QML ListView and Segmentation fault - c++

Question

I'm using a QML ListView with a SectionScroller & QAbstractListModel. I noticed that I get a segmentation fault in memcpy (never called explicitly) when I'm normally scrolling (without usage of SectionScroller)
Do you have any idea why it's happening?
I tried to reproduce it, and now the segmentation fault is
0x402f9c3a in ?? () from /usr/lib/libQtScript.so.4
0x402f9c3a: ldrh r1, [r7, r3]
The debug symbols are there, though no valuable info is dumped. The other time the Segfault was
0x0000cab8 in QBasicAtomicInt::ref (this=0x0)
at /usr/include/QtCore/qatomic_armv6.h: 119
It's strange since AFAIK N900's processor is armv7 /edit: on N950 it uses the same and in Qt sources are only for ARM qatomic_arm.h and qatomic_armv6.h so it should be ok.
ListView{
id: irrview
width: parent.width
model: irregulars
anchors.top: caption.bottom
anchors.bottom: parent.bottom
spacing: 5
clip: true
section.criteria: ViewSection.FirstCharacter
section.property: "form0"
delegate: Rectangle{
id: del
property int fontSize: 20
height: 60
width: parent.width
color: "#E0E1E2"
Row{
height: parent.height
width: parent.width - 10
anchors.horizontalCenter: parent.horizontalCenter
property real columnWidth: (width - 10) / 3
property int rad: 10
spacing: 5
Rectangle{
height: parent.height
width: parent.columnWidth
radius: parent.rad
color: "lightsteelblue"
Text{
anchors.centerIn: parent
text: form0
font.pointSize: del.fontSize
}
}
Rectangle{
height: parent.height
width: parent.columnWidth
radius: parent.rad
color: "lightsteelblue"
Text{
anchors.centerIn: parent
text: form1
font.pointSize: del.fontSize
}
}
Rectangle{
height: parent.height
width: parent.columnWidth
radius: parent.rad
color: "lightsteelblue"
Text{
anchors.centerIn: parent
text: form2
font.pointSize: del.fontSize
}
}
}
}
}
The model is:
#ifndef IRREGULARLISTWRAPPER_H
#define IRREGULARLISTWRAPPER_H
#include <QObject>
#include <QList>
#include <QAbstractListModel>
#include <QMap>
#include "IrregularVerb.h"
#include "AbstractIrregularList.h"
class IrregularListWrapper : public QAbstractListModel
{
Q_OBJECT
Q_PROPERTY(QString langName READ getLangName NOTIFY langChanged)
Q_PROPERTY(int count READ rowCount NOTIFY langChanged)
Q_ENUMS(Language)
public:
Q_INVOKABLE int rowCount(const QModelIndex& = QModelIndex()) const { return db->count(); }
Q_INVOKABLE QObject* get(int index) const {return db->at(index);}
QVariant data(const QModelIndex &index, int role) const;
enum Language
{
English = 0,
German = 1
};
enum IrregularVerbRoles
{
Form0Role = Qt::UserRole + 1,
Form1Role,
Form2Role
};
IrregularListWrapper();
// ~IrregularListWrapper() { delete db; }
// QList<QObject*> getdb() const { return *db; }
QString getLangName() const { return langName; }
Q_INVOKABLE void changeLang(Language l) { beginResetModel(); db = 0; /*QList<IrregularVerb*>();*/ setLang(l); endResetModel(); }
static QMap<Language, QString> plugins;
signals:
void langChanged();
protected:
void setLang(Language);
//QList<IrregularVerb*> db;
QString langName;
AbstractIrregularList * db;
};
#endif // IRREGULARLISTWRAPPER_H
QMap<IrregularListWrapper::Language, QString> IrregularListWrapper::plugins;
IrregularListWrapper::IrregularListWrapper()
{
QHash<int, QByteArray> roles;
roles[Form0Role] = "form0";
roles[Form1Role] = "form1";
roles[Form2Role] = "form2";
const QString pluginPath = "/opt/MeeIrregulars/share/lib%1.so";
plugins[English] = pluginPath.arg("english");
plugins[German] = pluginPath.arg("german");
setRoleNames(roles);
setLang(German);
}
QVariant IrregularListWrapper::data(const QModelIndex &index, int role) const
{
if (!index.isValid()) return QVariant();
const IrregularVerb* verb = db->at(index.row());
switch (role)
{
case Form0Role:
return verb->getForm0();
break;
case Form1Role:
return verb->getForm1();
break;
case Form2Role:
return verb->getForm2();
break;
}
return QVariant();
}
void IrregularListWrapper::setLang(Language l)
{
QPluginLoader loader(plugins[l]);
db = qobject_cast<AbstractIrregularList*>(loader.instance());
if (db == 0) db = new AbstractIrregularList;
switch (l)
{
case English:
langName = "English";
break;
case German:
langName = "German";
break;
}
emit langChanged();
}
class IrregularVerb : public QObject
{
Q_OBJECT
Q_PROPERTY(QString form0 READ getForm0 NOTIFY formChanged)
Q_PROPERTY(QString form1 READ getForm1 NOTIFY formChanged)
Q_PROPERTY(QString form2 READ getForm2 NOTIFY formChanged)
public:
QString forms[3];
QString getForm0() const { return forms[0]; }
QString getForm1() const { return forms[1]; }
QString getForm2() const { return forms[2]; }
IrregularVerb(QString a, QString b, QString c) { forms[0] = a; forms[1] = b; forms[2] = c; }
signals:
void formChanged();
};
Backtrace:
#0 QBasicAtomicInt::ref (this=0x18)
#1 QString (this=0xbe88d2a0, other=...)
#2 IrregularVerb::getForm2 (this=0x9e6de8)
#3 IrregularVerbWrapper::data(this=0x9e31b8, index=..., role=35) // the model// some calls to libQtDeclarative
Thanks.

Answer 1

It was a problem with ownership. The elements returned by get were owned by JS and automatically destroyed. See this answer for more information.