Re: UCOMIStream, MSHTML and WebBrowser control Persistence Problem

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From: Ken Hanson (khanson_at_capstonetechnology.com)
Date: 03/16/04 

Date: Tue, 16 Mar 2004 11:04:13 -0800

Charels,

I have seen several threads where it appears you have been sucesfull loading
the WebBrowser control from a stream in the DocumentComplete event from
vb.net. I have been struggeling with this myself and was hoping you might
illuminate me.

Bottom line is that when I try to load from a stream, no error is thrown but
I seem to go into a infinite event loop where DocumentComplete keeps being
fired.

Any help would be appreciated.

Thanks,

Ken

Here are the bits that appear to be important:

Dim TrendHTML As Stream =
System.Reflection.Assembly.GetExecutingAssembly().GetManifestResourceStream(
"CTCTrend.TrendGraphics.htm")

...

Private Sub WebBrowser1_DocumentComplete(ByVal eventSender As System.Object,
ByVal eventArgs As AxSHDocVw.DWebBrowserEvents2_DocumentCompleteEvent)
Handles WebBrowser1.DocumentComplete

Dim bResult As Boolean

Dim strm As UCOMIStream

Dim objPersistStreamInit As IPersistStreamInit

Dim hGlobal As IntPtr

Dim strHTML As String

Dim objSR As New StreamReader(TrendHTML)

Try

objDocument = WebBrowser1.Document

strHTML = objSR.ReadToEnd() 'objSR is a stream reader initialized durring
form load

hGlobal = Marshal.StringToHGlobalAnsi(strHTML)

CreateStreamOnHGlobal(hGlobal, True, strm)

objPersistStreamInit = DirectCast(objDocument, IPersistStreamInit)

objPersistStreamInit.InitNew()

objPersistStreamInit.Load(strm)

Catch ex As Exception

msgbox ex.Mesage

End Try

End Sub

"Charles Law" <blank@nowhere.com> wrote in message
news:efMqFaW%23DHA.3812@TK2MSFTNGP09.phx.gbl...
> Sorry for the cross post, but I'm not sure who is best placed to answer
this
> one.
>
> This is the most bizarre behaviour of MSHTML and streams.
>
> I have a WebBrowser control that contains nothing but some default HTML. I
> want to copy the document and modify it before saving it to disk.
>
> So, I clone the document like this:
>
> <code>
> Private Function CloneDocument(ByVal doc As mshtml.IHTMLDocument2) As
> mshtml.IHTMLDocument2
>
> Dim newdoc2 As mshtml.IHTMLDocument2
> Dim ips As IPersistStreamInit
>
> Dim strm As UCOMIStream
>
> Dim source As String
>
> ' Create and initialise a new document object
> newdoc2 = New mshtml.HTMLDocument
>
> ips = DirectCast(newdoc2, IPersistStreamInit)
>
> ips.InitNew()
>
> Do Until newdoc2.readyState = "complete"
> Application.DoEvents()
> Loop
>
> ' Get the current document HTML as a stream
> source = GetDocumentSource(AxWebBrowser1.Document) ' see below
> strm = GetStream(source) ' see below
>
> ' Load the new document from the stream
> ips.Load(strm)
>
> ' Wait until the new document has settled
> Do Until newdoc2.readyState = "complete"
> Application.DoEvents()
> Loop
>
> Return newdoc2
>
> End Function
>
> Private Function GetStream(ByVal s As String) As UCOMIStream
>
> Dim iptr As IntPtr
> Dim istrm As UCOMIStream
>
> ' Get a pointer to the string
> iptr = Marshal.StringToHGlobalAuto(s)
>
> ' Create the stream from the pointer
> CreateStreamOnHGlobal(iptr, True, istrm)
>
> Return istrm
>
> End Function
> Private Function GetStream(ByVal size As Integer) As UCOMIStream
>
> Dim iptr As IntPtr
> Dim strm As UCOMIStream
>
> ' Create a pointer to a block of the required size
> iptr = Marshal.AllocHGlobal(size)
>
> ' Create the stream from the pointer
> CreateStreamOnHGlobal(iptr, True, strm)
>
> Return strm
>
> End Function
>
> Private Function GetDocumentSource(ByVal doc As mshtml.IHTMLDocument2,
> ByVal resetIsDirty As Boolean) As String
>
> Dim stream As UCOMIStream
>
> Dim ips As IPersistStreamInit
>
> Dim s As String
>
> ips = DirectCast(doc, IPersistStreamInit)
>
> If ips Is Nothing Then
> s = Nothing
> Else
> stream = GetStream(2048)
>
> ' Save the document into the comstream, without clearing the
> IsDirty flag
> ips.Save(stream, resetIsDirty)
>
> s = StreamToString(stream)
> End If
>
> Return s
>
> End Function
>
> Private Function StreamToString(ByVal strm As UCOMIStream) As String
>
> Dim iptr As IntPtr
>
> Dim s As String
>
> GetHGlobalFromStream(strm, iptr)
>
> ' *** THIS IS ODD TOO ***
> ' If the source is the WebBrowser control then Ansi must be used
***
> s = Marshal.PtrToStringAnsi(iptr)
>
> ' If the source is the cloned and modified document then Auto must
> be used ***
> s = Marshal.PtrToStringAuto(iptr)
>
> ' ***
>
> Return s
>
> End Function
> </code>
>
> Having cloned the document, I modify it by inserting some tags into the
body
> element. I then call GetDocumentSource() to get the HTML from the cloned
> document.
>
> However, the HTML that is returned is the original HTML, from the
WebBrowser
> control, and not from the cloned document. I know that the cloned document
> contains the correct HTML because if I execute the following for the
cloned
> document
>
> ?doc.all.tags("html").Item(0).outerhtml
>
> in the command window, I get what I expect in the body element.
>
> Can anyone suggest why this is happening?
>
> I have also highlighted an oddity in function StreamToString(), which I do
> not understand. Why would the encoding of the HTML change between the
> browser and a cloned document?
>
> TIA
>
> Charles
>
>

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