Android Sensor (1) -- Sensor服务获取

 

目录

1.1 app调用sensor

1.4 createService and CachedServiceFetcher

1.5 SystemSensorManager init

1.6 app getDefaultSensor

1.7 app registerListener

1.8 SensorEventListener 数据回调 onSensorChanged

---

 

 

1.1 app调用sensor

//getSystemService --> getDefaultSensor --> registerListener

//getSystemService -- getDefaultSensor -- registerListener
//第一步：通过getSystemService获得SensorManager实例对象
mSensorManager = (SensorManager) getSystemService(Context.SENSOR_SERVICE);
//第二步：通过SensorManager实例对象获得想要的传感器对象:参数决定获取哪个传感器
mSensor = mSensorManager.getDefaultSensor(Sensor.TYPE_LIGHT);
mSensorManager.registerListener(this, mSensor, SensorManager.SENSOR_DELAY_NORMAL);

 

1.2 getSystemService流程

@frameworks/base/core/java/android/app/ContextImpl.java
@Override
public Object getSystemService(String name) {
    return SystemServiceRegistry.getSystemService(this, name);
}

//得到的是fetcher.getService(ctx)
/**
 * Gets a system service from a given context.
 */
public static Object getSystemService(ContextImpl ctx, String name) {
    ServiceFetcher<?> fetcher = SYSTEM_SERVICE_FETCHERS.get(name);
    return fetcher != null ? fetcher.getService(ctx) : null;
}

1.3 SystemServiceRegistry register Sensor Service流程

//保存到SYSTEM_SERVICE_NAMES SYSTEM_SERVICE_FETCHERS，然后重写 createService

@/frameworks/base/core/java/android/app/SystemServiceRegistry.java
registerService(Context.SENSOR_SERVICE, SensorManager.class,
        new CachedServiceFetcher<SensorManager>() {
    @Override
    public SensorManager createService(ContextImpl ctx) {
        return new SystemSensorManager(ctx.getOuterContext(),
          ctx.mMainThread.getHandler().getLooper());
    }});

/**
 * Statically registers a system service with the context.
 * This method must be called during static initialization only.
 */
private static <T> void registerService(String serviceName, Class<T> serviceClass,
        ServiceFetcher<T> serviceFetcher) {
    SYSTEM_SERVICE_NAMES.put(serviceClass, serviceName);
    SYSTEM_SERVICE_FETCHERS.put(serviceName, serviceFetcher);
}

1.4 createService and CachedServiceFetcher

//CachedServiceFetcher如下，fetcher.getService(ctx)获取到的返回参数就是 service = createService(ctx);也就是createService里面内容

@frameworks/base/core/java/android/app/SystemServiceRegistry.java
static abstract interface ServiceFetcher<T> {
    T getService(ContextImpl ctx);
}

/**
 * Override this class when the system service constructor needs a
 * ContextImpl and should be cached and retained by that context.
 */
static abstract class CachedServiceFetcher<T> implements ServiceFetcher<T> {
    private final int mCacheIndex;

    public CachedServiceFetcher() {
        mCacheIndex = sServiceCacheSize++;
    }

    @Override
    @SuppressWarnings("unchecked")
    public final T getService(ContextImpl ctx) {
        final Object[] cache = ctx.mServiceCache;
        synchronized (cache) {
            // Fetch or create the service.
            Object service = cache[mCacheIndex];
            if (service == null) {
                try {
                    service = createService(ctx);
                    cache[mCacheIndex] = service;
                } catch (ServiceNotFoundException e) {
                    onServiceNotFound(e);
                }
            }
            return (T)service;
        }
    }

    public abstract T createService(ContextImpl ctx) throws ServiceNotFoundException;
}

1.5 SystemSensorManager init

//getSystemService 获取到的对象就是SystemSensorManager

@frameworks/base/core/java/android/hardware/SystemSensorManager.java
public class SystemSensorManager extends SensorManager {
    /** {@hide} */
    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);
        }
    }
}

1.6 app getDefaultSensor

@frameworks/base/core/java/android/hardware/SensorManager.java
public Sensor getDefaultSensor(int type) {
    // TODO: need to be smarter, for now, just return the 1st sensor
    List<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 || type == Sensor.TYPE_DYNAMIC_SENSOR_META) {
        wakeUpSensor = true;
    }

    for (Sensor sensor : l) {
        if (sensor.isWakeUpSensor() == wakeUpSensor) return sensor;
    }
    return null;
}

1.7 app registerListener

@frameworks/base/core/java/android/hardware/SensorManager.java
//SensorEventListener
public boolean registerListener(SensorEventListener listener, Sensor sensor,
        int samplingPeriodUs) {
    return registerListener(listener, sensor, samplingPeriodUs, null);
}

public boolean registerListener(SensorEventListener listener, Sensor sensor,
        int samplingPeriodUs, int maxReportLatencyUs) {
    int delay = getDelay(samplingPeriodUs);
    return registerListenerImpl(listener, sensor, delay, null, maxReportLatencyUs, 0);
}
/** @hide */
protected abstract boolean registerListenerImpl(SensorEventListener listener, Sensor sensor,
        int delayUs, Handler handler, int maxReportLatencyUs, int reservedFlags);

@frameworks/base/core/java/android/hardware/SystemSensorManager.java
/** @hide */
@Override
protected boolean registerListenerImpl(SensorEventListener listener, Sensor sensor,
        int delayUs, Handler handler, int maxBatchReportLatencyUs, int reservedFlags) {
    ...

    // We map SensorEventListener to a SensorEventQueue, which holds the looper
    synchronized (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);
        }
    }
}

1.8 SensorEventListener 数据回调 onSensorChanged

@Override
  public final void onSensorChanged(SensorEvent event) {
    // 大部分传感器会返回三个轴方向x,y,x的event值，值的意义因传感器而异
    float x = event.values[0];
    float y = event.values[1];
    float z = event.values[2];
    //TODO 利用获得的三个float传感器值做些操作
  }

 

参考Link:

https://blog.youkuaiyun.com/pengtgimust/article/details/51227289

http://www.360doc.com/content/19/0128/11/15700426_811745365.shtml

https://www.jianshu.com/p/8440a5897944