Sensor.getRotationMatrix (float[] R, float[] I, float[] gravity, float[] geomagnetic)

public class MainActivity extends AppCompatActivity implements SensorEventListener {
  private static final String TAG = "CompassActivity";
  private SensorManager sensorManager;
  //記錄rotationMatrix矩陣值
  private float[] r = new float[9];
  private float[] gravity = null;
  private float[] geomagnetic = null;
  private float[] I=new float[9];
  private Handler handler=new Handler(){
    @Override
    public void handleMessage(Message msg) {
      if(gravity!=null&&geomagnetic!=null)
      {
        if(SensorManager.getRotationMatrix(r, I, gravity, geomagnetic)) {
          float gri = gravity[0] * r[6] + gravity[1] * r[7] + gravity[2] * r[8];
          float h= (I[3]*r[0]+I[4]*r[3]+I[5]*r[6])*geomagnetic[0]+
              (I[3]*r[1]+I[4]*r[4]+I[5]*r[7])*geomagnetic[1]+
              (I[3]*r[2]+I[4]*r[5]+I[5]*r[8])*geomagnetic[2];
          TextView textView = (TextView) findViewById(R.id.textView);
          textView.setText("重力加速度" + gri + "\n"+"磁場強度" + h + "\n");
        }
      }
    }
  };
  @Override
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    sensorManager = (SensorManager) getSystemService(SENSOR_SERVICE);
  }
  @Override
  public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.menu_main, menu);
    return true;
  }
  @Override
  public boolean onOptionsItemSelected(MenuItem item) {
    // Handle action bar item clicks here. The action bar will
    // automatically handle clicks on the Home/Up button, so long
    // as you specify a parent activity in AndroidManifest.xml.
    int id = item.getItemId();
    //noinspection SimplifiableIfStatement
    if (id == R.id.action_settings) {
      return true;
    }
    return super.onOptionsItemSelected(item);
  }
  @Override
  public void onSensorChanged(SensorEvent sensorEvent) {
    switch (sensorEvent.sensor.getType()){
      case Sensor.TYPE_ACCELEROMETER:
        gravity=sensorEvent.values;
        handler.sendEmptyMessage(0);
        break;
      case Sensor.TYPE_MAGNETIC_FIELD:
        geomagnetic=sensorEvent.values;
        handler.sendEmptyMessage(0);
        break;
      default:break;
    }
  }
  @Override
  public void onAccuracyChanged(Sensor sensor, int i) {
  }
  private void showMessage(String message){
    View view=findViewById(R.id.fab);
    final Snackbar snackbar=Snackbar.make(view, message, Snackbar.LENGTH_INDEFINITE);
    snackbar.setAction("關(guān)閉", new View.OnClickListener() {
      @Override
      public void onClick(View view) {
        snackbar.dismiss();
      }
    });
    snackbar.show();
  }
  @Override
  protected void onPause() {
    super.onPause();
    sensorManager.unregisterListener(this);
  }
  @Override
  protected void onResume() {
    super.onResume();
    Sensor sensor1=sensorManager.getDefaultSensor(Sensor.TYPE_ACCELEROMETER);
    sensorManager.registerListener(this,sensor1,SensorManager.SENSOR_DELAY_UI);
    Sensor sensor2=sensorManager.getDefaultSensor(Sensor.TYPE_MAGNETIC_FIELD);
    sensorManager.registerListener(this,sensor2,SensorManager.SENSOR_DELAY_UI);
  }
}