Using MSHTML.IHTMLElementRender from VB

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Garett - 25 Feb 2008 19:18 GMT

Hi,

I am getting a type mismatch error when attempting to use the
IHTMLElementRender inteface from VB6. I noticed that this interface does not
implement IDispatch, just IUnknown. Does this have something to do with it?

Also, I had to create a type library with the IHTMLElementRender::DrawToDC
definition, which accepts a long, because the definition that is provided
with the MSHTML type library uses a parameter type called RemoteHandle,
which VB does not recognize. In this type library I inherited from
stdole.IUnknown instead. Could this be a problem? Thanks in advanced for all
the help.

Sample code is provided below:

Type library definitions:

typedef LONG HDC;

[
odl,
uuid(3050F669-98B5-11CF-BB82-00AA00BDCE0B)
]
interface IHTMLElementRender : stdole.IUnknown {
HRESULT DrawToDC([in] HDC hdc);
HRESULT SetDocumentPrinter(
[in] BSTR bstrPrinterName,
[in] HDC hdc);
};

VB Code:

Public Function CreateWebPageImage() As Object
Dim lErrorNum As Long
Dim sSource As String
Dim sDescription As String

Dim pDocument As MSHTML.IHTMLDocument2
Dim pBody As MSHTML.IHTMLElement2
Dim pRender As cptsoleapi.IHTMLElementRender ' type library containing
new definition of IHTMLElementRender
Dim hwndBrowser As Long

On Error GoTo ERROR_HANDLER

Set pDocument = Parent.Script.document
Set pBody = pDocument.body

'hwndBrowser = GetBrowserWindow()

'Call LockWindowUpdate(hwndBrowser)

'Call GetBodyElement(pBody)

If Not pBody Is Nothing Then
Set pRender = pBody ' This causes a type mismatch error

End If

CLEAN_UP:
On Error Resume Next

If lErrorNum <> 0 Then
On Error GoTo 0

Call Err.Raise(lErrorNum, sSource, sDescription)
End If

' unlock window
'Call LockWindowUpdate(0)

Exit Function
ERROR_HANDLER:
lErrorNum = Err.Number
sSource = Err.Source
sDescription = Err.Description

Resume CLEAN_UP
End Function

Regards,

Garett

Reply to this Message

Anthony Jones - 26 Feb 2008 12:06 GMT

> Hi,
>
[quoted text clipped - 75 lines]
> Resume CLEAN_UP
> End Function

The fact that IHTMLElementRender derives from IUnknown would not cause a
type mismatch. However,according mshtml.tlb HTMLbody doesn't implement
IHTMLElementRender, in which case that would cause a type mismatch.

Signature

Anthony Jones - MVP ASP/ASP.NET

Reply to this Message

Garett - 26 Feb 2008 14:00 GMT

Hi Anthony,

Thanks for the reply. You are correct, I looked at mshtml.tlb and I realized
this, but now I'm a little confused. There are quite a few examples out
there, written in other languages admittedly, that use a similar approach as
I am attempting. For example,

http://www.codeproject.com/KB/IP/htmlimagecapture.aspx?msg=783507
http://www.developerfusion.co.uk/show/4712/
http://blogs.msdn.com/rfarber/archive/2004/10/12/240943.aspx
http://www.delphipages.com/tips/thread.cfm?ID=292&SR=html

Maybe there some subletly in these approaches that I am missing? Maybe I
need to navigate the DOM from the IWebBrowser2 interface? Thanks again from
the response.

Regards,

Garett

>> Hi,
>>
[quoted text clipped - 84 lines]
> type mismatch. However,according mshtml.tlb HTMLbody doesn't implement
> IHTMLElementRender, in which case that would cause a type mismatch.

Reply to this Message

Anthony Jones - 28 Feb 2008 08:32 GMT

> Hi Anthony,
>
[quoted text clipped - 7 lines]
> http://blogs.msdn.com/rfarber/archive/2004/10/12/240943.aspx
> http://www.delphipages.com/tips/thread.cfm?ID=292&SR=html

I see. It is possible for QueryInterface to respond positively to a request
for an interface that isn't listed in the type library. From those articles
it does look like it ought to work.

> Maybe there some subletly in these approaches that I am missing? Maybe I
> need to navigate the DOM from the IWebBrowser2 interface? Thanks again from
> the response.

Signature

Anthony Jones - MVP ASP/ASP.NET

Reply to this Message

Ajay Porwal - 14 Apr 2008 15:31 GMT

Hi, I am trying to convert html text into an image, below is my code:

using System;
using System.Collections.Generic;
using System.Text;
using mshtml;
using System.Drawing;
using System.Runtime.InteropServices;
using System.Drawing.Imaging;
using SHDocVw;
namespace WhiteHallClasses
{
[
Guid("3050f669-98b5-11cf-bb82-00aa00bdce0b"),
InterfaceTypeAttribute(ComInterfaceType.InterfaceIsIUnknown),
ComVisible(true),
ComImport
]
interface IHTMLElementRender
{
void DrawToDC([In] IntPtr hDC);
void SetDocumentPrinter([In, MarshalAs(UnmanagedType.BStr)] string bstrPrinterName, [In] IntPtr hDC);
};

public class Class1
{

public void Draw()
{

HTMLDocumentClass hc = new HTMLDocumentClass();

IHTMLBodyElement b = (IHTMLBodyElement)hc.createElement("body");

b.text = "<b>Hi</b>";

IHTMLElementRender render = (IHTMLElementRender)b;

Bitmap oCanvas = new Bitmap(850, 1100);
Graphics g = Graphics.FromImage(oCanvas);
g.FillRectangle(System.Drawing.Brushes.Bisque, 0, 0, 850, 1100);
g.Clear(Color.BurlyWood);
IntPtr memDC = g.GetHdc();
render.DrawToDC(memDC);

string TempBlankPage = "c:\\" + System.Guid.NewGuid().ToString() + "BlankPage.tif";
oCanvas.Save(TempBlankPage, ImageFormat.Tiff);

g.Dispose();
oCanvas.Dispose();
}

}
}

I am getting the exception on line
IHTMLElementRender render = (IHTMLElementRender)b;

The exception detail is as below:

Unable to cast COM object of type 'mshtml.HTMLBodyClass' to interface type 'WhiteHallClasses.IHTMLElementRender'. This operation failed because the QueryInterface call on the COM component for the interface with IID '{3050F669-98B5-11CF-BB82-00AA00BDCE0B}' failed due to the following error: No such interface supported (Exception from HRESULT: 0x80004002 (E_NOINTERFACE)).

Could you please me, what's wrong in my sample code. I refered many articles and forums but no luck till now.....

Reply to this Message

Ralph - 14 Apr 2008 15:48 GMT

> Hi, I am trying to convert html text into an image, below is my code:
>
[quoted text clipped - 7 lines]
> using SHDocVw;
> namespace WhiteHallClasses

You need to post to a dotNet newsgroup. This newsgroup is for classic VB
(VB6 and lower) and COM. Your question has nothing to do with any of that.

-ralph

Reply to this Message

Ajay Porwal - 14 Apr 2008 15:34 GMT

Reply to this Message

Anthony Jones - 19 Apr 2008 21:30 GMT

> Hi, I am trying to convert html text into an image, below is my code:
>
[quoted text clipped - 57 lines]
>
> Unable to cast COM object of type 'mshtml.HTMLBodyClass' to interface type 'WhiteHallClasses.IHTMLElementRender'. This operation failed because the

QueryInterface call on the COM component for the interface with IID
'{3050F669-98B5-11CF-BB82-00AA00BDCE0B}' failed due to the following error:
No such interface supported (Exception from HRESULT: 0x80004002
(E_NOINTERFACE)).

> Could you please me, what's wrong in my sample code. I refered many articles and forums but no luck till now.....

We'll it has me stumped as to how that previous set of references ever
worked. Clearly the code is making a QI call for the correct interface and
is being told its not implemented. This fact is backed up by the content of
the mshtml.tlb indicates that the Body doesn't implement this interface.

It doesn't help you're using C#. Perhaps the best place for this question
is microsoft.public.dotnet.framework.interop. There you should find people
who are doing C# to COM library stuff a lot and they'll like have a better
insight.

Signature

Anthony Jones - MVP ASP/ASP.NET

Reply to this Message

Ryan - 27 Aug 2008 18:23 GMT

You can host System.Windows.Forms.WebBrowser in a form to get to IHTMLElementRender.

// method 1
IWebBrowser2 browser2 = ((IWebBrowser2)Browser.ActiveXInstance);
IHTMLDocument3 doc3 = (IHTMLDocument3)browser2.Document;
IHTMLElement element = (IHTMLElement)doc3.documentElement;
IHTMLElementRender render = (IHTMLElementRender)element;

// method 2
IHTMLDocument2 doc2 = (IHTMLDocument2)browser2.Document;
IHTMLElement doc2Element = (IHTMLElement)doc2.body;
IHTMLElementRender doc2Render = (IHTMLElementRender)doc2Element;

// method 3 (frameset, code not verified)
IHTMLElementCollection elementColl = (IHTMLElementCollection) doc3.getElementsByTagName("FRAMESET");
IHTMLElement framesetElement = (IHTMLElement) elementColl.item(0, 0);
IHTMLElementRender framesetRender = (IHTMLElementRender) framesetElement;

Reply to this Message

Ryan S - 27 Aug 2008 18:28 GMT

You can host System.Windows.Forms.WebBrowser in a form to get to
IHTMLElementRender.

// method 1
IWebBrowser2 browser2 = ((IWebBrowser2)Browser.ActiveXInstance);
IHTMLDocument3 doc3 = (IHTMLDocument3)browser2.Document;
IHTMLElement element = (IHTMLElement)doc3.documentElement;
IHTMLElementRender render = (IHTMLElementRender)element;

// method 2
IHTMLDocument2 doc2 = (IHTMLDocument2)browser2.Document;
IHTMLElement doc2Element = (IHTMLElement)doc2.body;
IHTMLElementRender doc2Render = (IHTMLElementRender)doc2Element;

// method 3 (frameset, code not verified)
IHTMLElementCollection elementColl = (IHTMLElementCollection)
doc3.getElementsByTagName("FRAMESET");
IHTMLElement framesetElement = (IHTMLElement) elementColl.item(0, 0);
IHTMLElementRender framesetRender = (IHTMLElementRender)
framesetElement;

Reply to this Message

Tony Proctor - 29 Aug 2008 11:10 GMT

This is not a VB.Net newsgroup Ryan. It's for versions of VB up to and not
including the VB.Net.

The "com" in the newsgroup name must have been a clue, eh? :-)

Tony Proctor

> You can host System.Windows.Forms.WebBrowser in a form to get to
> IHTMLElementRender.
[quoted text clipped - 18 lines]
>
> *** Sent via Developersdex http://www.developersdex.com ***

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VB Forum / COM / August 2008

Using MSHTML.IHTMLElementRender from VB