本节主要分析的是java层次相关的软件内容

Application开发

谷歌开发者网站 sensors 中提供了AOSP提供的sensor相关的api介绍及demo；

可以参考下相关资源：

传感器
动态传感器
位置传感器
环境传感器
Accelerometer Play
API 演示 (OS - RotationVectorDemo)

App demo 实现

public class MainActivity extends AppCompatActivity implements SensorEventListener {private SensorManager mSensorManager;private Sensor mSensorAcc, mSensorMag;private TextView tvAcc, tvMag;@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);Toolbar toolbar = findViewById(R.id.toolbar);setSupportActionBar(toolbar);tvAcc = findViewById(R.id.tvAcc);tvMag = findViewById(R.id.tvMag);mSensorManager = (SensorManager) getSystemService(Context.SENSOR_SERVICE);//!< 通过getSystemService获得SensorManager实例对象 >! NoteBy: yujixuanmSensorAcc = mSensorManager.getDefaultSensor(Sensor.TYPE_ACCELEROMETER);//!< 通过SensorManager 获取sensor对象 >! NoteBy: yujixuan}@Overridepublic final void onSensorChanged(SensorEvent event) {float x = event.values[0];float y = event.values[1];float z = event.values[2];if(event.sensor == mSensorAcc)tvAcc.setText("x:" + x + "\ny:" + y + "\nz:" + z);}@Overrideprotected void onResume() {super.onResume();mSensorManager.registerListener(this, mSensorAcc, SensorManager.SENSOR_DELAY_NORMAL);}@Overrideprotected void onPause() {super.onPause();mSensorManager.unregisterListener(this);}
}

实现的步骤：

通过调用通过getSystemService获得传感器服务，实现返回的是封装了SensorService的SensorManager对象
通过SensorManager 来获得指定类型的传感器对象，用来获得传感器的数据
通过SensorManager.registerListener注册SensorEventListener监听器，监听传感器
实现对sensor上报数据内容的具体操作

运行demo

以下是在Android Studio中实际demo

SensorManager

通过上面简单的app demo可知，主要过程均是通过SensorManager来完成；

改SensorManager是通过 getSystemService获取系统name 为“sensor” service得到；

/*** Use with {@link #getSystemService(String)} to retrieve a {@link* android.hardware.SensorManager} for accessing sensors.** @see #getSystemService(String)* @see android.hardware.SensorManager*/
public static final String SENSOR_SERVICE = "sensor";

Sensor服务用户程序不能直接访问， android.hardware.SensorManager 是真正用来在java程序中操作sensor的类，它是SensorService提供服务接口的封装。

因为 Manager是应用程序直接面对的接口， Manager里维护对应的Service，应用程序不能直接访问Service；

Service是服务，被所有的应用共享的服务，并非属于某一个特定的进程，也即Sensor application与SensorService不在同一个进程内，App需要使用Sensor

service就需要进程间通信，这显然不利于很高效率的开发程序，为此由manager类操作,隐藏共享操作，把细节实现隐藏封装，app应用程序只需要通过访问被暴

露出来的api接口，所以应用中与之直接交互的是SensorManager；

SensorManager提供了各种方法来访问和列出传感器，注册和取消注册传感器事件监听器，它还提供了几个传感器常量，用于报

告传感器精确度，设置数据采集频率和校准传感器；下面是这个类的定义：

public abstract class SensorManager protected static final String TAG = "SensorManager";public static final int RAW_DATA_Z = 5;/** Standard gravity (g) on Earth. This value is equivalent to 1G */public static final float STANDARD_GRAVITY = 9.80665f;
......public SensorManager() {}protected abstract List<Sensor> getFullSensorList();protected abstract List<Sensor> getFullDynamicSensorList();@Deprecatedpublic int getSensors() {return getLegacySensorManager().getSensors();}public List<Sensor> getSensorList(int type) {// cache the returned lists the first timeList<Sensor> list;final List<Sensor> fullList = getFullSensorList();synchronized (mSensorListByType) {list = mSensorListByType.get(type);if (list == null) {if (type == Sensor.TYPE_ALL) {list = fullList;} else {list = new ArrayList<Sensor>();for (Sensor i : fullList) {if (i.getType() == type)list.add(i);}}list = Collections.unmodifiableList(list);mSensorListByType.append(type, list);}}return list;}@Deprecatedpublic boolean registerListener(SensorListener listener, int sensors) {return registerListener(listener, sensors, SENSOR_DELAY_NORMAL);}public boolean registerListener(SensorEventListener listener, Sensor sensor,int samplingPeriodUs, Handler handler) {int delay = getDelay(samplingPeriodUs);return registerListenerImpl(listener, sensor, delay, handler, 0, 0);}public void unregisterListener(SensorEventListener listener, Sensor sensor) {if (listener == null || sensor == null) {return;}unregisterListenerImpl(listener, sensor);}public boolean flush(SensorEventListener listener) {return flushImpl(listener);}
.......
}

通过上面的内容可以看出SensorManager是个抽象类，真正完成管理控制sensor的是它的子类SystemSensorManager；

SystemSensorManager继承了它做具体的实现；

SystemSensorManager.java extends SensorManagerpublic class SystemSensorManager extends SensorManager {//TODO: disable extra logging before releaseprivate static boolean DEBUG_DYNAMIC_SENSOR = true;private static native void nativeClassInit();private static native long nativeCreate(String opPackageName);private static native boolean nativeGetSensorAtIndex(long nativeInstance,Sensor sensor, int index);private static native void nativeGetDynamicSensors(long nativeInstance, List<Sensor> list);private static native boolean nativeIsDataInjectionEnabled(long nativeInstance);private static final Object sLock = new Object();@GuardedBy("sLock")private static boolean sNativeClassInited = false;@GuardedBy("sLock")private static InjectEventQueue sInjectEventQueue = null;private final ArrayList<Sensor> mFullSensorsList = new ArrayList<>();private List<Sensor> mFullDynamicSensorsList = new ArrayList<>();private boolean mDynamicSensorListDirty = true;private final HashMap<Integer, Sensor> mHandleToSensor = new HashMap<>();
......public SystemSensorManager(Context context, Looper mainLooper) {synchronized(sLock) {if (!sNativeClassInited) {sNativeClassInited = true;nativeClassInit();}}mMainLooper = mainLooper;mTargetSdkLevel = context.getApplicationInfo().targetSdkVersion;mContext = context;mNativeInstance = nativeCreate(context.getOpPackageName());// initialize the sensor listfor (int index = 0;;++index) {Sensor sensor = new Sensor();if (!nativeGetSensorAtIndex(mNativeInstance, sensor, index)) break;mFullSensorsList.add(sensor);mHandleToSensor.put(sensor.getHandle(), sensor);}}
......@Overrideprotected List<Sensor> getFullSensorList() {return mFullSensorsList;
......private static abstract class BaseEventQueue {private static native long nativeInitBaseEventQueue(long nativeManager,WeakReference<BaseEventQueue> eventQWeak, MessageQueue msgQ,String packageName, int mode, String opPackageName);private static native int nativeEnableSensor(long eventQ, int handle, int rateUs,int maxBatchReportLatencyUs);private static native int nativeDisableSensor(long eventQ, int handle);private static native void nativeDestroySensorEventQueue(long eventQ);private static native int nativeFlushSensor(long eventQ);private static native int nativeInjectSensorData(long eventQ, int handle,}
......}

从这个类中可以本地的native方法，如：

nativeClassInit();
nativeCreate(String opPackageName);
nativeGetSensorAtIndex(long nativeInstance，Sensor sensor, int index);
nativeGetDynamicSensors(long nativeInstance, List<Sensor> list);
nativeIsDataInjectionEnabled(long nativeInstance);

通过load到的JNI访问到libc中的native方法，有关jni 和c++ 本地方法实现后面博客介绍；

除了对本地native方法的调用，SystemSensorManager 还在其构造函数中初始化了对应的sensor list；

        for (int index = 0;;++index) {Sensor sensor = new Sensor();if (!nativeGetSensorAtIndex(mNativeInstance, sensor, index)) break;mFullSensorsList.add(sensor);mHandleToSensor.put(sensor.getHandle(), sensor);}

Sensor对象

从app的demo代码中可以看出，一个存在的sensor是由一个Sensor类的对象来标识的，它获取自Sensor Manager，通过给定的参数，获取一个实例sensor对象；该类提供了各种方法来确定传感器的特性。

mSensorAcc = mSensorManager.getDefaultSensor(Sensor.TYPE_ACCELEROMETER);

public Sensor getDefaultSensor(int type) {// TODO: need to be smarter, for now, just return the 1st sensorList<Sensor> l = getSensorList(type);boolean wakeUpSensor = false;// For the following sensor types, return a wake-up sensor. These types are by default// defined as wake-up sensors. For the rest of the SDK defined sensor types return a// non_wake-up version.if (type == Sensor.TYPE_PROXIMITY || type == Sensor.TYPE_SIGNIFICANT_MOTION ||type == Sensor.TYPE_TILT_DETECTOR || type == Sensor.TYPE_WAKE_GESTURE ||type == Sensor.TYPE_GLANCE_GESTURE || type == Sensor.TYPE_PICK_UP_GESTURE ||type == Sensor.TYPE_WRIST_TILT_GESTURE) {wakeUpSensor = true;}for (Sensor sensor : l) {if (sensor.isWakeUpSensor() == wakeUpSensor) return sensor;}return null;
}

Sensor类的内容如下：

public final class Sensor {mNamemVendormVersionmHandlemTypemMaxRangemResolutionmPowermMinDelaymFifoReservedEventCountmFifoMaxEventCountmStringTypemRequiredPermissionmMaxDelaymFlagsmld
// funcSensorgetNamegetVendorgetTypegetVersiongetMaximumRangegetResolutiongetPowergetMinDelaygetFifoReservedEventCountgetFifoMaxEventCountgetStringTypegetUuidgetldgetRequiredPermissiongetHandlegetMaxDelayisWakeUpSensorisDynamicSensorisAdditionallnfoSupportedisDatalnjectionSupportedsetRangetoStringsetTypesetUuid
}

Sensor Event 处理

SensorEventListener

回到app demo中，可以看出，sensor数据的处理是override了onSensorChanged方法，它在有sensor数据上报时被回调，详细的回调过程后面的内容会做分析；暂时只关注demo中的代码实现；

通过activity的定义可知，onSensorChanged方法是来自接口SensorEventListener；

接口类interface SensorEventListener （方法都是public abstract, 变量都是public static final）

用于接收新的sensor 数据上报时回调其中的抽象方法；

code:frameworks\base\core\java\android\hardware\SensorEvent.java
public interface SensorEventListener {public void onSensorChanged(SensorEvent event); //sensor数据变化public void onAccuracyChanged(Sensor sensor, int accuracy); //精度变化
}

它处理的参数类型是SensorEvent类对象；这个类的对象表示一个SensorEvent事件，并保存诸如传感器类型、时间戳、精度等信息，还有传感器的数据。

values float数组里保存了app需要用到的数据信息；按照固定的格式去读取需要的参数即可；具体参考android API介绍，拿到event之后，对应固定的格式，拆解出的value即是我们需要的sensor数据；

public class SensorEvent {public final float[] values;
public Sensor sensor;
public int accuracy;
public long timestamp;
SensorEvent(int valueSize) {values = new float[valueSize];}
}

registerListener

实现一个sensor监听，是先通过SensorManager.registerListener注册SensorEventListener监听器，监听sensor，注册监听器的方法实现同样是有SensorManager对象来管理，appdemo中使用获取到的mSensorManager，以及设置指定类型获取的sensor对象 acc msensor来注册监听；

mSensorManager.registerListener(this, mSensorAcc, SensorManager.SENSOR_DELAY_NORMAL);

以下是registerListener在SystemSensorManager类中的定义：

SystemSensorManager::registerListener
protected boolean registerListenerImpl(SensorEventListener listener, Sensor sensor,int delayUs, Handler handler, int maxBatchReportLatencyUs, int reservedFlags) {//......// listener 是activity// - one Looper per SensorEventListener// - one Looper per SensorEventQueue//   将SensorEventListener映射到一个SensorEventQueuesynchronized (mSensorListeners) {SensorEventQueue queue = mSensorListeners.get(listener);if (queue == null) {Looper looper = (handler != null) ? handler.getLooper() : mMainLooper;final String fullClassName = listener.getClass().getEnclosingClass() != null ?listener.getClass().getEnclosingClass().getName() :listener.getClass().getName();queue = new SensorEventQueue(listener, looper, this, fullClassName);if (!queue.addSensor(sensor, delayUs, maxBatchReportLatencyUs)) {queue.dispose();return false;}mSensorListeners.put(listener, queue);return true;} else {return queue.addSensor(sensor, delayUs, maxBatchReportLatencyUs);}}//......
}

将SensorEventListener映射到一个SensorEventQueue，如果SensorEventQueue已经存在，将该sensor（mSensorAcc）添加到queue中去，如果不存在，则创建SensorEventQueue；以下是SensorEventQueue 队列的实现：

SensorEventQueue

prj\frameworks\base\core\java\android\hardware\SystemSensorManager.java
static final class SensorEventQueue extends BaseEventQueue {private final SensorEventListener mListener;private final SparseArray<SensorEvent> mSensorsEvents = new SparseArray<SensorEvent>();public SensorEventQueue(SensorEventListener listener, Looper looper,SystemSensorManager manager, String packageName) {super(looper, manager, OPERATING_MODE_NORMAL, packageName);mListener = listener;}@Overridepublic void addSensorEvent(Sensor sensor) {SensorEvent t = new SensorEvent(Sensor.getMaxLengthValuesArray(sensor,mManager.mTargetSdkLevel));synchronized (mSensorsEvents) {mSensorsEvents.put(sensor.getHandle(), t);}}
}// Called from native code.protected void dispatchSensorEvent(int handle, float[] values, int inAccuracy,long timestamp) {final Sensor sensor = mManager.mHandleToSensor.get(handle);if (sensor == null) {// sensor disconnectedreturn;}SensorEvent t = null;synchronized (mSensorsEvents) {t = mSensorsEvents.get(handle);}// Copy from the values array.System.arraycopy(values, 0, t.values, 0, t.values.length);t.timestamp = timestamp;t.accuracy = inAccuracy;t.sensor = sensor;// call onAccuracyChanged() only if the value changesfinal int accuracy = mSensorAccuracies.get(handle);if ((t.accuracy >= 0) && (accuracy != t.accuracy)) {mSensorAccuracies.put(handle, t.accuracy);mListener.onAccuracyChanged(t.sensor, t.accuracy);}mListener.onSensorChanged(t);}

BaseEventQueue

它继承自BaseBaseEventQueue；以下是 BaseEventQueue的定义：

prj\frameworks\base\core\java\android\hardware\SystemSensorManager.java
private static abstract class BaseEventQueue {private static native long nativeInitBaseEventQueue(long nativeManager,WeakReference<BaseEventQueue> eventQWeak, MessageQueue msgQ,String packageName, int mode, String opPackageName);private static native int nativeEnableSensor(long eventQ, int handle, int rateUs,int maxBatchReportLatencyUs);private static native int nativeDisableSensor(long eventQ, int handle);private static native void nativeDestroySensorEventQueue(long eventQ);private static native int nativeFlushSensor(long eventQ);private static native int nativeInjectSensorData(long eventQ, int handle,float[] values,int accuracy, long timestamp);private long nSensorEventQueue;private final SparseBooleanArray mActiveSensors = new SparseBooleanArray();protected final SparseIntArray mSensorAccuracies = new SparseIntArray();private final CloseGuard mCloseGuard = CloseGuard.get();protected final SystemSensorManager mManager;protected static final int OPERATING_MODE_NORMAL = 0;protected static final int OPERATING_MODE_DATA_INJECTION = 1;BaseEventQueue(Looper looper, SystemSensorManager manager, int mode, String packageName) {if (packageName == null) packageName = "";nSensorEventQueue = nativeInitBaseEventQueue(manager.mNativeInstance,new WeakReference<>(this), looper.getQueue(),packageName, mode, manager.mContext.getOpPackageName());mCloseGuard.open("dispose");mManager = manager;}public boolean addSensor(Sensor sensor, int delayUs, int maxBatchReportLatencyUs) {// Check if already present.int handle = sensor.getHandle();if (mActiveSensors.get(handle)) return false;// Get ready to receive events before calling enable.mActiveSensors.put(handle, true);addSensorEvent(sensor);if (enableSensor(sensor, delayUs, maxBatchReportLatencyUs) != 0) {// Try continuous mode if batching fails.if (maxBatchReportLatencyUs == 0 ||maxBatchReportLatencyUs > 0 && enableSensor(sensor, delayUs, 0) != 0) {removeSensor(sensor, false);return false;}}return true;}@Overridepublic void addSensorEvent(Sensor sensor) {SensorEvent t = new SensorEvent(Sensor.getMaxLengthValuesArray(sensor,mManager.mTargetSdkLevel));synchronized (mSensorsEvents) {mSensorsEvents.put(sensor.getHandle(), t);}}private int enableSensor(Sensor sensor, int rateUs, int maxBatchReportLatencyUs) {if (nSensorEventQueue == 0) throw new NullPointerException();if (sensor == null) throw new NullPointerException();return nativeEnableSensor(nSensorEventQueue, sensor.getHandle(), rateUs,maxBatchReportLatencyUs);}

SensorList获取

前面SensorManager构造函数中，有提过获取sensor list的过程，它在java代码中的实现如下；

public List<Sensor> getSensorList(int type) {// cache the returned lists the first timeList<Sensor> list;final List<Sensor> fullList = getFullSensorList();synchronized (mSensorListByType) {list = mSensorListByType.get(type);if (list == null) {if (type == Sensor.TYPE_ALL) {list = fullList;} else {list = new ArrayList<Sensor>();for (Sensor i : fullList) {if (i.getType() == type)list.add(i);}}list = Collections.unmodifiableList(list);mSensorListByType.append(type, list);}}return list;}

protected List<Sensor> getFullSensorList() {return mFullSensorsList;
}

实际上是反回了mFullSensorsList 列表，实际的初始化过程是子类SystemSensorManager的构造过程中实现的，如下；

// initialize the sensor list
for (int index = 0;;++index) {Sensor sensor = new Sensor();if (!nativeGetSensorAtIndex(mNativeInstance, sensor, index)) break;mFullSensorsList.add(sensor);mHandleToSensor.put(sensor.getHandle(), sensor);
}

可以看到每一个sensor都是通过new Sensor对象，再调用本地native方法nativeGetSensorAtIndex去做实例；

本节主要分析的是java层次相关的软件内容，nativeGetSensorAtIndex通过jni访问到C++中的sensor manager，在后续的博客汇总介绍；

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