|  | Home · Examples

# Address Book Example

The address book example shows how to use proxy models to display different views onto data from a single model.

This example provides an address book that allows contacts to be grouped alphabetically into 9 groups: ABC, DEF, GHI, ... , VW, ..., XYZ. This is achieved by using multiple views on the same model, each of which is filtered using an instance of the QSortFilterProxyModel class.

## Overview

The address book contains 5 classes: `MainWindow`, `AddressWidget`, `TableModel`, `NewAddressTab` and `AddDialog`. The `MainWindow` class uses `AddressWidget` as its central widget and provides File and Tools menus.
The `AddressWidget` class is a QTabWidget subclass that is used to manipulate the 10 tabs displayed in the example: the 9 alphabet group tabs and an instance of `NewAddressTab`. The `NewAddressTab` class is a subclass of QWidget that is only used whenever the address book is empty, prompting the user to add some contacts. `AddressWidget` also interacts with an instance of `TableModel` to add, edit and remove entries to the address book.

`TableModel` is a subclass of QAbstractTableModel that provides the standard model/view API to access data. It also holds a QList of QPairs corresponding to the contacts added. However, this data is not all visible in a single tab. Instead, QTableView is used to provide 9 different views of the same data, according to the alphabet groups.

QSortFilterProxyModel is the class responsible for filtering the contacts for each group of contacts. Each proxy model uses a QRegExp to filter out contacts that do not belong in the corresponding alphabetical group. The `AddDialog` class is used to obtain information from the user for the address book. This QDialog subclass is instantiated by `NewAddressTab` to add contacts, and by `AddressWidget` to add and edit contacts.

We begin by looking at the `TableModel` implementation.

## TableModel Class Definition

The `TableModel` class provides standard API to access data in its QList of QPairs by subclassing QAbstractTableModel. The basic functions that must be implemented in order to do so are: `rowCount()`, `columnCount()`, `data()`, `headerData()`. For TableModel to be editable, it has to provide implementations `insertRows()`, `removeRows()`, `setData()` and `flags()` functions.

    class TableModel : public QAbstractTableModel
    {
        Q_OBJECT

    public:
        TableModel(QObject *parent=0);
        TableModel(QList< QPair<QString, QString> > listofPairs, QObject *parent=0);

        int rowCount(const QModelIndex &parent) const;
        int columnCount(const QModelIndex &parent) const;
        QVariant data(const QModelIndex &index, int role) const;
        QVariant headerData(int section, Qt::Orientation orientation, int role) const;
        Qt::ItemFlags flags(const QModelIndex &index) const;
        bool setData(const QModelIndex &index, const QVariant &value, int role=Qt::EditRole);
        bool insertRows(int position, int rows, const QModelIndex &index=QModelIndex());
        bool removeRows(int position, int rows, const QModelIndex &index=QModelIndex());
        QList< QPair<QString, QString> > getList();

    private:
        QList< QPair<QString, QString> > listOfPairs;
    };

Two constructors are used, a default constructor which uses `TableModel`'s own `QList<QPair<QString, QString>>` and one that takes `QList<QPair<QString, QString>` as an argument, for convenience.

## TableModel Class Implementation

We implement the two constructors as defined in the header file. The second constructor initializes the list of pairs in the model, with the parameter value.
The following code example is written in c++.

    TableModel::TableModel(QObject *parent)
        : QAbstractTableModel(parent)
    {
    }

    TableModel::TableModel(QList< QPair<QString, QString> > pairs, QObject *parent)
        : QAbstractTableModel(parent)
    {
        listOfPairs=pairs;
    }

The `rowCount()` and `columnCount()` functions return the dimensions of the model. Whereas, `rowCount()`'s value will vary depending on the number of contacts added to the address book, `columnCount()`'s value is always 2 because we only need space for the Name and Address columns.

Note: The `Q_UNUSED()` macro prevents the compiler from generating warnings regarding unused parameters.
The following code example is written in c++.

    int TableModel::rowCount(const QModelIndex &parent) const
    {
        Q_UNUSED(parent);
        return listOfPairs.size();
    }

    int TableModel::columnCount(const QModelIndex &parent) const
    {
        Q_UNUSED(parent);
        return 2;
    }

The `data()` function returns either a Name or Address, based on the contents of the model index supplied. The row number stored in the model index is used to reference an item in the list of pairs. Selection is handled by the QItemSelectionModel, which will be explained with `AddressWidget`.
The following code example is written in c++.

    QVariant TableModel::data(const QModelIndex &index, int role) const
    {
        if (!index.isValid())
            return QVariant();

        if (index.row() >= listOfPairs.size() || index.row() < 0)
            return QVariant();

        if (role == Qt::DisplayRole) {
            QPair<QString, QString> pair = listOfPairs.at(index.row());

            if (index.column() == 0)
                return pair.first;
            else if (index.column() == 1)
                return pair.second;
        }
        return QVariant();
    }

The `headerData()` function displays the table's header, Name and Address. If you require numbered entries for your address book, you can use a vertical header which we have hidden in this example (see the `AddressWidget` implementation).
The following code example is written in c++.

    QVariant TableModel::headerData(int section, Qt::Orientation orientation, int role) const
    {
        if (role != Qt::DisplayRole)
            return QVariant();

        if (orientation == Qt::Horizontal) {
            switch (section) {
                case 0:
                    return tr("Name");

                case 1:
                    return tr("Address");

                default:
                    return QVariant();
            }
        }
        return QVariant();
    }

The `insertRows()` function is called before new data is added, otherwise the data will not be displayed. The `beginInsertRows()` and `endInsertRows()` functions are called to ensure all connected views are aware of the changes.
The following code example is written in c++.

    bool TableModel::insertRows(int position, int rows, const QModelIndex &index)
    {
        Q_UNUSED(index);
        beginInsertRows(QModelIndex(), position, position+rows-1);

        for (int row=0; row < rows; row++) {
            QPair<QString, QString> pair(" ", " ");
            listOfPairs.insert(position, pair);
        }

        endInsertRows();
        return true;
    }

The `removeRows()` function is called to remove data. Again, beginRemoveRows() and endRemoveRows() are called to ensure all connected views are aware of the changes.
The following code example is written in c++.

    bool TableModel::removeRows(int position, int rows, const QModelIndex &index)
    {
        Q_UNUSED(index);
        beginRemoveRows(QModelIndex(), position, position+rows-1);

        for (int row=0; row < rows; ++row) {
            listOfPairs.removeAt(position);
        }

        endRemoveRows();
        return true;
    }

The `setData()` function is the function that inserts data into the table, item by item and not row by row. This means that to fill a row in the address book, `setData()` must be called twice, as each row has 2 columns. It is important to emit the dataChanged() signal as it tells all connected views to update their displays.
The following code example is written in c++.

    bool TableModel::setData(const QModelIndex &index, const QVariant &value, int role)
    {
    	if (index.isValid() && role == Qt::EditRole) {
    		int row = index.row();

    		QPair<QString, QString> p = listOfPairs.value(row);

    		if (index.column() == 0)
    			p.first = value.toString();
    		else if (index.column() == 1)
    			p.second = value.toString();
            else
                return false;

            listOfPairs.replace(row, p);
    		emit(dataChanged(index, index));

            return true;
    	}

    	return false;
    }

The `flags()` function returns the item flags for the given index.
The following code example is written in c++.

    Qt::ItemFlags TableModel::flags(const QModelIndex &index) const
    {
        if (!index.isValid())
            return Qt::ItemIsEnabled;

        return QAbstractTableModel::flags(index) | Qt::ItemIsEditable;
    }

We set the Qt::ItemIsEditable flag because we want to allow the `TableModel` to be edited. Although for this example we don't use the editing features of the QTableView object, we enable them here so that we can reuse the model in other programs.

The last function in `TableModel`, `getList()` returns the QList<QPair<QString, QString>> object that holds all the contacts in the address book. We use this function later to obtain the list of contacts to check for existing entries, write the contacts to a file and read them back. Further explanation is given with `AddressWidget`.
The following code example is written in c++.

    QList< QPair<QString, QString> > TableModel::getList()
    {
        return listOfPairs;
    }

## AddressWidget Class Definition

The `AddressWidget` class is technically the main class involved in this example as it provides functions to add, edit and remove contacts, to save the contacts to a file and to load them from a file.

    class AddressWidget : public QTabWidget
    {
        Q_OBJECT

    public:
        AddressWidget(QWidget *parent=0);
        void readFromFile(QString fileName);
        void writeToFile(QString fileName);

    public slots:
        void addEntry();
        void addEntry(QString name, QString address);
        void editEntry();
        void removeEntry();

    signals:
        void selectionChanged (const QItemSelection &selected);

    private:
        void setupTabs();

        TableModel *table;
        NewAddressTab *newAddressTab;
        QSortFilterProxyModel *proxyModel;
    };

`AddressWidget` extends QTabWidget in order to hold 10 tabs (`NewAddressTab` and the 9 alphabet group tabs) and also manipulates `table`, the `TableModel` object, `proxyModel`, the QSortFilterProxyModel object that we use to filter the entries, and `tableView`, the QTableView object.

## AddressWidget Class Implementation

The `AddressWidget` constructor accepts a parent widget and instantiates `NewAddressTab`, `TableModel` and QSortFilterProxyModel. The `NewAddressTab` object, which is used to indicate that the address book is empty, is added and the rest of the 9 tabs are set up with `setupTabs()`.
The following code example is written in c++.

    AddressWidget::AddressWidget(QWidget *parent)
        : QTabWidget(parent)
    {
        table = new TableModel(this);
        newAddressTab = new NewAddressTab(this);
        connect(newAddressTab, SIGNAL(sendDetails(QString, QString)),
            this, SLOT(addEntry(QString, QString)));

        addTab(newAddressTab, "Address Book");

        setupTabs();
    }

The `setupTabs()` function is used to set up the 9 alphabet group tabs, table views and proxy models in `AddressWidget`. Each proxy model in turn is set to filter contact names according to the relevant alphabet group using a case-insensitive QRegExp object. The table views are also sorted in ascending order using the corresponding proxy model's sort() function.

Each table view's selectionMode is set to QAbstractItemView::SingleSelection and selectionBehavior is set to QAbstractItemView::SelectRows, allowing the user to select all the items in one row at the same time. Each QTableView object is automatically given a QItemSelectionModel that keeps track of the selected indexes.
The following code example is written in c++.

    void AddressWidget::setupTabs()
    {
        QStringList groups;
        groups << "ABC" << "DEF" << "GHI" << "JKL" << "MNO" << "PQR" << "STU" << "VW" << "XYZ";

        for (int i = 0; i < groups.size(); ++i) {
            QString str = groups.at(i);

            proxyModel = new QSortFilterProxyModel(this);
            proxyModel->setSourceModel(table);
            proxyModel->setDynamicSortFilter(true);

            QTableView *tableView = new QTableView;
            tableView->setModel(proxyModel);
            tableView->setSortingEnabled(true);
            tableView->setSelectionBehavior(QAbstractItemView::SelectRows);
            tableView->horizontalHeader()->setStretchLastSection(true);
            tableView->verticalHeader()->hide();
            tableView->setEditTriggers(QAbstractItemView::NoEditTriggers);
            tableView->setSelectionMode(QAbstractItemView::SingleSelection);

            QString newStr = QString("^[%1].*").arg(str);

            proxyModel->setFilterRegExp(QRegExp(newStr, Qt::CaseInsensitive));
            proxyModel->setFilterKeyColumn(0);
            proxyModel->sort(0, Qt::AscendingOrder);

            connect(tableView->selectionModel(),
                SIGNAL(selectionChanged(const QItemSelection &, const QItemSelection &)),
                this, SIGNAL(selectionChanged(const QItemSelection &)));

            addTab(tableView, str);
        }
    }

The QItemSelectionModel class provides a selectionChanged signal that is connected to `AddressWidget`'s `selectionChanged()` signal. This signal to signal connection is necessary to enable the Edit Entry... and Remove Entry actions in `MainWindow`'s Tools menu. This connection is further explained in `MainWindow`'s implementation.

Each table view in the address book is added as a tab to the QTabWidget with the relevant label, obtained from the QStringList of groups.

We provide 2 `addEntry()` functions: 1 which is intended to be used to accept user input, and the other which performs the actual task of adding new entries to the address book. We divide the responsibility of adding entries into two parts to allow `newAddressTab` to insert data without having to popup a dialog.

The first `addEntry()` function is a slot connected to the `MainWindow`'s Add Entry... action. This function creates an `AddDialog` object and then calls the second `addEntry()` function to actually add the contact to `table`.
The following code example is written in c++.

    void AddressWidget::addEntry()
    {
        AddDialog aDialog;

        if (aDialog.exec()) {
            QString name = aDialog.nameText->text();
            QString address = aDialog.addressText->toPlainText();

            addEntry(name, address);
        }
    }

Basic validation is done in the second `addEntry()` function to prevent duplicate entries in the address book. As mentioned with `TableModel`, this is part of the reason why we require the getter method `getList()`.
The following code example is written in c++.

    void AddressWidget::addEntry(QString name, QString address)
    {
        QList< QPair<QString, QString> >list = table->getList();
        QPair<QString, QString> pair(name, address);

        if (!list.contains(pair)) {
            table->insertRows(0, 1, QModelIndex());

            QModelIndex index = table->index(0, 0, QModelIndex());
            table->setData(index, name, Qt::EditRole);
            index = table->index(0, 1, QModelIndex());
            table->setData(index, address, Qt::EditRole);
            removeTab(indexOf(newAddressTab));
        } else {
            QMessageBox::information(this, tr("Duplicate Name"),
                tr("The name \"%1\" already exists.").arg(name));
        }
    }

If the model does not already contain an entry with the same name, we call `setData()` to insert the name and address into the first and second columns. Otherwise, we display a QMessageBox to inform the user.

Note: The `newAddressTab` is removed once a contact is added as the address book is no longer empty.

Editing an entry is a way to update the contact's address only, as the example does not allow the user to change the name of an existing contact.

Firstly, we obtain the active tab's QTableView object using QTabWidget::currentWidget(). Then we extract the `selectionModel` from the `tableView` to obtain the selected indexes.
The following code example is written in c++.

    void AddressWidget::editEntry()
    {
        QTableView *temp = static_cast<QTableView*>(currentWidget());
        QSortFilterProxyModel *proxy = static_cast<QSortFilterProxyModel*>(temp->model());
        QItemSelectionModel *selectionModel = temp->selectionModel();

        QModelIndexList indexes = selectionModel->selectedRows();
        QModelIndex index, i;
        QString name;
        QString address;
        int row;

        foreach (index, indexes) {
            row = proxy->mapToSource(index).row();
            i = table->index(row, 0, QModelIndex());
            QVariant varName = table->data(i, Qt::DisplayRole);
            name = varName.toString();

            i = table->index(row, 1, QModelIndex());
            QVariant varAddr = table->data(i, Qt::DisplayRole);
            address = varAddr.toString();
        }

Next we extract data from the row the user intends to edit. This data is displayed in an instance of `AddDialog` with a different window title. The `table` is only updated if changes have been made to data in `aDialog`.
The following code example is written in c++.

        AddDialog aDialog;
        aDialog.setWindowTitle(tr("Edit a Contact"));

        aDialog.nameText->setReadOnly(true);
        aDialog.nameText->setText(name);
        aDialog.addressText->setText(address);

        if (aDialog.exec()) {
            QString newAddress = aDialog.addressText->toPlainText();
            if (newAddress != address) {
                i = table->index(row, 1, QModelIndex());
                table->setData(i, newAddress, Qt::EditRole);
            }
        }
    }

Entries are removed using the `removeEntry()` function. The selected row is removed by accessing it through the QItemSelectionModel object, `selectionModel`. The `newAddressTab` is re-added to the `AddressWidget` only if the user removes all the contacts in the address book.
The following code example is written in c++.

    void AddressWidget::removeEntry()
    {
        QTableView *temp = static_cast<QTableView*>(currentWidget());
        QSortFilterProxyModel *proxy = static_cast<QSortFilterProxyModel*>(temp->model());
        QItemSelectionModel *selectionModel = temp->selectionModel();

        QModelIndexList indexes = selectionModel->selectedRows();
        QModelIndex index;

        foreach (index, indexes) {
            int row = proxy->mapToSource(index).row();
            table->removeRows(row, 1, QModelIndex());
        }

        if (table->rowCount(QModelIndex()) == 0) {
            insertTab(0, newAddressTab, "Address Book");
        }
    }

The `writeToFile()` function is used to save a file containing all the contacts in the address book. The file is saved in a custom `.dat` format. The contents of the QList of QPairs are written to `file` using QDataStream. If the file cannot be opened, a QMessageBox is displayed with the related error message.
The following code example is written in c++.

    void AddressWidget::writeToFile(QString fileName)
    {
        QFile file(fileName);

        if (!file.open(QIODevice::WriteOnly)) {
            QMessageBox::information(this, tr("Unable to open file"), file.errorString());
            return;
        }

        QList< QPair<QString, QString> > pairs = table->getList();
        QDataStream out(&file);
        out << pairs;
    }

The `readFromFile()` function loads a file containing all the contacts in the address book, previously saved using `writeToFile()`. QDataStream is used to read the contents of a `.dat` file into a list of pairs and each of these is added using `addEntry()`.
The following code example is written in c++.

    void AddressWidget::readFromFile(QString fileName)
    {
        QFile file(fileName);

        if (!file.open(QIODevice::ReadOnly)) {
            QMessageBox::information(this, tr("Unable to open file"),
                file.errorString());
            return;
        }

        QList< QPair<QString, QString> > pairs = table->getList();
        QDataStream in(&file);
        in >> pairs;

        if (pairs.isEmpty()) {
            QMessageBox::information(this, tr("No contacts in file"),
                tr("The file you are attempting to open contains no contacts."));
        } else {
            for (int i=0; i<pairs.size(); ++i) {
                QPair<QString, QString> p = pairs.at(i);
                addEntry(p.first, p.second);
            }
        }
    }

## NewAddressTab Class Definition

The `NewAddressTab` class provides an informative tab telling the user that the address book is empty. It appears and disappears according to the contents of the address book, as mentioned in `AddressWidget`'s implementation.
The `NewAddressTab` class extends QWidget and contains a QLabel and QPushButton.

    class NewAddressTab : public QWidget
    {
        Q_OBJECT

    public:
        NewAddressTab(QWidget *parent=0);

    public slots:
        void addEntry();

    signals:
        void sendDetails(QString name, QString address);

    private:
        QLabel *descriptionLabel;
        QPushButton *addButton;
        QVBoxLayout *mainLayout;

    };

## NewAddressTab Class Implementation

The constructor instantiates the `addButton`, `descriptionLabel` and connects the `addButton`'s signal to the `addEntry()` slot.
The following code example is written in c++.

    NewAddressTab::NewAddressTab(QWidget *parent)
    {
        Q_UNUSED(parent);

        descriptionLabel = new QLabel(tr("There are currently no contacts in your address book. "
                                          "\nClick Add to add new contacts."));

        addButton = new QPushButton(tr("Add"));

        connect(addButton, SIGNAL(clicked()), this, SLOT(addEntry()));

        mainLayout = new QVBoxLayout;
        mainLayout->addWidget(descriptionLabel);
        mainLayout->addWidget(addButton, 0, Qt::AlignCenter);

        setLayout(mainLayout);
    }

The `addEntry()` function is similar to `AddressWidget`'s `addEntry()` in the sense that both functions instantiate an `AddDialog` object. Data from the dialog is extracted and sent to `AddressWidget`'s `addEntry()` slot by emitting the `sendDetails()` signal.
The following code example is written in c++.

    void NewAddressTab::addEntry()
    {
        AddDialog aDialog;

        if (aDialog.exec()) {
            QString name = aDialog.nameText->text();
            QString address = aDialog.addressText->toPlainText();

            emit sendDetails(name, address);
        }
    }

## AddDialog Class Definition

The `AddDialog` class extends QDialog and provides the user with a QLineEdit and a QTextEdit to input data into the address book.

    class AddDialog : public QDialog
    {
        Q_OBJECT

    public:
        AddDialog(QWidget *parent=0);
        QLineEdit *nameText;
        QTextEdit *addressText;

    private:
        QLabel *nameLabel;
        QLabel *addressLabel;
        QPushButton *okButton;
        QPushButton *cancelButton;
    };

## AddDialog Class Implementation

The `AddDialog`'s constructor sets up the user interface, creating the necessary widgets and placing them into layouts.
The following code example is written in c++.

    AddDialog::AddDialog(QWidget *parent)
        : QDialog(parent)
    {
        nameLabel = new QLabel("Name");
        addressLabel = new QLabel("Address");
        okButton = new QPushButton("OK");
        cancelButton = new QPushButton("Cancel");

        nameText = new QLineEdit;
        addressText = new QTextEdit;

        QGridLayout *gLayout = new QGridLayout;
        gLayout->setColumnStretch(1, 2);
        gLayout->addWidget(nameLabel, 0, 0);
        gLayout->addWidget(nameText, 0, 1);

        gLayout->addWidget(addressLabel, 1, 0, Qt::AlignLeft|Qt::AlignTop);
        gLayout->addWidget(addressText, 1, 1, Qt::AlignLeft);

        QHBoxLayout *buttonLayout = new QHBoxLayout;
        buttonLayout->addWidget(okButton);
        buttonLayout->addWidget(cancelButton);

        gLayout->addLayout(buttonLayout, 2, 1, Qt::AlignRight);

        QVBoxLayout *mainLayout = new QVBoxLayout;
        mainLayout->addLayout(gLayout);
        setLayout(mainLayout);

        connect(okButton, SIGNAL(clicked()),
                this, SLOT(accept()));

        connect(cancelButton, SIGNAL(clicked()),
                this, SLOT(reject()));

        setWindowTitle(tr("Add a Contact"));
    }

To give the dialog the desired behavior, we connect the OK and Cancel buttons to the dialog's accept() and reject() slots. Since the dialog only acts as a container for name and address information, we do not need to implement any other functions for it.

## MainWindow Class Definition

The `MainWindow` class extends QMainWindow and implements the menus and actions necessary to manipulate the address book.

    class MainWindow : public QMainWindow
    {
        Q_OBJECT

    public:
        MainWindow();

    private slots:
        void updateActions(const QItemSelection &selection);
        void openFile();
        void saveFile();

    private:
        void createMenus();

        AddressWidget *addressWidget;
        QMenu *fileMenu;
        QMenu *toolMenu;
        QAction *openAct;
        QAction *saveAct;
        QAction *exitAct;
        QAction *addAct;
        QAction *editAct;
        QAction *removeAct;
    };

The `MainWindow` class uses an `AddressWidget` as its central widget and provides the File menu with Open, Close and Exit actions, as well as the Tools menu with Add Entry..., Edit Entry... and Remove Entry actions.

## MainWindow Class Implementation

The constructor for `MainWindow` instantiates AddressWidget, sets it as its central widget and calls the `createMenus()` function.
The following code example is written in c++.

    MainWindow::MainWindow()
    {
        addressWidget = new AddressWidget;
        setCentralWidget(addressWidget);
        createMenus();
        setWindowTitle(tr("Address Book"));
    }

The `createMenus()` function sets up the File and Tools menus, connecting the actions to their respective slots. Both the Edit Entry... and Remove Entry actions are disabled by default as such actions cannot be carried out on an empty address book. They are only enabled when one or more contacts are added.
The following code example is written in c++.

    void MainWindow::createMenus()
    {
        fileMenu = menuBar()->addMenu(tr("&File"));

        openAct = new QAction(tr("&Open..."), this);
        fileMenu->addAction(openAct);
        connect(openAct, SIGNAL(triggered()),
            this, SLOT(openFile()));
    ...

        editAct = new QAction(tr("&Edit Entry..."), this);
        editAct->setEnabled(false);
        toolMenu->addAction(editAct);
        connect(editAct, SIGNAL(triggered()),
            addressWidget, SLOT(editEntry()));

        toolMenu->addSeparator();

        removeAct = new QAction(tr("&Remove Entry"), this);
        removeAct->setEnabled(false);
        toolMenu->addAction(removeAct);
        connect(removeAct, SIGNAL(triggered()),
            addressWidget, SLOT(removeEntry()));

        connect(addressWidget, SIGNAL(selectionChanged(const QItemSelection &)),
            this, SLOT(updateActions(const QItemSelection &)));
    }

Apart from connecting all the actions' signals to their respective slots, we also connect `AddressWidget`'s `selectionChanged()` signal to its `updateActions()` slot.

The `openFile()` function allows the user to choose a file with the open file dialog. The chosen file has to be a custom `.dat` file that contains address book contacts. This function is a slot connected to `openAct` in the File menu.
The following code example is written in c++.

    void MainWindow::openFile()
    {
        QString fileName = QFileDialog::getOpenFileName(this);
        if (!fileName.isEmpty()) {
            addressWidget->readFromFile(fileName);
        }
    }

The `saveFile()` function allows the user to save a file with the save file dialog. This function is a slot connected to `saveAct` in the File menu.
The following code example is written in c++.

    void MainWindow::saveFile()
    {
        QString fileName = QFileDialog::getSaveFileName(this);
        if (!fileName.isEmpty()) {
            addressWidget->writeToFile(fileName);
        }
    }

The `updateActions()` function enables and disables Edit Entry... and Remove Entry depending on the contents of the address book. If the address book is empty, these actions are disabled; otherwise, they are enabled. This function is a slot is connected to the `AddressWidget`'s `selectionChanged()` signal.
The following code example is written in c++.

    void MainWindow::updateActions(const QItemSelection &selection)
    {
        QModelIndexList indexes = selection.indexes();

        if (!indexes.isEmpty()) {
            removeAct->setEnabled(true);
            editAct->setEnabled(true);
        } else {
            removeAct->setEnabled(false);
            editAct->setEnabled(false);
        }
    }

## main() Function

The main function for the address book instantiates QApplication and opens a `MainWindow` before running the event loop.
The following code example is written in c++.

    int main(int argc, char *argv[])
    {
        QApplication app(argc, argv);
        MainWindow mw;
        mw.show();
        return app.exec();
    }