Studio .NET 2002 should right click on their toolbox and select customize toolbox, click COM components, then select Microsoft Web Browser. Users of Visual Studio .NET 2003 should right click on their toolbox and select Add/Remove Items, and then follow the same procedure as mentioned above. In Visual Studio .NET 2005, you do not need to add the web browser to the toolbox, just drag the WebBrowser control to the form.
An important distinction between the Internet Explorer object used in Visual Studio .NET 2002/03 and the 2005 version is that, the latter uses a native .NET class to interact with Internet Explorer, whereas the former uses a .NET wrapper around a COM (Common Object Model) object. This creates some syntactic differences between how Internet Explorer is used within .NET 2.0 and .NET 1.x. The first example in this chapter will cover both versions of .NET for completeness. Further examples will show .NET 2.0 code only, unless the equivalent .NET 1.x code would differ substantially.
The first thing you will need to know when using Internet Explorer is how to navigate to a web page. Since Internet Explorer works asynchronously, you will also need to know when Internet Explorer is finished loading a web page. In the following example, we will simply navigate to www.google.com and popup a message box once the page is loaded.
To begin this example, drop an Internet Explorer object onto a form, as described above, and call it WebBrowser. Now add a button to the form and name it btnNavigate. Click on the button and add the following code
C#
private void btnNavigate_Click(object sender, System.EventArgs e)
{
NavigateToUrlSync("http://www.google.com");
MessageBox.Show("page loaded");
}
VB.NET
Private Sub btnNavigate_Click(ByVal sender As System.Object, _
ByVal e As System.EventArgs) Handles btnNavigate.Click
NavigateToUrlSync("http://www.google.com")
MessageBox.Show("page loaded")
End Sub
We then create the NavigateToUrlSync method. Note how the C# version differs in version 1.x and 2.0. This is because the COM object is expecting four optional ref object parameters. These parameters can optionally define the flags, target frame name, post data and headers sent with the request. They are not used in this case, yet since C# does not support optional parameters they have to be passed in nonetheless.
C# 1.x
public void NavigateToUrlSync(string url)
{
object oMissing = null;
bBusy=true;
WebBrowser.Navigate(url,ref oMissing,ref oMissing,ref oMissing,ref oMissing);
while(bBusy)
{
Application.DoEvents();
}
}
C# 2.0
public void NavigateToUrlSync(string url)
{
bBusy=true;
WebBrowser.Navigate(url);
while(bBusy)
{
Application.DoEvents();
}
}
VB.NET
Public Sub NavigateToUrlSync(ByVal url As String)
bBusy = True
WebBrowser.Navigate(url)
While (bBusy)
Application.DoEvents()
End While
End Sub
The while loop is polls until the public bBusy flag is cleared. The DoEvents command ensures that the application remains responsive whilst waiting for a response from the web server.
To clear the bBusy flag, we handle either the DocumentComplete (.NET 1.x) or DocumentCompleted (.NET 2.0) thus:
C# 1.x
private void WebBrowser_DocumentComplete(object sender, AxSHDocVw.DWebBrowserEvents2_DocumentCompleteEvent e)
{
bBusy = false;
}
C# 2.0
private void WebBrowser_DocumentCompleted(object sender, WebBrowserDocumentCompletedEventArgs e)
{
bBusy = false;
}
VB.NET 1.x
Private Sub WebBrowser_DocumentComplete(ByVal sender As Object, _
ByVal e As AxSHDocVw.DWebBrowserEvents2_DocumentCompleteEvent) _
Handles WebBrowser.DocumentComplete
bBusy = False
End Sub
VB.NET 2.0
Private Sub WebBrowser_DocumentCompleted(ByVal sender As Object, _
ByVal e As WebBrowserDocumentCompletedEventArgs) _
Handles WebBrowser.DocumentCompleted
bBusy = False
End Sub
To finish off the example, don抰 forget to declare the public bBusy flag.
C#
public bool bBusy = false;
VB.NET
public bBusy As Boolean = false
To test the application, compile and run it in Visual Studio, then press the navigate button.
5.2 Manipulating web pages
An advantage of using Internet Explorer over raw HTTP requests is that you get access to the DOM (Document Object Model) of web pages, once they are loaded into Internet Explorer. For developers familiar with JavaScript, this should be an added bonus, since you will be able to control the web page in much the same way as if you were using JavaScript within a HTML page.
The main difference however, between using the DOM in .NET versus JavaScript, is that .NET is a strongly typed language, and therefore you must know the type of the element you are interacting with before you can access its full potential.
If you are using .NET 1.x you will need to reference the HTML type library, by clicking Projects > Add Reference. Then select Microsoft.mshtml from the list. For each of the examples in this section you must import the namespace into your code thus:
C#
using mshtml;
VB.NET
Imports mshtml
If you then cast the WebBrowser.Document object to an HTMLDocument class, many of the code examples shown below should word equally well for .NET 1.x as .NET 2.0
5.2.1 Frames
Frames may be going out of fashion in modern websites, but oftentimes, you may need to extract data from a website that uses frames, and you need to be aware how to handle them within Internet Explorer. In this section, you will notice that the code differs substantially between version 1.x and 2.0 of .NET, therefore source code for both are included.
To create a simple frameset, create three files, Frameset.html, left.html and right.html, these files containing the following HTML code respectively.
Frameset.html
<html>
<frameset cols="50%,50%">
<frame name="LeftFrame" src="Left.html">
<frame name="LeftFrame" src="right.html">
</frameset>
</html>
Left.html
<html>
This is the left frame
</html>
Right.html
<html>
This is the right frame
</html>
In the following example, we will use Internet Explorer to read the HTML contents of the left frame. This example uses code from the program listing in section 5.1, and assumes you have saved the HTML files in C:\
VB.NET 1.x
Private Sub btnNavigate_Click(ByVal sender As System.Object, _
ByVal e As System.EventArgs) Handles btnNavigate.Click
NavigateToUrlSync("C:\frameset.html")
Dim hDoc As HTMLDocument
hDoc = WebBrowser.Document
hDoc = CType(hDoc.frames.item(0), HTMLWindow2).document
MessageBox.Show(hDoc.body.innerHTML)
End Sub
VB.NET 2.0
Private Sub btnNavigate_Click(ByVal sender As System.Object, _
ByVal e As System.EventArgs) Handles btnNavigate.Click
NavigateToUrlSync("C:\frameset.html")
Dim hDoc As HtmlDocument
hDoc = WebBrowser.Document.Window.Frames(0).Document
MessageBox.Show(hDoc.Body.InnerHtml)
End Sub
C# 1.x
private void btnNavigate_Click(object sender, System.EventArgs e)
{
NavigateToUrlSync(@"C:\frameset.html");
HTMLDocument hDoc;
object oFrameIndex = 0;
hDoc = (HTMLDocument)WebBrowser.Document;
hDoc = (HTMLDocument)((HTMLWindow2)hDoc.frames.item(
ref oFrameIndex)).document;
MessageBox.Show(hDoc.body.innerHTML);
}
C# 2.0
private void btnNavigate_Click(object sender, System.EventArgs e)
{
NavigateToUrlSync(@"C:\frameset.html");
HtmlDocument hDoc;
hDoc = WebBrowser.Document.Window.Frames[0].Document;
MessageBox.Show(hDoc.Body.InnerHtml);
}
The main difference between the .NET 2.0 and .NET 1.x versions of the above code is that the indexer on the frames collection returns an object, which must be cast to an HTMLWindow2 under the COM wrapper in .NET 1.x. In .NET 2.0 the indexer performs the cast internally, and returns an HtmlWindow object.
To test the application, compile and run it from Visual Studio .NET, press the navigate button, and a message box should pop up saying this is the left frame.
5.2.2 Input boxes
Input boxes are used in HTML to allow the user enter text into a web page. Here we will automatically populate an input box with some data.
Given a some HTML, which we save as InputBoxes.html as follows
<html>
<form name="myForm">
My Name is :
<input type="text" value="" name="myName">
</form>
</html>
We can get a reference to the input box on the form by calling getElementById on the HtmlDocument. In .NET 1.x this should be then cast to an IHTMLInputElement.
C# 2.0
private void btnNavigate_Click(object sender, System.EventArgs e)
{
NavigateToUrlSync(@"C:\InputBoxes.html");
HtmlElement hElement;
hElement = WebBrowser.Document.GetElementById("myName");
hElement.SetAttribute("value", "Joe Bloggs");
}
VB.NET 2.0
Private Sub btnNavigate_Click(ByVal sender As System.Object, _
ByVal e As System.EventArgs) Handles btnNavigate.Click
NavigateToUrlSync("C:\InputBoxes.html")
Dim hElement As HtmlElement
hElement = WebBrowser.Document.GetElementById("myName")
hElement.SetAttribute("value", "Joe Bloggs")
End Sub
In order to enter the text into the input box, we call the SetAttribute method of the HtmlElement, passing in the property to change, and the new text. In .NET 1.x we would set the value property of the IHTMLInputElement to the new text.
To test the application, compile and run it from Visual Studio .NET, then press the navigate button.
5.2.3 Drop down lists
In HTML, drop down lists are used in web pages to allow users input from a list of pre-defined values. In the following example, we will demonstrate how to set a value of a drop down list, and then read it back.
We shall start off with a HTML file, which we save as DropDownList.html
<html>
<form name="myForm">
My favourite colour is:
<select name="myColour">
<option value="Blue">Blue</option>
<option value="Red">Red</option>
</select>
</form>
</html>
We can get a reference to the drop down list by calling getElementById on the HtmlDocument. In .NET 1.x this should be then cast to an IHTMLSelectElement.
C# 2.0
private void btnNavigate_Click(object sender, System.EventArgs e)
{
NavigateToUrlSync(@"C:\dropdownlists.html");
HtmlElement hElement;
hElement = WebBrowser.Document.GetElementById("myColour");
hElement.SetAttribute("selectedIndex", "1");
MessageBox.Show("My favourite colour is:" + hElement.GetAttribute("value"));
}
VB.NET 2.0
Private Sub btnNavigate_Click(ByVal sender As System.Object, _
ByVal e As System.EventArgs) Handles btnNavigate.Click
NavigateToUrlAsync("C:\dropdownlists.html")
Dim hElement As HtmlElement
hElement = WebBrowser.Document.GetElementById("myColour")
hElement.SetAttribute("selectedIndex", "1")
MessageBox.Show("My favourite colour is:" + hElement.GetAttribute("value"))
End Sub
Here, we can see that in order to set our selection we pass ?/span>selectedIndex? and the selection number to SetAttribute. We then pass ?/span>value? to GetAttribute in order to read back the selection. In .NET 1.x, we achieve the same results by setting the selectedIndex property on the IHTMLSelectElement and reading back the selection from the value property.
To test the application, compile and run it from Visual Studio .NET, press the navigate button, and you should see a message box appear saying my favorite color is: Red.
5.2.4 Check boxes and radio buttons
Check boxes and radio buttons are generally used on web pages to allow the user to select between small numbers of options. In the following example, we shall demonstrate how to toggle check boxes and radio buttons.
We shall start off with a HTML file, which we will save as CheckBoxes.html
<html>
<form name="myForm">
<input type="checkbox" name="myCheckBox">Check this.<br>
<input type="radio" name="myRadio" value="Yes">Yes
<input type="radio" name="myRadio" checked="true" value="No">No
</form>
</html>
As before we can get a reference to the checkbox by calling getElementById. However, since the two radio buttons have the same name, we need to use
Document.All.GetElementsByName and then select the required radio button from the HtmlElementCollection returned.
In .NET 1.x, we would use a call to getElementsByName on the HTMLDocument. This returns an IHTMLElementCollection. We can then get the reference to the IHTMLInputElement with the method item(null,1).
C# 2.0
private void btnNavigate_Click(object sender, System.EventArgs e)
{
NavigateToUrlSync(@"C:\checkboxes.html");
HtmlElement hElement;
HtmlElementCollection hElements;
hElement = WebBrowser.Document.GetElementById("mycheckBox");
hElement.SetAttribute("checked", "true");
hElements = WebBrowser.Document.All.GetElementsByName("myRadio");
hElement = hElements[0];
hElement.SetAttribute("checked", "true");
}
VB.NET 2.0
Private Sub btnNavigate_Click(ByVal sender As System.Object, _
ByVal e As System.EventArgs) Handles btnNavigate.Click
NavigateToUrlSync("C:\checkboxes.html")
Dim hElement As HtmlElement
hElement = WebBrowser.Document.GetElementById("mycheckBox")
hElement.SetAttribute("checked", "true")
hElement = WebBrowser.Document.All.GetElementsByName("myRadio").Item(0)
hElement.SetAttribute("checked", "true")
End Sub
As before, we set the property of the HtmlElement using the SetAttribute method. In .NET 1.x, you need to set the @checked property on the IHTMLInputElement
To test the application, compile and run it from Visual Studio, then press the navigate button. You should see the check box and radio button toggle simultaneously.
5.2.5 Buttons
Submit buttons and standard buttons are generally used to submit forms in HTML. They form a crucial part in navigating any website.
Given a simple piece of HTML, which we save as Buttons.html as follows:
<html>
<form action="http://www.google.com/search" method="get" name="myForm">
<input type="text" value=".NET" name="q">
<input type="submit" name="btnSubmit" value="Google Search">
</form>
</html>
We can get a reference to the button on the form by calling getElementById on the HtmlDocument. In .NET 1.x this should be then cast to an IHTMLElement.
C# 2.0
private void btnNavigate_Click(object sender, System.EventArgs e)
{
NavigateToUrlSync(@"C:\buttons.html");
HtmlElement hElement;
hElement = WebBrowser.Document.GetElementById("btnSubmit");
hElement.InvokeMember("click");
}
VB.NET 2.0
Private Sub btnNavigate_Click(ByVal sender As System.Object, _
ByVal e As System.EventArgs) Handles btnNavigate.Click
NavigateToUrlSync("C:\buttons.html")
Dim hElement As HtmlElement
hElement = WebBrowser.Document.GetElementById("btnSubmit")
hElement.InvokeMember("click")
End Sub
In the above example, we can see that after we get a reference to the button, we call the click method using InvokeMember. Similarly, if we wanted to submit the form without clicking the button, we could get a reference to myForm and pass ?/span>submit? to the InvokeMember method.
In .NET 1.x, there is no InvokeMember method of IHTMLElement, so therefore you must call the click method of the IHTMLElement. In the case of a form, you should cast the IHTMLElement to an IHTMLFormElement and call it submit method.
To test this application, compile and run it from Visual Studio .NET, and press the navigate button. The form should load and then automatically forward itself to a google.com search result page..
5.2.6 JavaScript
Many web pages use JavaScript to perform complex interactions between the user and the page. It is important to know how to execute JavaScript functions from within Internet explorer. The simplest method is to use Navigate with the prefix javascript: then the function name. However, this does not give us a return value, nor will it work correctly in all situations.
We shall start with a HTML page, which contains a JavaScript function to display some text. This will be saved as JavaScript.html
<html>
<span id="hiddenText" style="display:none">This was displayed by javascript</span>
<script language="javascript">
function jsFunction()
{
window.document.all["hiddenText"].style.display="block";
return "ok";
}
</script>
</html>
We can then use the Document.InvokeScript method to execute the JavaScript thus:
C# 2.0
private void btnNavigate_Click(object sender, System.EventArgs e)
{
NavigateToUrlSync(@"C:\javascript.html");
string strRetVal = "";
strRetVal = (string)WebBrowser.Document.InvokeScript("jsFunction");
MessageBox.Show(strRetVal);
}
VB.NET 2.0
Private Sub btnNavigate_Click(ByVal sender As System.Object, _
ByVal e As System.EventArgs) Handles btnNavigate.Click
NavigateToUrlSync("C:\javascript.html")
Dim strRetVal As String
strRetVal = WebBrowser.Document.InvokeScript("jsFunction").ToString()
MessageBox.Show(strRetVal)
End Sub
In .NET 1.x, we would call the parentWindow.execScript method on the HTMLDocument. Not forgetting to add empty parenthesis after the JavaScript function name. Unfortunately execScript returns null instead of the JavaScript return value.
To test the application, compile and run it from Visual Studio .NET, then press the Navigate button.
5.3 Extracting data from web pages
In order to extract HTML from a web page using Internet Explorer, you need to call Body.Parent.OuterHtml in .NET 2.0 or body.parentElement.outerHTML in .NET 1.x. You should be aware that the HTML returned by this method is different to the actual HTML content of the page.
Internet Explorer will correct HTML in the page by adding <BODY>, <TBODY> and <HEAD> tags where missing. It will also capitalize existing HTML Tags, and make other formatting changes that you should be aware of.
Techniques for parsing this textual data are explained later in the book under the section concerning Regular Expressions.
5.4 Advanced user interaction
When designing an application which uses Internet Explorer as a tool for data mining, it comes of added benefit, that the user can interact with the control in a natural fashion, in order to manipulate its behavior. The following sections describe ways in which a user can interact with Internet Explorer, and how these events can be handled within .NET
5.4.1 Design mode
If you wanted to provide the user with the ability to manipulate web pages on-the-fly, there is no simpler way to do it, than using the in-built design mode?in internet explorer. This particular feature is not supported with the managed .NET 2.0 WebBrowser control. However, it is possible to access the unmanaged interfaces, which we were using in .NET 1.x through the Document.DomDocument property. This can be then cast to the HTMLDocument in the mshtml library (Not to be confused with the managed HtmlDocument class). Therefore, in the case, you will need to add a reference to the mshtml library and add a using mshtml? statement to the top of your code.
In this example, we will create a simple rich text editor based on Internet Explorer design mode. Within design mode the user can perform a wide variety of tasks using intuitive actions, for example, you can insert an image by right clicking on the browser, or convert text to bold by pressing CTRL+B. Many of these tasks can be further automated using the execCommand method of the HTMLDocument object. In the following example, we will demonstrate how to set fonts using this method.
Open a new project in Visual Studio .NET, and drag a WebBrowser control onto the form, followed by a button, named btnFont. Also Add a FontDialog control named fontDialog. Click on the form and type the following code for the form load event.
C# 2.0
private void Form1_Load(object sender, EventArgs e)
{
string url = "about:blank";
webBrowser.Navigate(url);
Application.DoEvents();
HTMLDocument hDoc = (HTMLDocument)webBrowser.Document.DomDocument;
hDoc.designMode = "On";
}
VB.NET 2.0
Private Sub Form1_Load(ByVal sender As System.Object, _
ByVal e As System.EventArgs) Handles MyBase.Load
Dim url As String = "about:blank"
webBrowser.Navigate(url)
Application.DoEvents()
Dim hDoc As HTMLDocument = webBrowser.Document.DomDocument
hDoc.designMode = "On"
End Sub
In .NET 1.x, we would cast the Document to an HTMLDocument, rather than referencing the DomDocument property, and also, the Navigate method would be as described in section 5.1.
Now click on the font button and enter some code as follows
C# 2.0
private void btnFont_Click(object sender, EventArgs e)
{
fontDialog.ShowDialog();
HTMLDocument hDoc = (HTMLDocument)webBrowser.Document.DomDocument;
IHTMLTxtRange selection = (IHTMLTxtRange)hDoc.selection.createRange();
hDoc.execCommand("FontName", false, fontDialog.Font.FontFamily.Name);
hDoc.execCommand("FontSize", false, fontDialog.Font.Size);
selection.select();
}
VB.NET 2.0
Private Sub btnFont_Click(ByVal sender As System.Object, _
ByVal e As System.EventArgs) Handles btnFont.Click
fontDialog.ShowDialog()
Dim hDoc As HTMLDocument = webBrowser.Document.DomDocument
Dim selection As IHTMLTxtRange = hDoc.selection.createRange()
hDoc.execCommand("FontName", False, fontDialog.Font.FontFamily.Name)
hDoc.execCommand("FontSize", False, fontDialog.Font.Size)
selection.select()
End Sub
From the above code we can see that we get a reference to the text currently highlighted by the user using the selection.createRange method. We then execute two commands on this selection, FontName and FontSize. Other commands that could be used would be ForeColor Italic, Bold and so forth.
To test the application, compile and run it from Visual Studio .NET, enter some text into the space provided, then highlight it. Click on the font button and choose a new font and size. The text should change to the selected font.
5.4.2 Capturing Post data
When a user is navigating through web pages, it may be necessary to keep track of what URLs they are going to, and post data sent between Internet Explorer and the web server. Although there are ways and means of doing this using packet sniffing, or third party tools, these do sometimes tend to listen to too much data and record traffic from other applications. Due to a bug in the .NET wrapper for Internet Explorer (see Microsoft Knowledge base 311298), the beforeNaviate event will not fire as you move between pages.
In order to subscribe to this event, we need to know a little about how COM events work under the hood? Every COM object which generates events will implement the IConnetionPointContainer interface. A client wishing to subscribe to events from this COM object must call the FindConnectionPoint method on this interface, passing the IID (Interface ID) of the required set of events.
Some COM objects support multiple sets of events or connection Points? for example, Internet Explorer supports the DWebBrowserEvents connection point, and the DWebBrowserEvents2 connection point. Herein lies the problem, the .NET wrapper will by default attach to the DWebBrowserEvents2 connection point, which contains a version of BeforeNavigate which is incompatible with .NET due to unsupported variant types.
If you open the ILDASM utility, then click file open, and select Interop.SHDocVw.DLL.
From the information in Figure 5.8 we can see that the Dispatch ID is set to 64 Hex (100 decimal). While using ILDASM we can also find the IID of the DWebBrowserEvents connection point by double clicking on class interface?that is, eab22ac2-30c1-11cf-a7eb-0000c05bae0b. At this point we have everything we need to create an interface in C# for this event.
C#
[Guid("eab22ac2-30c1-11cf-a7eb-0000c05bae0b"),
InterfaceType(ComInterfaceType.InterfaceIsIDispatch)]
public interface IWebBrowserEvents
{
[DispId(100)]
void RaiseBeforeNavigate(String url, int flags, String targetFrameName,
ref Object postData, String headers, ref Boolean cancel);
}
To put this all together, create a new project in Visual Studio .NET, and drop in a Web Browser control (not the .NET 2.0 version, but the COM version). Add a reference to Microsoft Internet Controls under COM references. You will need to include both SHDocVw and System.Runtime.InteropServices in the using list at the head of your code. Now add the code for the interface listed above.
C#
private void Form1_Load(object sender, System.EventArgs e)
{
UCOMIConnectionPointContainer icpc;
UCOMIConnectionPoint icp;
int cookie = -1;
icpc = (UCOMIConnectionPointContainer)axWebBrowser1.GetOcx();
Guid g = typeof(DWebBrowserEvents).GUID;
icpc.FindConnectionPoint(ref g, out icp);
icp.Advise(this, out cookie);
}
What this code does, is that it obtains a reference to Internet Explorer underlying IConnectionPointContainer, by calling the GetOcx method, that axWebBrowser1 has inherited from AxHost. From this, we can then obtain a reference to the required connection point by passing its GUID / IID to the FindConnectionPoint method. To subscribe to events, we call the Advise method. To unsubscribe we should call the unAdvise method, if required.
To handle the event, we shall simply pop up a message box immediately before the page navigates. We shall also display any post data being sent.
C#
public void RaiseBeforeNavigate(String url, int flags, String
targetFrameName, ref Object postData, String headers, ref Boolean cancel)
{
string strPostData="";
if (postData!=null)
{
strPostData= System.Text.Encoding.UTF8.GetString((byte[])postData);
MessageBox.Show(strPostData);
}
}
Since we have specified that our class should implement IWebBrowserEvents, this dictates that the post data must be received as an object. This object should then be cast to a byte array, and then to a UTF8 string for readability.
To finish off the example, add a button to the form, and attach some code to it, to allow it to navigate to some website with a post-form on it, in this example, Amazon.com
C#
private void button1_Click(object sender, EventArgs e)
{
object o = null;
this.axWebBrowser1.Navigate("http://www.amazon.com",ref o,ref o,ref o,ref o);
}
To test the application, run it from Visual Studio .NET, press the navigate button, enter something in the Amazon search box, and press go. You should see a message box appearing, containing the post data which you sent to the web server.
5.4.3 Capturing click events
Although you can capture events such as DocumentComplete to determine when a user navigates to a new page, it is a little trickier to trap events which do not involve page navigation, such as entering text into a text box for instance.
The event trapping technique differs substantially between .NET 1.x and .NET 2.0. In the latter version, you need to implement the default COM interop method, this an entry point in your application which is marked as Dispatch ID 0, which COM uses to call back whenever your application subscribes to an event. In order to use COM interoperability, you need to include a using System.Runtime.InteropServices statement at the top of your code, in .NET 1.x.
In .NET 2.0, it is a little more straightforward. Here, we attach an HtmlElementEventHandler delegate to the Document.Click event, and implement it in our own event handler.
Basing this example on the sample code in section 5.1, we shall now add some extra event handling capabilities to pop up a message box whenever the user clicks a HTML element in the web browser.
C# 2.0
private void btnNavigate_Click(object sender, System.EventArgs e)
{
NavigateToUrlSync(@"http://www.google.com");
WebBrowser.Document.Click += new HtmlElementEventHandler(Document_Click);
}
C# 1.x
private void btnNavigate_Click(object sender, System.EventArgs e)
{
NavigateToUrlSync(@"http://www.google.com");
HTMLDocument hDoc = (HTMLDocument)WebBrowser.Document;
hDoc.onclick = this;
}
At this point we have now subscribed to the click event, and in the case of .NET 2.0, supplied a call back delegate named Document_Click. For demonstration purposes, we shall simply display the tag name of the element clicked, and the event type (which should always be click?in our case).
C# 2.0
public void Document_Click(object sender, HtmlElementEventArgs e)
{
string sTag = WebBrowser.Document.GetElementFromPoint(e.MousePosition).TagName;
MessageBox.Show("Object: " + sTag + ", type:" + e.EventType);
}
C# 1.x
[DispId(0)]
public void DefaultMethod()
{
HTMLDocument hDoc = (HTMLDocument)WebBrowser.Document;
HTMLWindow2 hWin = (HTMLWindow2)hDoc.parentWindow;
MessageBox.Show("Object: " + hWin.@event.srcElement.tagName +
", Type: " + hWin.@event.type);
}
In order to get a reference to the element clicked, we have used a different technique for each version of .NET. In .NET 2.0, the GetElementFromPoint method is used to determine the element from the mouse location. In .NET 1.x, we can get the reference to the element via the Document.parentWindow.@event.srcElement property.
To test the application, compile and run it from Visual Studio .NET, press the navigate button, then click anywhere on the screen. You should see a message box appear with the tag name of the HTML element that you clicked on.
5.5 Extending Internet Explorer
The examples so far have dealt with embedding Internet Explorer in our applications, rather than embedding our applications in Internet Explorer. This may not be ideal for all users, as we loose the familiar interface that users are accustomed to. This section deals with how build applications around running instances of Internet Explorer.
5.5.1 Menu extensions
When you right click on a web page, you can see a context menu, which you can extend with a simple registry tweak. In this example, you can add a link to 揝end to a friend?in the context menu, which will link to a website that allows you to send emails. Firstly create the following registry key:
HKEY_CURRENT_USER\Software\Microsoft\Internet Explorer\MenuExt\Send to a friend
Then set the default value to a location on your hard drive, say c:\SendToAFriend.html, which would contain the following HTML:
<script language="JavaScript">
window.open("http://www.pop3webmail.info/reply.aspx?url=" + external.menuArguments.document.URL);
</script>
After making the change to the registry, close all browser windows.
5.5.2 Spawning a new instance of Internet Explorer
A simple way of controlling instances of Internet Explorer is to create them yourself using COM. In this example I use COM late binding, which differs from the early-bound examples used earlier in this chapter, specifically in the .NET 1.x examples. Early bound COM objects are compiled into the application at design time. Late bound COM objects are loaded dynamically at run time.
The benefit of early bound objects is that the development environment will be aware of the object model of the component, and Intellisense will assist you determine which methods you can call. We do not have such a luxury with late bound objects. However, there is an advantage that we can bind to COM objects hosted as executables, such as in the following example.
To start off, create a new windows forms application in Visual Studio .NET, drop a button on the form, and attach the following code to it.
C#
public Type tIE;
public object oIE;
private void btnNavigate_Click(object sender, EventArgs e)
{
object[] oParameter = new object[1];
tIE = Type.GetTypeFromProgID("InternetExplorer.Application");
oIE = Activator.CreateInstance(tIE);
oParameter[0] = (bool)true;
tIE.InvokeMember("Visible", BindingFlags.SetProperty, null, oIE, oParameter);
oParameter[0] = (string)"http://www.google.com";
tIE.InvokeMember("Navigate2", BindingFlags.InvokeMethod,
null, oIE, oParameter);
}
VB.NET
Public tIE As Type
Public oIE As Object
Private Sub btnNavigate_Click(ByVal sender As System.Object, _
ByVal e As System.EventArgs) Handles btnNavigate.Click
Dim oParameter(0) As Object
tIE = Type.GetTypeFromProgID("InternetExplorer.Application")
oIE = Activator.CreateInstance(tIE)
oParameter(0) = CType(True, Boolean)
tIE.InvokeMember("Visible", BindingFlags.SetProperty, Nothing, oIE, oParameter)
oParameter(0) = CType("http://www.google.com", String)
tIE.InvokeMember("Navigate2", BindingFlags.InvokeMethod,
Nothing, oIE, oParameter)
End Sub
You should also add references to System.Threading and System.Reflection at the top of your code.
The above code retrieves a reference to the COM object model for the Internet Explorer application by inspecting the ProgID ?/span>InternetExplorer.Application? It then creates an instance of this COM object. It sets its Visible property to true, then calls the Navigate2 method, passing the URL www.google.com as a parameter.
Unfortunately it is not trivial to subscribe to events from this late bound object, so therefore, if it is necessary to detect navigation between pages, it may be necessary to poll on the LocationURL property of the browser.
To test this application, compile and run it from Visual Studio .NET, then press the button on the form. You should see a new browser window open.
5.5.3 Browser Helper Objects
When you need to get really tight integration with Internet Explorer, in cases where you want code to execute completely transparently to the user, and yet have full control of the browsers document model and be able to subscribe to events, Browser Helper Objects (BHO) is the way to go.
BHO technology is widely associated with Spyware applications, which silently run in the background, as a user is browsing websites. Since the BHO would have access to the HTMLDocument object of the Internet Explorer instance hosting it, it would be possible to read the text of the webpage being visited, and duly display context-sensitive advertisements.
Internet Explorer expects the BHO object to be COM based, not a .NET assembly. Therefore it is necessary to create a CCW (Com Callable Wrapper) for our assembly. This CCW has a unique Class ID, which we store in the registry at the following location:
HKLM\Software\Microsoft\Windows\CurrentVersion\Explorer\
Browser Helper Objects
When Internet Explorer (or Windows Explorer) starts, it reads all the Class ID抯 listed in at the registry location listed above, and creates instances of their respective COM objects, and in our case, the underlying .NET assembly. It then interrogates the COM object to ensure that it implements the IObjectWithSite interface. This interface is very strictly defined and implemented as follows:
C#
using System;
using System.Runtime.InteropServices;
namespace BrowserHelperObject
{
[ComVisible(true),
InterfaceType(ComInterfaceType.InterfaceIsIUnknown),
Guid("FC4801A3-2BA9-11CF-A229-00AA003D7352")]
public interface IObjectWithSite
{
[PreserveSig]
int SetSite([MarshalAs(UnmanagedType.IUnknown)]object site);
[PreserveSig]
int GetSite(ref Guid guid, out IntPtr ppvSite);
}
}
Internet Explorer uses the two methods listed above to interact with the BHO. The SetSite method is called by Internet Explorer whenever it starts up, or shuts down. This is to update the BHO with the status of any internal references it may hold to the instance of Internet Explorer which is hosting it. GetSite may be called by Internet Explorer to query the reference a BHO holds to it. Every BHO must implement both of these methods, and handle requests to and from the hosting instance correctly.
To demonstrate Browser Helper Objects, we shall go though a simple example, where we attach a BHO to Internet Explorer, which will append the current date to every page visited by the user.
Start a new class library project in Visual Studio, add a reference to the Microsoft.mstml .NET assembly, and also to the COM object named Microsoft Internet Controls? Add a new class file containing the definition of IObjectWithSite as listed above. Then you can create the skeleton of your BHO thus:
C#
using System;
using System.Runtime.InteropServices;
using SHDocVw;
using Microsoft.Win32;
using mshtml;
namespace BrowserHelperObject
{
[ComVisible(true),
Guid("F839CC51-A6D8-4e9c-ACE5-F05071AD0C74"),
ClassInterface(ClassInterfaceType.None)]
public class DateStamp : IObjectWithSite
{
WebBrowser webBrowser;
}
}
What you can see from the code above is that the class implements the IObjectWithSite interface, which is a pre-requisite of any BHO. It also has a GUID (Genuinely Unique Identifier), - this is used to uniquely identify the CCW, and can be chosen arbitrarily, using the GuidGen.exe tool or similar. The WebBrowser class in the code does not refer to the familiar WebBrowser class as used in .NET 2.0, but instead is a class defined within SHDocVw. It is this object which will contain a reference to the hosting instance of Internet Explorer.
As mentioned previously, it is necessary for every BHO to implement both the GetSite and SetSite methods. In most cases, there is little need to perform any custom actions within GetSite, so therefore its implementation would remain standard for most types of BHO. A typical implementation would be as follows:
C#
public int GetSite(ref Guid guid, out IntPtr ppvSite)
{
IntPtr punk = Marshal.GetIUnknownForObject(webBrowser);
int hr = Marshal.QueryInterface(punk, ref guid, out ppvSite);
Marshal.Release(punk);
return hr;
}
What this code does, is that it firstly obtains a pointer to the IUnknown COM interface for our reference to the hosting instance of Internet Explorer. It then queries the IUnknown interface with a GUID issued internally by Internet Explorer. This returns a pointer to another object, as required by Internet Explorer. The code then frees the resources associated with the IUnknown pointer, and returns a HRESULT in the event that an error occurred whilst trying to query the interface.
What is of more interest is the SetSite method. This is where we have the opportunity to attach custom event handlers to the hosting web browser. In this case, we attach the DocumentComplete event handler.
C#
public int SetSite(object site)
{
if (site != null)
{
webBrowser = (WebBrowser)site;
webBrowser.DocumentComplete += new
DWebBrowserEvents2_DocumentCompleteEventHandler(
this.OnDocumentComplete);
}
else
{
webBrowser.DocumentComplete -= new
DWebBrowserEvents2_DocumentCompleteEventHandler(
this.OnDocumentComplete);
webBrowser = null;
}
return 0;
}
As mentioned earlier, Internet Explorer may also call this method as it is shutting down, therefore, in which case the passed parameter is null. It is required that we should detach event handlers and free any associated resources at the point when the host closes.
At this point we are in a position to add our own custom logic, which we place within the OnDocumentComplete function thus:
C#
private void OnDocumentComplete(object frame, ref object urlObj)
{
if (webBrowser != frame) return;
IHTMLDocument2 document = (IHTMLDocument2)webBrowser.Document; document.body.innerHTML = document.body.innerHTML +
DateTime.Now.ToShortDateString();
return;
}
In the above code, we retrieve a reference to the HTMLDocument contained within the hosting Internet Explorer instance, and simply add the current date to the HTML of the page.
Before we are ready to try out our new BHO, we should add some extra plumbing to enable the assembly to store the Class ID of it CCW in the registry with the other Browser Helper Objects installed on the system.
C#
public static string BHOKEYNAME = "Software\\Microsoft\\Windows\\CurrentVersion\\Explorer\\Browser Helper Objects";
[ComRegisterFunction]
public static void RegisterBHO(Type t)
{
RegistryKey key = Registry.LocalMachine.OpenSubKey(BHOKEYNAME, true);
if (key == null) key = Registry.LocalMachine.CreateSubKey(BHOKEYNAME);
string guidString = t.GUID.ToString("B");
RegistryKey bhoKey = key.OpenSubKey(guidString);
if (bhoKey == null) bhoKey = key.CreateSubKey(guidString);
key.Close();
bhoKey.Close();
}
The above code is called whenever we create a CCW from the assembly. It inserts a new key containing the Class ID, at the registry location as specified.
Similarly, as we un-register the CCW, we will want to remove that key from the registry. This would be implemented thus:
C#
[ComUnregisterFunction]
public static void UnregisterBHO(Type t)
{
RegistryKey key = Registry.LocalMachine.OpenSubKey(BHOKEYNAME, true);
string guidString = t.GUID.ToString("B");
if (key != null) key.DeleteSubKey(guidString, false);
}
You will find that whilst developing a BHO, you may need to recompile and test the code several times to perfect your application. Every time that you attach a BHO to Internet Explorer, it will also attach itself to Windows Explorer, and the assembly will be locked for the duration of the lifetime of these two processes. When the assembly is locked you will not be able to delete it, or modify it by building a new version of the BHO over it.
To unlock the BHO, you will need to un-register it using regasm /unregister then stop all iexplore.exe and explore.exe processes, through either task manager, or by logging off and logging back in again.
To test the above application, compile the above code, then open up the Visual Studio .NET command prompt and navigate to the folder that contains the output DLL. then run the command
Regasm /codebase browserHelperObject.dll
Now open up an Internet Explorer window and you should see the date written at the bottom of the page.
If you receive the following warning ?do not panic, as long the GUID you used in your assembly is unique, it will not cause a problem
RegAsm warning: Registering an unsigned assembly with /codebase can cause your assembly to interfere with other applications that may be installed on the same computer. The /codebase switch is intended to be used only with signed assemblies. Please give your assembly a strong name and re-register it.
5.6 Conclusion
This chapter has demonstrated how to control Internet Explorer from within a .NET application. It should pave the way for automating data mining processes using this versatile component.
With the added benefit of enabling a user to interact with web pages in a natural fashion, and being able to trap events from within Internet Explorer, it should be possible to implement data mining training tools, and website test automation utilities with the examples shown in this chapter. 
Life is like a boat, and I'm at sea.
