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/*!
    \example widgets/sliders
    \title Sliders Example
    \ingroup examples-widgets
    \brief The Sliders example shows how to use the different types of sliders
    available in Qt: QSlider, QScrollBar and QDial.

    Qt provides three types of slider-like widgets: QSlider,
    QScrollBar and QDial. They all inherit most of their
    functionality from QAbstractSlider, and can in theory replace
    each other in an application since the differences only concern
    their look and feel. This example shows what they look like, how
    they work and how their behavior and appearance can be
    manipulated through their properties.

    The example also demonstrates how signals and slots can be used to
    synchronize the behavior of two or more widgets.

    \borderedimage sliders-example.png
    \caption Screenshot of the Sliders example

    The Sliders example consists of two classes:

    \list

    \li \c SlidersGroup is a custom widget. It combines a QSlider, a
    QScrollBar and a QDial.

    \li \c Window is the main widget combining a QGroupBox and a
    QStackedWidget. In this example, the QStackedWidget provides a
    stack of two \c SlidersGroup widgets. The QGroupBox contain
    several widgets that control the behavior of the slider-like
    widgets.

    \endlist

    First we will review the \c Window class, then we
    will take a look at the \c SlidersGroup class.

    \section1 Window Class Definition

    \snippet widgets/sliders/window.h 0

    The \c Window class inherits from QWidget. It displays the slider
    widgets and allows the user to set their minimum, maximum and
    current values and to customize their appearance, key bindings
    and orientation. We use a private \c createControls() function to
    create the widgets that provide these controlling mechanisms and
    to connect them to the slider widgets.

    \section1 Window Class Implementation

    \snippet widgets/sliders/window.cpp 0

    In the constructor we first create the two \c SlidersGroup
    widgets that display the slider widgets horizontally and
    vertically, and add them to the QStackedWidget. QStackedWidget
    provides a stack of widgets where only the top widget is visible.
    With \c createControls() we create a connection from a
    controlling widget to the QStackedWidget, making the user able to
    choose between horizontal and vertical orientation of the slider
    widgets. The rest of the controlling mechanisms is implemented by
    the same function call.

    \snippet widgets/sliders/window.cpp 1
    \snippet widgets/sliders/window.cpp 2

    Then we connect the \c horizontalSliders, \c verticalSliders and
    \c valueSpinBox to each other, so that the slider widgets and the
    control widget will behave synchronized when the current value of
    one of them changes. The \c valueChanged() signal is emitted with
    the new value as argument. The \c setValue() slot sets the
    current value of the widget to the new value, and emits \c
    valueChanged() if the new value is different from the old one.

    We put the group of control widgets and the stacked widget in a
    horizontal layout before we initialize the minimum, maximum and
    current values. The initialization of the current value will
    propagate to the slider widgets through the connection we made
    between \c valueSpinBox and the \c SlidersGroup widgets. The
    minimum and maximum values propagate through the connections we
    created with \c createControls().

    \snippet widgets/sliders/window.cpp 3
    \snippet widgets/sliders/window.cpp 4

    In the private \c createControls() function, we let a QGroupBox
    (\c controlsGroup) display the control widgets. A group box can
    provide a frame, a title and a keyboard shortcut, and displays
    various other widgets inside itself. The group of control widgets
    is composed by two checkboxes, three spin boxes (with labels) and
    one combobox.

    After creating the labels, we create the two checkboxes.
    Checkboxes are typically used to represent features in an
    application that can be enabled or disabled. When \c
    invertedAppearance is enabled, the slider values are inverted.
    The table below shows the appearance for the different
    slider-like widgets:

    \table
    \header \li                \li{2,1} QSlider                   \li{2,1} QScrollBar                \li{2,1} QDial
    \header \li                \li Normal        \li Inverted      \li Normal        \li Inverted      \li Normal         \li Inverted
    \row    \li Qt::Horizontal \li Left to right \li Right to left \li Left to right \li Right to left \li Clockwise \li Counterclockwise
    \row    \li Qt::Vertical   \li Bottom to top \li Top to bottom \li Top to bottom \li Bottom to top \li Clockwise \li Counterclockwise
    \endtable

    It is common to invert the appearance of a vertical QSlider. A
    vertical slider that controls volume, for example, will typically
    go from bottom to top (the non-inverted appearance), whereas a
    vertical slider that controls the position of an object on screen
    might go from top to bottom, because screen coordinates go from
    top to bottom.

    When the \c invertedKeyBindings option is enabled (corresponding
    to the QAbstractSlider::invertedControls property), the slider's
    wheel and key events are inverted. The normal key bindings mean
    that scrolling the mouse wheel "up" or using keys like page up
    will increase the slider's current value towards its maximum.
    Inverted, the same wheel and key events will move the value
    toward the slider's minimum. This can be useful if the \e
    appearance of a slider is inverted: Some users might expect the
    keys to still work the same way on the value, whereas others
    might expect \uicontrol PageUp to mean "up" on the screen.

    Note that for horizontal and vertical scroll bars, the key
    bindings are inverted by default: \uicontrol PageDown increases the
    current value, and \uicontrol PageUp decreases it.

    \snippet widgets/sliders/window.cpp 5
    \snippet widgets/sliders/window.cpp 6

    Then we create the spin boxes. QSpinBox allows the user to choose
    a value by clicking the up and down buttons or pressing the \uicontrol
    Up and \uicontrol Down keys on the keyboard to modify the value
    currently displayed. The user can also type in the value
    manually. The spin boxes control the minimum, maximum and current
    values for the QSlider, QScrollBar, and QDial widgets.

    We create a QComboBox that allows the user to choose the
    orientation of the slider widgets. The QComboBox widget is a
    combined button and popup list. It provides a means of presenting
    a list of options to the user in a way that takes up the minimum
    amount of screen space.

    \snippet widgets/sliders/window.cpp 7
    \snippet widgets/sliders/window.cpp 8

    We synchronize the behavior of the control widgets and the slider
    widgets through their signals and slots. We connect each control
    widget to both the horizontal and vertical group of slider
    widgets. We also connect \c orientationCombo to the
    QStackedWidget, so that the correct "page" is shown. Finally, we
    lay out the control widgets in a QGridLayout within the \c
    controlsGroup group box.

    \section1 SlidersGroup Class Definition

    \snippet widgets/sliders/slidersgroup.h 0

    The \c SlidersGroup class inherits from QGroupBox. It provides a
    frame and a title, and contains a QSlider, a QScrollBar and a
    QDial.

    We provide a \c valueChanged() signal and a public \c setValue()
    slot with equivalent functionality to the ones in QAbstractSlider
    and QSpinBox. In addition, we implement several other public
    slots to set the minimum and maximum value, and invert the slider
    widgets' appearance as well as key bindings.

    \section1 SlidersGroup Class Implementation

    \snippet widgets/sliders/slidersgroup.cpp 0

    First we create the slider-like widgets with the appropriate
    properties. In particular we set the focus policy for each
    widget. Qt::FocusPolicy is an enum type that defines the various
    policies a widget can have with respect to acquiring keyboard
    focus. The Qt::StrongFocus policy means that the widget accepts
    focus by both tabbing and clicking.

    Then we connect the widgets with each other, so that they will
    stay synchronized when the current value of one of them changes.

    \snippet widgets/sliders/slidersgroup.cpp 1
    \snippet widgets/sliders/slidersgroup.cpp 2

    We connect \c {dial}'s \c valueChanged() signal to the
    \c{SlidersGroup}'s \c valueChanged() signal, to notify the other
    widgets in the application (i.e., the control widgets) of the
    changed value.

    \snippet widgets/sliders/slidersgroup.cpp 3
    \codeline
    \snippet widgets/sliders/slidersgroup.cpp 4

    Finally, depending on the \l {Qt::Orientation}{orientation} given
    at the time of construction, we choose and create the layout for
    the slider widgets within the group box.

    \snippet widgets/sliders/slidersgroup.cpp 5
    \snippet widgets/sliders/slidersgroup.cpp 6

    The \c setValue() slot sets the value of the QSlider. We don't
    need to explicitly call
    \l{QAbstractSlider::setValue()}{setValue()} on the QScrollBar and
    QDial widgets, since QSlider will emit the
    \l{QAbstractSlider::valueChanged()}{valueChanged()} signal when
    its value changes, triggering a domino effect.

    \snippet widgets/sliders/slidersgroup.cpp 7
    \snippet widgets/sliders/slidersgroup.cpp 8
    \codeline
    \snippet widgets/sliders/slidersgroup.cpp 9
    \snippet widgets/sliders/slidersgroup.cpp 10

    The \c setMinimum() and \c setMaximum() slots are used by the \c
    Window class to set the range of the QSlider, QScrollBar, and
    QDial widgets.

    \snippet widgets/sliders/slidersgroup.cpp 11
    \snippet widgets/sliders/slidersgroup.cpp 12
    \codeline
    \snippet widgets/sliders/slidersgroup.cpp 13
    \snippet widgets/sliders/slidersgroup.cpp 14

    The \c invertAppearance() and \c invertKeyBindings() slots
    control the child widgets'
    \l{QAbstractSlider::invertedAppearance}{invertedAppearance} and
    \l{QAbstractSlider::invertedControls}{invertedControls}
    properties.
*/