[QGIS-Developer] Fw: [ccrook/QGIS-Contour-Plugin] RuntimeError : wrapped C/C++ object of type ContourGeneratorAlgorithm has been deleted (Issue #46)

[Nyall Dawson]

On Mon, 5 Dec 2022 at 07:35, Chris Crook via QGIS-Developer
<qgis-developer at lists.osgeo.org> wrote:
>
> Hi Developers
>
> The contour plugin I have been maintaining seems to occasionally lose the C++ object that its processing algorithm is using.
> In particular this happens when changing settings.
>
> Before I get lost trying to track this through the Python/SWIG bindings and comparing with other processing algorithms I am wondering if this is familiar or you can offer ideas about how to track it down.  It seems either my python object is persisting too long or or the underlying C++ object not long enough, but I'm very unfamiliar with SWIG so any suggestions would be very welcome 🙂

There's a bug in your loadAlgorithms() implementation. In this you
need to create a NEW instance of each algorithm, rather then adding an
instance which has previously been add in an earlier call to
loadAlgorithms().

Ie DON'T do this:

def __init__(self):

    self.algs = [MyAlgorithm()]

def loadAlgorithms(self):
    for alg in self.algs:
        self.addAlgorithm(alg)

Rather do something like this:

def loadAlgorithms(self):
    for alg in [MyAlgorithm()]:
        self.addAlgorithm(alg)

(or alternatively:


def __init__(self):

    self.alg_classes = [MyAlgorithm]

def loadAlgorithms(self):
    for alg_class in self.alg_classes:
        self.addAlgorithm(alg_class())


)

Hope that helps!

Nyall



>
> Thanks
> Chris
> ________________________________
> From: Taras Dubrava <notifications at github.com>
> Sent: 04 December 2022 01:11
> To: ccrook/QGIS-Contour-Plugin <QGIS-Contour-Plugin at noreply.github.com>
> Cc: Subscribed <subscribed at noreply.github.com>
> Subject: [ccrook/QGIS-Contour-Plugin] RuntimeError : wrapped C/C++ object of type ContourGeneratorAlgorithm has been deleted (Issue #46)
>
>
> Every time when I change the background colour in QGIS the following error appears
>
> QGIS 3.28 Firenze
>
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