Qt Quick Application crashing on updating the ListView using QAbstractListModel class

James A

I am trying to update the Listview from c++ data model which is the subclass of QAbstractListModel.
When the run the program the application is crashing immediately with this Error

During debugging I observed that after calling the below functions the application is getting crashed , I think this is related to updating the listview

QHash<int, QByteArray> roleNames() const;

I have added the required snippsets of the code below

================wifi_model.h=================================

#ifndef WIFI_MODEL_H
#define WIFI_MODEL_H

#include <QAbstractListModel>

class WiFi_data{

QString m_name ;

public:
WiFi_data();
WiFi_data(const QString &name);
QString getName() const;
void setName(const QString &value);
};

class WiFi_model : public QAbstractListModel
{
Q_OBJECT

public:

enum WiFi_properties{
    name = Qt::UserRole + 1,
};

explicit WiFi_model(QObject *parent = nullptr);

// Basic functionality:
QModelIndex index(int row, int column,
                  const QModelIndex &parent = QModelIndex()) const override;
QModelIndex parent(const QModelIndex &index) const override;

int rowCount(const QModelIndex &parent = QModelIndex()) const override;
//    int columnCount(const QModelIndex &parent = QModelIndex()) const override;

// Get data:
QVariant data(const QModelIndex &index, int role = Qt::DisplayRole) const override;
// Remove data:
bool removeRows(int row, int count, const QModelIndex &parent = QModelIndex()) override;
// Add data:
void appendRows(const WiFi_data &data);

QHash<int,QByteArray> roleNames() const;

private:

QList<WiFi_data> wifi_model_list;

};

#endif // WIFI_MODEL_H

================wifi_model.cpp=================================

#include "wifi_model.h"

WiFi_data::WiFi_data()
{

}

WiFi_data::WiFi_data(const QString &name)
:m_name(name)
{

}

QString WiFi_data::getName() const
{
return m_name;
}

void WiFi_data::setName(const QString &value)
{
m_name = value;
}

WiFi_model::WiFi_model(QObject *parent)
: QAbstractListModel(parent)
{
}

QModelIndex WiFi_model::index(int row, int column, const QModelIndex &parent) const
{
// FIXME: Implement me!
}

QModelIndex WiFi_model::parent(const QModelIndex &index) const
{
// FIXME: Implement me!
}

int WiFi_model::rowCount(const QModelIndex &parent) const
{
Q_UNUSED(parent);
return wifi_model_list.count();
}

//int WiFi_model::columnCount(const QModelIndex &parent) const
//{
// if (!parent.isValid())
// return 0;

// // FIXME: Implement me!
//}

QVariant WiFi_model::data(const QModelIndex &index, int role) const
{

if (index.row() < 0 || index.row() >= wifi_model_list.count())
    return QVariant();

const WiFi_data &model_data = wifi_model_list[index.row()];
if (role == name)
    return model_data.getName();

return QVariant();

}

bool WiFi_model::removeRows(int row, int count, const QModelIndex &parent)
{
beginRemoveRows(parent, row, row + count - 1);
// FIXME: Implement me!
endRemoveRows();
}

void WiFi_model::appendRows(const WiFi_data &data)
{
beginInsertRows(QModelIndex(), rowCount(), rowCount());
wifi_model_list << data;
endInsertRows();

}

QHash<int, QByteArray> WiFi_model::roleNames() const
{
QHash<int, QByteArray> roles;
roles[name] = "name";

return roles;

}

==============main.cpp========================================

#include <QGuiApplication>
#include <QQmlApplicationEngine>
#include <QQmlContext>
#include "wifi_model.h"

int main(int argc, char *argv[])
{
#if QT_VERSION < QT_VERSION_CHECK(6, 0, 0)
QCoreApplication::setAttribute(Qt::AA_EnableHighDpiScaling);
#endif

QGuiApplication app(argc, argv);

QQmlApplicationEngine engine;
const QUrl url(QStringLiteral("qrc:/main.qml"));
QObject::connect(&engine, &QQmlApplicationEngine::objectCreated,
                 &app, [url](QObject *obj, const QUrl &objUrl) {
    if (!obj && url == objUrl)
        QCoreApplication::exit(-1);
}, Qt::QueuedConnection);

WiFi_model m_wifi_model;

m_wifi_model.appendRows(WiFi_data("name"));
m_wifi_model.appendRows(WiFi_data("data"));

QQmlContext* context = engine.rootContext();
context->setContextProperty("wifi_model", &m_wifi_model);

engine.load(url);


return app.exec();

}

===================main.qml=================================

import QtQuick 2.11
import QtQuick.Window 2.11
import QtQuick.Controls 2.15

Window {
width: 640
height: 480
visible: true
title: qsTr("Hello World")

GroupBox {
    id: groupBox
    x: 14
    y: 13
    width: 318
    height: 397
    title: qsTr("Group Box")

    ListView {

        model : wifi_model
        delegate: Text {
            text: name
            anchors.verticalCenter: parent.verticalCenter
            font.bold: true
        }

        onCountChanged: console.log("count changed: " + count)
    }
}

}

raven-worx

@James-A
start with QtCreator debugger and post the full stack trace when it crashes.

James A

@raven-worx

I added the full stack trace below

1 QQmlDMCachedModelData::metaCall(QMetaObject::Call, int, void * *) 0x7fffe8114b83
2 loadProperty(QV4::ExecutionEngine *, QObject *, QQmlPropertyData const&) [clone .constprop.350] 0x7ffff71b99ce
3 QV4::QObjectWrapper::getQmlProperty(QV4::ExecutionEngine *, QQmlContextData *, QObject *, QV4::String *, QV4::QObjectWrapper::RevisionMode, bool *, QQmlPropertyData * *) 0x7ffff71ba7da
4 QV4::QQmlContextWrapper::getPropertyAndBase(QV4::QQmlContextWrapper const *, QV4::PropertyKey, QV4::Value const *, bool *, QV4::Value *, QV4::Lookup *) 0x7ffff7193954
5 QV4::QQmlContextWrapper::resolveQmlContextPropertyLookupGetter(QV4::Lookup *, QV4::ExecutionEngine *, QV4::Value *) 0x7ffff71940ed
6 QV4::Moth::VME::interpret(QV4::CppStackFrame *, QV4::ExecutionEngine *, const char *) 0x7ffff71d53bc
7 QV4::Moth::VME::exec(QV4::CppStackFrame *, QV4::ExecutionEngine *) 0x7ffff71d958b
8 QV4::Function::call(QV4::Value const *, QV4::Value const *, int, QV4::ExecutionContext const *) 0x7ffff716e1e5
9 QQmlJavaScriptExpression::evaluate(QV4::CallData *, bool *) 0x7ffff72ef43a
10 QQmlBinding::evaluate(bool *) 0x7ffff72f4b47
11 QQmlNonbindingBinding::doUpdate(QQmlJavaScriptExpression::DeleteWatcher const&, QFlagsQQmlPropertyData::WriteFlag, QV4::Scope&) 0x7ffff72f9805
12 QQmlBinding::update(QFlagsQQmlPropertyData::WriteFlag) 0x7ffff72f6363
13 QQmlObjectCreator::finalize(QQmlInstantiationInterrupt&) 0x7ffff7306442
14 QQmlIncubatorPrivate::incubate(QQmlInstantiationInterrupt&) 0x7ffff72953e9
15 QQmlEnginePrivate::incubate(QQmlIncubator&, QQmlContextData *) 0x7ffff7295904
16 QQmlDelegateModelPrivate::object(QQmlListCompositor::Group, int, QQmlIncubator::IncubationMode) 0x7fffe8125252
17 QQmlDelegateModel::object(int, QQmlIncubator::IncubationMode) 0x7fffe8125572
18 QQuickItemViewPrivate::createItem(int, QQmlIncubator::IncubationMode) 0x7fffe865288f
19 QQuickListViewPrivate::addVisibleItems(double, double, double, double, bool) 0x7fffe86617f8
20 QQuickItemViewPrivate::refill(double, double) 0x7fffe8653c3a
21 QQuickItemView::componentComplete() 0x7fffe8659088
22 QQmlObjectCreator::finalize(QQmlInstantiationInterrupt&) 0x7ffff73067c1
23 QQmlComponentPrivate::complete(QQmlEnginePrivate *, QQmlComponentPrivate::ConstructionState *) 0x7ffff728e5f1
24 QQmlComponentPrivate::completeCreate() 0x7ffff7290ef7
25 QQmlComponent::create(QQmlContext *) 0x7ffff728e0db
26 QQmlApplicationEnginePrivate::finishLoad(QQmlComponent *) 0x7ffff72fb5cc
27 QQmlApplicationEnginePrivate::startLoad(QUrl const&, QByteArray const&, bool) 0x7ffff72fb7e6
28 QQmlApplicationEngine::load(QUrl const&) 0x7ffff72fba1d
29 main main.cpp 30 0x555555557c5c

raven-worx

@James-A
i dont think that the code you've posted is causing this issue.

The only code which doesn't make sense is the line

anchors.verticalCenter: parent.verticalCenter

in your delegate.

James A

@raven-worx

I tried changing the delegate to delegate: Text { text: name }
But the issue is persisting

raven-worx

@James-A
as i said, i don't think that the code you've posted is causing this issue, at least i don't spot an issue.
Try a full rebuild.

If the issue persists, try removing single items to check which Item is causing it.

Also your ListView has no size set.

James A

@raven-worx

I tried deleting the output folder and then rebuild gain , and also tried commenting out individually the code under WiFi_model, from that what I observed is when I remove the below line from the "roleNames()" functions the application is starting , but not updating the data on the ListView

roles[name] = "name";

Again when I try adding it back , the application gets crashed
So I found the line of code which is causing the problem , but not sure why it is causing the crash and what I am missing in it

And I also set the ListView size as below

anchors.fill: parent

raven-worx

@James-A
strange.
Does it work when you rename the enum value from name to e.g. NameRole?

QHash<int, QByteArray> WiFi_model::roleNames() const
{
QHash<int, QByteArray> roles;
roles[NameRole] = QByteArrayLiteral("name");
return roles;
}

dheerendra

Can u also try removing the columnCount implementation completely ? This is not required. Some times this is also a issue.

James A

@raven-worx

I changed the roleNames() function implementation as suggested above.

@dheerendra

I completely removed the commented columnCount() function

But there is no change , still the error exist

dheerendra

Issue is coming from index() and parent() method. Comment them.
Also qml code needs correction.
This should work.

GroupBox {
        id: groupBox
        anchors.fill: parent
        ListView {
            anchors.fill: parent
            model : wifi_model
            delegate: Text {
                text: name
                width: 300;height: 40
                font.bold: true
            }
            onCountChanged: console.log("count changed: " + count)
        }
    }

James A

@dheerendra

Thanks for pointing it out. Yes it was due to index() and parent() . I removed it completely
Now the application is running