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/*!

    \title Calendar Widget Example

    \example widgets/calendarwidget

    The Calendar Widget example shows use of \c QCalendarWidget.

    \image calendarwidgetexample.png

    QCalendarWidget displays one calendar month

    at a time and lets the user select a date.

    The calendar consists of four components: a navigation

    bar that lets the user change the month that is

    displayed, a grid where each cell represents one day

    in the month, and two headers that display weekday names

    and week numbers.

    The Calendar Widget example displays a QCalendarWidget and lets the user

    configure its appearance and behavior using

    \l{QComboBox}es, \l{QCheckBox}es, and \l{QDateEdit}s. In

    addition, the user can influence the formatting of individual dates

    and headers.

    The properties of the QCalendarWidget are summarized in the table

    below.

    \table

    \header \o Property

            \o Description

    \row \o \l{QCalendarWidget::}{selectedDate}

         \o The currently selected date.

    \row \o \l{QCalendarWidget::}{minimumDate}

         \o The earliest date that can be selected.

    \row \o \l{QCalendarWidget::}{maximumDate}

         \o The latest date that can be selected.

    \row \o \l{QCalendarWidget::}{firstDayOfWeek}

         \o The day that is displayed as the first day of the week

            (usually Sunday or Monday).

    \row \o \l{QCalendarWidget::}{gridVisible}

         \o Whether the grid should be shown.

    \row \o \l{QCalendarWidget::}{selectionMode}

         \o Whether the user can select a date or not.

    \row \o \l{QCalendarWidget::}{horizontalHeaderFormat}

         \o The format of the day names in the horizontal header

            (e.g., "M", "Mon", or "Monday").

    \row \o \l{QCalendarWidget::}{verticalHeaderFormat}

         \o The format of the vertical header.

    \row \o \l{QCalendarWidget::}{navigationBarVisible}

         \o Whether the navigation bar at the top of the calendar

            widget is shown.

    \endtable

    The example consists of one class, \c Window, which creates and

    lays out the QCalendarWidget and the other widgets that let the

    user configure the QCalendarWidget.

    \section1 Window Class Definition

    Here is the definition of the \c Window class:

    \snippet examples/widgets/calendarwidget/window.h 0

    \dots

    \snippet examples/widgets/calendarwidget/window.h 1

    As is often the case with classes that represent self-contained

    windows, most of the API is private. We will review the private

    members as we stumble upon them in the implementation.

    \section1 Window Class Implementation

    Let's now review the class implementation, starting with the constructor:

    \snippet examples/widgets/calendarwidget/window.cpp 0

    We start by creating the four \l{QGroupBox}es and their child

    widgets (including the QCalendarWidget) using four private \c

    create...GroupBox() functions, described below. Then we arrange

    the group boxes in a QGridLayout.

    We set the grid layout's resize policy to QLayout::SetFixedSize to

    prevent the user from resizing the window. In that mode, the

    window's size is set automatically by QGridLayout based on the

    size hints of its contents widgets.

    To ensure that the window isn't automatically resized every time

    we change a property of the QCalendarWidget (e.g., hiding the

    navigation bar, trhe vertical header, or the grid), we set the

    minimum height of row 0 and the minimum width of column 0 to the

    initial size of the QCalendarWidget.

    Let's move on to the \c createPreviewGroupBox() function:

    \snippet examples/widgets/calendarwidget/window.cpp 9

    The \gui Preview group box contains only one widget: the

    QCalendarWidget. We set it up, connect its

    \l{QCalendarWidget::}{currentPageChanged()} signal to our \c

    reformatCalendarPage() slot to make sure that every new page gets

    the formatting specified by the user.

    The \c createGeneralOptionsGroupBox() function is somewhat large

    and several widgets are set up the same way; we look at parts of

    its implementation here and skip the rest:

    \snippet examples/widgets/calendarwidget/window.cpp 10

    \dots

    We start with the setup of the \gui{Week starts on} combobox.

    This combobox controls which day should be displayed as the first

    day of the week.

    The QComboBox class lets us attach user data as a QVariant to

    each item. The data can later be retrieved with QComboBox's

    \l{QComboBox::}{itemData()} function. QVariant doesn't directly

    support the Qt::DayOfWeek data type, but it supports \c int, and

    C++ will happily convert any enum value to \c int.

    \dots

    \snippet examples/widgets/calendarwidget/window.cpp 11

    \dots

    After creating the widgets, we connect the signals and slots. We

    connect the comboboxes to private slots of \c Window or to

    public slots provided by QComboBox.

    \dots

    \snippet examples/widgets/calendarwidget/window.cpp 12

    At the end of the function, we call the slots that update the calendar to ensure

    that the QCalendarWidget is synchronized with the other widgets on startup.

    Let's now take a look at the \c createDatesGroupBox() private function:

    \snippet examples/widgets/calendarwidget/window.cpp 13

    In this function, we create the \gui {Minimum Date}, \gui {Maximum Date},

    and \gui {Current Date} editor widgets,

    which control the calendar's minimum, maximum, and selected dates.

    The calendar's minimum and maximum dates have already been

    set in \c createPrivewGroupBox(); we can then set the widgets

    default values to the calendars values.

    \snippet examples/widgets/calendarwidget/window.cpp 14

    \dots

    \snippet examples/widgets/calendarwidget/window.cpp 15

    We connect the \c currentDateEdit's

    \l{QDateEdit::}{dateChanged()} signal directly to the calendar's

    \l{QCalendarWidget::}{setSelectedDate()} slot. When the calendar's

    selected date changes, either as a result of a user action or

    programmatically, our \c selectedDateChanged() slot updates

    the \gui {Current Date} editor. We also need to react when the user

    changes the \gui{Minimum Date} and \gui{Maximum Date} editors.

    Here is the \c createTextFormatsGroup() function:

    \snippet examples/widgets/calendarwidget/window.cpp 16

    We set up the \gui {Weekday Color} and \gui {Weekend Color} comboboxes

    using \c createColorCombo(), which instantiates a QComboBox and

    populates it with colors ("Red", "Blue", etc.).

    \snippet examples/widgets/calendarwidget/window.cpp 17

    The \gui {Header Text Format} combobox lets the user change the

    text format (bold, italic, or plain) used for horizontal and

    vertical headers. The \gui {First Friday in blue} and \gui {May 1

    in red} check box affect the rendering of specific dates.

    \snippet examples/widgets/calendarwidget/window.cpp 18

    We connect the check boxes and comboboxes to various private

    slots. The \gui {First Friday in blue} and \gui {May 1 in red}

    check boxes are both connected to \c reformatCalendarPage(),

    which is also called when the calendar switches month.

    \dots

    \snippet examples/widgets/calendarwidget/window.cpp 19

    At the end of \c createTextFormatsGroupBox(), we call private

    slots to synchronize the QCalendarWidget with the other widgets.

    We're now done reviewing the four \c create...GroupBox()

    functions. Let's now take a look at the other private functions

    and slots.

    \snippet examples/widgets/calendarwidget/window.cpp 20

    In \c createColorCombo(), we create a combobox and populate it with

    standard colors. The second argument to QComboBox::addItem()

    is a QVariant storing user data (in this case, QColor objects).

    This function was used to set up the \gui {Weekday Color}

    and \gui {Weekend Color} comboboxes.

    \snippet examples/widgets/calendarwidget/window.cpp 1

    When the user changes the \gui {Week starts on} combobox's

    value, \c firstDayChanged() is invoked with the index of the

    combobox's new value. We retrieve the custom data item

    associated with the new current item using

    \l{QComboBox::}{itemData()} and cast it to a Qt::DayOfWeek.

    \c selectionModeChanged(), \c horizontalHeaderChanged(), and \c

    verticalHeaderChanged() are very similar to \c firstDayChanged(),

    so they are omitted.

    \snippet examples/widgets/calendarwidget/window.cpp 2

    The \c selectedDateChanged() updates the \gui{Current Date}

    editor to reflect the current state of the QCalendarWidget.

    \snippet examples/widgets/calendarwidget/window.cpp 3

    When the user changes the minimum date, we tell the

    QCalenderWidget. We also update the \gui {Maximum Date} editor,

    because if the new minimum date is later than the current maximum

    date, QCalendarWidget will automatically adapt its maximum date

    to avoid a contradicting state.

    \snippet examples/widgets/calendarwidget/window.cpp 4

    \c maximumDateChanged() is implemented similarly to \c

    minimumDateChanged().

    \snippet examples/widgets/calendarwidget/window.cpp 5

    Each combobox item has a QColor object as user data corresponding to the

    item's text. After fetching the colors from the comboboxes, we

    set the text format of each day of the week.

    The text format of a column in the calendar is given as a

    QTextCharFormat, which besides the foreground color lets us

    specify various character formatting information. In this

    example, we only show a subset of the possibilities.

    \snippet examples/widgets/calendarwidget/window.cpp 6

    \c weekendFormatChanged() is the same as \c

    weekdayFormatChanged(), except that it affects Saturday and

    Sunday instead of Monday to Friday.

    \snippet examples/widgets/calendarwidget/window.cpp 7

    The \c reformatHeaders() slot is called when the user

    changes the text format of

    the headers. We compare the current text of the \gui {Header Text Format}

    combobox to determine which format to apply. (An alternative would

    have been to store \l{QTextCharFormat} values alongside the combobox

    items.)

    \snippet examples/widgets/calendarwidget/window.cpp 8

    In \c reformatCalendarPage(), we set the text format of the first

    Friday in the month and May 1 in the current year. The text

    formats that are actually used depend on which check boxes are

    checked.

    QCalendarWidget lets us set the text format of individual dates

    with the \l{QCalendarWidget::}{setDateTextFormat()}. We chose to

    set the dates when the calendar page changes, i.e., a new month is

    displayed. We check which of the \c mayFirstCheckBox and \c

    firstDayCheckBox, if any, are checked

    and set the text formats accordingly.

*/