android - 即使传感器读数没有变化，也会调用 OnSensorChanged

Question

我将传感器用作 Sensor.TYPE_ACCELEROMETER。我正在按如下方式实现 OnSensorChanged() 方法:

    @Override
    public void onSensorChanged(SensorEvent event) {
        if (event.sensor.getType() == Sensor.TYPE_ACCELEROMETER)
            mGravity = event.values;
        float[] vector;
        vector = event.values.clone();
        double normVector =
                Math.sqrt(vector[0] * vector[0] + vector[1] * vector[1] + vector[2] * vector[2]);
        vector[0] = vector[0] / (float) normVector;
        vector[1] = vector[1] / (float) normVector;
        vector[2] = vector[2] / (float) normVector;
        angle = (int) Math.round(Math.toDegrees(Math.acos(vector[2])));
       // do something with angle
   }

但是，即使我的设备平放在 table 上并且我看到 angle 的稳定值 (7)，也会调用此方法。为什么会这样？有什么方法可以确保仅当 angle 的读数发生变化时才调用此方法？

Answer 1

直接来自 documentation :

A sensor of this type measures the acceleration applied to the device (Ad). Conceptually, it does so by measuring forces applied to the sensor itself (Fs) using the relation: Ad = - ∑Fs / mass

In particular, the force of gravity is always influencing the measured acceleration: Ad = -g - ∑F / mass

For this reason, when the device is sitting on a table (and obviously not accelerating), the accelerometer reads a magnitude of g = 9.81 m/s^2

Similarly, when the device is in free-fall and therefore dangerously accelerating towards to ground at 9.81 m/s^2, its accelerometer reads a magnitude of 0 m/s^2.