QSensor Class

Property Documentation

active : bool

This property holds a value to indicate if the sensor is active.

This is true if the sensor is active (returning values). This is false otherwise.

Note that setting this value to true will not have an immediate effect. Instead, the sensor will be started once the event loop has been reached.

Access functions:

bool	isActive() const
void	setActive(bool active)

Notifier signal:

void	activeChanged()

alwaysOn : bool

This property holds a value to indicate if the sensor should remain running when the screen is off.

Some platforms have a policy of suspending sensors when the screen turns off. Setting this property to true will ensure the sensor continues to run.

Access functions:

bool	isAlwaysOn() const
void	setAlwaysOn(bool alwaysOn)

Notifier signal:

void	alwaysOnChanged()

availableDataRates : const qrangelist

This property holds the data rates that the sensor supports.

This is a list of the data rates that the sensor supports. Measured in Hertz.

Entries in the list can represent discrete rates or a continuous range of rates. A discrete rate is noted by having both values the same.

See the sensor_explorer example for an example of how to interpret and use this information.

Note that this information is not mandatory as not all sensors have a rate at which they run. In such cases, the list will be empty.

Access functions:

qrangelist

availableDataRates() const

See also QSensor::dataRate and qrangelist.

bufferSize : const int

This property holds the size of the buffer. By default (and if the property is left undefined), the buffer size is 1, which means no buffering. If the maximum buffer size is 1 (or undefined), then buffering is not supported by the sensor.

Setting bufferSize greater than maxBufferSize will cause maxBufferSize to be used.

Buffering is turned on when bufferSize is greater than 1. The sensor will collect the requested number of samples and deliver them all to the application at one time. They will be delivered to the application as a burst of changed readings so it is particularly important that the application processes each reading immediately or saves the values somewhere else.

If stop() is called when buffering is on-going, the partial buffer is not delivered.

When the sensor is started with buffering option, values are collected from that moment onwards. There is no pre-existing buffer that can be utilized.

The buffer size can only be changed while the sensor is not active.

See also QSensor::maxBufferSize and QSensor::efficientBufferSize.

busy : const bool

This property holds a value to indicate if the sensor is busy.

Some sensors may be on the system but unavailable for use. This function will return true if the sensor is busy. You will not be able to start() the sensor.

Note that this function does not return true if you are using the sensor, only if another process is using the sensor.

Access functions:

bool	isBusy() const

See also busyChanged().

connectedToBackend : const bool

This property holds a value indicating if the sensor has connected to a backend.

A sensor that has not been connected to a backend cannot do anything useful.

Call the connectToBackend() method to force the sensor to connect to a backend immediately. This is automatically called if you call start() so you only need to do this if you need access to sensor properties (ie. to poll the sensor's meta-data before you use it).

Access functions:

bool	isConnectedToBackend() const

dataRate : int

This property holds the data rate that the sensor should be run at.

Measured in Hertz.

The data rate is the maximum frequency at which the sensor can detect changes.

Setting this property is not portable and can cause conflicts with other applications. Check with the sensor backend and platform documentation for any policy regarding multiple applications requesting a data rate.

The default value (0) means that the app does not care what the data rate is. Applications should consider using a timer-based poll of the current value or ensure that the code that processes values can run very quickly as the platform may provide updates hundreds of times each second.

This should be set before calling start() because the sensor may not notice changes to this value while it is running.

Note that there is no mechanism to determine the current data rate in use by the platform.

Access functions:

int	dataRate() const
void	setDataRate(int rate)

See also QSensor::availableDataRates.

description : const QString

This property holds a descriptive string for the sensor.

Access functions:

QString

description() const

efficientBufferSize : const int

The property holds the most efficient buffer size. Normally this is 1 (which means no particular size is most efficient). Some sensor drivers have a FIFO buffer which makes it more efficient to deliver the FIFO's size worth of readings at one time.

Note that this may be undefined, in which case the sensor does not support any form of buffering.

See also QSensor::bufferSize and QSensor::maxBufferSize.

error : const int

This property holds the last error code set on the sensor.

Note that error codes are sensor-specific.

Access functions:

int	error() const

Notifier signal:

void	sensorError(int error)

maxBufferSize : const int

The property holds the maximum buffer size.

Note that this may be undefined, in which case the sensor does not support any form of buffering.

See also QSensor::bufferSize and QSensor::efficientBufferSize.

outputRange : int

This property holds the output range in use by the sensor.

This value represents the index in the QSensor::outputRanges list to use.

Setting this property is not portable and can cause conflicts with other applications. Check with the sensor backend and platform documentation for any policy regarding multiple applications requesting an output range.

The default value (-1) means that the app does not care what the output range is.

Note that there is no mechanism to determine the current output range in use by the platform.

Access functions:

int	outputRange() const
void	setOutputRange(int index)

See also QSensor::outputRanges.

outputRanges : const qoutputrangelist

This property holds a list of output ranges the sensor supports.

A sensor may have more than one output range. Typically this is done to give a greater measurement range at the cost of lowering accuracy.

Note that this information is not mandatory. This information is typically only available for sensors that have selectable output ranges (such as typical accelerometers).

Access functions:

qoutputrangelist

outputRanges() const

See also QSensor::outputRange and qoutputrangelist.

reading : QSensorReading * const

This property holds the reading class.

The reading class provides access to sensor readings. The reading object is a volatile cache of the most recent sensor reading that has been received so the application should process readings immediately or save the values somewhere for later processing.

Note that this will return 0 until a sensor backend is connected to a backend.

Also note that readings are not immediately available after start() is called. Applications must wait for the readingChanged() signal to be emitted.

Access functions:

QSensorReading *

reading() const

Notifier signal:

void	readingChanged()

See also isConnectedToBackend() and start().

sensorid : QByteArray

This property holds the backend identifier for the sensor.

Note that the identifier is filled out automatically when the sensor is connected to a backend. If you want to connect a specific backend, you should call setIdentifier() before connectToBackend().

Access functions:

QByteArray	identifier() const
void	setIdentifier(const QByteArray & identifier)

type : const QByteArray

This property holds the type of the sensor.

Access functions:

QByteArray

type() const

 sensor.start();
 if (sensor.isBusy()) {
     // need to wait for busyChanged signal and try again
 }

 sensor->start();
 sensor->reading()->x(); // no data available

     connect(sensor, SIGNAL(readingChanged()), this, SLOT(checkReading()));
     sensor->start();
 }
 void MyClass::checkReading() {
     sensor->reading()->x();

 typedef QList<qoutputrange> qoutputrangelist;

 typedef QPair<int,int> qrange;

 typedef QList<qrange> qrangelist;