Adding QPixmap item to QGraphicsScene using QGraphicsScene::addItem crashes PySide

Question

I am trying to add an image to a QGraphicsView/QGraphicsScene so later I can paint simple geometries on it based on user's input. I need to make sure that the image fits in QGraphicsView regardless of its aspect ratio. And to do that I am using QGraphicsView::fitInView

Working Version:

I can add, display and fit the image successfully if I use QGraphicsScene::addPixmap

from PySide import QtGui
import sys
app = QtGui.QApplication(sys.argv)

scn = QtGui.QGraphicsScene()
view = QtGui.QGraphicsView(scn)

pixmap = QtGui.QPixmap("image.png")
gfxPixItem = scn.addPixmap(pixmap)

view.fitInView(gfxPixItem)
view.show()

sys.exit(app.exec_())

Non-Working Version:

However if instead of using QGraphicsScene::addPixmap, I first create a QGraphicsPixmapItem and add it to the scene using QGraphicsScene::addItem I get a segfault!

from PySide import QtGui
import sys

app = QtGui.QApplication(sys.argv)
scn = QtGui.QGraphicsScene()
view = QtGui.QGraphicsView(scn)

pixmap = QtGui.QPixmap("image.png")
pixItem = QtGui.QGraphicsPixmapItem(pixmap)
gfxPixItem = scn.addItem(pixItem)

view.fitInView(gfxPixItem) # Crashes, see below for call stack in OSX
view.show()

sys.exit(app.exec_())

I tried this on OSX as well as Linux with the same result. What I am doing wrong here?

The reason I need the second approach is so that I can sub-class QGraphicsPixmapItem to reimplement mouseEvent functions.

---

This is the thread that crashes:

0   QtGui               0x000000011073bb52 QGraphicsItem::isClipped() const + 4
1   QtGui               0x0000000110779ad6 QGraphicsView::fitInView(QGraphicsItem const*, Qt::AspectRatioMode) + 32
2   QtGui.so            0x000000010f72333d Sbk_QGraphicsViewFunc_fitInView + 1153
3   org.python.python   0x000000010f2895a9 PyEval_EvalFrameEx + 9244
4   org.python.python   0x000000010f287147 PyEval_EvalCodeEx + 1934
5   org.python.python   0x000000010f2869b3 PyEval_EvalCode + 54
6   org.python.python   0x000000010f2c2c70 0x10f270000 + 339056
7   org.python.python   0x000000010f2c2d3c PyRun_FileExFlags + 165
8   org.python.python   0x000000010f2c2726 PyRun_SimpleFileExFlags + 410
9   org.python.python   0x000000010f2e6e27 Py_Main + 2715
10  libdyld.dylib       0x00007fff861b47e1 start + 1

Answer 1

QGraphicsScene::addItem(QGraphicsItem *item) returns void, so gfxPixItem is None. When you try to call view.fitInView(None), it causes the crash.

Corrected code:

pixmap = QtGui.QPixmap("image.png")
pixItem = QtGui.QGraphicsPixmapItem(pixmap)
scn.addItem(pixItem)
view.fitInView(pixItem)