Weather Info (C++/QML)▲
Key Qt Positioning classes used in this example:
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.
Weather Data Providers▲
The example uses two unrelated weather data providers:
The provider to be used is selected automatically at runtime and can be changed if the selected provider is not available. However, it can't be specified manually.
Free plans are used for both providers, which implies certain limitations on the amount of weather requests. If the limits are exceeded, the providers become temporary unavailable. When both providers are unavailable, the application would not be able to show any weather information. In this case it is required to wait until at least one of the providers becomes available again.
Application Data Models▲
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 use Q_PROPERTY to expose it nicely to QML later. It also uses QML_ANONYMOUS macro, which makes it recognized in QML.
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)
QML_ANONYMOUS
public:
explicit WeatherData(QObject *parent = 0);
WeatherData(const WeatherData &other);
WeatherData(const WeatherInfo &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, we get the platform's default position source using QGeoPositionInfoSource::createDefaultSource().
AppModel::AppModel(QObject *parent) :
QObject(parent),
d(new AppModelPrivate)
{
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(errorOccurred(QGeoPositionInfoSource::Error)),
this, SLOT(positionError(QGeoPositionInfoSource::Error)));
d->src->startUpdates();
} else {
d->useGps = false;
d->city = "Brisbane";
emit cityChanged();
requestWeatherByCity();
}
}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 weather data for the specified location.
void AppModel::positionUpdated(QGeoPositionInfo gpsPos)
{
d->coord = gpsPos.coordinate();
if (!d->useGps)
return;
requestWeatherByCoordinates();
}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.
The model also uses QML_ELEMENT macro, which makes it available in QML.
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)
QML_ELEMENT
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);
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 weather forecast for the next days (the number of days is provider-specific). This makes it easy to access the forecast from QML.
Expose Custom Models to QML▲
To expose the models to the QML UI layer, we use the QML_ELEMENT and QML_ANONYMOUS macros. See the QQmlEngine class description for more details on these macros.
To make the types available in QML, we need to update our build accordingly.
CMake Build▲
For a CMake-based build, we need to add the following to the CMakeLists.txt:
qt_add_qml_module(weatherinfo
URI WeatherInfo
VERSION 1.0
QML_FILES
components/BigForecastIcon.qml
components/ForecastIcon.qml
components/WeatherIcon.qml
weatherinfo.qml
RESOURCES
icons/weather-few-clouds.png
icons/weather-fog.png
icons/weather-haze.png
icons/weather-icy.png
icons/weather-overcast.png
icons/weather-showers.png
icons/weather-sleet.png
icons/weather-snow.png
icons/weather-storm.png
icons/weather-sunny-very-few-clouds.png
icons/weather-sunny.png
icons/weather-thundershower.png
icons/weather-showers-scattered.png
NO_RESOURCE_TARGET_PATH
)qmake Build▲
For a qmake build, we need to modify the weatherinfo.pro file in the following way:
CONFIG += qmltypes
QML_IMPORT_NAME = WeatherInfo
QML_IMPORT_MAJOR_VERSION = 1Instantiate the Models in QML▲
Finally, in the actual QML, we instantiate the AppModel:
import WeatherInfo 1.0
Item {
id: window
AppModel {
id: appModel
onReadyChanged: {
if (appModel.ready)
window.state = "ready"
else
window.state = "loading"
}
}
}Once the model is 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: (appModel.hasValidWeather
? appModel.weather.weatherIcon
: "sunny")
}Files and Attributions▲
The example bundles the following images from Third-Party sources:
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Public Domain |
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Public Domain |