WebBrowser控件捕捉DHTML事件

　和其他控件一样，我们可以用WebBrowser控件来构筑我们的Windows form应用程序。从工具箱中选择Windows 窗体控件组，单击“Microsoft Web 浏览器”，Visual Studio .NET 在后台使用AxImp.exe工具创建ActiveX 控件，控件名字为“AxWebBrowser”。在VB.NET中，不能直接使用COM组件，COM都是Unmanaged Code,在VB.NET中使用这些组件，必须完成从Unmanaged Code到Managed Code的转换。
　　一般地，你可以像使用原来的WebBrowser控件一样，如call 方法，指定属性，捕捉事件等。
　　有些事情并不是那么简单的。我们要捕捉页面事件，如当用户点击页面元素（如背景）时，引发页面元素的onclick事件。发果我们没有捕捉到事件，就要提升DHTML的等级，直到Document对象的最高层次。这样，我们就能捕捉到任何事件了。在VB6中，我们可以简单地用WithEvents关键词指定WebBrowser.Document到MSHTML.HTMLDocument。
　　在VB.NET中，这个简单方法不再有效。因为ActiveX控件创建了两个接口，两个接口中使用了同样的方法名，导致出现运行时错误。所以，你必须明确指定Document对象使用的接口，并创建事件处理句柄。

　　以下是示例代码：

' IMPORTANT: this code assumes that you've added a reference to the
'            Microsoft HTML Object Library type library

Private Sub Form1_Load(ByVal sender As System.Object, _
    ByVal e As System.EventArgs) Handles MyBase.Load
    AxWebBrowser1.Navigate("http://localhost/default.asp")
End Sub

Private Sub AxWebBrowser1_NavigateComplete2(ByVal sender As Object, _
    ByVal e As AxSHDocVw.DWebBrowserEvents2_NavigateComplete2Event) Handles _
    AxWebBrowser1.NavigateComplete2
    ' must wait for this event to grab a valid refernece to the Document
    ' property
    Dim doc As mshtml.HTMLDocument = DirectCast(AxWebBrowser1.Document, _
        mshtml.HTMLDocument)

    ' Cast to the interface that defines the event you're interested in
    Dim docevents As mshtml.HTMLDocumentEvents2_Event = DirectCast(doc, _
        mshtml.HTMLDocumentEvents2_Event)
    ' Define a handler to the onclick event
    AddHandler docevents.onclick, AddressOf onclickproc
End Sub

' Notice that the signature of this event is different from usual, as it
' is expected to return a Boolean - if false the default effect associated
' with the event (for example, jumping to another page if the click is on
' an hyperlink) is canceled.

Private Function onclickproc(ByVal obj As mshtml.IHTMLEventObj) As Boolean
    ' an object on the page has been clicked - you can learn more about
    ' type and position of this object by querying the obj's properties
    ' ...
End Function