Android Sensor App demo相关
public class MainActivity extends AppCompatActivity implements SensorEventListener {
private SensorManager mSensorManager;
private Sensor mSensorAcc, mSensorMag;
private TextView tvAcc, tvMag;
@Override
protected 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: yujixuan
mSensorAcc = mSensorManager.getDefaultSensor(Sensor.TYPE_ACCELEROMETER);
//!< 通过SensorManager 获取sensor对象 >! NoteBy: yujixuan
}
@Override
public 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);
}
@Override
protected void onResume() {
super.onResume();
mSensorManager.registerListener(this, mSensorAcc, SensorManager.SENSOR_DELAY_NORMAL);
}
@Override
protected 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
以下是在Android Studio中实际demo
ServiceManage 管理：
通过上面的demo代码段可以发现，app中并未直接使用sensor service，而是用过Activity调用父类的方法获取SensorManger对象 用来操作；
应用程序demo和service运行在不同的进程中，需要进程间通信，android中使用Binder实现这一过程； 通过ServiceManage 封装共享服务，只暴露操作接口，操作细节；
这里获取到的实例对象即SensorManage，维护对其管理Service的引用，各个app提出Service操作申请，Manager将操作申请交由其管理的Service处理，然后将处理结果再交给用户程序或回调用户注册的监听接口。
看下SensorManage的实现：
代码路径：rameworks\base\core\java\android\hardware\SensorManager.java
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;
/** Sun's gravity in SI units (m/s^2) */
public static final float GRAVITY_SUN = 275.0f;
/** Mercury's gravity in SI units (m/s^2) */
public static final float GRAVITY_MERCURY = 3.70f;
/** Venus' gravity in SI units (m/s^2) */
public static final float GRAVITY_VENUS = 8.87f;
/** Earth's gravity in SI units (m/s^2) */
public static final float GRAVITY_EARTH = 9.80665f;
......
public SensorManager() {
}
protected abstract List<Sensor> getFullSensorList();
protected abstract List<Sensor> getFullDynamicSensorList();
@Deprecated
public int getSensors() {
return getLegacySensorManager().getSensors();
}
public List<Sensor> getSensorList(int type) {
// cache the returned lists the first time
List<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;
}
@Deprecated
public boolean registerListener(SensorListener listener, int sensors) {
return registerListener(listener, sensors, SENSOR_DELAY_NORMAL);
}
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SensorManager类的定义可知，它是个抽象类，类中封装了各类方法供app去调用；实际的对象它的子类，SystemSensorManager集成重写了相关方法，以下是SystemSensorManager；
代码路径：frameworks\base\core\java\android\hardware\SystemSensorManager.java
public class SystemSensorManager extends SensorManager {
//TODO: disable extra logging before release
private 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 list
for (int index = 0;;++index) {
Sensor sensor = new Sensor();
if (!nativeGetSensorAtIndex(mNativeInstance, sensor, index)) break;
mFullSensorsList.add(sensor);
mHandleToSensor.put(sensor.getHandle(), sensor);
}
}
......
@Override
protected 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,
}
......
}内容比较多，都是对sensor相关功能接口的封装，不详细分析实现，贴出的代码主要是，在SystemSensorManager 定义使用了大量的native方法； 即对应JNI 库中的本地方法；
主要调用部分在其构造函数的实现，依次调用了：
nativeClassInit();
nativeCreate
for (int index = 0;;++index) {
Sensor sensor = new Sensor();
if (!nativeGetSensorAtIndex(mNativeInstance, sensor, index)) break;
mFullSensorsList.add(sensor);
mHandleToSensor.put(sensor.getHandle(), sensor);
}对应本地C库中的调用，看下JNI的实现；
代码路径：./base/core/jni/android_hardware_SensorManager.cpp
关键函数：
int register_android_hardware_SensorManager(JNIEnv *env)
{
RegisterMethodsOrDie(env, "android/hardware/SystemSensorManager",
gSystemSensorManagerMethods, NELEM(gSystemSensorManagerMethods));
RegisterMethodsOrDie(env, "android/hardware/SystemSensorManager$BaseEventQueue",
gBaseEventQueueMethods, NELEM(gBaseEventQueueMethods));
gBaseEventQueueClassInfo.clazz = FindClassOrDie(env,
"android/hardware/SystemSensorManager$BaseEventQueue");
gBaseEventQueueClassInfo.dispatchSensorEvent = GetMethodIDOrDie(env,
gBaseEventQueueClassInfo.clazz, "dispatchSensorEvent", "(I[FIJ)V");
gBaseEventQueueClassInfo.dispatchFlushCompleteEvent = GetMethodIDOrDie(env,
gBaseEventQueueClassInfo.clazz, "dispatchFlushCompleteEvent", "(I)V");
gBaseEventQueueClassInfo.dispatchAdditionalInfoEvent = GetMethodIDOrDie(env,
gBaseEventQueueClassInfo.clazz, "dispatchAdditionalInfoEvent", "(III[F[I)V");
return 0;
}
以gSystemSensorManagerMethods为例：
static const JNINativeMethod gSystemSensorManagerMethods[] = {
{"nativeClassInit",
"()V",
(void*)nativeClassInit },
{"nativeCreate",
"(Ljava/lang/String;)J",
(void*)nativeCreate },
{"nativeGetSensorAtIndex",
"(JLandroid/hardware/Sensor;I)Z",
(void*)nativeGetSensorAtIndex },
{"nativeGetDynamicSensors",
"(JLjava/util/List;)V",
(void*)nativeGetDynamicSensors },
{"nativeIsDataInjectionEnabled",
"(J)Z",
(void*)nativeIsDataInjectionEnabled},
};
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