[QGIS-Developer] QgsLayout.itemById returns wrong object

[Etienne Trimaille]

Is-it possible to remove this function from SIP bindings? According to SIP
version?

It's a common issue, already raised on the mailing list and in plugin issue
trackers.

I'm copy/pasting another message/snippet from Martin which works perfectly:

Not sure if that is related, was just looking into code of a plugin we
use with QGIS 2.18 and there for getting composer items we have this
helper method:

    @staticmethod
    def get_composition_item(comp, item_id, item_class):
        for item in comp.items():
            if isinstance(item, item_class):
                if item.id() == item_id:
                    return item

And you would call it e.g.:
ver_label = self.get_composition_item(self.oview_compn, 'version',
QgsComposerLabel)

Not sure if that is to work around the same problem as you have - I
didn't write that code. And to get composer map items, we use
composition.getComposerMapById(id)

2018-01-24 10:09 GMT+03:00 Nyall Dawson <nyall.dawson at gmail.com>:

> On 23 January 2018 at 22:34, Enrico Ferreguti <enricofer at gmail.com> wrote:
> > I'm trying to programmatically set a QgsLayoutPicture content in QGIS3.0:
> >
> > 1) I create a new print composition and I name it 'test'
> > 2) I create a picture frame in the composition and I call it 'picture'
> > 3) I run the following code:
> >
> > from qgis.core import QgsProject
> > myLayout = QgsProject.instance().layoutManager().layoutByName('test')
> > myLayoutPicture = myLayout.itemById("picture")
> > myLayoutPicture.setPicturePath("path to an image")
> >
> > and I get the following Exception:
> > AttributeError: 'QgsLayoutItem' object has no attribute 'setPicturePath'
> >
> > If I inspect myLayoutPicture object I found it is a
> qgis._core.QgsLayoutItem
> > not a QgsLayoutPicture
> >
> > Is this a correct behaviour or is it an issue? How can I get the right
> > Layout object?
>
> This became an issue after a certain sip version. It affects QGIS 2.x
> also, and seems to be caused by sip being unable to automatically cast
> classes which use multiple inheritance (like QgsComposerItem,
> QgsLayoutItem). The consequence is that Python is only aware of the
> base class, not the actual item subclass.
>
> I can't find anyway to fix this properly. So I hack around by forcing
> sip to manually cast to the correct item type, e.g. by inserting two
> lines* which look like this:
>
>         # screw you sip, I'll just manually cast
>         real_item = sip.cast(item, QgsLayoutItemPicture)
>
> It's not pretty, but it works...
>
> Nyall
>
> * the first line is critical for the fix to work correctly
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