Qt Sensors C++ 概述

Sensor Types

On a device there can be many types of sensors. Not all of the types that the Qt Sensors API supports may be available. There may also be types available that are not defined in the Qt Sensors API. The types of sensors available on a device is found using the QSensor::sensorTypes () 函数。

For a list of built-in sensor types, see the Sensor Classes 以下章节。

Common Conventions

Unless specified otherwise, Qt Sensors uses the Right Hand Cartesian coordinate system .

To allow for measurements in all 6 directions, negative values are used.

Where rotation around an axis is used, the rotation shall be expressed as a Right Hand rotation.

In general, sensor data is oriented relative to QScreen::nativeOrientation , that is to the top of the device when the device is held in its natural orientation (normally when the device logo appears the right side up). If values are to be displayed on the screen, the values may need to be transformed so that they match the user interface orientation. A sensor may define its data as being oriented to the UI. This will be noted in the documentation for the sensor.

Using a Sensor

The life cycle of a QSensor is typically:

  • Create an instance of QSensor or one of its sub-classes on the stack or heap.
  • 通过应用程序按要求设置。
  • 开始接收值。
  • 通过应用程序使用传感器数据。
  • 停止接收值。

Here is an example of creating a sensor on the heap and on the stack.

// On the heap (deleted when this object is deleted)
QAccelerometer *sensor = new QAccelerometer(this);
// On the stack (deleted when the current scope ends)
QOrientationSensor orient_sensor;
					

Accessing Sensor Data in a Generic Fashion

The preferred way to deal with sensor data is via the Reading Classes . However, sometimes this may not be possible. For example, you may be deploying an application to a device that has a new sensor type but no C++ header describing the reading class is available.

Thanks to Qt's property system you can still access the sensor data. You need to know 3 pieces of information in order to do this:

  • The sensor type.
  • The property name or index.
  • The property type or a comparable type.

For example, here is an example of how you can access a property of the accelerometer. This code does not require any compile-time links to QAccelerometer or QAccelerometerReading .

// start the sensor
QSensor sensor("QAccelerometer");
sensor.start();
// later
QSensorReading *reading = sensor.reading();
qreal x = reading->property("x").value<qreal>();
qreal y = reading->value(1).value<qreal>();
					

You can discover all of this information at runtime too.

Discovering Sensors And Reading Properties At Runtime

Sometimes it may be that the available sensors are not known at development time. It is possible to find out which sensors are available as illustrated below:

QList<QSensor*> mySensorList;
for (const QByteArray &type : QSensor::sensorTypes()) {
    qDebug() << "Found a sensor type:" << type;
    for (const QByteArray &identifier : QSensor::sensorsForType(type)) {
        qDebug() << "    " << "Found a sensor of that type:" << identifier;
        QSensor* sensor = new QSensor(type, this);
        sensor->setIdentifier(identifier);
        mySensorList.append(sensor);
    }
}
					

Furthermore it is possible to discover the reading details for these sensors, as illustrated below:

for (QSensor* sensor : mySensorList) {
    const int firstProperty = QSensorReading::staticMetaObject.propertyOffset();
    // Connect to backend first in case start() hasn't been called yet
    if (!sensor->connectToBackend())
        continue;
    qDebug() << "Sensor" << sensor->identifier() << "reading properties:";
    QSensorReading *reading = sensor->reading();
    if (reading) {
        const QMetaObject *mo = reading->metaObject();
        for (int i = firstProperty; i < mo->propertyCount(); ++i) {
            QByteArray name = mo->property(i).name();
            qDebug() << "    " << name << reading->property(name).toByteArray();
        }
    }
}
					

Front End, Back End

The Qt Sensors API has a front end, for application developers to use and a back end, where device implementors write code to access their hardware. As an application developer you do not need to access the back end though it may be useful to understand how it works.

Commands from the application are delivered through QSensor and then down to the device plugin. Data comes back through the QSensorReading 类。

More information about the back end can be found in Qt Sensors Backend .

主类

The primary classes that make up the Qt Sensors API.

QSensor Represents a single hardware sensor
QSensorFilter Efficient callback facility for asynchronous notifications of sensor changes
QSensorReading Holds the readings from the sensor

Reading Classes

The best way to access sensor data is via one of these classes.

QAccelerometerReading Reports on linear acceleration along the X, Y and Z axes
QAmbientLightReading Represents one reading from the ambient light sensor
QAmbientTemperatureReading Holds readings of the ambient temperature
QCompassReading Represents one reading from a compass
QGyroscopeReading Represents one reading from the gyroscope sensor
QHumidityReading Holds readings from the humidity sensor
QLightReading Represents one reading from the light sensor
QMagnetometerReading Represents one reading from the magnetometer
QOrientationReading Represents one reading from the orientation sensor
QPressureReading Holds readings from the pressure sensor
QProximityReading Represents one reading from the proximity sensor
QRotationReading Represents one reading from the rotation sensor
QTiltReading 保持来自倾斜传感器的读数

Sensor Classes

These classes provide convenience wrappers that reduce the need for casting. Each of these classes represents a sensor type that the Qt Sensors API knows about. Note that additional types may be made available at run-time. See Sensor Types 了解更多信息。

QAccelerometer 围绕 QSensor 的方便包裹器
QAmbientLightSensor 围绕 QSensor 的方便包裹器
QAmbientTemperatureSensor 围绕 QSensor 的方便包裹器
QCompass 围绕 QSensor 的方便包裹器
QGyroscope 围绕 QSensor 的方便包裹器
QHumiditySensor 围绕 QSensor 的方便包裹器
QLightSensor 围绕 QSensor 的方便包裹器
QMagnetometer 围绕 QSensor 的方便包裹器
QOrientationSensor 围绕 QSensor 的方便包裹器
QPressureSensor 围绕 QSensor 的方便包裹器
QProximitySensor 围绕 QSensor 的方便包裹器
QRotationSensor 围绕 QSensor 的方便包裹器
QTiltSensor 围绕 QSensor 的方便包裹器

Filter Classes

As with the sensor classes, these provide convenience wrappers that reduce the need for casting.

QAccelerometerFilter 围绕 QSensorFilter 的方便包裹器
QAmbientLightFilter 围绕 QSensorFilter 的方便包裹器
QAmbientTemperatureFilter 围绕 QSensorFilter 的方便包裹器
QCompassFilter 围绕 QSensorFilter 的方便包裹器
QGyroscopeFilter 围绕 QSensorFilter 的方便包裹器
QHumidityFilter 围绕 QSensorFilter 的方便包裹器
QLightFilter 围绕 QSensorFilter 的方便包裹器
QMagnetometerFilter 围绕 QSensorFilter 的方便包裹器
QOrientationFilter 围绕 QSensorFilter 的方便包裹器
QPressureFilter 围绕 QSensorFilter 的方便包裹器
QProximityFilter 围绕 QSensorFilter 的方便包裹器
QRotationFilter 围绕 QSensorFilter 的方便包裹器
QTiltFilter 围绕 QSensorFilter 的方便包裹器