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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. Where \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
*/
