Web Browser Link Trapping

• Download demo and source project - 16.2 KB

Introduction

I'm new to programming, and was trying to create a browser (using the web browser control) that connected through a TCP client. I soon realized that I would need to trap the links on the page, so I could redirect them through my application. A little bit of time and coffee later, I realized that no one appears to have ever needed this. Or at the very least, I was unable to find any information on it. However, I eventually gave up and decided to give it a shot myself. I am trying to get better with my programming, and would really like to try and make a career out of it, so please comment on this and let me know what you think or where I can improve.

Description of the solution

The web browser control shipped with the .NET Framework provides many useful functions and properties. As well as this, many of the events are available without too much fiddling around. First off, I monitored the DocumentCompleted event, and then made any changes to the document that I required. In this case, I used a HTMLElementCollection object to store all the links on the page. I then created an event handler, LinkClicked, and assigned it to the OnClick event of all links. This way, I was aware of any navigation that was occurring. I'll explain the code first.

Document Completed

Setting up the event handler is as simple as this:

Private Sub webControl_DocumentCompleted(ByVal sender As Object, _ 
        ByVal e As WebBrowserDocumentCompletedEventArgs) _
        Handles webControl.DocumentCompleted
    Dim link As HtmlElement
    Dim links As HtmlElementCollection = webControl.Document.Links
    For Each link In links
        If btnChange.Checked Then
            link.SetAttribute("href", newLink)
        End If 

        link.AttachEventHandler("onclick", AddressOf LinkClicked)
    Next
End Sub

This code gets all the links on the page, and then assigns the LinkClicked event handler to the 'OnClick' event of those links.

Link Clicked

Here's the LinkClicked event:

Private Sub LinkClicked(ByVal sender As Object, ByVal e As EventArgs) 
    Dim link As HtmlElement = webControl.Document.ActiveElement
    Dim url As String = link.GetAttribute("href") 
    MsgBox("Link Clicked: " & link.InnerText & _
            vbCrLf & "Destination: " & url)
End Sub

Now we know that a link was clicked. So next, I simply grab the document's currently active item (the link) and read in the 'href' string.

Additional Features

Cancel Navigation

The Navigating event occurs before the page is loaded, so it's the best place to cancel any navigation we don't want to occur:

Private Sub webControl_Navigating(ByVal sender As Object, _ 
        ByVal e As WebBrowserNavigatingEventArgs) _
        Handles webControl.Navigating
    If btnCancel.Checked Then
        e.Cancel = True
    End If 
End Sub

Conclusion

The best thing about this solution is it involves only managed code. You get a managed event for any JavaScript event that occurs. There are many other properties and ideas that can be exploited here, but I think that's pretty much self explanatory. I hope this code is useful to someone; if not, at least, I finally got to post something on here.