MeeGo 1.2 Harmattan Developer Documentation Develop for the Nokia N9

QSensor Class Reference

The QSensor class represents a single hardware sensor. More...

 #include <QSensor>

Inherits: QObject.

Inherited by: QAccelerometer, QAmbientLightSensor, QCompass, QGyroscope, QLightSensor, QMagnetometer, QOrientationSensor, QProximitySensor, QRotationSensor, and QTapSensor.

This class was introduced in Qt Mobility 1.0.

Properties

  • 1 property inherited from QObject

Public Functions

QSensor ( const QByteArray & type, QObject * parent = 0 )
virtual ~QSensor ()
void addFilter ( QSensorFilter * filter )
qrangelist availableDataRates () const
bool connectToBackend ()
int dataRate () const
QString description () const
int error () const
QList<QSensorFilter *> filters () const
QByteArray identifier () const
bool isActive () const
bool isBusy () const
bool isConnectedToBackend () const
int outputRange () const
qoutputrangelist outputRanges () const
QSensorReading * reading () const
void removeFilter ( QSensorFilter * filter )
void setActive ( bool active )
void setDataRate ( int rate )
void setIdentifier ( const QByteArray & identifier )
void setOutputRange ( int index )
QByteArray type () const
  • 29 public functions inherited from QObject

Public Slots

bool start ()
void stop ()
  • 1 public slot inherited from QObject

Signals

void activeChanged ()
void availableSensorsChanged ()
void busyChanged ()
void readingChanged ()
void sensorError ( int error )

Static Public Members

QByteArray defaultSensorForType ( const QByteArray & type )
QList<QByteArray> sensorTypes ()
QList<QByteArray> sensorsForType ( const QByteArray & type )
  • 4 static public members inherited from QObject

Related Non-Members

typedef qoutputrangelist
typedef qrange
typedef qrangelist
typedef qtimestamp

Additional Inherited Members

  • 1 public variable inherited from QObject
  • 7 protected functions inherited from QObject
  • 2 protected variables inherited from QObject

Detailed Description

The QSensor class represents a single hardware sensor.

The life cycle of a sensor is typically:

  • Create a sub-class of QSensor on the stack or heap.
  • Setup as required by the application.
  • Start receiving values.
  • Sensor data is used by the application.
  • Stop receiving values.

The sensor data is delivered via QSensorData and its sub-classes.

See also QSensorReading.

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.

This property was introduced in Qt Mobility 1.1.

Access functions:

bool isActive () const
void setActive ( bool active )

Notifier signal:

void activeChanged ()

availableDataRates : const QtMobility::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.

This property was introduced in Qt Mobility 1.0.

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.

This property was introduced in Qt Mobility 1.0.

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).

This property was introduced in Qt Mobility 1.0.

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.

This property was introduced in Qt Mobility 1.0.

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.

This property was introduced in Qt Mobility 1.0.

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.

This property was introduced in Qt Mobility 1.0.

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.

This property was introduced in Qt Mobility 1.0.

Access functions:

int outputRange () const
void setOutputRange ( int index )

See also QSensor::outputRanges.

outputRanges : const QtMobility::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).

This property was introduced in Qt Mobility 1.0.

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.

This property was introduced in Qt Mobility 1.0.

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().

This property was introduced in Qt Mobility 1.0.

Access functions:

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

type : const QByteArray

This property holds the type of the sensor.

This property was introduced in Qt Mobility 1.0.

Access functions:

QByteArray type () const

Member Function Documentation

QSensor::QSensor ( const QByteArray & type, QObject * parent = 0 )

Construct the type sensor as a child of parent.

This function was introduced in Qt Mobility 1.0.

QSensor::~QSensor () [virtual]

Destroy the sensor. Stops the sensor if it has not already been stopped.

This function was introduced in Qt Mobility 1.0.

void QSensor::activeChanged () [signal]

This signal is emitted when the QSensor::active property has changed.

This function was introduced in Qt Mobility 1.1.

See also QSensor::active.

void QSensor::addFilter ( QSensorFilter * filter )

Add a filter to the sensor.

The sensor does not take ownership of the filter. QSensorFilter will inform the sensor if it is destroyed.

This function was introduced in Qt Mobility 1.0.

See also QSensorFilter.

void QSensor::availableSensorsChanged () [signal]

This signal is emitted when the list of available sensors has changed. The sensors available to a program will not generally change over time however some of the avilable sensors may represent hardware that is not permanently connected. For example, a game controller that is connected via bluetooth would become available when it was on and would become unavailable when it was off.

This function was introduced in Qt Mobility 1.2.

See also QSensor::sensorTypes() and QSensor::sensorsForType().

void QSensor::busyChanged () [signal]

This signal is emitted when the sensor is no longer busy. This can be used to grab a sensor when it becomes available.

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

This function was introduced in Qt Mobility 1.0.

bool QSensor::connectToBackend ()

Try to connect to a sensor backend.

Returns true if a suitable backend could be found, false otherwise.

The type must be set before calling this method if you are using QSensor directly.

This function was introduced in Qt Mobility 1.0.

See also isConnectedToBackend().

QByteArray QSensor::defaultSensorForType ( const QByteArray & type ) [static]

Returns the default sensor identifier for type. This is set in a config file and can be overridden if required. If no default is available the system will return the first registered sensor for type.

Note that there is special case logic to prevent the generic plugin's backends from becoming the default when another backend is registered for the same type. This logic means that a backend identifier starting with generic. will only be the default if no other backends have been registered for that type or if it is specified in Sensors.conf.

This function was introduced in Qt Mobility 1.0.

See also Determining the default sensor for a type.

QList<QSensorFilter *> QSensor::filters () const

Returns the filters currently attached to the sensor.

This function was introduced in Qt Mobility 1.2.

See also QSensorFilter.

void QSensor::readingChanged () [signal]

This signal is emitted when a new sensor reading is received.

The sensor reading can be found in the QSensor::reading property. Note that the reading object is a volatile cache of the most recent sensor reading that has been received so the application should process the reading immediately or save the values somewhere for later processing.

Before this signal has been emitted for the first time, the reading object will have uninitialized data.

This function was introduced in Qt Mobility 1.0.

See also start().

void QSensor::removeFilter ( QSensorFilter * filter )

Remove filter from the sensor.

This function was introduced in Qt Mobility 1.0.

See also QSensorFilter.

void QSensor::sensorError ( int error ) [signal]

This signal is emitted when an error code is set on the sensor. Note that some errors will cause the sensor to stop working. You should call isActive() to determine if the sensor is still running.

This function was introduced in Qt Mobility 1.0.

QList<QByteArray> QSensor::sensorTypes () [static]

Returns a list of all sensor types.

This function was introduced in Qt Mobility 1.0.

QList<QByteArray> QSensor::sensorsForType ( const QByteArray & type ) [static]

Returns a list of ids for each of the sensors for type. If there are no sensors of that type available the list will be empty.

This function was introduced in Qt Mobility 1.0.

bool QSensor::start () [slot]

Start retrieving values from the sensor. Returns true if the sensor was started, false otherwise.

The sensor may fail to start for several reasons.

Once an application has started a sensor it must wait until the sensor receives a new value before it can query the sensor's values. This is due to how the sensor receives values from the system. Sensors do not (in general) poll for new values, rather new values are pushed to the sensors as they happen.

For example, this code will not work as intended.

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

To work correctly, the code that accesses the reading should ensure the readingChanged() signal has been emitted.

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

This function was introduced in Qt Mobility 1.0.

See also QSensor::busy.

void QSensor::stop () [slot]

Stop retrieving values from the sensor.

This releases the sensor so that other processes can use it.

This function was introduced in Qt Mobility 1.0.

See also QSensor::busy.

Related Non-Members

typedef qoutputrangelist

This type is defined as a list of qoutputrange values.

 typedef QList<qoutputrange> qoutputrangelist;

See also QList, qoutputrange, and QSensor::outputRanges.

typedef qrange

This type is defined as a QPair.

 typedef QPair<int,int> qrange;

See also QPair, qrangelist, and QSensor::availableDataRates.

typedef qrangelist

This type is defined as a list of qrange values.

 typedef QList<qrange> qrangelist;

See also QList, qrange, and QSensor::availableDataRates.

typedef qtimestamp

Sensor timestamps are represented by this typedef which is a 64 bit unsigned integer.

Timestamps values are microseconds since a fixed point. You can use timestamps to see how far apart two sensor readings are.

Note that sensor timestamps from different sensors may not be directly comparable (as they may choose different fixed points for their reference).

Note that some platforms do not deliver timestamps correctly. Applications should be prepared for occasional issues that cause timestamps to jump forwards or backwards. The platform notes have more details.