MSXML vb.net: Using MSHTML and IPersistStreamInit to load documents from memory

The basic code to load any string and convert it into a DOM tree which you can easily manipulate using VB.net or C#. Once you load the HTML code you can use getElementById and other functions to manipulate the document.This code can be used to parse a HTML document in VB.net

  Private Function LoadHTML(ByVal value As String) As MSHTML.HTMLDocument
        Dim clsDocument As New MSHTML.HTMLDocument
        clsDocument.createDocumentFromUrl("about:blank", vbNullString)
        DirectCast(clsDocument, IPersistStreamInit).InitNew()
        Dim ptrValue As IntPtr = System.Runtime.InteropServices.Marshal.StringToHGlobalAuto(value)
        Dim clsStream As System.Runtime.InteropServices.ComTypes.IStream = Nothing
        CreateStreamOnHGlobal(ptrValue, True, clsStream)
        ' load the content into the browser..
        DirectCast(clsDocument, IPersistStreamInit).Load(clsStream)
        Return clsDocument
    End Function

You also need to add the following code to the class you are going to use LoadHTML function.

Import System.Runtime.InteropServices
    Public Enum HRESULT
        S_OK = 0
        S_FALSE = 1
        E_NOTIMPL = &H80004001
        E_INVALIDARG = &H80070057
        E_NOINTERFACE = &H80004002
        E_FAIL = &H80004005
        E_UNEXPECTED = &H8000FFFF
    End Enum
    <ComVisible(True), ComImport(), Guid("7FD52380-4E07-101B-AE2D-08002B2EC713"), _
        InterfaceTypeAttribute(ComInterfaceType.InterfaceIsIUnknown)> _
    Public Interface IPersistStreamInit : Inherits IPersist
        Shadows Sub GetClassID(ByRef pClassID As Guid)
        <PreserveSig()> Function IsDirty() As Integer
        <PreserveSig()> Function Load(ByVal pstm As ComTypes.IStream) As HRESULT
        <PreserveSig()> Function Save(ByVal pstm As ComTypes.IStream, _
            <MarshalAs(UnmanagedType.Bool)> ByVal fClearDirty As Boolean) As HRESULT
        <PreserveSig()> Function GetSizeMax(<InAttribute(), Out(), _
        MarshalAs(UnmanagedType.U8)> ByRef pcbSize As Long) As HRESULT
        <PreserveSig()> Function InitNew() As HRESULT
    End Interface

    <ComVisible(True), ComImport(), Guid("0000010c-0000-0000-C000-000000000046"), _
        InterfaceTypeAttribute(ComInterfaceType.InterfaceIsIUnknown)> _
    Public Interface IPersist
        Sub GetClassID(ByRef pClassID As Guid)
    End Interface

    Declare Function CreateStreamOnHGlobal Lib "ole32" (ByVal hGlobal As IntPtr, ByVal fDeleteOnRelease As Boolean, ByRef ppstm As UCOMIStream) As Long
   

I got the basic idea from Balaji's blog which he got inturn from sp!ke. This code has been slightly modified to work in Visual Studio 2005.

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