Re: UCOMIStream, MSHTML and WebBrowser control Persistence Problem

From: Charles Law (blank_at_nowhere.com)
Date: 03/17/04 

Date: Wed, 17 Mar 2004 07:49:42 -0000

Ken

Unfortunately, I cannot get your example to run. Firstly, I get an 'object
variable not set' error when trying to access AxWebBrowser1.Document. I
would always recommend a navigate to "about:blank" before anything else,
even if you go on to navigate somewhere else afterwards. In ensures that the
control is properly initialised.

After adding the extra navigate to the form load, I get an 'Unknown error'
in mscorlib when trying to run the script. Is there any other code missed
out?

Also, just as an aside, you may prefer to turn Option Strict On, to ensure
that all calls and bindings are correct.

HTH

Charles

"Ken Hanson" <khanson@capstonetechnology.com> wrote in message
news:OLxmfR9CEHA.3472@TK2MSFTNGP09.phx.gbl...
> Charles,
>
> I can recreate the problem very easily:
>
> Create a simple vb winform app with two forms, the first form will
> showdialog the second from from a command button. The second form has the
> followng load event
>
>
AxWebBrowser1.Navigate2("C:\Capstone\Applications\TestApp\WindowsApplication
> 1\test.htm")
>
> Do While AxWebBrowser1.ReadyState <>
> SHDocVw.tagREADYSTATE.READYSTATE_COMPLETE
>
> Application.DoEvents()
>
> Loop
>
> Call AxWebBrowser1.Document.Script.evaluate(0.5)
>
> --------------------------------
>
> The test.htm file contains the following:
>
> <HTML>
> <HEAD>
> <TITLE>Evaluate</TITLE>
>
> <SCRIPT>
> function evaluate(x)
> {
> alert("hello")
> return eval(x)
> }
> </SCRIPT>
> </HEAD>
>
> <BODY>
> </BODY>
> </HTML>
>
> The dialog form will work once, Close and re-open, the second time it is
> instantiated the call to evaluate fails. I will be calling Microsoft
> tommorow.
>
> - Ken
>
> "Ken Hanson" <khanson@capstonetechnology.com> wrote in message
> news:O41u5N8CEHA.1812@TK2MSFTNGP12.phx.gbl...
> > Charles,
> >
> > Actually I had chopped off the top of the Form Load script which
correctly
> > did the navigate. As it turns out the problem does not seem to have
> > anything to do with loading from a stream. If I navigate to a file
> > containing the html directly instead of loading from a stream I get the
> same
> > behaivour.
> >
> > Basically I can call into the DHTML only after the first navigate, if
the
> > web control is disposed and the form is released (but the app still runs
> of
> > course) and the the form and webbrowser is re-instantiated and navigates
> to
> > the same html I cannot call into the same dhtml script function.
> Something
> > must be left hanging around but I can't figure out what it is.
> >
> > If you have any thoughts please let me know. I may play around with a
> > simpler dhtml sample to see if it has something to do with my script,
> > however in vb6 calling the same dhtml function gives me no problems. I
am
> > beginning to suspect there is something broken in the interop regarding
> > support for this type script calling.
> >
> > Thanks for all your help.
> >
> > - Ken
> >
> > Call WebBrowser1.Script.PopupDrawXYPlot(strXMLData, lngCurveFitStyles)
> >
> > Works once on first instance, after second time the WebBrowser is
> > instantiated it fails, saying it is unable to find PopupDrawXYPlot, even
> > though the innerHTML of the document shows it has loaded correctly.
> >
> >
> >
> >
> > "Charles Law" <blank@nowhere.com> wrote in message
> > news:utl18A7CEHA.2888@TK2MSFTNGP09.phx.gbl...
> > > Ken
> > >
> > > Although probably not the problem, it looks like you might be caching
> the
> > > document object. It is best to retrieve it from the control each time
> you
> > > need a reference.
> > >
> > > When you talk about 'dialog form unload', do you mean that you close
the
> > > form that hosts the browser control and then re-open it? The browser
> > control
> > > needs to be disposed explicitly, so you should have a call to Dispose
> when
> > > you close the form.
> > >
> > > You say that objects are not available on subsequent occasions. Do you
> get
> > > an error? When you load the form, I do not see a
> Navigate("about:blank").
> > > This is required to initialise the control before you do anything
else,
> > and
> > > then you must wait for DocumentComplete (readyState = "complete")
before
> > you
> > > continue.
> > >
> > > HTH
> > >
> > > Charles
> > >
> > >
> > > "Ken Hanson" <khanson@capstonetechnology.com> wrote in message
> > > news:eTyO2t6CEHA.2800@tk2msftngp13.phx.gbl...
> > > > Charles,
> > > >
> > > > Thanks for the advice. Per your suggestion I moved the load from
> stream
> > > > logic to the form load event and it worked great. After looking a
> > little
> > > > closer I saw that the C++ example that Microsoft shows avoids the
> infite
> > > > event firing loop by checking the interface pointer of the document
to
> > > make
> > > > sure it is the one you want, this is difficult to do in .NET and not
> > worth
> > > > the effort since it works as seen below.
> > > >
> > > > Unfortantely I Now I have a new problem. It appears that I can only
> > load
> > > > once from the stream. If I let the dialog form unload and release
> > object
> > > > accordingly a second attempt at loading the document seems to
succeed
> > but
> > > > objects in the document are not available as they were the first
time.
> > > >
> > > > Are you familiar with any thing I need to explicity clean up to
avoid
> > > > confusing COM/WebBrowser interface?
> > > >
> > > > Thanks much for your help.
> > > >
> > > > - Ken
> > > >
> > > > In Form load:
> > > >
> > > > objDocument = WebBrowser1.Document
> > > >
> > > > strHTML = objSR.ReadToEnd()
> > > >
> > > > hGlobal = Marshal.StringToHGlobalAnsi(strHTML)
> > > >
> > > > CreateStreamOnHGlobal(hGlobal, True, strm)
> > > >
> > > > objPersistStreamInit = DirectCast(objDocument, IPersistStreamInit)
> > > >
> > > > objPersistStreamInit.InitNew()
> > > >
> > > > objPersistStreamInit.Load(strm)
> > > >
> > > > Do While WebBrowser1.ReadyState <> tagREADYSTATE.READYSTATE_COMPLETE

> > > >
> > > > Application.DoEvents()
> > > >
> > > > Loop
> > > >
> > > > objDocument = WebBrowser1.Document
> > > >
> > > > ...
> > > >
> > > > Subsequent call to vbscript function in document, works once, does
not
> > > work
> > > > on subsequent doucment loads?
> > > >
> > > > Call objDocument.Script.PopupDrawXYPlot(strXMLData,
lngCurveFitStyles)
> > > >
> > > >
> > > > "Charles Law" <blank@nowhere.com> wrote in message
> > > > news:OWLSze6CEHA.2628@TK2MSFTNGP11.phx.gbl...
> > > > > Hi Ken
> > > > >
> > > > > It looks to me that your technique is correct. The problem, I
> suspect,
> > > is
> > > > > where you load the document from the stream. Since documents are
> > loaded
> > > > > asynchronously, the logic of the load process is
> > > > >
> > > > > 1. Put html into stream
> > > > > 2. Load document from stream
> > > > > 3. Wait for operation to complete
> > > > > 4. Continue ...
> > > > >
> > > > > Step 3 means waiting for the readyState to become 'complete', and
> when
> > > > that
> > > > > happens the DocumentComplete event fires. As you are loading the
> > > document
> > > > in
> > > > > the DocumentComplete event, you will get into a continuous loop.
> > > > >
> > > > > I would suggest that you either load the document outside the
> > > > > DocumentComplete event (preferred), or set a flag in the event,
> before
> > > you
> > > > > load, to say that you are currently loading. This way you can
avoid
> > > > > reloading the document.
> > > > >
> > > > > The preferred way would be to wait for the browser initialisation
to
> > > > > complete (that is, it finishes navigating to about:blank, which
you
> > must
> > > > > instruct it to do), and then load the document, waiting for
> readyState
> > > > > before continuing
> > > > >
> > > > > HTH
> > > > >
> > > > > Charles
> > > > >
> > > > >
> > > > > "Ken Hanson" <khanson@capstonetechnology.com> wrote in message
> > > > > news:%23cYb7l4CEHA.1604@TK2MSFTNGP11.phx.gbl...
> > > > > > 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
> > > > > > >
> > > > > > >
> > > > > >
> > > > > >
> > > > >
> > > > >
> > > >
> > > >
> > >
> > >
> >
> >
>
>