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/****************************************************************************
**
** Copyright (C) 2021 The Qt Company Ltd.
** Contact: https://www.qt.io/licensing/
**
** This file is part of the documentation of the Qt Toolkit.
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** $QT_BEGIN_LICENSE:FDL$
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****************************************************************************/
/*!
\example weatherinfo
\title Weather Info (C++/QML)
\brief The Weather Info example shows how to use the user's current position
to retrieve local content from a web service in a C++ plugin for QML.
\ingroup qtpositioning-examples
Key \l{Qt Positioning} classes used in this example:
\list
\li \l{QGeoPositionInfo}
\li \l{QGeoPositionInfoSource}
\endlist
\image ../images/example-weatherinfo.png
\include examples-run.qdocinc
\section1 Weather Data Providers
The example uses two unrelated weather data providers:
\list
\li \l {http://www.openweathermap.org}{OpenWeather}
\li \l {https://www.weatherapi.com/}{WeatherAPI.com}
\endlist
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.
\note 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.
\section1 Application Data Models
The key part of this example is the application's data model, contained
in the \c WeatherData and \c AppModel classes. \c WeatherData represents
the weather information taken from the HTTP service. It is a simple data
class, but we use \l Q_PROPERTY to expose it nicely to QML later.
It also uses \l QML_ANONYMOUS macro, which makes it recognized in QML.
\snippet weatherinfo/appmodel.h 0
\snippet weatherinfo/appmodel.h 1
\c AppModel models the state of the entire application. At startup, we
get the platform's default position source using
\l QGeoPositionInfoSource::createDefaultSource().
\snippet weatherinfo/appmodel.cpp 0
\snippet weatherinfo/appmodel.cpp 1
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 \l {QGeoPositionInfoSource::}{positionUpdated()} signal to a slot on the
\c AppModel and call \l {QGeoPositionInfoSource::}{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.
\snippet weatherinfo/appmodel.cpp 2
To inform the UI about this process, the \c cityChanged() signal is emitted
when a new city is used, and the \c weatherChanged() signal whenever a
weather update occurs.
The model also uses \l QML_ELEMENT macro, which makes it available in QML.
\snippet weatherinfo/appmodel.h 2
\snippet weatherinfo/appmodel.h 3
\snippet weatherinfo/appmodel.h 4
We use a \l 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.
\section1 Expose Custom Models to QML
To expose the models to the QML UI layer, we use the \l QML_ELEMENT and
\l QML_ANONYMOUS macros. See the \l QQmlEngine class description for more
details on these macros.
To make the types available in QML, we need to update our build accordingly.
\section2 CMake Build
For a CMake-based build, we need to add the following to the
\c {CMakeLists.txt}:
\quotefromfile weatherinfo/CMakeLists.txt
\skipto qt_add_qml_module(weatherinfo
\printuntil )
\section2 qmake Build
For a qmake build, we need to modify the \c {weatherinfo.pro} file in the
following way:
\quotefromfile weatherinfo/weatherinfo.pro
\skipto CONFIG
\printuntil QML_IMPORT_MAJOR_VERSION
\section1 Instantiate the Models in QML
Finally, in the actual QML, we instantiate the \c {AppModel}:
\snippet weatherinfo/weatherinfo.qml 0
\snippet weatherinfo/weatherinfo.qml 1
\snippet weatherinfo/weatherinfo.qml 2
Once the model is instantiated like this, we can use its properties
elsewhere in the QML document:
\snippet weatherinfo/weatherinfo.qml 3
\snippet weatherinfo/weatherinfo.qml 4
\section1 Files and Attributions
The example bundles the following images from Third-Party sources:
\table
\row
\li \l{weatherinfo-tango-icons}{Tango Icons}
\li Public Domain
\row
\li \l{weatherinfo-tango-weather-pack}{Tango Weather Icon Pack by Darkobra}
\li Public Domain
\endtable
*/
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