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/****************************************************************************
**
** Copyright (C) 2009 Nokia Corporation and/or its subsidiary(-ies).
** Contact: Nokia Corporation (qt-info@nokia.com)
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****************************************************************************/
/*!
\example widgets/sliders
\title Sliders Example
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.
\image sliders-example.png Screenshot of the Sliders example
The Sliders example consists of two classes:
\list
\o \c SlidersGroup is a custom widget. It combines a QSlider, a
QScrollBar and a QDial.
\o \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 examples/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 examples/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 examples/widgets/sliders/window.cpp 1
\snippet examples/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 examples/widgets/sliders/window.cpp 3
\snippet examples/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 \o \o{2,1} QSlider \o{2,1} QScrollBar \o{2,1} QDial
\header \o \o Normal \o Inverted \o Normal \o Inverted \o Normal \o Inverted
\row \o Qt::Horizontal \o Left to right \o Right to left \o Left to right \o Right to left \o Clockwise \o Counterclockwise
\row \o Qt::Vertical \o Bottom to top \o Top to bottom \o Top to bottom \o Bottom to top \o Clockwise \o 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 \key PageUp to mean "up" on the screen.
Note that for horizontal and vertical scroll bars, the key
bindings are inverted by default: \key PageDown increases the
current value, and \key PageUp decreases it.
\snippet examples/widgets/sliders/window.cpp 5
\snippet examples/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 \key
Up and \key 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 examples/widgets/sliders/window.cpp 7
\snippet examples/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 examples/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 examples/widgets/sliders/slidersgroup.cpp 0
First we create the slider-like widgets with the appropiate
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 examples/widgets/sliders/slidersgroup.cpp 1
\snippet examples/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 examples/widgets/sliders/slidersgroup.cpp 3
\codeline
\snippet examples/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 examples/widgets/sliders/slidersgroup.cpp 5
\snippet examples/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 examples/widgets/sliders/slidersgroup.cpp 7
\snippet examples/widgets/sliders/slidersgroup.cpp 8
\codeline
\snippet examples/widgets/sliders/slidersgroup.cpp 9
\snippet examples/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 examples/widgets/sliders/slidersgroup.cpp 11
\snippet examples/widgets/sliders/slidersgroup.cpp 12
\codeline
\snippet examples/widgets/sliders/slidersgroup.cpp 13
\snippet examples/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.
*/
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