Android资料Android传感器入门Android

Android开发高级进阶——传感器

2016-09-19  本文已影响896人  trampcr

Android系统提供了对传感器的支持，如果手机设备的硬件提供了这些传感器，Android应用可以通过传感器来获取设备的外界条件，包括手机设备的运行状态、当前摆放方向、外界的磁场、温度和压力等。Android系统提供了驱动程序去管理这些传感器硬件，当传感器感知到外部环境发生改变时，Android系统负责管理这些传感器数据。

一. Android中11中常见的传感器

  1. 加速度传感器：SENSOR_TYPE_ACCELEROMETER

二. 使用传感器

使用传感器的步骤分为5步：

  1. 获取SensorManager对象
    调用Context的getSystemService(Context.SENSOR_SERVICE)方法获取SensorManager对象，SensorManager对象代表系统的传感器管理服务。
  2. 获取Sensor对象
    调用SensorManager的getDefaultSensor(int type)方法获取指定类型的传感器。
  3. 注册Sensor对象
    在Activity的onResume()方法中调用SensorManager的registerListener()方法为指定的传感器注册监听器，程序通过实现监听器即可获取传感器传来的数据。
  4. 重写onAccuracyChanged，onSensorChanged方法
    当传感器的精度和数据发送变化时，在这两个方法中做相应的操作。
  5. 注销Sensor对象
    在Activity的onPause()方法中调用SensorManager的unregisterListener()方法注销指定的传感器监听器。

SensorManager提供的注册传感器的方法为registerListener(SensorEventListener listener, Sensor sensor, int rate)，该方法的三个参数说明如下：

三. 读取传感器数据

在onSensorChanged(SensorEvent event)方法中有一个参数event，通过event可以获取传感器的类型以及传感器的数据。

* <h4>{@link android.hardware.Sensor#TYPE_ACCELEROMETER
     * Sensor.TYPE_ACCELEROMETER}:</h4> All values are in SI units (m/s^2)
     * <ul>
     * <li> values[0]: Acceleration minus Gx on the x-axis </li>
     * <li> values[1]: Acceleration minus Gy on the y-axis </li>
     * <li> values[2]: Acceleration minus Gz on the z-axis </li>
     * </ul>
     * <p>
     * A sensor of this type measures the acceleration applied to the device
     * (<b>Ad</b>). Conceptually, it does so by measuring forces applied to the
     * sensor itself (<b>Fs</b>) using the relation:
     * </p>
     * <b><center>Ad = - &#8721;Fs / mass</center></b>
     * <p>
     * In particular, the force of gravity is always influencing the measured
     * acceleration:
     * </p>
     * <b><center>Ad = -g - &#8721;F / mass</center></b>
     * <p>
     * For this reason, when the device is sitting on a table (and obviously not
     * accelerating), the accelerometer reads a magnitude of <b>g</b> = 9.81
     * m/s^2
     * </p>
     * <p>
     * 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.
     * </p>
     * <p>
     * It should be apparent that in order to measure the real acceleration of
     * the device, the contribution of the force of gravity must be eliminated.
     * This can be achieved by applying a <i>high-pass</i> filter. Conversely, a
     * <i>low-pass</i> filter can be used to isolate the force of gravity.
     * </p>
     * <pre class="prettyprint">
     *     public void onSensorChanged(SensorEvent event)
     *     {
     *          // alpha is calculated as t / (t + dT)
     *          // with t, the low-pass filter's time-constant
     *          // and dT, the event delivery rate
     *          final float alpha = 0.8;
     *          gravity[0] = alpha * gravity[0] + (1 - alpha) * event.values[0];
     *          gravity[1] = alpha * gravity[1] + (1 - alpha) * event.values[1];
     *          gravity[2] = alpha * gravity[2] + (1 - alpha) * event.values[2];
     *          linear_acceleration[0] = event.values[0] - gravity[0];
     *          linear_acceleration[1] = event.values[1] - gravity[1];
     *          linear_acceleration[2] = event.values[2] - gravity[2];
     *     }
     * </pre>
     * <p>
     * <u>Examples</u>:
     * <ul>
     * <li>When the device lies flat on a table and is pushed on its left side
     * toward the right, the x acceleration value is positive.</li>
     * <li>When the device lies flat on a table, the acceleration value is
     * +9.81, which correspond to the acceleration of the device (0 m/s^2) minus
     * the force of gravity (-9.81 m/s^2).</li>
     * <li>When the device lies flat on a table and is pushed toward the sky
     * with an acceleration of A m/s^2, the acceleration value is equal to
     * A+9.81 which correspond to the acceleration of the device (+A m/s^2)
     * minus the force of gravity (-9.81 m/s^2).</li>
     * </ul>

从加速度传感器源代码中可以看出，values[0]表示x轴上的加速度，values[1]表示y轴上的加速度，values[2]表示z轴上的加速度。

四. 针对是否有传感器功能优化

因为并非所有手机都支持所有传感器，不用系统引入的传感器不同，所以在使用之前有必要判断一下，、从而提高性能。

判断是否有传感器有两种方法：

  1. 运行时检测
SensorManager sensorManager = (SensorManager) getSystemService(SENSOR_SERVICE);
Sensor sensor = sensorManager.getDefaultSensor(Sensor.TYPE_ORIENTATION);
if (sensor != null){
          //传感器存在
}else{
          //传感器不存在
}
  1. 使用Android Market过滤器来限定目标设备必须带有指定传感器配置。
<use-feature 
       name = "android.hardware.sensor.orientation"
       android:required = "true"/>

五. 方向传感器小Demo

利用方向传感器，界面中的图片向手机旋转的反方向旋转。代码如下：

public class MainActivity extends AppCompatActivity implements SensorEventListener{

    private ImageView mIvSensor;
    private Sensor mSensor;
    private SensorManager mSensorManager;
    private float mDegress = 0f;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        mIvSensor = (ImageView) findViewById(R.id.iv_sensor);

        mSensorManager = (SensorManager) getSystemService(SENSOR_SERVICE);
        mSensor = mSensorManager.getDefaultSensor(Sensor.TYPE_ORIENTATION);

    }

    @Override
    protected void onResume() {
        super.onResume();
        mSensorManager.registerListener(this, mSensor, SensorManager.SENSOR_DELAY_UI); //rate suitable for the user interface
    }

    @Override
    protected void onPause() {
        super.onPause();
        mSensorManager.unregisterListener(this);
    }

    @Override
    public void onSensorChanged(SensorEvent event) {
        if (event.sensor.getType() == Sensor.TYPE_ORIENTATION){
            float degree = - event.values[0];
            RotateAnimation rotateAnimation = new RotateAnimation(mDegress, degree, Animation.RELATIVE_TO_SELF, 0.5f, Animation.RELATIVE_TO_SELF, 0.5f);
            rotateAnimation.setDuration(100);
            mIvSensor.startAnimation(rotateAnimation);
            mDegress = degree;
        }
    }

    @Override
    public void onAccuracyChanged(Sensor sensor, int accuracy) {
        //TODO:当传感器精度发生变化时
    }
}

演示效果：

orientation_sensor_demo.gif

六. 注意

  1. 别忘记注销。
  2. 不要阻塞onSensorChanged方法。
  3. 避免使用过时的方法或传感器类型。
  4. 在使用前先验证传感器是否存在。
  5. 谨慎选择传感器延时。
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