Nick Collier wrote:
> I'm working with some ESRI com libraries. I've managed to retrieve an
> ILayer from an IMap and then cast IFeatureLayer from the ILayer.
>
> fc = layer.QueryInterface(comtypes.gen.esriGeoDatabase.IFeatureLayer)
>
> I don't have much experience at all with COM and what's confusing me
> now is difference between methods and properties as they are seen by
> comtypes. I can do
>
> feature.DataSourceType
>
> and get:
>
> u'Personal Geodatabase Feature Class'
Under the hood, COM properties are methods. VB just wraps the method
calls for you. So in a TLB there are both _get* (read) and _put*
(write) prefixed methods for each property as declared in the TLB.
_putREF* methods are a variant of _put* methods which are exclusively
used for passing interface pointers instead of simple values. I get the
distinct impression that ESRI's use of _putREF* is different from a lot
of other vendors...
I've not used comtypes as it currently exists, but from the snippet:
> (<class 'ctypes.HRESULT'>, '_get_FeatureClass', (<class
> 'ctypes.LP_POINTER(IFeatureClass)'>,), ((10, 'fclass'),), ('propget',
> u"The layer's feature class."), u" The layer's feature class.")
>
> (<class 'ctypes.HRESULT'>, 'FeatureClass', (<class 'comtypes.POINTER
> (IFeatureClass)'>,), ((1, 'fclass'),), ('propputref', u"The layer's
> feature class."), u"The layer's feature class.")
... the FeatureClass method is the property put, so you must use
_get_FeatureClass() to retrieve the IFeatureClass you seek.
I'm not sure why Thomas chose to drop the "_put_" prefix from such
propputref methods, but the following snippet:
> (<class 'ctypes.HRESULT'>, '_get_DataSourceType', (<class
> 'ctypes.LP_BSTR'>,), ((10, 'Text'),), ('propget', u'Data source
> type.'), u'Data source type.')
>
> (<class 'ctypes.HRESULT'>, '_set_DataSourceType', (<class
> 'comtypes.BSTR'>,), ((1, 'Text'),), ('propput', u'Data source type.'),
> u'Data source type.')
... is a the more common _get/_put method pair for simple properties.
The fact that this a propputref may be throwing the translation code,
resulting in it being treated as a method rather than a property.
I'm still using the COM support in ctypes 0.6.3 (positively ancient!)
and have built a wrapper layer making it more VB like on top. However
it's a hand built wrapping which I extend every time I need a new
coclass or interface. At some point I'll get my boss to agree to
updating... but for the time being it works well.
> FeatureClass is read-only. Would that have anything to do with it?
Not according to my 8.3 ArcObjects docco.
-------------------------> "These thoughts are mine alone!" <---------
Andrew MacIntyre National Licensing and Allocations Branch
tel: +61 2 6219 5356 Inputs to Industry Division
fax: +61 2 6253 3277 Australian Communications & Media Authority
email: [EMAIL PROTECTED]
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