- Qt 5.5
- Qt Positioning
- Weather Info (C++/QML)
- Qt 5.5.1 Reference Documentation

# Weather Info (C++/QML)

Key Qt Positioning classes used in this example:

- QGeoPositionInfo
- QGeoPositionInfoSource

## Running the Example

To run the example from Qt Creator, open the Welcome mode and select the example from Examples. For more information, visit Building and Running an Example.

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.

    class WeatherData : public QObject {
        Q_OBJECT
        Q_PROPERTY(QString dayOfWeek
                   READ dayOfWeek WRITE setDayOfWeek
                   NOTIFY dataChanged)
        Q_PROPERTY(QString weatherIcon
                   READ weatherIcon WRITE setWeatherIcon
                   NOTIFY dataChanged)
        Q_PROPERTY(QString weatherDescription
                   READ weatherDescription WRITE setWeatherDescription
                   NOTIFY dataChanged)
        Q_PROPERTY(QString temperature
                   READ temperature WRITE setTemperature
                   NOTIFY dataChanged)

    public:
        explicit WeatherData(QObject *parent = 0);
        WeatherData(const WeatherData &other);

        QString dayOfWeek() const;
        QString weatherIcon() const;
        QString weatherDescription() const;
        QString temperature() const;

        void setDayOfWeek(const QString &value);
        void setWeatherIcon(const QString &value);
        void setWeatherDescription(const QString &value);
        void setTemperature(const QString &value);

    signals:
        void dataChanged();
    };

AppModel models the state of the entire application. At startup, the application first begins by waiting for network connectivity. We do this using the QNetworkConfigurationManager and QNetworkSession family of C++ APIs.

    AppModel::AppModel(QObject *parent) :
            QObject(parent),
            d(new AppModelPrivate)
    {
        // make sure we have an active network session
        d->nam = new QNetworkAccessManager(this);

        QNetworkConfigurationManager ncm;
        d->ns = new QNetworkSession(ncm.defaultConfiguration(), this);
        connect(d->ns, SIGNAL(opened()), this, SLOT(networkSessionOpened()));
        // the session may be already open. if it is, run the slot directly
        if (d->ns->isOpen())
            this->networkSessionOpened();
        // tell the system we want network
        d->ns->open();
    }

Once the network session is open, we proceed to get the platform's default position source using QGeoPositionInfo::createDefaultSource()

    void AppModel::networkSessionOpened()
    {
        d->src = QGeoPositionInfoSource::createDefaultSource(this);

        if (d->src) {
            d->useGps = true;
            connect(d->src, SIGNAL(positionUpdated(QGeoPositionInfo)),
                    this, SLOT(positionUpdated(QGeoPositionInfo)));
            connect(d->src, SIGNAL(error(QGeoPositionInfoSource::Error)),
                    this, SLOT(positionError(QGeoPositionInfoSource::Error)));
            d->src->startUpdates();
        } else {
            d->useGps = false;
            d->city = "Brisbane";
            emit cityChanged();
            this->refreshWeather();
        }
    }

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.

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.

    void AppModel::positionUpdated(QGeoPositionInfo gpsPos)
    {
        d->coord = gpsPos.coordinate();

        if (!(d->useGps))
            return;

        queryCity();
    }

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.

    class AppModel : public QObject
    {
        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(QString city
                   READ city WRITE setCity
                   NOTIFY cityChanged)
        Q_PROPERTY(WeatherData *weather
                   READ weather
                   NOTIFY weatherChanged)
        Q_PROPERTY(QQmlListProperty<WeatherData> forecast
                   READ forecast
                   NOTIFY weatherChanged)

    public:
        explicit AppModel(QObject *parent = 0);
        ~AppModel();

        bool ready() const;
        bool hasSource() const;
        bool useGps() const;
        bool hasValidCity() const;
        bool hasValidWeather() const;
        void setUseGps(bool value);
        void hadError(bool tryAgain);

        QString city() const;
        void setCity(const QString &value);

        WeatherData *weather() const;
        QQmlListProperty<WeatherData> forecast() const;

    public slots:
        Q_INVOKABLE void refreshWeather();

    signals:
        void readyChanged();
        void useGpsChanged();
        void cityChanged();
        void weatherChanged();

    };

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.

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.

    #include "appmodel.h"

    int main(int argc, char *argv[])
    {
        QLoggingCategory::setFilterRules("wapp.*.debug=false");
        QGuiApplication application(argc, argv);

        qmlRegisterType<WeatherData>("WeatherInfo", 1, 0, "WeatherData");
        qmlRegisterType<AppModel>("WeatherInfo", 1, 0, "AppModel");

        const QString mainQmlApp = QStringLiteral("qrc:///weatherinfo.qml");
        QQuickView view;
        view.setSource(QUrl(mainQmlApp));
        view.setResizeMode(QQuickView::SizeRootObjectToView);

        QObject::connect(view.engine(), SIGNAL(quit()), qApp, SLOT(quit()));
        view.setGeometry(QRect(100, 100, 360, 640));
        view.show();
        return application.exec();
    }

Finally, in the actual QML, we instantiate the AppModel.

    import WeatherInfo 1.0

    Item {
        id: window
        AppModel {
            id: model
            onReadyChanged: {
                if (model.ready)
                    window.state = "ready"
                else
                    window.state = "loading"
            }
        }
    }

Once instantiated like this, we can use its properties elsewhere in the QML document:

                BigForecastIcon {
                    id: current

                    width: main.width -12
                    height: 2 * (main.height - 25 - 12) / 3

                    weatherIcon: (model.hasValidWeather
                              ? model.weather.weatherIcon
                              : "01d")
                }

Files:

- weatherinfo/appmodel.cpp
- weatherinfo/appmodel.h
- weatherinfo/weatherinfo.qml
- weatherinfo/components/BigForecastIcon.qml
- weatherinfo/components/ForecastIcon.qml
- weatherinfo/components/WeatherIcon.qml
- weatherinfo/main.cpp
- weatherinfo/weatherinfo.pro
- weatherinfo/weatherinfo.qrc