IShellFolder.GetUIObjectsOf fails while accessing un unistatiated object

[Nicola Garone]

Hi all,
here I am again :-( , this turn I'm in trouble with
IShellFolder.GetUIObjectsOf, which raise an exception while accessing an
uninstantiated object (I have Italian version softwares and I litteraly
translate the error, the original error may sound a little different).

I'm using VB.Net, and I need to access ThumbImage extractor, I got
IShellFolder interface object pointing to the Directory where my file is in
(in following code it's named item), I know it' Ok since I can enumerate
contained objects through EnumObjects. Also Pidl is okay since
PathFromPidl(pidl) return a correct value. IntPtr.Zero, 1 and prgf should be
okay too .
So the problem seems to be IUnknown but shouldn't it be an output parameter?
Or It may be interface definition...

(by the way: how to instantiate a com object like IUnknown interface ?)

This is the code

Dim pidlPath As String = PathFromPidl(pidl)

' pidl is a relative pidl, so only the filename portion is relevant
If Path.GetFileName(pidlPath).Equals(Path.GetFileName(file)) Then
ret = True

Dim iUnk As IUnknown
' Try and get the IExtractImage interface:
Dim prgf As UInt32
Dim iidExtractImage As Guid = New
Guid("BB2E617C-0920-11d1-9A0B-00C04FC2D6C1")
item.GetUIObjectOf(IntPtr.Zero, 1, pidl, iidExtractImage, prgf,
iUnk)

'some code
End If

Here is the interface (just the method)

<PreserveSig()> _
Function GetUIObjectOf(ByVal hwndOwner As IntPtr,
<MarshalAs(UnmanagedType.U8)> ByVal cidl As Long, ByRef apidl As IntPtr,
ByVal riid As Guid, ByRef rgfReserved As UInt32, ByRef ppv As IUnknown) As
Int32

What's wrong?

Thanks, Nicola

 

[Mattias Sjögren]

Nicola,

<PreserveSig()> _
Function GetUIObjectOf(ByVal hwndOwner As IntPtr,
<MarshalAs(UnmanagedType.U8)> ByVal cidl As Long, ByRef apidl As IntPtr,
ByVal riid As Guid, ByRef rgfReserved As UInt32, ByRef ppv As IUnknown) As
Int32

What's wrong?

cidl should be an Integer. riid should be passed ByRef.



Mattias