source: trunk/doc/src/tutorials/addressbook.qdoc@ 651

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/*!
    \page tutorials-addressbook.html

    \startpage {index.html}{Qt Reference Documentation}
    \contentspage Tutorials
    \nextpage {tutorials/addressbook/part1}{Chapter 1}

    \title Address Book Tutorial
    \brief An introduction to GUI programming, showing how to put together a
    simple yet fully-functioning application.

    This tutorial gives an introduction to GUI programming using the Qt
    cross-platform framework.

    \image addressbook-tutorial-screenshot.png

    \omit
    It doesn't cover everything; the emphasis is on teaching the programming
    philosophy of GUI programming, and Qt's features are introduced as needed.
    Some commonly used features are never used in this tutorial.
    \endomit

    In the process, we will learn about some basic technologies provided by Qt,
    such as

    \list
    \o Widgets and layout managers
    \o Container classes
    \o Signals and slots
    \o Input and output devices
    \endlist

    If you are completely new to Qt, please read \l{How to Learn Qt} if you
    have not already done so.

    The tutorial's source code is located in Qt's \c examples/tutorials/addressbook
    directory.

    Tutorial chapters:

    \list 1
    \o \l{tutorials/addressbook/part1}{Designing the User Interface}
    \o \l{tutorials/addressbook/part2}{Adding Addresses}
    \o \l{tutorials/addressbook/part3}{Navigating between Entries}
    \o \l{tutorials/addressbook/part4}{Editing and Removing Addresses}
    \o \l{tutorials/addressbook/part5}{Adding a Find Function}
    \o \l{tutorials/addressbook/part6}{Loading and Saving}
    \o \l{tutorials/addressbook/part7}{Additional Features}
    \endlist

    Although this little application does not look much like a fully-fledged
    modern GUI application, it uses many of the basic techniques that are used
    in more complex applications. After you have worked through it, we
    recommend checking out the \l{mainwindows/application}{Application}
    example, which presents a small GUI application, with menus, toolbars, a
    status bar, and so on.
*/

/*!
    \page tutorials-addressbook-part1.html
    \contentspage {Address Book Tutorial}{Contents}
    \nextpage {tutorials/addressbook/part2}{Chapter 2}
    \example tutorials/addressbook/part1
    \title Address Book 1 - Designing the User Interface

    The first part of this tutorial covers the design of the basic graphical
    user interface (GUI) we use for the Address Book application.

    The first step to creating a GUI program is to design the user interface.
    In this chapter, our goal is to set up the labels and input fields needed
    to implement a basic address book application. The figure below is a
    screenshot of our expected output.

    \image addressbook-tutorial-part1-screenshot.png

    We require two QLabel objects, \c nameLabel and \c addressLabel, as well
    as two input fields, a QLineEdit object, \c nameLine, and a QTextEdit
    object, \c addressText, to enable the user to enter a contact's name and
    address. The widgets used and their positions are shown in the figure
    below.

    \image addressbook-tutorial-part1-labeled-screenshot.png

    There are three files used to implement this address book:

    \list
        \o \c{addressbook.h} - the definition file for the \c AddressBook
            class,
        \o \c{addressbook.cpp} - the implementation file for the
            \c AddressBook class, and
        \o \c{main.cpp} - the file containing a \c main() function, with
            an instance of \c AddressBook.
    \endlist

    \section1 Qt Programming - Subclassing

    When writing Qt programs, we usually subclass Qt objects to add
    functionality. This is one of the essential concepts behind creating
    custom widgets or collections of standard widgets. Subclassing to
    extend or change the behavior of a widget has the following advantages:

    \list
    \o We can write implementations of virtual or pure virtual functions to
    obtain exactly what we need, falling back on the base class's implementation
    when necessary.
    \o It allows us to encapsulate parts of the user interface within a class,
    so that the other parts of the application don't need to know about the
    individual widgets in the user interface.
    \o The subclass can be used to create multiple custom widgets in the same
    application or library, and the code for the subclass can be reused in other
    projects.
    \endlist

    Since Qt does not provide a specific address book widget, we subclass a
    standard Qt widget class and add features to it. The \c AddressBook class
    we create in this tutorial can be reused in situations where a basic address
    book widget is needed.

    \section1 Defining the AddressBook Class

    The \l{tutorials/addressbook/part1/addressbook.h}{\c addressbook.h} file is
    used to define the \c AddressBook class.

    We start by defining \c AddressBook as a QWidget subclass and declaring
    a constructor. We also use the Q_OBJECT macro to indicate that the class
    uses internationalization and Qt's signals and slots features, even
    if we do not use all of these features at this stage.

    \snippet tutorials/addressbook/part1/addressbook.h class definition

    The class holds declarations of \c nameLine and \c addressText, the
    private instances of QLineEdit and QTextEdit mentioned earlier.
    You will see, in the coming chapters, that data stored in \c nameLine and
    \c addressText is needed for many of the address book's functions.

    We do not need to include declarations of the QLabel objects we will use
    because we will not need to reference them once they have been created.
    The way Qt tracks the ownership of objects is explained in the next section.

    The Q_OBJECT macro itself implements some of the more advanced features of Qt.
    For now, it is useful to think of the Q_OBJECT macro as a shortcut which allows
    us to use the \l{QObject::}{tr()} and \l{QObject::}{connect()} functions.

    We have now completed the \c addressbook.h file and we move on to
    implement the corresponding \c addressbook.cpp file.

    \section1 Implementing the AddressBook Class

    The constructor of \c AddressBook accepts a QWidget parameter, \a parent.
    By convention, we pass this parameter to the base class's constructor.
    This concept of ownership, where a parent can have one or more children,
    is useful for grouping widgets in Qt. For example, if you delete a parent,
    all of its children will be deleted as well.

    \snippet tutorials/addressbook/part1/addressbook.cpp constructor and input fields

    Within this constructor, we declare and instantiate two local QLabel objects,
    \c nameLabel and \c addressLabel, as well as instantiate \c nameLine and
    \c addressText. The
    \l{QObject::tr()}{tr()} function returns a translated version of the
    string, if there is one available; otherwise, it returns the string itself.
    Think of this function as an \c{<insert translation here>} marker to mark
    QString objects for translation. You will notice, in the coming chapters as
    well as in the \l{Qt Examples}, that we include it whenever we use a
    translatable string.

    When programming with Qt, it is useful to know how layouts work.
    Qt provides three main layout classes: QHBoxLayout, QVBoxLayout
    and QGridLayout to handle the positioning of widgets.

    \image addressbook-tutorial-part1-labeled-layout.png

    We use a QGridLayout to position our labels and input fields in a
    structured manner. QGridLayout divides the available space into a grid and
    places widgets in the cells we specify with row and column numbers. The
    diagram above shows the layout cells and the position of our widgets, and
    we specify this arrangement using the following code:

    \snippet tutorials/addressbook/part1/addressbook.cpp layout

    Notice that \c addressLabel is positioned using Qt::AlignTop as an
    additional argument. This is to make sure it is not vertically centered in
    cell (1,0). For a basic overview on Qt Layouts, refer to the 
    \l{Layout Management} documentation.

    In order to install the layout object onto the widget, we have to invoke
    the widget's \l{QWidget::setLayout()}{setLayout()} function:

    \snippet tutorials/addressbook/part1/addressbook.cpp setting the layout

    Lastly, we set the widget's title to "Simple Address Book".

    \section1 Running the Application

    A separate file, \c main.cpp, is used for the \c main() function. Within
    this function, we instantiate a QApplication object, \c app. QApplication
    is responsible for various application-wide resources, such as the default
    font and cursor, and for running an event loop. Hence, there is always one
    QApplication object in every GUI application using Qt.

    \snippet tutorials/addressbook/part1/main.cpp main function

    We construct a new \c AddressBook widget on the stack and invoke
    its \l{QWidget::show()}{show()} function to display it.
    However, the widget will not be shown until the application's event loop
    is started. We start the event loop by calling the application's
    \l{QApplication::}{exec()} function; the result returned by this function
    is used as the return value from the \c main() function. At this point,
    it becomes apparent why we instanciated \c AddressBook on the stack: It
    will now go out of scope. Therefore, \c AddressBook and all its child widgets
    will be deleted, thus preventing memory leaks.
*/

/*!
    \page tutorials-addressbook-part2.html
    \previouspage Address Book 1 - Designing the User Interface
    \contentspage {Address Book Tutorial}{Contents}
    \nextpage {tutorials/addressbook/part3}{Chapter 3}
    \example tutorials/addressbook/part2
    \title Address Book 2 - Adding Addresses

    The next step to creating our basic address book application is to allow
    a little bit of user interaction.

    \image addressbook-tutorial-part2-add-contact.png

    We will provide a push button that the user can click to add a new contact.
    Also, some form of data structure is needed to store these contacts in an
    organized way.

    \section1 Defining the AddressBook Class

    Now that we have the labels and input fields set up, we add push buttons to
    complete the process of adding a contact. This means that our
    \c addressbook.h file now has three QPushButton objects declared and three
    corresponding public slots.

    \snippet tutorials/addressbook/part2/addressbook.h slots

    A slot is a function that responds to a particular signal. We will discuss
    this concept in further detail when implementing the \c AddressBook class.
    However, for an overview of Qt's signals and slots concept, you can refer
    to the \l{Signals and Slots} document.

    Three QPushButton objects: \c addButton, \c submitButton and
    \c cancelButton, are now included in our private variable declarations,
    along with \c nameLine and \c addressText from the last chapter.

    \snippet tutorials/addressbook/part2/addressbook.h pushbutton declaration

    We need a container to store our address book contacts, so that we can
    traverse and display them. A QMap object, \c contacts, is used for this
    purpose as it holds a key-value pair: the contact's name as the \e key,
    and the contact's address as the \e{value}.

    \snippet tutorials/addressbook/part2/addressbook.h remaining private variables

    We also declare two private QString objects, \c oldName and \c oldAddress.
    These objects are needed to hold the name and address of the contact that
    was last displayed, before the user clicked \gui Add. So, when the user clicks
    \gui Cancel, we can revert to displaying the details of the last contact.

    \section1 Implementing the AddressBook Class

    Within the constructor of \c AddressBook, we set the \c nameLine and
    \c addressText to read-only, so that we can only display but not edit
    existing contact details.

    \dots
    \snippet tutorials/addressbook/part2/addressbook.cpp setting readonly 1
    \dots
    \snippet tutorials/addressbook/part2/addressbook.cpp setting readonly 2

    Then, we instantiate our push buttons: \c addButton, \c submitButton, and
    \c cancelButton.

    \snippet tutorials/addressbook/part2/addressbook.cpp pushbutton declaration

    The \c addButton is displayed by invoking the \l{QPushButton::show()}
    {show()} function, while the \c submitButton and \c cancelButton are
    hidden by invoking \l{QPushButton::hide()}{hide()}. These two push
    buttons will only be displayed when the user clicks \gui Add and this is
    handled by the \c addContact() function discussed below.

    \snippet tutorials/addressbook/part2/addressbook.cpp connecting signals and slots

    We connect the push buttons' \l{QPushButton::clicked()}{clicked()} signal
    to their respective slots. The figure below illustrates this.

    \image addressbook-tutorial-part2-signals-and-slots.png

    Next, we arrange our push buttons neatly to the right of our address book
    widget, using a QVBoxLayout to line them up vertically.

    \snippet tutorials/addressbook/part2/addressbook.cpp vertical layout

    The \l{QBoxLayout::addStretch()}{addStretch()} function is used to ensure
    the push buttons are not evenly spaced, but arranged closer to the top of
    the widget. The figure below shows the difference between using
    \l{QBoxLayout::addStretch()}{addStretch()} and not using it.

    \image addressbook-tutorial-part2-stretch-effects.png

    We then add \c buttonLayout1 to \c mainLayout, using
    \l{QGridLayout::addLayout()}{addLayout()}. This gives us nested layouts
    as \c buttonLayout1 is now a child of \c mainLayout.

    \snippet tutorials/addressbook/part2/addressbook.cpp grid layout

    Our layout coordinates now look like this:

    \image addressbook-tutorial-part2-labeled-layout.png

    In the \c addContact() function, we store the last displayed contact
    details in \c oldName and \c oldAddress. Then we clear these input
    fields and turn off the read-only mode. The focus is set on \c nameLine
    and we display \c submitButton and \c cancelButton.

    \snippet tutorials/addressbook/part2/addressbook.cpp addContact

    The \c submitContact() function can be divided into three parts:

    \list 1
    \o We extract the contact's details from \c nameLine and \c addressText
    and store them in QString objects. We also validate to make sure that the
    user did not click \gui Submit with empty input fields; otherwise, a
    QMessageBox is displayed to remind the user for a name and address.

    \snippet tutorials/addressbook/part2/addressbook.cpp submitContact part1

    \o We then proceed to check if the contact already exists. If it does not
    exist, we add the contact to \c contacts and we display a QMessageBox to
    inform the user that the contact has been added.

    \snippet tutorials/addressbook/part2/addressbook.cpp submitContact part2

    If the contact already exists, again, we display a QMessageBox to inform
    the user about this, preventing the user from adding duplicate contacts.
    Our \c contacts object is based on key-value pairs of name and address,
    hence, we want to ensure that \e key is unique.

    \o Once we have handled both cases mentioned above, we restore the push
    buttons to their normal state with the following code:

    \snippet tutorials/addressbook/part2/addressbook.cpp submitContact part3

    \endlist

    The screenshot below shows the QMessageBox object we use to display
    information messages to the user.

    \image addressbook-tutorial-part2-add-successful.png

    The \c cancel() function restores the last displayed contact details and
    enables \c addButton, as well as hides \c submitButton and
    \c cancelButton.

    \snippet tutorials/addressbook/part2/addressbook.cpp cancel

    The general idea behind adding a contact is to give the user the
    flexibility to click \gui Submit or \gui Cancel at any time. The flowchart below
    further explains this concept:

    \image addressbook-tutorial-part2-add-flowchart.png
*/

/*!
    \page tutorials-addressbook-part3.html
    \previouspage Address Book 2 - Adding Addresses
    \contentspage {Address Book Tutorial}{Contents}
    \nextpage {tutorials/addressbook/part4}{Chapter 4}
    \example tutorials/addressbook/part3
    \title Address Book 3 - Navigating between Entries

    The address book application is now half complete. We need to add some
    functions to navigate between contacts. But first, we have to decide
    what sort of a data structure we would like to use to hold these contacts.

    In Chapter 2, we used a QMap of key-value pairs with the contact's name
    as the \e key, and the contact's address as the \e value. This works well
    for our case. However, in order to navigate and display each entry, a
    little bit of enhancement is needed.

    We enhance the QMap by making it replicate a data structure similar to a
    circularly-linked list, where all elements are connected, including the
    first element and the last element. The figure below illustrates this data
    structure.

    \image addressbook-tutorial-part3-linkedlist.png

    \section1 Defining the AddressBook Class

    In order to add navigation functions to the address book application, we
    need to add two more slots to our \c AddressBook class: \c next() and
    \c previous(). These are added to our \c addressbook.h file:

    \snippet tutorials/addressbook/part3/addressbook.h navigation functions

    We also require another two QPushButton objects, so we declare \c nextButton
    and \c previousButton as private variables:

    \snippet tutorials/addressbook/part3/addressbook.h navigation pushbuttons

    \section1 Implementing the AddressBook Class

    In the \c AddressBook constructor in \c addressbook.cpp, we instantiate
    \c nextButton and \c previousButton and disable them by default. This is
    because navigation is only enabled when there is more than one contact
    in the address book.

    \snippet tutorials/addressbook/part3/addressbook.cpp navigation pushbuttons

    We then connect these push buttons to their respective slots:

    \snippet tutorials/addressbook/part3/addressbook.cpp connecting navigation signals

    The image below is our expected graphical user interface. Notice that it
    is getting closer to our final application.

    \image addressbook-tutorial-part3-screenshot.png

    We follow basic conventions for \c next() and \c previous() functions by
    placing the \c nextButton on the right and the \c previousButton on the
    left. In order to achieve this intuitive layout, we use QHBoxLayout to
    place the widgets side-by-side:

    \snippet tutorials/addressbook/part3/addressbook.cpp navigation layout

    The QHBoxLayout object, \c buttonLayout2, is then added to \c mainLayout.

    \snippet tutorials/addressbook/part3/addressbook.cpp adding navigation layout

    The figure below shows the coordinates of the widgets in \c mainLayout.
    \image addressbook-tutorial-part3-labeled-layout.png

    Within our \c addContact() function, we have to disable these buttons so
    that the user does not attempt to navigate while adding a contact.

    \snippet tutorials/addressbook/part3/addressbook.cpp disabling navigation

    Also, in our \c submitContact() function, we enable the navigation
    buttons, \c nextButton and \c previousButton, depending on the size
    of \c contacts. As mentioned earlier, navigation is only enabled when
    there is more than one contact in the address book. The following lines
    of code demonstrates how to do this:

    \snippet tutorials/addressbook/part3/addressbook.cpp enabling navigation

    We also include these lines of code in the \c cancel() function.

    Recall that we intend to emulate a circularly-linked list with our QMap
    object, \c contacts. So, in the \c next() function, we obtain an iterator
    for \c contacts and then:

    \list
        \o If the iterator is not at the end of \c contacts, we increment it
        by one.
        \o If the iterator is at the end of \c contacts, we move it to the
        beginning of \c contacts. This gives us the illusion that our QMap is
        working like a circularly-linked list.
    \endlist

    \snippet tutorials/addressbook/part3/addressbook.cpp next() function

    Once we have iterated to the correct object in \c contacts, we display
    its contents on \c nameLine and \c addressText.

    Similarly, for the \c previous() function, we obtain an iterator for
    \c contacts and then:

    \list
        \o If the iterator is at the end of \c contacts, we clear the
        display and return.
        \o If the iterator is at the beginning of \c contacts, we move it to
        the end.
        \o We then decrement the iterator by one.
    \endlist

    \snippet tutorials/addressbook/part3/addressbook.cpp previous() function

    Again, we display the contents of the current object in \c contacts.

*/

/*!
    \page tutorials-addressbook-part4.html
    \previouspage Address Book 3 - Navigating between Entries
    \contentspage {Address Book Tutorial}{Contents}
    \nextpage {tutorials/addressbook/part5}{Chapter 5}
    \example tutorials/addressbook/part4
    \title Address Book 4 - Editing and Removing Addresses

    In this chapter, we look at ways to modify the contents of contacts stored
    in the address book application.

    \image addressbook-tutorial-screenshot.png

    We now have an address book that not only holds contacts in an organized
    manner, but also allows navigation. It would be convenient to include
    edit and remove functions so that a contact's details can be changed
    when needed. However, this requires a little improvement, in the form of
    enums. In our previous chapters, we had two modes: \c{AddingMode} and
    \c{NavigationMode} - but they were not defined as enums. Instead, we
    enabled and disabled the corresponding buttons manually, resulting in
    multiple lines of repeated code.

    In this chapter, we define the \c Mode enum with three different values:

    \list
        \o \c{NavigationMode},
        \o \c{AddingMode}, and
        \o \c{EditingMode}.
    \endlist

    \section1 Defining the AddressBook Class

    The \c addressbook.h file is updated to contain the \c Mode enum:

    \snippet tutorials/addressbook/part4/addressbook.h Mode enum

    We also add two new slots, \c editContact() and \c removeContact(), to
    our current list of public slots.

    \snippet tutorials/addressbook/part4/addressbook.h edit and remove slots

    In order to switch between modes, we introduce the \c updateInterface() function
    to control the enabling and disabling of all QPushButton objects. We also
    add two new push buttons, \c editButton and \c removeButton, for the edit
    and remove functions mentioned earlier.

    \snippet tutorials/addressbook/part4/addressbook.h updateInterface() declaration
    \dots
    \snippet tutorials/addressbook/part4/addressbook.h buttons declaration
    \dots
    \snippet tutorials/addressbook/part4/addressbook.h mode declaration

    Lastly, we declare \c currentMode to keep track of the enum's current mode.

    \section1 Implementing the AddressBook Class

    We now have to implement the mode-changing features of the address book
    application. The \c editButton and \c removeButton are instantiated and
    disabled by default, as the address book starts up with zero contacts in
    memory.

    \snippet tutorials/addressbook/part4/addressbook.cpp edit and remove buttons

    These buttons are then connected to their respective slots, \c editContact()
    and \c removeContact(), and we add them to \c buttonLayout1.

    \snippet tutorials/addressbook/part4/addressbook.cpp connecting edit and remove
    \dots
    \snippet tutorials/addressbook/part4/addressbook.cpp adding edit and remove to the layout

    The \c editContact() function stores the contact's old details in
    \c oldName and \c oldAddress, before switching the mode to \c EditingMode.
    In this mode, the \c submitButton and \c cancelButton are both enabled,
    hence, the user can change the contact's details and click either button.

    \snippet tutorials/addressbook/part4/addressbook.cpp editContact() function

    The \c submitContact() function has been divided in two with an \c{if-else}
    statement. We check \c currentMode to see if it's in \c AddingMode. If it is,
    we proceed with our adding process.

    \snippet tutorials/addressbook/part4/addressbook.cpp submitContact() function beginning
    \dots
    \snippet tutorials/addressbook/part4/addressbook.cpp submitContact() function part1

    Otherwise, we check to see if \c currentMode is in \c EditingMode. If it
    is, we compare \c oldName with \c name. If the name has changed, we remove
    the old contact from \c contacts and insert the newly updated contact.

    \snippet tutorials/addressbook/part4/addressbook.cpp submitContact() function part2

    If only the address has changed (i.e., \c oldAddress is not the same as \c address),
    we update the contact's address. Lastly, we set \c currentMode to
    \c NavigationMode. This is an important step as it re-enables all the
    disabled push buttons.

    To remove a contact from the address book, we implement the
    \c removeContact() function. This function checks to see if the contact
    exists in \c contacts.

    \snippet tutorials/addressbook/part4/addressbook.cpp removeContact() function

    If it does, we display a QMessageBox, to confirm the removal with the
    user. Once the user has confirmed, we call \c previous() to ensure that the
    user interface shows another contact, and we remove the contact using \l{QMap}'s
    \l{QMap::remove()}{remove()} function. As a courtesy, we display a QMessageBox
    to inform the user. Both the message boxes used in this function are shown below:

    \image addressbook-tutorial-part4-remove.png

    \section2 Updating the User Interface

    We mentioned the \c updateInterface() function earlier as a means to
    enable and disable the push buttons depending on the current mode.
    The function updates the current mode according to the \c mode argument
    passed to it, assigning it to \c currentMode before checking its value.

    Each of the push buttons is then enabled or disabled, depending on the
    current mode. The code for \c AddingMode and \c EditingMode is shown below:

    \snippet tutorials/addressbook/part4/addressbook.cpp update interface() part 1

    For \c NavigationMode, however, we include conditions within the parameters
    of the QPushButton::setEnabled() function. This is to ensure that
    \c editButton and \c removeButton are enabled when there is at least one
    contact in the address book; \c nextButton and \c previousButton are only
    enabled when there is more than one contact in the address book.

    \snippet tutorials/addressbook/part4/addressbook.cpp update interface() part 2

    By performing the task of setting the mode and updating the user interface in
    the same function, we avoid the possibility of the user interface getting "out
    of sync" with the internal state of the application.
*/

/*!
    \page tutorials-addressbook-part5.html
    \previouspage Address Book 4 - Editing and Removing Addresses
    \contentspage {Address Book Tutorial}{Contents}
    \nextpage {tutorials/addressbook/part6}{Chapter 6}
    \example tutorials/addressbook/part5
    \title Address Book 5 - Adding a Find Function

    In this chapter, we look at ways to locate contacts and addresses in
    the address book application.

    \image addressbook-tutorial-part5-screenshot.png

    As we keep adding contacts to our address book application, it becomes
    tedious to navigate them with the \e Next and \e Previous buttons. In this
    case, a \e Find function would be more efficient in looking up contacts.
    The screenshot above shows the \e Find button and its position on the panel
    of buttons.

    When the user clicks on the \e Find button, it is useful to display a
    dialog that can prompt the user for a contact's name. Qt provides QDialog,
    which we subclass in this chapter, to implement a \c FindDialog class.

    \section1 Defining the FindDialog Class

    \image addressbook-tutorial-part5-finddialog.png

    In order to subclass QDialog, we first include the header for QDialog in
    the \c finddialog.h file. Also, we use forward declaration to declare
    QLineEdit and QPushButton since we will be using those widgets in our
    dialog class.

    As in our \c AddressBook class, the \c FindDialog class includes
    the Q_OBJECT macro and its constructor is defined to accept a parent
    QWidget, even though the dialog will be opened as a separate window.

    \snippet tutorials/addressbook/part5/finddialog.h FindDialog header

    We define a public function, \c getFindText(), to be used by classes that
    instantiate \c FindDialog. This function allows these classes to obtain the
    search string entered by the user. A public slot, \c findClicked(), is also
    defined to handle the search string when the user clicks the \gui Find
    button.

    Lastly, we define the private variables, \c findButton, \c lineEdit
    and \c findText, corresponding to the \gui Find button, the line edit
    into which the user types the search string, and an internal string
    used to store the search string for later use.

    \section1 Implementing the FindDialog Class

    Within the constructor of \c FindDialog, we set up the private variables,
    \c lineEdit, \c findButton and \c findText. We use a QHBoxLayout to
    position the widgets.

    \snippet tutorials/addressbook/part5/finddialog.cpp constructor

    We set the layout and window title, as well as connect the signals to their
    respective slots. Notice that \c{findButton}'s \l{QPushButton::clicked()}
    {clicked()} signal is connected to to \c findClicked() and
    \l{QDialog::accept()}{accept()}. The \l{QDialog::accept()}{accept()} slot
    provided by QDialog hides the dialog and sets the result code to
    \l{QDialog::}{Accepted}. We use this function to help \c{AddressBook}'s
    \c findContact() function know when the \c FindDialog object has been
    closed. We will explain this logic in further detail when discussing the
    \c findContact() function.

    \image addressbook-tutorial-part5-signals-and-slots.png

    In \c findClicked(), we validate \c lineEdit to ensure that the user
    did not click the \gui Find button without entering a contact's name. Then, we set
    \c findText to the search string, extracted from \c lineEdit. After that,
    we clear the contents of \c lineEdit and hide the dialog.

    \snippet tutorials/addressbook/part5/finddialog.cpp findClicked() function

    The \c findText variable has a public getter function, \c getFindText(),
    associated with it. Since we only ever set \c findText directly in both the
    constructor and in the \c findClicked() function, we do not create a
    setter function to accompany \c getFindText().
    Because \c getFindText() is public, classes instantiating and using
    \c FindDialog can always access the search string that the user has
    entered and accepted.

    \snippet tutorials/addressbook/part5/finddialog.cpp getFindText() function

    \section1 Defining the AddressBook Class

    To ensure we can use \c FindDialog from within our \c AddressBook class, we
    include \c finddialog.h in the \c addressbook.h file.

    \snippet tutorials/addressbook/part5/addressbook.h include finddialog's header

    So far, all our address book features have a QPushButton and a
    corresponding slot. Similarly, for the \gui Find feature we have
    \c findButton and \c findContact().

    The \c findButton is declared as a private variable and the
    \c findContact() function is declared as a public slot.

    \snippet tutorials/addressbook/part5/addressbook.h findContact() declaration
    \dots
    \snippet tutorials/addressbook/part5/addressbook.h findButton declaration

    Lastly, we declare the private variable, \c dialog, which we will use to
    refer to an instance of \c FindDialog.

    \snippet tutorials/addressbook/part5/addressbook.h FindDialog declaration

    Once we have instantiated a dialog, we will want to use it more than once;
    using a private variable allows us to refer to it from more than one place
    in the class.

    \section1 Implementing the AddressBook Class

    Within the \c AddressBook class's constructor, we instantiate our private
    objects, \c findButton and \c findDialog:

    \snippet tutorials/addressbook/part5/addressbook.cpp instantiating findButton
    \dots
    \snippet tutorials/addressbook/part5/addressbook.cpp instantiating FindDialog

    Next, we connect the \c{findButton}'s
    \l{QPushButton::clicked()}{clicked()} signal to \c findContact().

    \snippet tutorials/addressbook/part5/addressbook.cpp signals and slots for find

    Now all that is left is the code for our \c findContact() function:

    \snippet tutorials/addressbook/part5/addressbook.cpp findContact() function

    We start out by displaying the \c FindDialog instance, \c dialog. This is
    when the user enters a contact name to look up. Once the user clicks
    the dialog's \c findButton, the dialog is hidden and the result code is
    set to QDialog::Accepted. This ensures that
    our \c if statement is always true.

    We then proceed to extract the search string, which in this case is
    \c contactName, using \c{FindDialog}'s \c getFindText() function. If the
    contact exists in our address book, we display it immediately. Otherwise,
    we display the QMessageBox shown below to indicate that their search
    failed.

    \image addressbook-tutorial-part5-notfound.png
*/

/*!
    \page tutorials-addressbook-part6.html
    \previouspage Address Book 5 - Adding a Find Function
    \contentspage {Address Book Tutorial}{Contents}
    \nextpage {tutorials/addressbook/part7}{Chapter 7}
    \example tutorials/addressbook/part6
    \title Address Book 6 - Loading and Saving

    This chapter covers the file handling features of Qt that we use to write
    loading and saving routines for the address book application.

    \image addressbook-tutorial-part6-screenshot.png

    Although browsing and searching for contacts are useful features, our
    address book is not ready for use until we can save existing contacts and
    load them again at a later time.

    Qt provides a number of classes for \l{Input/Output and Networking}
    {input and output}, but we have chosen to use two which are simple to use
    in combination: QFile and QDataStream.

    A QFile object represents a file on disk that can be read from and written
    to. QFile is a subclass of the more general QIODevice class which
    represents many different kinds of devices.

    A QDataStream object is used to serialize binary data so that it can be
    stored in a QIODevice and retrieved again later. Reading from a QIODevice
    and writing to it is as simple as opening the stream - with the respective
    device as a parameter - and reading from or writing to it.


    \section1 Defining the AddressBook Class

    We declare two public slots, \c saveToFile() and \c loadFromFile(), as well
    as two QPushButton objects, \c loadButton and \c saveButton.

    \snippet tutorials/addressbook/part6/addressbook.h save and load functions declaration
    \dots
    \snippet tutorials/addressbook/part6/addressbook.h save and load buttons declaration

    \section1 Implementing the AddressBook Class

    In our constructor, we instantiate \c loadButton and \c saveButton.
    Ideally, it would be more user-friendly to set the push buttons' labels
    to "Load contacts from a file" and "Save contacts to a file". However, due
    to the size of our other push buttons, we set the labels to \gui{Load...}
    and \gui{Save...}. Fortunately, Qt provides a simple way to set tooltips with
    \l{QWidget::setToolTip()}{setToolTip()} and we use it in the following way
    for our push buttons:

    \snippet tutorials/addressbook/part6/addressbook.cpp tooltip 1
    \dots
    \snippet tutorials/addressbook/part6/addressbook.cpp tooltip 2

    Although it is not shown here, just like the other features we implemented,
    we add the push buttons to the layout panel on the right, \c button1Layout,
    and we connect the push buttons' \l{QPushButton::clicked()}{clicked()}
    signals to their respective slots.

    For the saving feature, we first obtain \c fileName using
    QFileDialog::getSaveFileName(). This is a convenience function provided
    by QFileDialog, which pops up a modal file dialog and allows the user to
    enter a file name or select any existing \c{.abk} file. The \c{.abk} file
    is our Address Book extension that we create when we save contacts.

    \snippet tutorials/addressbook/part6/addressbook.cpp saveToFile() function part1

    The file dialog that pops up is displayed in the screenshot below:

    \image addressbook-tutorial-part6-save.png

    If \c fileName is not empty, we create a QFile object, \c file, with
    \c fileName. QFile works with QDataStream as QFile is a QIODevice.

    Next, we attempt to open the file in \l{QIODevice::}{WriteOnly} mode.
    If this is unsuccessful, we display a QMessageBox to inform the user.

    \snippet tutorials/addressbook/part6/addressbook.cpp saveToFile() function part2

    Otherwise, we instantiate a QDataStream object, \c out, to write the open
    file. QDataStream requires that the same version of the stream is used
    for reading and writing. We ensure that this is the case by setting the
    version used to the \l{QDataStream::Qt_4_5}{version introduced with Qt 4.5}
    before serializing the data to \c file.

    \snippet tutorials/addressbook/part6/addressbook.cpp saveToFile() function part3

    For the loading feature, we also obtain \c fileName using
    QFileDialog::getOpenFileName(). This function, the counterpart to
    QFileDialog::getSaveFileName(), also pops up the modal file dialog and
    allows the user to enter a file name or select any existing \c{.abk} file
    to load it into the address book.

    \snippet tutorials/addressbook/part6/addressbook.cpp loadFromFile() function part1

    On Windows, for example, this function pops up a native file dialog, as
    shown in the following screenshot.

    \image addressbook-tutorial-part6-load.png

    If \c fileName is not empty, again, we use a QFile object, \c file, and
    attempt to open it in \l{QIODevice::}{ReadOnly} mode. Similar to our
    implementation of \c saveToFile(), if this attempt is unsuccessful, we
    display a QMessageBox to inform the user.

    \snippet tutorials/addressbook/part6/addressbook.cpp loadFromFile() function part2

    Otherwise, we instantiate a QDataStream object, \c in, set its version as
    above and read the serialized data into the \c contacts data structure.
    The \c contacts object is emptied before data is read into it to simplify
    the file reading process. A more advanced method would be to read the
    contacts into a temporary QMap object, and copy over non-duplicate contacts
    into \c contacts.

    \snippet tutorials/addressbook/part6/addressbook.cpp loadFromFile() function part3

    To display the contacts that have been read from the file, we must first
    validate the data obtained to ensure that the file we read from actually
    contains address book contacts. If it does, we display the first contact;
    otherwise, we display a QMessageBox to inform the user about the problem.
    Lastly, we update the interface to enable and disable the push buttons
    accordingly.
*/

/*!
    \page tutorials-addressbook-part7.html
    \previouspage Address Book 6 - Loading and Saving
    \contentspage {Address Book Tutorial}{Contents}
    \example tutorials/addressbook/part7
    \title Address Book 7 - Additional Features

    This chapter covers some additional features that make the address book
    application more convenient for everyday use.

    \image addressbook-tutorial-part7-screenshot.png

    Although our address book application is useful in its own right, it would
    be useful if we could exchange contact data with other applications.
    The vCard format is a popular file format that can be used for this purpose.
    In this chapter, we extend our address book client to allow contacts to
    be exported to vCard \c{.vcf} files.

    \section1 Defining the AddressBook Class

    We add a QPushButton object, \c exportButton, and a corresponding public
    slot, \c exportAsVCard() to our \c AddressBook class in the
    \c addressbook.h file.

    \snippet tutorials/addressbook/part7/addressbook.h exportAsVCard() declaration
    \dots
    \snippet tutorials/addressbook/part7/addressbook.h exportButton declaration

    \section1 Implementing the AddressBook Class

    Within the \c AddressBook constructor, we connect \c{exportButton}'s
    \l{QPushButton::clicked()}{clicked()} signal to \c exportAsVCard().
    We also add this button to our \c buttonLayout1, the layout responsible
    for our panel of buttons on the right.

    In our \c exportAsVCard() function, we start by extracting the contact's
    name into \c name. We declare \c firstName, \c lastName and \c nameList.
    Next, we look for the index of the first white space in \c name. If there
    is a white space, we split the contact's name into \c firstName and
    \c lastName. Then, we replace the space with an underscore ("_").
    Alternately, if there is no white space, we assume that the contact only
    has a first name.

    \snippet tutorials/addressbook/part7/addressbook.cpp export function part1

    As with the \c saveToFile() function, we open a file dialog to let the user
    choose a location for the file. Using the file name chosen, we create an
    instance of QFile to write to.

    We attempt to open the file in \l{QIODevice::}{WriteOnly} mode. If this
    process fails, we display a QMessageBox to inform the user about the
    problem and return. Otherwise, we pass the file as a parameter to a
    QTextStream object, \c out. Like QDataStream, the QTextStream class
    provides functionality to read and write plain text to files. As a result,
    the \c{.vcf} file generated can be opened for editing in a text editor.

    \snippet tutorials/addressbook/part7/addressbook.cpp export function part2

    We then write out a vCard file with the \c{BEGIN:VCARD} tag, followed by
    the \c{VERSION:2.1} tag. The contact's name is written with the \c{N:}
    tag. For the \c{FN:} tag, which fills in the "File as" property of a vCard,
    we have to check whether the contact has a last name or not. If the contact
    does, we use the details in \c nameList to fill it. Otherwise, we write
    \c firstName only.

    \snippet tutorials/addressbook/part7/addressbook.cpp export function part3

    We proceed to write the contact's address. The semicolons in the address
    are escaped with "\\", the newlines are replaced with semicolons, and the
    commas are replaced with spaces. Lastly, we write the \c{ADR;HOME:;}
    tag, followed by \c address and then the \c{END:VCARD} tag.

    \snippet tutorials/addressbook/part7/addressbook.cpp export function part4

    In the end, a QMessageBox is displayed to inform the user that the vCard
    has been successfully exported.

    \e{vCard is a trademark of the \l{http://www.imc.org}
    {Internet Mail Consortium}}.
*/