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<li>Qt 5.5</li>
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<h3><a name="toc">Contents</a></h3>
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<li class="level1"><a href="#running-the-example">Running the Example</a></li>
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<h1 class="title">Weather Info (C++/QML)</h1>
<span class="subtitle"></span>
<!-- $$$weatherinfo-description -->
<div class="descr"> <a name="details"></a>
<p>Key <a href="qtpositioning-index.html">Qt Positioning</a> classes used in this example:</p>
<ul>
<li><a href="qgeopositioninfo.html">QGeoPositionInfo</a></li>
<li><a href="qgeopositioninfosource.html">QGeoPositionInfoSource</a></li>
</ul>
<p class="centerAlign"><img src="images/example-weatherinfo.png" alt="" /></p><a name="running-the-example"></a>
<h2 id="running-the-example">Running the Example</h2>
<p>To run the example from Qt Creator, open the <b>Welcome</b> mode and select the example from <b>Examples</b>. For more information, visit Building and Running an Example.</p>
<p>The key part of this example is the application's data model, contained in the WeatherData and AppModel classes. WeatherData represents the weather information taken from the HTTP service. It is a simple data class, but we give it Q_PROPERTies to expose it nicely to QML, later.</p>
<pre class="cpp"><span class="keyword">class</span> WeatherData : <span class="keyword">public</span> <span class="type"><a href="../qtcore/qobject.html">QObject</a></span> {
Q_OBJECT
Q_PROPERTY(<span class="type"><a href="../qtcore/qstring.html">QString</a></span> dayOfWeek
READ dayOfWeek WRITE setDayOfWeek
NOTIFY dataChanged)
Q_PROPERTY(<span class="type"><a href="../qtcore/qstring.html">QString</a></span> weatherIcon
READ weatherIcon WRITE setWeatherIcon
NOTIFY dataChanged)
Q_PROPERTY(<span class="type"><a href="../qtcore/qstring.html">QString</a></span> weatherDescription
READ weatherDescription WRITE setWeatherDescription
NOTIFY dataChanged)
Q_PROPERTY(<span class="type"><a href="../qtcore/qstring.html">QString</a></span> temperature
READ temperature WRITE setTemperature
NOTIFY dataChanged)
<span class="keyword">public</span>:
<span class="keyword">explicit</span> WeatherData(<span class="type"><a href="../qtcore/qobject.html">QObject</a></span> <span class="operator">*</span>parent <span class="operator">=</span> <span class="number">0</span>);
WeatherData(<span class="keyword">const</span> WeatherData <span class="operator">&</span>other);
<span class="type"><a href="../qtcore/qstring.html">QString</a></span> dayOfWeek() <span class="keyword">const</span>;
<span class="type"><a href="../qtcore/qstring.html">QString</a></span> weatherIcon() <span class="keyword">const</span>;
<span class="type"><a href="../qtcore/qstring.html">QString</a></span> weatherDescription() <span class="keyword">const</span>;
<span class="type"><a href="../qtcore/qstring.html">QString</a></span> temperature() <span class="keyword">const</span>;
<span class="type">void</span> setDayOfWeek(<span class="keyword">const</span> <span class="type"><a href="../qtcore/qstring.html">QString</a></span> <span class="operator">&</span>value);
<span class="type">void</span> setWeatherIcon(<span class="keyword">const</span> <span class="type"><a href="../qtcore/qstring.html">QString</a></span> <span class="operator">&</span>value);
<span class="type">void</span> setWeatherDescription(<span class="keyword">const</span> <span class="type"><a href="../qtcore/qstring.html">QString</a></span> <span class="operator">&</span>value);
<span class="type">void</span> setTemperature(<span class="keyword">const</span> <span class="type"><a href="../qtcore/qstring.html">QString</a></span> <span class="operator">&</span>value);
<span class="keyword">signals</span>:
<span class="type">void</span> dataChanged();
};</pre>
<p>AppModel models the state of the entire application. At startup, the application first begins by waiting for network connectivity. We do this using the <a href="../qtnetwork/qnetworkconfigurationmanager.html">QNetworkConfigurationManager</a> and <a href="../qtnetwork/qnetworksession.html">QNetworkSession</a> family of C++ APIs.</p>
<pre class="cpp">AppModel<span class="operator">::</span>AppModel(<span class="type"><a href="../qtcore/qobject.html">QObject</a></span> <span class="operator">*</span>parent) :
<span class="type"><a href="../qtcore/qobject.html">QObject</a></span>(parent)<span class="operator">,</span>
d(<span class="keyword">new</span> AppModelPrivate)
{
<span class="comment">// make sure we have an active network session</span>
d<span class="operator">-</span><span class="operator">></span>nam <span class="operator">=</span> <span class="keyword">new</span> <span class="type"><a href="../qtnetwork/qnetworkaccessmanager.html">QNetworkAccessManager</a></span>(<span class="keyword">this</span>);
<span class="type"><a href="../qtnetwork/qnetworkconfigurationmanager.html">QNetworkConfigurationManager</a></span> ncm;
d<span class="operator">-</span><span class="operator">></span>ns <span class="operator">=</span> <span class="keyword">new</span> <span class="type"><a href="../qtnetwork/qnetworksession.html">QNetworkSession</a></span>(ncm<span class="operator">.</span>defaultConfiguration()<span class="operator">,</span> <span class="keyword">this</span>);
connect(d<span class="operator">-</span><span class="operator">></span>ns<span class="operator">,</span> SIGNAL(opened())<span class="operator">,</span> <span class="keyword">this</span><span class="operator">,</span> SLOT(networkSessionOpened()));
<span class="comment">// the session may be already open. if it is, run the slot directly</span>
<span class="keyword">if</span> (d<span class="operator">-</span><span class="operator">></span>ns<span class="operator">-</span><span class="operator">></span>isOpen())
<span class="keyword">this</span><span class="operator">-</span><span class="operator">></span>networkSessionOpened();
<span class="comment">// tell the system we want network</span>
d<span class="operator">-</span><span class="operator">></span>ns<span class="operator">-</span><span class="operator">></span>open();
}</pre>
<p>Once the network session is open, we proceed to get the platform's default position source using QGeoPositionInfo::createDefaultSource()</p>
<pre class="cpp"><span class="type">void</span> AppModel<span class="operator">::</span>networkSessionOpened()
{
d<span class="operator">-</span><span class="operator">></span>src <span class="operator">=</span> <span class="type"><a href="qgeopositioninfosource.html">QGeoPositionInfoSource</a></span><span class="operator">::</span>createDefaultSource(<span class="keyword">this</span>);
<span class="keyword">if</span> (d<span class="operator">-</span><span class="operator">></span>src) {
d<span class="operator">-</span><span class="operator">></span>useGps <span class="operator">=</span> <span class="keyword">true</span>;
connect(d<span class="operator">-</span><span class="operator">></span>src<span class="operator">,</span> SIGNAL(positionUpdated(<span class="type"><a href="qgeopositioninfo.html">QGeoPositionInfo</a></span>))<span class="operator">,</span>
<span class="keyword">this</span><span class="operator">,</span> SLOT(positionUpdated(<span class="type"><a href="qgeopositioninfo.html">QGeoPositionInfo</a></span>)));
connect(d<span class="operator">-</span><span class="operator">></span>src<span class="operator">,</span> SIGNAL(error(<span class="type"><a href="qgeopositioninfosource.html">QGeoPositionInfoSource</a></span><span class="operator">::</span>Error))<span class="operator">,</span>
<span class="keyword">this</span><span class="operator">,</span> SLOT(positionError(<span class="type"><a href="qgeopositioninfosource.html">QGeoPositionInfoSource</a></span><span class="operator">::</span>Error)));
d<span class="operator">-</span><span class="operator">></span>src<span class="operator">-</span><span class="operator">></span>startUpdates();
} <span class="keyword">else</span> {
d<span class="operator">-</span><span class="operator">></span>useGps <span class="operator">=</span> <span class="keyword">false</span>;
d<span class="operator">-</span><span class="operator">></span>city <span class="operator">=</span> <span class="string">"Brisbane"</span>;
<span class="keyword">emit</span> cityChanged();
<span class="keyword">this</span><span class="operator">-</span><span class="operator">></span>refreshWeather();
}
}</pre>
<p>If no default source is available, we take a static position and fetch weather for that. If, however, we do have a position source, we connect its positionUpdated() signal to a slot on the AppModel and call startUpdates(), which begins regular updates of device position.</p>
<p>When a position update is received, we use the longitude and latitude of the returned coordinate to retrieve the current "city" name for use in the weather lookup.</p>
<pre class="cpp"><span class="type">void</span> AppModel<span class="operator">::</span>positionUpdated(<span class="type"><a href="qgeopositioninfo.html">QGeoPositionInfo</a></span> gpsPos)
{
d<span class="operator">-</span><span class="operator">></span>coord <span class="operator">=</span> gpsPos<span class="operator">.</span>coordinate();
<span class="keyword">if</span> (<span class="operator">!</span>(d<span class="operator">-</span><span class="operator">></span>useGps))
<span class="keyword">return</span>;
queryCity();
}</pre>
<p>To inform the UI about this process, the cityChanged() signal is emitted when a new city is used, and the weatherChanged() signal whenever a weather update occurs.</p>
<pre class="cpp"><span class="keyword">class</span> AppModel : <span class="keyword">public</span> <span class="type"><a href="../qtcore/qobject.html">QObject</a></span>
{
Q_OBJECT
Q_PROPERTY(bool ready
READ ready
NOTIFY readyChanged)
Q_PROPERTY(bool hasSource
READ hasSource
NOTIFY readyChanged)
Q_PROPERTY(bool hasValidCity
READ hasValidCity
NOTIFY cityChanged)
Q_PROPERTY(bool hasValidWeather
READ hasValidWeather
NOTIFY weatherChanged)
Q_PROPERTY(bool useGps
READ useGps WRITE setUseGps
NOTIFY useGpsChanged)
Q_PROPERTY(<span class="type"><a href="../qtcore/qstring.html">QString</a></span> city
READ city WRITE setCity
NOTIFY cityChanged)
Q_PROPERTY(WeatherData <span class="operator">*</span>weather
READ weather
NOTIFY weatherChanged)
Q_PROPERTY(<span class="type">QQmlListProperty</span><span class="operator"><</span>WeatherData<span class="operator">></span> forecast
READ forecast
NOTIFY weatherChanged)
<span class="keyword">public</span>:
<span class="keyword">explicit</span> AppModel(<span class="type"><a href="../qtcore/qobject.html">QObject</a></span> <span class="operator">*</span>parent <span class="operator">=</span> <span class="number">0</span>);
<span class="operator">~</span>AppModel();
bool ready() <span class="keyword">const</span>;
bool hasSource() <span class="keyword">const</span>;
bool useGps() <span class="keyword">const</span>;
bool hasValidCity() <span class="keyword">const</span>;
bool hasValidWeather() <span class="keyword">const</span>;
<span class="type">void</span> setUseGps(bool value);
<span class="type">void</span> hadError(bool tryAgain);
<span class="type"><a href="../qtcore/qstring.html">QString</a></span> city() <span class="keyword">const</span>;
<span class="type">void</span> setCity(<span class="keyword">const</span> <span class="type"><a href="../qtcore/qstring.html">QString</a></span> <span class="operator">&</span>value);
WeatherData <span class="operator">*</span>weather() <span class="keyword">const</span>;
<span class="type">QQmlListProperty</span><span class="operator"><</span>WeatherData<span class="operator">></span> forecast() <span class="keyword">const</span>;
<span class="keyword">public</span> <span class="keyword">slots</span>:
Q_INVOKABLE <span class="type">void</span> refreshWeather();
<span class="keyword">signals</span>:
<span class="type">void</span> readyChanged();
<span class="type">void</span> useGpsChanged();
<span class="type">void</span> cityChanged();
<span class="type">void</span> weatherChanged();
};</pre>
<p>We use a QQmlListProperty for the weather forecast information, which contains the next 4 days of forecast weather. This makes it easy to access from QML.</p>
<p>To expose these to the QML UI layer, we use the qmlRegisterType() function. We call this once for each type we wish to register, before loading the actual QML file.</p>
<pre class="cpp"><span class="preprocessor">#include "appmodel.h"</span>
<span class="type">int</span> main(<span class="type">int</span> argc<span class="operator">,</span> <span class="type">char</span> <span class="operator">*</span>argv<span class="operator">[</span><span class="operator">]</span>)
{
<span class="type"><a href="../qtcore/qloggingcategory.html">QLoggingCategory</a></span><span class="operator">::</span>setFilterRules(<span class="string">"wapp.*.debug=false"</span>);
<span class="type">QGuiApplication</span> application(argc<span class="operator">,</span> argv);
qmlRegisterType<span class="operator"><</span>WeatherData<span class="operator">></span>(<span class="string">"WeatherInfo"</span><span class="operator">,</span> <span class="number">1</span><span class="operator">,</span> <span class="number">0</span><span class="operator">,</span> <span class="string">"WeatherData"</span>);
qmlRegisterType<span class="operator"><</span>AppModel<span class="operator">></span>(<span class="string">"WeatherInfo"</span><span class="operator">,</span> <span class="number">1</span><span class="operator">,</span> <span class="number">0</span><span class="operator">,</span> <span class="string">"AppModel"</span>);
<span class="keyword">const</span> <span class="type"><a href="../qtcore/qstring.html">QString</a></span> mainQmlApp <span class="operator">=</span> <span class="type"><a href="../qtcore/qstring.html#QStringLiteral">QStringLiteral</a></span>(<span class="string">"qrc:///weatherinfo.qml"</span>);
<span class="type">QQuickView</span> view;
view<span class="operator">.</span>setSource(<span class="type"><a href="../qtcore/qurl.html">QUrl</a></span>(mainQmlApp));
view<span class="operator">.</span>setResizeMode(<span class="type">QQuickView</span><span class="operator">::</span>SizeRootObjectToView);
<span class="type"><a href="../qtcore/qobject.html">QObject</a></span><span class="operator">::</span>connect(view<span class="operator">.</span>engine()<span class="operator">,</span> SIGNAL(quit())<span class="operator">,</span> qApp<span class="operator">,</span> SLOT(quit()));
view<span class="operator">.</span>setGeometry(<span class="type"><a href="../qtcore/qrect.html">QRect</a></span>(<span class="number">100</span><span class="operator">,</span> <span class="number">100</span><span class="operator">,</span> <span class="number">360</span><span class="operator">,</span> <span class="number">640</span>));
view<span class="operator">.</span>show();
<span class="keyword">return</span> application<span class="operator">.</span>exec();
}</pre>
<p>Finally, in the actual QML, we instantiate the AppModel.</p>
<pre class="qml">import WeatherInfo 1.0
<span class="type">Item</span> {
<span class="name">id</span>: <span class="name">window</span>
<span class="type">AppModel</span> {
<span class="name">id</span>: <span class="name">model</span>
<span class="name">onReadyChanged</span>: {
<span class="keyword">if</span> (<span class="name">model</span>.<span class="name">ready</span>)
<span class="name">window</span>.<span class="name">state</span> <span class="operator">=</span> <span class="string">"ready"</span>
<span class="keyword">else</span>
<span class="name">window</span>.<span class="name">state</span> <span class="operator">=</span> <span class="string">"loading"</span>
}
}
}</pre>
<p>Once instantiated like this, we can use its properties elsewhere in the QML document:</p>
<pre class="qml"> <span class="type">BigForecastIcon</span> {
<span class="name">id</span>: <span class="name">current</span>
<span class="name">width</span>: <span class="name">main</span>.<span class="name">width</span> <span class="operator">-</span><span class="number">12</span>
<span class="name">height</span>: <span class="number">2</span> <span class="operator">*</span> (<span class="name">main</span>.<span class="name">height</span> <span class="operator">-</span> <span class="number">25</span> <span class="operator">-</span> <span class="number">12</span>) <span class="operator">/</span> <span class="number">3</span>
<span class="name">weatherIcon</span>: (<span class="name">model</span>.<span class="name">hasValidWeather</span>
? <span class="name">model</span>.<span class="name">weather</span>.<span class="name">weatherIcon</span>
: <span class="string">"01d"</span>)
}</pre>
<p>Files:</p>
<ul>
<li><a href="qtpositioning-weatherinfo-appmodel-cpp.html">weatherinfo/appmodel.cpp</a></li>
<li><a href="qtpositioning-weatherinfo-appmodel-h.html">weatherinfo/appmodel.h</a></li>
<li><a href="qtpositioning-weatherinfo-weatherinfo-qml.html">weatherinfo/weatherinfo.qml</a></li>
<li><a href="qtpositioning-weatherinfo-components-bigforecasticon-qml.html">weatherinfo/components/BigForecastIcon.qml</a></li>
<li><a href="qtpositioning-weatherinfo-components-forecasticon-qml.html">weatherinfo/components/ForecastIcon.qml</a></li>
<li><a href="qtpositioning-weatherinfo-components-weathericon-qml.html">weatherinfo/components/WeatherIcon.qml</a></li>
<li><a href="qtpositioning-weatherinfo-main-cpp.html">weatherinfo/main.cpp</a></li>
<li><a href="qtpositioning-weatherinfo-weatherinfo-pro.html">weatherinfo/weatherinfo.pro</a></li>
<li><a href="qtpositioning-weatherinfo-weatherinfo-qrc.html">weatherinfo/weatherinfo.qrc</a></li>
</ul>
</div>
<!-- @@@weatherinfo -->
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