Extending QStandardItem doesnt return data

Question

I have a custom class ConnectionStandardItem which is a subclass of QStandardItem. This item should contain information like server, username, password etc to be used later in QSqlDatabase.

ConnectionStandardItem::ConnectionStandardItem(QString const& connectionId) : QStandardItem()
{  
    QMap<QString, QVariant>  m_connectionDefinition;
    QSettings settings(QSettings::IniFormat, QSettings::UserScope, "goat", "connections");

    if (!connectionId.isEmpty())
    {
        settings.beginGroup(connectionId.trimmed());

        m_connectionDefinition[connectionId] = QVariant(connectionId.trimmed());

        foreach(QString key, settings.childKeys())
        {
            m_connectionDefinition[key] = settings.value(key);
        }

        setText(m_connectionDefinition["name"].toString());
        setData(m_connectionDefinition, Qt::UserRole);

        settings.endGroup();
    }
}

Extended QStandardItem is used in a dialog:

NewConnectionDialog::NewConnectionDialog(QWidget *parent) : QDialog(parent), ui(new Ui::NewConnectionDialog) {
    ui->setupUi(this);

    m_model = new QStandardItemModel(this);
    m_driversModel = new QStandardItemModel(this);
    m_connectionListModel = new QStandardItemModel(this);

    ui->listDropdownDBDriver->setModel(m_driversModel);
    ui->listViewConnections->setModel(m_connectionListModel);

    /* set combobox */
    QStandardItem* item_psql = new QStandardItem();
    item_psql->setText("PostgreSQL");
    item_psql->setData("QPSQL", Qt::UserRole);
    m_driversModel->appendRow(item_psql);

    QStandardItem* item_mysql = new QStandardItem();
    item_mysql->setText("MySQL/MariaDB");
    item_mysql->setData("QMYSQL", Qt::UserRole);
    m_driversModel->appendRow(item_mysql);

    updateConnectionListModel();

    connect(ui->listViewConnections->selectionModel(), SIGNAL(selectionChanged(QItemSelection, QItemSelection)), this, SLOT(handleSelectionChanged(QItemSelection, QItemSelection)));
    connect(m_connectionListModel, SIGNAL(itemChanged(QStandardItem*)), this, SLOT(updateListViewItem(QStandardItem*)));
}

void NewConnectionDialog::handleSelectionChanged(QItemSelection current, QItemSelection previous) {
    const QModelIndex index = ui->listViewConnections->currentIndex();
    ConnectionStandardItem* connection = m_connectionListModel->itemFromIndex(index)->data().value<ConnectionStandardItem*>();


    QMap<QString, QVariant> connectionDefinition = connection->data().value<QMap<QString, QVariant>>();

    //ui->listDropdownDBDriver->setCurrentIndex(index);
    ui->txtUser->setText(connectionDefinition["username"].toString());
    ui->txtPass->setText(connectionDefinition["pass"].toString());
    ui->txtServer->setText(connectionDefinition["server"].toString());
    ui->txtPort->setText(connectionDefinition["port"].toString());
    ui->txtDatabase->setText(connectionDefinition["database"].toString());
}

void NewConnectionDialog::updateConnectionListModel() {
    QSettings settings(QSettings::IniFormat, QSettings::UserScope, "goat", "connections");

    foreach(QString key, settings.childGroups())
    {
        ConnectionStandardItem* item = new ConnectionStandardItem(key);
        m_connectionListModel->appendRow(item);
    }
}

Unfortunately, within dialog, i cannot access currently selected item's data. Method where i'm checking is handleSelectionChanged.

How can i properly extract Map object from the ConnenctionStandardItem so i can update GUI and vice versa, send changes in the gui back to the model (and through the model to the .ini settings file)? Is there a better way to approach this (differently organized classes)?

Answer 1

ConnectionStandardItem is not a data saved in the QStandardItem, but you have to cast ConnectionStandardItem from the QStandardItem.

On the other hand you save the data in the Qt::UserRole role:

setData(m_connectionDefinition, Qt::UserRole);

But when using data() you are using the Qt::UserRole + 1 role according to the documentation:

QVariant QStandardItem::data(int role = Qt::UserRole + 1) const

The solution is the next:

void NewConnectionDialog::handleSelectionChanged(QItemSelection current, QItemSelection previous) {
    const QModelIndex index = ui->listViewConnections->currentIndex();

    QStandardItem *item = m_connectionListModel->itemFromIndex(index);
    ConnectionStandardItem* connection  = static_cast<ConnectionStandardItem*>(item); // <---    
    QMap<QString, QVariant> connectionDefinition = connection->data(Qt::UserRole).value<QMap<QString, QVariant>>(); // <---

    //ui->listDropdownDBDriver->setCurrentIndex(index);
    ui->txtUser->setText(connectionDefinition["username"].toString());
    ui->txtPass->setText(connectionDefinition["pass"].toString());
    ui->txtServer->setText(connectionDefinition["server"].toString());
    ui->txtPort->setText(connectionDefinition["port"].toString());
    ui->txtDatabase->setText(connectionDefinition["database"].toString());
}

Although I see that casting is not necessary either, since we are not going to use a method implemented in ConnectionStandardItem, so we could only use QStandardItem:

void NewConnectionDialog::handleSelectionChanged(QItemSelection current, QItemSelection previous) {
    const QModelIndex index = ui->listViewConnections->currentIndex();

    QStandardItem *connection = m_connectionListModel->itemFromIndex(index);   
    QMap<QString, QVariant> connectionDefinition = connection->data(Qt::UserRole).value<QMap<QString, QVariant>>(); // <---

    //ui->listDropdownDBDriver->setCurrentIndex(index);
    ui->txtUser->setText(connectionDefinition["username"].toString());
    ui->txtPass->setText(connectionDefinition["pass"].toString());
    ui->txtServer->setText(connectionDefinition["server"].toString());
    ui->txtPort->setText(connectionDefinition["port"].toString());
    ui->txtDatabase->setText(connectionDefinition["database"].toString());
}