RE: [ctypes-users] ctypes.com

[Stefan S. <SSc...@ds...>]

> -----Original Message-----
> From: Thomas Heller [mailto:th...@py...]
> "Stefan Schukat" <SSc...@ds...> writes:
>=20
> >> > 4.  Properties with multiple signatures
> >> >
> >> > I've seen a couple of cases where interfaces have both a
> >> > _put_Property() and _putREF_Property()
> >> >
> >> > I think this can be coped with without much trouble, but note it=20
> >> > for reference.
> >>=20
> >> I have no idea about the difference between a propput and a=20
> >> propputref -
> >> can someone explain why a COM object would implement both?
> >
> > This is a VB helper for properties which expose objects.
> > You could write=20
> >
> > Window.Caption =3D "Text"
> >
> > which is internally translated to=20
> >
> > Window.Caption.Value =3D "Text" // calls propput method
> >
> > if value is the default property (DISPID=3D0) of the Caption=20
> interface.
> > If you want to set the Caption Object, e.g.
> >
> > Window.Caption =3D Caption =20
> >
> > you have to write
> >
> > Set Window.Caption =3D Caption // calls propputref method
> >
> > which exchanges the caption object. Therefore in pywin32 an extra
> > method SetCaption is generated in addition to the Caption=20
> put/get property
> > entries. This could lead to errors if the "SetCaption"=20
> method already
> > exists, but that is a rare case.
> >
> >
> > 	Stefan
> Stefan,  thanks for this explanation.
>=20
> I've scanned a few typelibs, and most of them, if they have proputref,
> don't have propput for the same property. And they have a COM=20
> interface
> pointer as parameter in this case.
> The IDictionary::Item, in windows\system32\scrrun.dll on XP Pro, is
> different.  It has this (thats what oleview disassembles):
>=20
>     interface IDictionary : IDispatch {
>         [id(00000000), propputref, helpstring("Set or get the=20
> item for a given key"),
> helpcontext(0x00214b3a)]
>         HRESULT Item(
>                         [in] VARIANT* Key,=20
>                         [in] VARIANT* pRetItem);
>         [id(00000000), propput, helpstring("Set or get the=20
> item for a given key"),
> helpcontext(0x00214b3a)]
>         HRESULT Item(
>                         [in] VARIANT* Key,=20
>                         [in] VARIANT* pRetItem);
>         [id(00000000), propget, helpstring("Set or get the=20
> item for a given key"),
> helpcontext(0x00214b3a)]
>         HRESULT Item(
>                         [in] VARIANT* Key,=20
>                         [out, retval] VARIANT* pRetItem);
>=20
> So, there are propputref, propput, and propget on the Item property.
> propput and propputref take exactly the same parameter types=20
> - would there
> be any difference in what happens when you call them?
>=20
> Thomas

As described above the internal IDispatch implementation would forward =
the call=20
to the default value of the interface, i.e. in pseudo code

if wflags =3D=3D DISPATCH_PROPERYPUT:
	if RetItem.vt =3D=3D VT_DISPATCH:
		InternalItemList[Key].DefaultValue =3D RetItem.DefaultValue
	else:
		InternalItemList[Key].DefaultValue =3D RetItem
if wflags =3D=3D DISPATCH_PROPERYPUTREF:
	if RetItem.vt =3D=3D VT_DISPATCH:
		InternalItemList[Key] =3D RetItem


	Stefan