[Qgis-developer] QgsRubberBand RuntimeError: underlying C/C++ object has been deleted

[Radim Blazek]

On Wed, Feb 12, 2014 at 2:50 PM, Martin Dobias <wonder.sk at gmail.com> wrote:
> Hi Radim
>
> On Wed, Feb 12, 2014 at 8:03 PM, Radim Blazek <radim.blazek at gmail.com> wrote:
>> On Wed, Feb 12, 2014 at 1:45 PM, Radim Blazek <radim.blazek at gmail.com> wrote:
>>> I am using rubber band in Python plugin:
>>>   self.rb = QgsRubberBand(self.canvas,  QGis.Polygon)
>>> and on mouse move
>>>   self.rb.addPoint( point, update )
>>>
>>> It works well on most systems only for Win7/32bit (QGIS 2.0.1, Python
>>> 2.7.4) it was reported that it fails with "RuntimeError: underlying
>>> C/C++ object has been deleted"
>
> When does it report the error - when closing QGIS?

I don't know but I presume when map tool is used, it is called from
QgsMapTool::canvasMoveEvent().

Radim

>>> I see that ownership of rubber band is passed to map canvas
>>>
>>>    QgsRubberBand( QgsMapCanvas* mapCanvas /TransferThis/,
>>> QGis::GeometryType geometryType = QGis::Line );
>>>
>>> that is OK, but QgsMapCanvas should not delete QGraphicsItem until it
>>> is destructed.
>>>
>>> So how can the QgsRubberBand be deleted before QGIS is closed?
>>
>> BTW, because true owner of QGraphicsItem is QGraphicsScene, should not
>> we first mScene->removeItem() (which returns ownership) before item is
>> deleted in QgsMapCanvas destructor?
>
> That's the correct approach in Python (IIRC). You can remove the item
> in your map tool's deactivate() method.
>
> Regards
> Martin