Interfaces between C++ and QML Code in Qt Positioning

Depending on the type of C++ class QtPositioning utilizes two methods to simplify exchange of position data between C++ and QML code.

Starting with Qt 5.5, it has become much easier to integrate non-QObject based data types into QML. This is achieved by adding Q_GADGET support to QtQml. The macro converts classes into a light-weight version of a QObject without the required QObject inheritance. At the same time it retains the reflection capabilities of QMetaObject. As a result they can be directly exposed to QML and do not require any further wrapper classes.

A significant number of Position and Location related data types were converted to Q_GADGETs. They retain their API and value type character but have become introspectable via QMetaObject. This conversion was done to the following classes:

• QGeoCircle

• QGeoCoordinate

• QGeoRectangle

• QGeoShape

Using QGeoCoordinate as an example, the C++ types are directly exposed to the QML environment via its meta type:

qRegisterMetaType<QGeoCoordinate>();
QMetaType::registerEqualsComparator<QGeoCoordinate>();

The above registration of QGeoCoordinate is automatically done once by the QtPositioning QML plugin. The Plane Spotter example demonstrates this feature.

This section provides information on how to integrate QGeoAddress and QGeoLocation.

Address - QGeoAddress▲

 QGeoAddress geoAddress = qmlObject->property("address").value<QGeoAddress>();

qmlObject->setProperty("address", QVariant::fromValue(geoAddress));

Location - QGeoLocation▲

QGeoLocation geoLocation = qmlObject->property("location").value<QGeoLocation>();

qmlObject->setProperty("location", QVariant::fromValue(geoLocation));