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<a href="index.html" class="qtref"><span>QtMobility Reference Documentation</span></a>
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<li><a href="http://qt.nokia.com/doc/4.7/all-examples.html">Examples</a></li>
<li>Accessing Publish and Subscribe from QML</li>
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<h3><a name="toc">Contents</a></h3>
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<li class="level2"><a href="#battery-subscriber">Battery Subscriber</a></li>
<li class="level3"><a href="#qml">QML</a></li>
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<h1 class="title">Accessing Publish and Subscribe from QML</h1>
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<p>Files:</p>
<ul>
<li><a href="battery-charge-battery-publisher-batterypublisher-cpp.html">battery-charge/battery-publisher/batterypublisher.cpp</a></li>
<li><a href="battery-charge-battery-publisher-batterypublisher-h.html">battery-charge/battery-publisher/batterypublisher.h</a></li>
<li><a href="battery-charge-battery-publisher-batterypublisher-ui.html">battery-charge/battery-publisher/batterypublisher.ui</a></li>
<li><a href="battery-charge-battery-subscriber-battery-subscriber-qml.html">battery-charge/battery-subscriber/battery-subscriber.qml</a></li>
<li><a href="battery-charge-battery-publisher-main-cpp.html">battery-charge/battery-publisher/main.cpp</a></li>
<li><a href="battery-charge-battery-charge-pro.html">battery-charge/battery-charge.pro</a></li>
<li><a href="battery-charge-battery-publisher-battery-publisher-pro.html">battery-charge/battery-publisher/battery-publisher.pro</a></li>
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<p>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</p>
<pre class="cpp"> <span class="operator">/</span>power<span class="operator">/</span>battery<span class="operator">/</span>charge
<span class="operator">/</span>power<span class="operator">/</span>battery<span class="operator">/</span>charging</pre>
<p>and provides controls for modifying their values.</p>
<p class="centerAlign"><img src="images/battery-publisher.png" alt="" /></p><p>The second program, namely battery-subscriber, consists of a QML application that accesses the actual value of the published battery-charge property via the <a href="qml-valuespacesubscriber.html">ValueSpaceSubscriber</a> QML element and displays the value to the end-user.</p>
<p>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.</p>
<p class="centerAlign"><img src="images/battery-subscriber.png" alt="" /></p><a name="battery-subscriber"></a>
<h3>Battery Subscriber</h3>
<p>The <a href="qvaluespacesubscriber.html">QValueSpaceSubscriber</a> 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 '<a href="qml-valuespacesubscriber.html">ValueSpaceSubscriber</a>' allows access to the valuespace, which is demonstrated below.</p>
<a name="qml"></a>
<h4>QML</h4>
<p>Firstly, import the plugin library that provides the <a href="qml-valuespacesubscriber.html">ValueSpaceSubscriber</a> QML element.</p>
<pre class="qml"> import QtMobility.publishsubscribe 1.1</pre>
<p>Two <a href="qml-valuespacesubscriber.html">ValueSpaceSubscriber</a> 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</i> properties to the Value Space path of the keys. Finally we set the <i>notify</i> properties to true to enable the emission of change notification signals.</p>
<pre class="qml"> <span class="type"><a href="qml-valuespacesubscriber.html">ValueSpaceSubscriber</a></span> {
<span class="name">id</span>: <span class="name">batteryCharge</span>
<span class="name">path</span>: <span class="string">"/power/battery/charge"</span>
}
<span class="type"><a href="qml-valuespacesubscriber.html">ValueSpaceSubscriber</a></span> {
<span class="name">id</span>: <span class="name">batteryCharging</span>
<span class="name">path</span>: <span class="string">"/power/battery/charging"</span>
}</pre>
<p>The default state of the rectangle used to visualize the battery charge uses the <i>charge</i> property of our BatteryCharge class in the expression for its height.</p>
<pre class="qml"> <span class="name">id</span>: <span class="name">visualCharge</span>
<span class="name">x</span>: <span class="number">12</span>
<span class="name">y</span>: <span class="number">22</span> <span class="operator">+</span> <span class="number">196</span> <span class="operator">-</span> <span class="name">height</span>
<span class="name">width</span>: <span class="number">76</span>
<span class="name">height</span>: <span class="number">196</span> <span class="operator">*</span> <span class="name">batteryCharge</span>.<span class="name">value</span> <span class="operator">/</span> <span class="number">100</span>
<span class="name">clip</span>: <span class="number">true</span>
<span class="name">color</span>: <span class="string">"green"</span></pre>
<p>When the battery charge changes the height of the rectangle will automatically change.</p>
<p>Next we define two additional states. The <i>low</i> 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.</p>
<pre class="qml"> <span class="type"><a href="http://qt.nokia.com/doc/4.7/qml-state.html">State</a></span> {
<span class="name">name</span>: <span class="string">"low"</span>
<span class="name">when</span>: <span class="name">batteryCharge</span>.<span class="name">value</span> <span class="operator"><</span> <span class="number">25</span> <span class="operator">&&</span> !<span class="name">batteryCharging</span>.<span class="name">value</span>
<span class="type"><a href="http://qt.nokia.com/doc/4.7/qml-propertychanges.html">PropertyChanges</a></span> {
<span class="name">target</span>: <span class="name">visualCharge</span>
<span class="name">color</span>: <span class="string">"red"</span>
}
}</pre>
<p>The <i>charging</i> state is entered when the battery is being recharged. When in this state a particle effect animation is enabled.</p>
<pre class="qml"> <span class="type"><a href="http://qt.nokia.com/doc/4.7/qml-state.html">State</a></span> {
<span class="name">name</span>: <span class="string">"charging"</span>
<span class="name">when</span>: <span class="name">batteryCharging</span>.<span class="name">value</span>
<span class="type"><a href="http://qt.nokia.com/doc/4.7/qml-propertychanges.html">PropertyChanges</a></span> {
<span class="name">target</span>: <span class="name">bubbles</span>
<span class="name">count</span>: <span class="name">batteryCharge</span>.<span class="name">value</span> <span class="operator">/</span> <span class="number">5</span>
<span class="name">emissionRate</span>: <span class="number">5</span>
}
},</pre>
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