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/*!
    \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
*/