Mike Krell schrieb:
> I'm running 0.6.0 under Python 2.6. Source code:
>
> ***********************************************************************
>
> from comtypes import *
> from comtypes.client import *
> import comtypes.gen.iTunesLib
>
> itunes = CreateObject("iTunes.Application")
> librarySource = itunes.LibrarySource
> playListCollection = librarySource.Playlists
> userPlayList = playListCollection.ItemByName("My Test PlayList")
>
> if userPlayList is None:
> userPlayList = itunes.CreatePlaylist("My Test PlayList")
>
> print userPlayList
>
> u2 = cast(userPlayList, POINTER(comtypes.gen.iTunesLib.IITUserPlaylist))
>
> print u2
>
> u2.Reveal()
>
> ***********************************************************************
>
> This fails with the following output:
>
> <POINTER(IITPlaylist) ptr=0x2a5a24 at 1ee1940>
> <POINTER(IITUserPlaylist) ptr=0x2a5a24 at 1ee18a0>
> ---------------------------------------------------------------------------
> WindowsError Traceback (most recent call last)
>
> e:\projects\Python\FetchAudio\aftp.py in <module>()
> 49 print u2
> 50
> ---> 51 u2.Reveal()
> 52
>
> WindowsError: exception: access violation reading 0x00000000
>
>
> ***********************************************************************
>
>
> I'm trying to do something equivalent the following, which works using
> win32com.client:
> u2 = win32com.client.CastTo(userPlayList, 'IITUserPlaylist')
>
> It's as if the downcast is failing. Please advise.
You should not use ctypes.cast with COM pointers.
Use QueryInterface(interface) instead:
> print userPlayList
>
> u2 = userPlayList.QueryInterface(comtypes.gen.iTunesLib.IITUserPlaylist)
>
> print u2
>
> u2.Reveal()
It is a bit unfortunate that win32com uses the name CastTo() for the same thing.
--
Thanks,
Thomas
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