（1）实现SensorEventListener接口
接着上一篇的重力传感器（一）——监听数据，可以发现OrientationEventListener实际上就是监听了加速度传感器，并实现了SensorEventListener接口而已，相当于一个特例。
public OrientationEventListener(Context context, int rate) {mSensorManager = (SensorManager)context.getSystemService(Context.SENSOR_SERVICE);mRate = rate;mSensor = mSensorManager.getDefaultSensor(Sensor.TYPE_ACCELEROMETER);if (mSensor != null) {mSensorEventListener = new SensorEventListenerImpl();}}public void enable() {if (mSensor == null) {Log.w(TAG, "Cannot detect sensors. Not enabled");return;}if (mEnabled == false) {if (localLOGV) Log.d(TAG, "OrientationEventListener enabled");mSensorManager.registerListener(mSensorEventListener, mSensor, mRate);mEnabled = true;}}class SensorEventListenerImpl implements SensorEventListener {public void onSensorChanged(SensorEvent event) {}public void onAccuracyChanged(Sensor sensor, int accuracy) {}}
（2）OrientationEventListener源码
//frameworks/base/core/java/android/view/OrientationEventListener.java/*** Helper class for receiving notifications from the SensorManager when* the orientation of the device has changed.*/public abstract class OrientationEventListener {private static final String TAG = "OrientationEventListener";private static final boolean DEBUG = false;private static final boolean localLOGV = false;private int mOrientation = ORIENTATION_UNKNOWN;private SensorManager mSensorManager;private boolean mEnabled = false;private int mRate;private Sensor mSensor;private SensorEventListener mSensorEventListener;private OrientationListener mOldListener;public static final int ORIENTATION_UNKNOWN = -1;public OrientationEventListener(Context context) {this(context, SensorManager.SENSOR_DELAY_NORMAL);}public OrientationEventListener(Context context, int rate) {mSensorManager = (SensorManager)context.getSystemService(Context.SENSOR_SERVICE);mRate = rate;mSensor = mSensorManager.getDefaultSensor(Sensor.TYPE_ACCELEROMETER);if (mSensor != null) {mSensorEventListener = new SensorEventListenerImpl();}}void registerListener(OrientationListener lis) {mOldListener = lis;}public void enable() {if (mSensor == null) {Log.w(TAG, "Cannot detect sensors. Not enabled");return;}if (mEnabled == false) {if (localLOGV) Log.d(TAG, "OrientationEventListener enabled");mSensorManager.registerListener(mSensorEventListener, mSensor, mRate);mEnabled = true;}}public void disable() {if (mSensor == null) {Log.w(TAG, "Cannot detect sensors. Invalid disable");return;}if (mEnabled == true) {if (localLOGV) Log.d(TAG, "OrientationEventListener disabled");mSensorManager.unregisterListener(mSensorEventListener);mEnabled = false;}}class SensorEventListenerImpl implements SensorEventListener {private static final int _DATA_X = 0;private static final int _DATA_Y = 1;private static final int _DATA_Z = 2;public void onSensorChanged(SensorEvent event) {float[] values = event.values;int orientation = ORIENTATION_UNKNOWN;float X = -values[_DATA_X];float Y = -values[_DATA_Y];float Z = -values[_DATA_Z];float magnitude = X*X + Y*Y;// Don't trust the angle if the magnitude is small compared to the y valueif (magnitude * 4 >= Z*Z) {float OneEightyOverPi = 57.29577957855f;float angle = (float)Math.atan2(-Y, X) * OneEightyOverPi;orientation = 90 - (int)Math.round(angle);// normalize to 0 - 359 rangewhile (orientation >= 360) {orientation -= 360;}while (orientation < 0) {orientation += 360;}}if (mOldListener != null) {mOldListener.onSensorChanged(Sensor.TYPE_ACCELEROMETER, event.values);}if (orientation != mOrientation) {mOrientation = orientation;onOrientationChanged(orientation);}}public void onAccuracyChanged(Sensor sensor, int accuracy) {}}public boolean canDetectOrientation() {return mSensor != null;}/*** Called when the orientation of the device has changed.* orientation parameter is in degrees, ranging from 0 to 359.*/abstract public void onOrientationChanged(int orientation);}
（3）可用的API
（4）Demo举例
监听手机旋转角度类：OrientationEventListener不只是判断屏幕旋转角度0，90，180，270 四个角度，还可以实时获取每一个角度的变化。
创建一个类继承OrientationEventListener；开启和关闭监听：调用该类的 enable() 和 disable() 方法；监测指定的屏幕旋转角度：onOrientationChanged的参数orientation是一个从0～359的变量；
OrientationEventListener mOrientationListener;@Overridepublic void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.main);mOrientationListener = new OrientationEventListener(this,SensorManager.SENSOR_DELAY_NORMAL) {@Overridepublic void onOrientationChanged(int orientation) {if (orientation == OrientationEventListener.ORIENTATION_UNKNOWN) {return; //手机平放时，检测不到有效的角度}//只检测是否有四个角度的改变if (orientation > 350 || orientation < 10) {//0度orientation = 0;} else if (orientation > 80 && orientation < 100) {//90度orientation = 90;} else if (orientation > 170 && orientation < 190) {//180度orientation = 180;} else if (orientation > 260 && orientation < 280) {//270度orientation = 270;} else {return;}}};if (mOrientationListener.canDetectOrientation()) {mOrientationListener.enable();} else {mOrientationListener.disable();}}@Overrideprotected void onDestroy() {super.onDestroy();mOrientationListener.disable();}
