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/****************************************************************************
**
** Copyright (C) 2012 Digia Plc and/or its subsidiary(-ies).
** Contact: http://www.qt-project.org/legal
**
** This file is part of the documentation of the Qt Toolkit.
**
** $QT_BEGIN_LICENSE:FDL$
** GNU Free Documentation License
** Alternatively, this file may be used under the terms of the GNU Free
** Documentation License version 1.3 as published by the Free Software
** Foundation and appearing in the file included in the packaging of
** this file.
**
** Other Usage
** Alternatively, this file may be used in accordance with the terms
** and conditions contained in a signed written agreement between you
** and Nokia.
**
**
**
**
**
** $QT_END_LICENSE$
**
****************************************************************************/
/*!
\example battery-charge
\title Accessing Publish and Subscribe from QML
This example shows how to access published context values from within QML. The example
consists of two programs. The first, battery-publisher, is a standard Qt GUI application that
is used to emulate a battery for the sole purpose of demonstrating the second program. It
publishes the keys
\code
/power/battery/charge
/power/battery/charging
\endcode
and provides controls for modifying their values.
\image battery-publisher.png
The second program, namely battery-subscriber, consists of a QML application that accesses
the actual value of the published battery-charge property via the ValueSpaceSubscriber QML element
and displays the value to the end-user.
The user interface of the battery subscriber program is described in QML. It has the following
features: A rectangular area representing the percent charge of the battery. It indicates a
low battery state by changing the color to red, it is green otherwise. An animation is shown
to indicate that the battery is being recharged.
\image battery-subscriber.png
\section2 Battery Subscriber
The QValueSpaceSubscriber class is available from within QML through the use of a plugin which
is parsed by the QML engine. This means that simply using the QML element 'ValueSpaceSubscriber'
allows access to the valuespace, which is demonstrated below.
\section3 QML
Firstly, import the plugin library that provides the ValueSpaceSubscriber QML element.
\snippet battery-charge/battery-subscriber/battery-subscriber.qml 4
Two ValueSpaceSubscriber instances are created, one for each of the battery values. We give
each object a unique id so that we can reference it from elsewhere in the QML. We set the
\i path properties to the Value Space path of the keys. Finally we set the \i notify
properties to true to enable the emission of change notification signals.
\snippet battery-charge/battery-subscriber/battery-subscriber.qml 0
The default state of the rectangle used to visualize the battery charge uses the \i charge
property of our BatteryCharge class in the expression for its height.
\snippet battery-charge/battery-subscriber/battery-subscriber.qml 1
When the battery charge changes the height of the rectangle will automatically change.
Next we define two additional states. The \i low state is entered when the battery charge
drops below 25% and the battery is not being recharged. When in this state the color is set to
red.
\snippet battery-charge/battery-subscriber/battery-subscriber.qml 2
The \i charging state is entered when the battery is being recharged. When in this state a
particle effect animation is enabled.
\snippet battery-charge/battery-subscriber/battery-subscriber.qml 3
*/
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