Bug report #20752

Qgis 3.4.1 crashes when accessing methods of feature

Added by Anja Sen almost 2 years ago. Updated over 1 year ago.

Category:Python bindings / sipify
Affected QGIS version:3.4.1 Regression?:No
Operating System: Easy fix?:No
Pull Request or Patch supplied:No Resolution:
Crashes QGIS or corrupts data:Yes Copied to github as #:28572


I am trying to implement a method to edit features in different geometry type. To start with, I found following example code from the book "BUILDING MAPPING APPLICATIONS WITH QGIS", but it always crashes when I call the method of self.feature in the function canvasMoveEvent. In function canvasPressEvent, it seems to work fine.

I tried to execute the code in a clean profile, but it still crashes. Then I tried with QGIS 2.18 and it worked there. I have attached the report below.

@class MovePointTool(QgsMapToolIdentify):

def init(self, mapCanvas, layer):
QgsMapToolIdentify.__init__(self, mapCanvas)
self.layer = layer
self.dragging = False
self.feature = None
def canvasPressEvent(self, event):
found_features = self.identify(event.x(), event.y(),
[self.layer], self.TopDownAll)
if len(found_features) > 0:
self.dragging = True
self.feature = found_features[0].mFeature
print (self.feature.id())
self.dragging = False
self.feature = None
def canvasMoveEvent(self, event):
if self.dragging and self.feature:
point = self.toLayerCoordinates(self.layer,
geometry = QgsGeometry.fromPointXY(point)
print (self.feature.isValid())
print (self.feature.id())
self.layer.changeGeometry(self.feature.id(), geometry)
def canvasReleaseEvent(self, event):
self.dragging = False
self.feature = None

tool = MovePointTool(iface.mapCanvas(), iface.activeLayer())

Crash Report:

Crash ID: 46eec519cad6876ebf2347eb73a9fc7f3df167fa

Stack Trace

QgsFeature::isValid :
PyInit__core :
PyMethodDef_RawFastCallKeywords :
PyMethodDef_RawFastCallKeywords :
PyEval_EvalFrameDefault :
PyFunction_FastCallDict :
PyMethodDef_RawFastCallDict :
PyObject_Call :
PyInit_sip :
PyInit__gui :
QgsMapCanvas::mouseReleaseEvent :
QWidget::event :
QFrame::event :
QGraphicsView::viewportEvent :
QCoreApplicationPrivate::sendThroughObjectEventFilters :
QApplicationPrivate::notify_helper :
QApplication::notify :
QgsApplication::notify :
QCoreApplication::notifyInternal2 :
QApplicationPrivate::sendMouseEvent :
QSizePolicy::QSizePolicy :
QSizePolicy::QSizePolicy :
QApplicationPrivate::notify_helper :
QApplication::notify :
QgsApplication::notify :
QCoreApplication::notifyInternal2 :
QGuiApplicationPrivate::processMouseEvent :
QWindowSystemInterface::sendWindowSystemEvents :
QEventDispatcherWin32::processEvents :
TranslateMessageEx :
TranslateMessage :
QEventDispatcherWin32::processEvents :
qt_plugin_query_metadata :
QEventLoop::exec :
QCoreApplication::exec :
main :
BaseThreadInitThunk :
RtlUserThreadStart :

QGIS Version: 3.4.1-Madeira
QGIS code revision: 383851c597
Compiled against Qt: 5.11.2
Running against Qt: 5.11.2
Compiled against GDAL: 2.3.2
Running against GDAL: 2.3.2

System Info
CPU Type: x86_64
Kernel Type: winnt
Kernel Version: 6.1.7601


#1 Updated by Giovanni Manghi almost 2 years ago

  • Priority changed from Normal to High
  • Category changed from Editing to Python bindings / sipify

#2 Updated by Hugo Mercier over 1 year ago

Reproduced on 3.4.4

I guess this is because you are storing a reference to a QgsFeature that sometimes no longer exist when you use it.

self.feature = found_features[0].mFeature

Copying the feature seems to fix the problem

self.feature = QgsFeature(found_features[0].mFeature)

#3 Updated by Hugo Mercier over 1 year ago

  • Status changed from Open to Closed

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