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:

Notifier signal:

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:

Notifier signal:

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:

See also QSensor::dataRate and qrangelist.

axesOrientationMode : AxesOrientationMode

This property holds the mode that affects how the screen orientation changes reading values.

When set to FixedOrientation, which is the default mode, no automatic rotation is applied to the reading. This is the only mode available for backends that do not support the QSensor::AxesOrientation feature.

When set to AutomaticOrientation, the reading values are automatically rotated when the screen orientation changes. In effect, the screen orientation is canceled out.

As an example, assume the device is rotated by 180 degrees and therefore the screen orientation also is rotated by 180 degrees from the native orientation. Without automatic axes orientation, the reading values would now be changed: Both the X and the Y values would be negated, forcing an application developer to manually cancel out the negation in application code. Automatic axes orientation does this automatically, in this mode the X and Y values would be the same as with the default screen orientation.

This automatic rotation of the axes is handy is some usecases, for example in a bubble level application that measures how level a surface is by looking at the X axis value of an accelerometer. When the device and screen orientation change by 90 degrees, an application developer does not need to change anything, he can continue using the X axis value even though the device is rotated. Without automatic axes orientation, the application developer would need to look at the Y values instead, thereby adding code to the application that reads from a different axis depending on the screen orientation.

The UserOrientation mode is quite similar to AutomaticOrientation, only that the screen orientation is manually controlled instead of automatically determined. The angle of the userOrientation property is then used for rotating the reading values.

Since the rotation of the reading values is based on the screen orientation, Z values will never change, as the Z axis is perpendicular to the screen. As screen orientation changes in 90 degree steps, rotating the reading values is also done in steps of 90 degrees.

This property is only used for orientable sensors.

This property was introduced in Qt 5.1.

Access functions:

Notifier signal:

bufferSize : int

This property holds the size of the buffer. By default, the buffer size is 1, which means no buffering. If the maximum buffer size is 1, 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.

Some backends only support enabling or disabling the buffer and do not give control over the size. In this case, the maxBufferSize and efficientBufferSize properties might not be set at all, even though buffering is supported. Setting the bufferSize property to any value greater than 1 will enable buffering. After the sensor has been started, the bufferSize property will be set to the actual value by the backend.

Access functions:

Notifier signal:

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:

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:

currentOrientation : const int

This property holds the current orientation that is used for rotating the reading values.

This might not be the same as the screen orientation. For example, in the FixedOrientation mode, the reading values are not rotated, and therefore the property is 0.

In the UserOrientation mode, the readings are rotated based on the userOrientation property, and therefore this property is equal to the userOrientation property.

In the AutomaticOrientation mode, the readings are rotated based on the screen orientation, and therefore this property will be equal to the current screen orientation.

This property is set by the backend and only valid for orientable sensors.

This property was introduced in Qt 5.1.

Access functions:

Notifier signal:

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:

Notifier signal:

See also QSensor::availableDataRates.

description : const QString

This property holds a descriptive string for the sensor.

Access functions:

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.

Access functions:

Notifier signal:

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:

Notifier signal:

identifier : 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:

maxBufferSize : const int

The property holds the maximum buffer size.

Note that this may be 1, in which case the sensor does not support any form of buffering. In that case, isFeatureSupported(QSensor::Buffering) will also return false.

Access functions:

Notifier signal:

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:

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:

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:

Notifier signal:

See also isConnectedToBackend() and start().

skipDuplicates : bool

Indicates whether duplicate reading values should be omitted.

When duplicate skipping is enabled, successive readings with the same or very similar values are omitted. This helps reducing the amount of processing done, as less sensor readings are made available. As a consequence, readings arrive at an irregular interval.

Duplicate skipping is not just enabled for readings that are exactly the same, but also for readings that are quite similar, as each sensor has a bit of jitter even if the device is not moved.

Support for this property depends on the backend. Use isFeatureSupported() to check if it is supported on the current platform.

Duplicate skipping is disabled by default.

Duplicate skipping takes effect when the sensor is started, changing the property while the sensor is active has no immediate effect.

This property was introduced in Qt 5.1.

Access functions:

Notifier signal:

type : const QByteArray

This property holds the type of the sensor.

Access functions:

userOrientation : int

This property holds the angle used for rotating the reading values in the UserOrientation mode.

When the axesOrientationMode property is set to UserOrientation, the angle for rotating the reading values is taken from this property. In other modes, the property has no effect.

The default is 0. The only valid values are 0, 90, 180 and 270, as those are the only possible screen orientations.

This property is only valid for orientable sensors.

This property was introduced in Qt 5.1.

Access functions:

Notifier signal: