Implementing a Dynamic QAbstractListModel in Qt 6 with Proper Change Notifications

Useful answer

To show a list that updates automatically when items are added or removed, subclass QAbstractListModel, store the data in a QVector<QString>, and wrap every structural change with the begin/end row methods. This guarantees that attached views (QListView, QML ListView, etc.) receive the correct signals and stay in sync.

Worked configuration

Header (mylistmodel.h)

#ifndef MYLISTMODEL_H
#define MYLISTMODEL_H

#include 
#include 

class MyListModel : public QAbstractListModel
{
    Q_OBJECT
public:
    explicit MyListModel(QObject *parent = nullptr);

    // QAbstractItemModel interface
    int rowCount(const QModelIndex &parent = QModelIndex()) const override;
    QVariant data(const QModelIndex &index, int role = Qt::DisplayRole) const override;
    QHash roleNames() const override;

public slots:
    void appendItem(const QString &text);
    void removeItem(int row);

private:
    QVector m_items;
};

#endif // MYLISTMODEL_H

Implementation (mylistmodel.cpp)

#include "mylistmodel.h"

MyListModel::MyListModel(QObject *parent)
    : QAbstractListModel(parent)
{
    // optional initial data
    m_items = {"Alpha", "Beta", "Gamma", "Delta", "Epsilon"};
}

int MyListModel::rowCount(const QModelIndex &parent) const
{
    if (parent.isValid())
        return 0;
    return m_items.size();
}

QVariant MyListModel::data(const QModelIndex &index, int role) const
{
    if (!index.isValid() || index.row() < 0 || index.row() >= m_items.size())
        return QVariant();

    if (role == Qt::DisplayRole)
        // Qt 6: returning QStringView avoids a copy when the backing vector owns the string
        return QStringView{m_items[index.row()]};
    return QVariant();
}

QHash MyListModel::roleNames() const
{
    QHash roles;
    roles[Qt::DisplayRole] = "display";
    return roles;
}

void MyListModel::appendItem(const QString &text)
{
    const int row = m_items.size();
    beginInsertRows(QModelIndex(), row, row);
    m_items.append(text);
    endInsertRows();
}

void MyListModel::removeItem(int row)
{
    if (row < 0 || row >= m_items.size())
        return;
    beginRemoveRows(QModelIndex(), row, row);
    m_items.removeAt(row);
    endRemoveRows();
}

Using the model in a Qt Widgets application

#include 
#include 
#include 
#include 
#include 
#include "mylistmodel.h"

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    QWidget w;
    QVBoxLayout *layout = new QVBoxLayout(&w);

    MyListModel *model = new MyListModel(&w);
    QListView *view = new QListView(&w);
    view->setModel(model);
    layout->addWidget(view);

    QPushButton *btn = new QPushButton("Add Item", &w);
    layout->addWidget(btn);
    QObject::connect(btn, &QPushButton::clicked, [model](){
        static int counter = 0;
        model->appendItem(QString("Item %1").arg(++counter));
    });

    w.resize(300, 200);
    w.show();
    return a.exec();
}

Using the model in QML

#include 
#include 
#include "mylistmodel.h"

int main(int argc, char *argv[])
{
    QGuiApplication app(argc, argv);
    qmlRegisterType("MyModels", 1, 0, "MyListModel");

    QQmlApplicationEngine engine;
    engine.load(QUrl(QStringLiteral("qrc:/main.qml")));
    if (engine.rootObjects().isEmpty())
        return -1;
    return app.exec();
}

// main.qml
import QtQuick 2.15
import QtQuick.Controls 2.15
import MyModels 1.0

ApplicationWindow {
    visible: true
    width: 400
    height: 300
    title: "QAbstractListModel Demo"

    MyListModel {
        id: myModel
    }

    ListView {
        anchors.fill: parent
        model: myModel
        delegate: Text { text: display; padding: 8 }
    }

    Button {
        text: "Add"
        anchors.bottom: parent.bottom
        anchors.horizontalCenter: parent.horizontalCenter
        onClicked: {
            myModel.appendItem("Item " + (myModel.count + 1))
        }
    }
}

Limits and common mistakes

Performance limits

QAbstractListModel works well for up to roughly 100 k rows when each row has uniform height. Beyond that, consider lazy loading with canFetchMore/fetchMore or a custom QAbstractItemModel that supplies only visible items.

Thread safety

The model must live in the GUI thread. If background work produces new data, emit a queued signal or use QMetaObject::invokeMethod to call appendItem (or similar) on the main thread.

Typical errors

• Modifying the underlying QVector without calling beginInsertRows/endInsertRows (or the remove/move equivalents). The view will show stale data, may crash when scrolling, or produce visual artifacts.
• Omitting roleNames() when using custom roles in QML. Delegates bound to those roles will receive empty values.
• Using layoutChanged() for simple insert/remove operations. This forces the view to rebuild everything, hurting performance and losing scroll position.
• Storing raw QObject* pointers in the model without ownership tracking. When the view releases an item, the pointer can dangle; use QPointer or QSharedPointer instead.

Practical verification

Run the widget example, click the "Add Item" button, and watch the list grow instantly. Then, temporarily comment out the beginInsertRows/endInsertRows lines in appendItem and rebuild. You will see the view not update (or crash on scroll), confirming that the signals are required.