[Qgis-developer] wrapped C/C++ object of type QgsMapRenderer has been deleted

[Radim Blazek]

On Wed, Dec 18, 2013 at 5:27 AM, Martin Dobias <wonder.sk at gmail.com> wrote:
> Hi Radim
>
> I have encountered this problem recently by chance when working on
> multi-threaded rendering. In SIP file for QgsMapCanvas, the
> mapRenderer() has /Transfer/ annotation (see commit 0246816e). The
> annotation has been obviously added to fix some other problem with
> "canvas.mapRenderer().hasCrsTransformEnabled()" idiom. I think the
> root of all evil is the fact that "hasCrsTransformEnabled" is both a
> signal (with one argument) and an ordinary function (no arguments). My
> guess is that SIP probably interprets that combination wrong, it seems
> that this is not a problem with other functions/signals.
>
> In any case, /Transfer/ annotation does not seem right. Maybe
> /KeepReference/ function annotation would solve the problem (I assume
> the python wrapper was getting destroyed too early). Also, having a
> signal and a normal function with the same name also does not feel
> right - but I guess we need to live with it until 3.0.

I have
* changed QgsMapCanvas mapRenderer() /Transfer/ to /KeepReference/
* added signal QgsMapRenderer::hasCrsTransformEnabledChanged()
* deprecated signal QgsMapRenderer::hasCrsTransformEnabled()

Radim

> Regards
> Martin
>
>
> On Tue, Dec 17, 2013 at 3:28 PM, Radim Blazek <radim.blazek at gmail.com> wrote:
>> I have got strange bug report for python plugin, when calling from initGui()
>>    iface.mapCanvas().mapRenderer().hasCrsTransformEnabled()
>> it gives
>>    RuntimeError: wrapped C/C++ object of type QgsMapRenderer has been deleted
>>
>> From C++ code I see that QgisApp mMapCanvas is created in QgisApp
>> constructor and never deleted and QgsMapCanvas mMapRenderer is created
>> in QgsMapCanvas constructor and deleted in QgsMapCanvas destructor. I
>> don't see how it can happen that QgsMapRenderer is deleted.
>>
>> Any clue?
>>
>> Radim
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