- Qt 5.15
- Qt Sensors
- C++ Classes
- QSensorBackend
- Qt 5.15.11 Reference Documentation

# QSensorBackend Class

The QSensorBackend class is a sensor implementation. More...

Header: | #include <QSensorBackend>
qmake: | QT += sensors
Since: | Qt 5.1

This class was introduced in Qt 5.1.

- List of all members, including inherited members

## Public Functions

void | addDataRate(qreal min, qreal max)
void | addOutputRange(qreal min, qreal max, qreal accuracy)
virtual bool | isFeatureSupported(QSensor::Feature feature) const
void | newReadingAvailable()
QSensorReading * | reading() const
QSensor * | sensor() const
void | sensorBusy()
void | sensorError(int error)
void | sensorStopped()
void | setDataRates(const QSensor *otherSensor)
void | setDescription(const QString &description)
T * | setReading(T *reading)
virtual void | start() = 0
virtual void | stop() = 0

## Detailed Description

Sensors on a device will be represented by sub-classes of QSensorBackend.

## Member Function Documentation

### void QSensorBackend::addDataRate(qreal min, qreal max)

Add a data rate (consisting of min and max values) for the sensor.

Note that this function should be called from the constructor so that the information is available immediately.

See also QSensor::availableDataRates.

### void QSensorBackend::addOutputRange(qreal min, qreal max, qreal accuracy)

Add an output range (consisting of min, max values and accuracy) for the sensor.

Note that this function should be called from the constructor so that the information is available immediately.

See also QSensor::outputRange and QSensor::outputRanges.

### `[virtual]` bool QSensorBackend::isFeatureSupported(QSensor::Feature feature) const

Checks whether a feature is supported by this sensor backend.

This is the backend side of QSensor::isFeatureSupported(). Reimplement this function if the backend supports one of the additional sensor features of QSensor::Feature.

Returns whether the feature feature is supported by this backend. The default implementation returns false.

This function was introduced in Qt 5.0.

### void QSensorBackend::newReadingAvailable()

Notify the QSensor class that a new reading is available.

### QSensorReading *QSensorBackend::reading() const

If the backend has lost its reference to the reading it can call this method to get the address.

Note that you will need to down-cast to the appropriate type.

See also setReading().

### QSensor *QSensorBackend::sensor() const

Returns the sensor front end associated with this backend.

### void QSensorBackend::sensorBusy()

Inform the front end that the sensor is busy. This implicitly calls sensorStopped() and is typically called from start().

Note that the front end must call QSensor::isBusy() to see if the sensor is busy. If the sensor has stopped due to an error the sensorError() function should be called to notify the class of the error condition.

### void QSensorBackend::sensorError(int error)

Inform the front end that a sensor error occurred. Note that this only reports an error code. It does not stop the sensor.

See also sensorStopped().

### void QSensorBackend::sensorStopped()

Inform the front end that the sensor has stopped. This can be due to start() failing or for some unexpected reason (eg. hardware failure).

Note that the front end must call QSensor::isActive() to see if the sensor has stopped. If the sensor has stopped due to an error the sensorError() function should be called to notify the class of the error condition.

### void QSensorBackend::setDataRates(const QSensor *otherSensor)

Set the data rates for the sensor based on otherSensor.

This is designed for sensors that are based on other sensors.

     setDataRates(otherSensor);

Note that this function must be called from the constructor.

See also QSensor::availableDataRates and addDataRate().

### void QSensorBackend::setDescription(const QString &description)

Set the description for the sensor.

Note that this function should be called from the constructor so that the information is available immediately.

### template <typename T> T *QSensorBackend::setReading(T *reading)

This function is called to initialize the reading classes used for a sensor.

If your backend has already allocated a reading you should pass the address of this to the function. Otherwise you should pass 0 and the function will return the address of the reading your backend should use when it wants to notify the sensor API of new readings.

Note that this is a template function so it should be called with the appropriate type.

     class MyBackend : public QSensorBackend
     {
         QAccelerometerReading m_reading;
     public:
         MyBackend(QSensor *sensor)
             : QSensorBackend(sensor)
         {
             setReading<QAccelerometerReading>(&m_reading);
         }

         ...

Note that this function must be called or you will not be able to send readings to the front end.

If you do not wish to store the address of the reading you may use the reading() method to get it again later.

     class MyBackend : public QSensorBackend
     {
     public:
         MyBackend(QSensor *sensor)
             : QSensorBackend(sensor)
         {
             setReading<QAccelerometerReading>(0);
         }

         void poll()
         {
             quint64 timestamp;
             qreal x, y, z;
             ...
             QAccelerometerReading *reading = static_cast<QAccelerometerReading*>(reading());
             reading->setTimestamp(timestamp);
             reading->setX(x);
             reading->setY(y);
             reading->setZ(z);
         }

         ...

See also reading().

### `[pure virtual]` void QSensorBackend::start()

Start reporting values.

### `[pure virtual]` void QSensorBackend::stop()

Stop reporting values.