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<a href="index.html" class="qtref"><span>QtMobility Reference Documentation</span></a>
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<li>Publish and Subscribe QML Plugin</li>
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<h3><a name="toc">Contents</a></h3>
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<li class="level1"><a href="#overview">Overview</a></li>
<li class="level2"><a href="#publisher">Publisher</a></li>
<li class="level2"><a href="#subscriber">Subscriber</a></li>
<li class="level1"><a href="#examples">Examples</a></li>
<li class="level1"><a href="#qml-elements">QML Elements</a></li>
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<h1 class="title">Publish and Subscribe QML Plugin</h1>
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<h2>Overview</h2>
<p>The Publish and Subscribe QML API enables QML applications to access values stored in the Value Space from QML. The publish/subscribe features therefore allow an easy to use form of IPC.</p>
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<h3>Publisher</h3>
<p>The <a href="qml-valuespacepublisher.html">ValueSpacePublisher</a> element allows us to publish key-value pairs of data to a known path. The path has the form of a directory structure path with the keys acting as files at the end of the path. The process is that the developer declares a <a href="qml-valuespacepublisher.html">ValueSpacePublisher</a> element and then with a given path defines a list of keys. For example</p>
<pre class="qml"> <span class="type"><a href="qml-valuespacepublisher.html">ValueSpacePublisher</a></span> {
<span class="name">id</span>: <span class="name">battery</span>
<span class="name">path</span>: <span class="string">"/power/battery"</span>
<span class="name">keys</span>: [<span class="string">"charge"</span>, <span class="string">"charging"</span>]
}</pre>
<p>To publish a value the key need only be set to the value. Here we see that the key is expressed as the last name in the path with dot notation followed by the key name.</p>
<pre class="qml"> battery.charge = 50
battery.charging = true</pre>
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<h3>Subscriber</h3>
<p>The <a href="qml-valuespacesubscriber.html">ValueSpaceSubscriber</a> element also defines the path to the key/value. For each <i>key</i> a different <a href="qml-valuespacesubscriber.html">ValueSpaceSubscriber</a> needs to be declared. In the above example using the keys 'charge' and 'charging' we will need subscribers for each one</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>Now the values being published can be read and used</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>
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<h2>Examples</h2>
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<li><a href="battery-charge.html">Accessing Publish and Subscribe from QML</a></li>
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<h2>QML Elements</h2>
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<tr class="odd topAlign"><td class="tblName"><p><a href="qml-valuespacepublisher.html">QML ValueSpacePublisher Element</a></p></td><td class="tblDescr"><p>The ValueSpacePublisher element represents a path in the value space where keys can be published.</p></td></tr>
<tr class="even topAlign"><td class="tblName"><p><a href="qml-valuespacesubscriber.html">QML ValueSpaceSubscriber Element</a></p></td><td class="tblDescr"><p>The QValueSpaceSubscriber class allows applications to read and subscribe to Value Space paths.</p></td></tr>
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