IPersistStreamInitInterface

[Onur Buyukcaglar]

Hi,
After reading and applying the following sample/example from Charles Law,
who responded Vibhu Bansal's "createDocumentFromUrl usage in VB.NET /
loading a url using mshtml.createDocumentFromUrl " questions, I have
encountered a problem which I was fail to overcome. The problem is when I
multithreaded the example even though I
set all the variables and the threads to nothing, applications threads are
incresing over and over and at a point the whole screen is bloating with all
empty Internet Explorer Windows. I think I was not able to properly release
/ destroy or dispose these objects after I have finished my job with them.
If anyone has any idea about this situation I would really appreciate for
your help.

Thanks in advance,
Onur Buyukcaglar

PS: I feel that I have to implement IUnknown -> Release on
IPersistStreamInit, but I do not know how to do it in VB.NET.


Sample provided by Charles Law about usage of "CreateDocumentFromUrl in
Vb.Net" as follows.


Imports System.Runtime.InteropServices

<ComVisible(True), ComImport(),
Guid("7FD52380-4E07-101B-AE2D-08002B2EC713"), _
InterfaceTypeAttribute(ComInterfaceType.InterfaceIsIUnknown)> _
Public Interface IPersistStreamInit
' IPersist interface
Sub GetClassID(ByRef pClassID As Guid)

<PreserveSig()> Function IsDirty() As Integer
<PreserveSig()> Function Load(ByVal pstm As UCOMIStream) As Integer
<PreserveSig()> Function Save(ByVal pstm As UCOMIStream, ByVal
ByValfClearDirty As Boolean) As Integer
<PreserveSig()> Function GetSizeMax(<InAttribute(), Out(),
MarshalAs(UnmanagedType.U8)> ByRef pcbSize As Long) As Integer
<PreserveSig()> Function InitNew() As Integer

End Interface


#Region " Imports "

Imports System
Imports System.Windows.Forms
Imports System.Runtime.InteropServices

#End Region

Module Module1

Dim IID_IHTMLElementRender As Guid = New
Guid("3050f669-98b5-11cf-bb82-00aa00bdce0b")

<MTAThread()> _
Sub Main()

Dim objMSHTML As mshtml.HTMLDocument
Dim objDocument As mshtml.IHTMLDocument2
Dim ips As IPersistStreamInit

objMSHTML = New mshtml.HTMLDocument

ips = DirectCast(objMSHTML, IPersistStreamInit)
ips.InitNew()

objDocument = objMSHTML.createDocumentFromUrl("http://www.msn.com",
String.Empty)

Do Until objDocument.readyState = "complete"
Threading.Thread.Sleep(1)
Loop

MessageBox.Show(objDocument.body.outerHTML)

End Sub

End Module

 

[Robin Tucker]

Yes, release is performed with Marshal.ReleaseComObject.

You would be well advised to wrap all of this inside a try/catch block also,
otherwise if your objects throw an exception, the exception will be handled
outside of the local space where they were created. Doing this enables you
to release COM objects even if an exception occurs, ie:

Dim myComObject as SomeCOMObjectReference

Try

myComObject = DoSomethingToGetReferenceToComObject()
.....

Catch Ex as Exception
....
Finally

if not MyObject is nothing then
Marshal.ReleaseCOMObject(MyObject)
end if

End Try

Also, its worth remembering that out of process COM objects will not be
destroyed purely by releasing your references to them. This is a particular
problem with Word Interop, because you must explicitly call "Quit" to remove
the application (Word) from memory. I'm not sure about the browser however.