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/*!

    \example itemviews/addressbook

    \title Address Book Example

    The address book example shows how to use proxy models to display

    different views onto data from a single model.

    \image addressbook-example.png Screenshot of the Address Book example

    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.

    \section1 Overview

    The address book contains 5 classes: \c MainWindow,

    \c AddressWidget, \c TableModel, \c NewAddressTab and

    \c AddDialog. The \c MainWindow class uses \c AddressWidget as

    its central widget and provides \gui File and \gui Tools menus.

    \image addressbook-classes.png Diagram for Address Book Example

    The \c 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 \c NewAddressTab.

    The \c NewAddressTab class is a subclass of QWidget that

    is only used whenever the address book is empty, prompting the

    user to add some contacts. \c AddressWidget also interacts with

    an instance of \c TableModel to add, edit and remove entries to

    the address book.

    \c TableModel is a subclass of QAbstractTableModel that provides

    the standard model/view API to access data. It also holds a

    QList of \l{QPair}s 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 \c AddDialog class is

    used to obtain information from the user for the address book.

    This QDialog subclass is instantiated by \c NewAddressTab to

    add contacts, and by \c AddressWidget to add and edit contacts.

    We begin by looking at the \c TableModel implementation.

    \section1 TableModel Class Definition

    The \c TableModel class provides standard API to access data in

    its QList of \l{QPair}s by subclassing QAbstractTableModel. The

    basic functions that must be implemented in order to do so are:

    \c rowCount(), \c columnCount(), \c data(), \c headerData().

    For TableModel to be editable, it has to provide implementations

    \c insertRows(), \c removeRows(), \c setData() and \c flags()

    functions.

    \snippet itemviews/addressbook/tablemodel.h 0

    Two constructors are used, a default constructor which uses

    \c TableModel's own \c {QList<QPair<QString, QString>>} and one

    that takes \c {QList<QPair<QString, QString>} as an argument,

    for convenience.

    \section1 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.

    \snippet itemviews/addressbook/tablemodel.cpp 0

    The \c rowCount() and \c columnCount() functions return the

    dimensions of the model. Whereas, \c rowCount()'s value will vary

    depending on the number of contacts added to the address book,

    \c columnCount()'s value is always 2 because we only need space

    for the \bold Name and \bold Address columns.

    \note The \c Q_UNUSED() macro prevents the compiler from

    generating warnings regarding unused parameters.

    \snippet itemviews/addressbook/tablemodel.cpp 1

    The \c data() function returns either a \bold Name or

    \bold {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

    \c AddressWidget.

    \snippet itemviews/addressbook/tablemodel.cpp 2

    The \c headerData() function displays the table's header,

    \bold Name and \bold 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 \c AddressWidget

    implementation).

    \snippet itemviews/addressbook/tablemodel.cpp 3

    The \c insertRows() function is called before new data is added,

    otherwise the data will not be displayed. The

    \c beginInsertRows() and \c endInsertRows() functions are called

    to ensure all connected views are aware of the changes.

    \snippet itemviews/addressbook/tablemodel.cpp 4

    The \c removeRows() function is called to remove data. Again,

    \l{QAbstractItemModel::}{beginRemoveRows()} and

    \l{QAbstractItemModel::}{endRemoveRows()} are called to ensure

    all connected views are aware of the changes.

    \snippet itemviews/addressbook/tablemodel.cpp 5

    The \c 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, \c setData() must be called

    twice, as each row has 2 columns. It is important to emit the

    \l{QAbstractItemModel::}{dataChanged()} signal as it tells all

    connected views to update their displays.

    \snippet itemviews/addressbook/tablemodel.cpp 6

    The \c flags() function returns the item flags for the given

    index.

    \snippet itemviews/addressbook/tablemodel.cpp 7

    We set the Qt::ItemIsEditable flag because we want to allow the

    \c 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 \c {TableModel}, \c 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 \c AddressWidget.

    \snippet itemviews/addressbook/tablemodel.cpp 8

    \section1 AddressWidget Class Definition

    The \c 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.

    \snippet itemviews/addressbook/addresswidget.h 0

    \c AddressWidget extends QTabWidget in order to hold 10 tabs

    (\c NewAddressTab and the 9 alphabet group tabs) and also

    manipulates \c table, the \c TableModel object, \c proxyModel,

    the QSortFilterProxyModel object that we use to filter the

    entries, and \c tableView, the QTableView object.

    \section1 AddressWidget Class Implementation

    The \c AddressWidget constructor accepts a parent widget and

    instantiates \c NewAddressTab, \c TableModel and

    QSortFilterProxyModel. The \c 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 \c setupTabs().

    \snippet itemviews/addressbook/addresswidget.cpp 0

    The \c setupTabs() function is used to set up the 9 alphabet

    group tabs, table views and proxy models in

    \c AddressWidget. Each proxy model in turn is set to filter

    contact names according to the relevant alphabet group using a

    \l{Qt::CaseInsensitive}{case-insensitive} QRegExp object. The

    table views are also sorted in ascending order using the

    corresponding proxy model's \l{QSortFilterProxyModel::}{sort()}

    function.

    Each table view's \l{QTableView::}{selectionMode} is set to

    QAbstractItemView::SingleSelection and

    \l{QTableView::}{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.

    \snippet itemviews/addressbook/addresswidget.cpp 1

    The QItemSelectionModel class provides a

    \l{QItemSelectionModel::selectionChanged()}{selectionChanged}

    signal that is connected to \c{AddressWidget}'s

    \c selectionChanged() signal. This signal to signal connection

    is necessary to enable the \gui{Edit Entry...} and

    \gui{Remove Entry} actions in \c MainWindow's Tools menu. This

    connection is further explained in \c 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.

    \image addressbook-signals.png Signals and Slots Connections

    We provide 2 \c 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

    \c newAddressTab to  insert data without having to popup a dialog.

    The first \c addEntry() function is a slot connected to the

    \c MainWindow's \gui{Add Entry...} action. This function creates an

    \c AddDialog object and then calls the second \c addEntry()

    function to actually add the contact to \c table.

    \snippet itemviews/addressbook/addresswidget.cpp 2

    Basic validation is done in the second \c addEntry() function to

    prevent duplicate entries in the address book. As mentioned with

    \c TableModel, this is part of the reason why we require the

    getter method \c getList().

    \snippet itemviews/addressbook/addresswidget.cpp 3

    If the model does not already contain an entry with the same name,

    we call \c setData() to insert the name and address into the

    first and second columns. Otherwise, we display a QMessageBox

    to inform the user.

    \note The \c 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

    \c selectionModel from the \c tableView to obtain the selected

    indexes.

    \snippet itemviews/addressbook/addresswidget.cpp 4a

    Next we extract data from the row the user intends to 

    edit. This data is displayed in an instance of \c AddDialog

    with a different window title. The \c table is only

    updated if changes have been made to data in \c aDialog.

    \snippet itemviews/addressbook/addresswidget.cpp 4b

    \image addressbook-editdialog.png Screenshot of Dialog to Edit a Contact

    Entries are removed using the \c removeEntry() function.

    The selected row is removed by accessing it through the

    QItemSelectionModel object, \c selectionModel. The

    \c newAddressTab is re-added to the \c AddressWidget only if

    the user removes all the contacts in the address book.

    \snippet itemviews/addressbook/addresswidget.cpp 5

    The \c writeToFile() function is used to save a file containing

    all the contacts in the address book. The file is saved in a

    custom \c{.dat} format. The contents of the QList of \l{QPair}s

    are written to \c file using QDataStream. If the file cannot be

    opened, a QMessageBox is displayed with the related error message.

    \snippet itemviews/addressbook/addresswidget.cpp 6

    The \c readFromFile() function loads a file containing all the

    contacts in the address book, previously saved using

    \c writeToFile(). QDataStream is used to read the contents of a

    \c{.dat} file into a list of pairs and each of these is added

    using \c addEntry().

    \snippet itemviews/addressbook/addresswidget.cpp 7

    \section1 NewAddressTab Class Definition

    The \c 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 \c{AddressWidget}'s implementation.

    \image addressbook-newaddresstab.png Screenshot of NewAddressTab

    The \c NewAddressTab class extends QWidget and contains a QLabel

    and QPushButton.

    \snippet itemviews/addressbook/newaddresstab.h 0

    \section1 NewAddressTab Class Implementation

    The constructor instantiates the \c addButton,

    \c descriptionLabel and connects the \c{addButton}'s signal to

    the \c{addEntry()} slot.

    \snippet itemviews/addressbook/newaddresstab.cpp 0

    The \c addEntry() function is similar to \c AddressWidget's

    \c addEntry() in the sense that both functions instantiate an

    \c AddDialog object. Data from the dialog is extracted and sent

    to \c AddressWidget's \c addEntry() slot by emitting the

    \c sendDetails() signal.

    \snippet itemviews/addressbook/newaddresstab.cpp 1

    \image signals-n-slots-aw-nat.png

    \section1 AddDialog Class Definition

    The \c AddDialog class extends QDialog and provides the user

    with a QLineEdit and a QTextEdit to input data into the

    address book.

    \snippet itemviews/addressbook/adddialog.h 0

    \image addressbook-adddialog.png

    \section1 AddDialog Class Implementation

    The \c AddDialog's constructor sets up the user interface,

    creating the necessary widgets and placing them into layouts.

    \snippet itemviews/addressbook/adddialog.cpp 0

    To give the dialog the desired behavior, we connect the \gui OK

    and \gui Cancel buttons to the dialog's \l{QDialog::}{accept()} and

    \l{QDialog::}{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.

    \section1 MainWindow Class Definition

    The \c MainWindow class extends QMainWindow and implements the

    menus and actions necessary to manipulate the address book.

    \table

    \row \o \inlineimage addressbook-filemenu.png

         \o \inlineimage addressbook-toolsmenu.png

    \endtable

    \snippet itemviews/addressbook/mainwindow.h 0

    The \c MainWindow class uses an \c AddressWidget as its central

    widget and provides the File menu with \gui Open, \gui Close and

    \gui Exit actions, as well as the \gui Tools menu with

    \gui{Add Entry...}, \gui{Edit Entry...} and \gui{Remove Entry}

    actions.

    \section1 MainWindow Class Implementation

    The constructor for \c MainWindow instantiates AddressWidget,

    sets it as its central widget and calls the \c createMenus()

    function.

    \snippet itemviews/addressbook/mainwindow.cpp 0

    The \c createMenus() function sets up the \gui File and

    \gui Tools menus, connecting the actions to their respective slots.

    Both the \gui{Edit Entry...} and \gui{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.

    \snippet itemviews/addressbook/mainwindow.cpp 1a

    \dots

    \codeline

    \snippet itemviews/addressbook/mainwindow.cpp 1b

    Apart from connecting all the actions' signals to their

    respective slots, we also connect \c AddressWidget's

    \c selectionChanged() signal to its \c updateActions() slot.

    The \c openFile() function allows the user to choose a file with

    the \l{QFileDialog::getOpenFileName()}{open file dialog}. The chosen

    file has to be a custom \c{.dat} file that contains address book

    contacts. This function is a slot connected to \c openAct in the

    \gui File menu.

    \snippet itemviews/addressbook/mainwindow.cpp 2

    The \c saveFile() function allows the user to save a file with

    the \l{QFileDialog::getSaveFileName()}{save file dialog}. This function

    is a slot connected to \c saveAct in the \gui File menu.

    \snippet itemviews/addressbook/mainwindow.cpp 3

    The \c updateActions() function enables and disables

    \gui{Edit Entry...} and \gui{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 \c AddressWidget's \c selectionChanged()

    signal.

    \snippet itemviews/addressbook/mainwindow.cpp 4

    \section1 main() Function

    The main function for the address book instantiates QApplication

    and opens a \c MainWindow before running the event loop.

    \snippet itemviews/addressbook/main.cpp 0

*/