android有關(guān)sensor的源碼總結(jié).doc

android有關(guān)sensor的源碼總結(jié) 雖然這篇文章寫得很差，因為趕時間，所以就匆匆忙忙地寫出來自己作一個筆記。但是我想對大家應(yīng)該有一點幫助。 1、有關(guān)sensor在Java應(yīng)用程序的編程（以注冊多個傳感器為例，這程序是我臨時弄出來的，可能有錯）package com.sensors.acc;import android.app.Activity;import android.os.Bundle;import android.util.Log;import android.widget.TextView;import android.hardware.SensorManager;import android.hardware.Sensor;import android.hardware.SensorEvent;import android.hardware.SensorEventListener;public class acc extends Activity float x, y, z; SensorManager sensormanager = null; Sensor accSensor = null; Sensor lightSensor = null; Sensor proximitySensor = null; TextView accTextView = null; /* Called when the activity is first created. */ Override public void onCreate(Bundle savedInstanceState) super.onCreate(savedInstanceState); setContentView(R.layout.main); sensormanager = (SensorManager)getSystemService(SENSOR_SERVICE); accSensor = sensormanager.getDefaultSensor(Sensor.TYPE_ACCELEROMETER); lightSensor = sensormanager.getDefaultSensor(Sensor.TYPE_LIGHT); proximitySensor = sensormanager.getDefaultSensor(Sensor.TYPE_PROXIMITY); accTextView = (TextView)findViewById(R.id.textview_name); SensorEventListener lsn = new SensorEventListener() public void onSensorChanged(SensorEvent e) if (e.sensor = accSensor) Log.d(sensor, found acc sensor); x = e.valuesSensorManager.DATA_X; y = e.valuesSensorManager.DATA_Y; z = e.valuesSensorManager.DATA_Z; accTextView.setText(x = + x + , ny = + y + , nz = + z); else if (e.sensor = lightSensor) Log.d(sensor, found light sensor); accTextView.setText(data is + e.values0); else if (e.sensor = proximitySensor) Log.d(sensor, found proximity sensor); accTextView.setText(distance is + e.values0); public void onAccuracyChanged(Sensor s, int accuracy) ; Override protected void onResume() super.onResume(); / register this class as a listener for the orientation and accelerometer sensors sensormanager.registerListener(lsn, accSensor, SensorManager.SENSOR_DELAY_NORMAL); sensormanager.registerListener(lsn, lightSensor, SensorManager.SENSOR_DELAY_NORMAL); sensormanager.registerListener(lsn, proximitySensor, SensorManager.SENSOR_DELAY_NORMAL);/ sensormanager.unregisterListener(lsn); Override protected void onStop() / unregister listener sensormanager.unregisterListener(lsn, accSensor); sensormanager.unregisterListener(lsn, lightSensor);sensormanager.unregisterListener(lsn, proximitySensor); super.onStop(); 在onCreate()函數(shù)中，調(diào)用getSystemService(SENSOR_SERVICE)初始化一個SensorManager實例，為什么要用getSystemService函數(shù)，而不直接用new SensorManager呢？我們看此函數(shù)的實現(xiàn)，在ApplicationContext.java中，if (SENSOR_SERVICE.equals(name) return getSensorManager();然后getSensorManager()的實現(xiàn) private SensorManager getSensorManager() synchronized (mSync) if (mSensorManager = null) mSensorManager = new SensorManager(mMainThread.getHandler().getLooper(); return mSensorManager;看到?jīng)]有？初始化SensorManager的時候需要mMainThread.getHandler().getLooper()這個參數(shù)，之個應(yīng)該是用來傳遞消息用的，在SensorManager類的構(gòu)造函數(shù)中會把此參數(shù)傳給類成員mMainLooper。如果用new SensorManager()就需要另外獲取mainLooper參數(shù)傳遞進去。2、在android中跟sensor有關(guān)的一些文件有SensorManager.java，位于frameworksbasecorejavaandroidhardware目錄下，SensorService.java，位于frameworksbaseservicesjavacomandroidserver目錄下，android_hardware_SensorManager.cpp，位于frameworksbasecorejni目錄下，與SensorManager.java相對應(yīng)，com_android_server_SensorService.cpp，在frameworksbaseservicesjni目錄下，與SensorService.java相對應(yīng)。還有SystemServer.java文件，HardwareLibhardwareIncludeHardware目錄下的Sensor.h頭文件。另外我們需要根據(jù)Sensor.h實現(xiàn)自己的一個源文件，一般取名為sensors_xxx.c或者sensors_xxx.cpp。3、SensorManager類分析有幾個函數(shù)比較重要，必須清晰理解它們的實現(xiàn)，才能了解整個傳感器系統(tǒng)的實現(xiàn)。從而更好地去實現(xiàn)硬件抽象層的實現(xiàn)。幾個比較重要的函數(shù)有構(gòu)造函數(shù)SensorManager(), registerListener()和unregisterListener()，其中registerListener()和unregisterListener()有多個，標志為 Deprecated的是過時的，就不要看了。（1）構(gòu)造函數(shù)SensorManager(Looper mainLooper)這個函數(shù)首先獲取得傳感器系統(tǒng)服務(wù)，并賦給類成員mSensorService， mSensorService = ISensorService.Stub.asInterface( ServiceManager.getService(Context.SENSOR_SERVICE);這里我要說一句，就是關(guān)于這個傳感器系統(tǒng)服務(wù)，很多書上都說用getSystemService()是獲得傳感器的系統(tǒng)服務(wù)，而它返回的是SensorManager類型，所以以為整個系統(tǒng)都是使用同一個SensorManager類的實例，以為我們在任何地方使用的SensorManager實例都是同一個，它們的公共成員是共享的。但是經(jīng)過這兩天的分析，這種說法是錯誤的。其實每次調(diào)用getSystemService()函數(shù)時都初始化一個新的SensorManager實例，而這個SensorManager實例會在構(gòu)造函數(shù)里通過取得傳感器系統(tǒng)服務(wù)SensorService來實現(xiàn)對下層傳感器的一些控制。而這個SensorService才是系統(tǒng)的傳感器服務(wù)，說服務(wù)，不如說它只是SensorService類的一個實例罷了。它只在系統(tǒng)初始化時初始化一次。Android中的系統(tǒng)服務(wù)機制應(yīng)該跟傳感器的都差不多一個樣，都是由不同的Manager調(diào)用下層相同的Service。你可以列舉其它的Manager。那它是什么時候初始化呢？它是系統(tǒng)初始化在SystemServer進程里創(chuàng)建的，SystemServer是一個管理很多系統(tǒng)服務(wù)的進程，我們轉(zhuǎn)到SystemServer.的main函數(shù)里，可以看到一直到調(diào)用int2()函數(shù)，它會創(chuàng)建一個ServerThread，最終調(diào)用AdbSettingsObserver類的run()函數(shù)，在run()函數(shù)里有這么有一句 / Sensor Service is needed by Window Manager, so this goes first Log.i(TAG, Sensor Service); ServiceManager.addService(Context.SENSOR_SERVICE, new SensorService(context);這里就創(chuàng)建SensorService實例了。在創(chuàng)建這個實例時會在SensorService構(gòu)造函數(shù)中調(diào)用jni函數(shù) public SensorService(Context context) if (localLOGV) Log.d(TAG, SensorService startup); _sensors_control_init(); 我們看_sensors_control_init();對應(yīng)的為static jintandroid_init(JNIEnv *env, jclass clazz) sensors_module_t* module; if (hw_get_module(SENSORS_HARDWARE_MODULE_ID, (const hw_module_t*)&module) = 0) if (sensors_control_open(&module-common, &sSensorDevice) = 0) const struct sensor_t* list; int count = module-get_sensors_list(module, &list); return count; return 0;它主要調(diào)用了sensor.h中的sensors_control_open()static inline int sensors_control_open(const struct hw_module_t* module, struct sensors_control_device_t* device) return module-methods-open(module, SENSORS_HARDWARE_CONTROL, (struct hw_device_t*)device);之后在系統(tǒng)任何地方使用的都是這個SensorService實例。最后run()函數(shù)調(diào)用Looper.loop();就進行消息循環(huán)等待了，這就是SystemServer進程的消息服務(wù)了。這才真正叫做系統(tǒng)服務(wù)嘛。我們繼續(xù)看SensorManager類的構(gòu)造函數(shù)，取得SensorService后， nativeClassInit();這是一個jni函數(shù)，SensorManager類調(diào)用的jni函數(shù)都在com_android_server_SensorService.cpp里，我們看這函數(shù)static voidnativeClassInit (JNIEnv *_env, jclass _this) jclass sensorClass = _env-FindClass(android/hardware/Sensor); SensorOffsets& sensorOffsets = gSensorOffsets; sensorO = _env-GetFieldID(sensorClass, mName, Ljava/lang/String;); sensorOffsets.vendor = _env-GetFieldID(sensorClass, mVendor, Ljava/lang/String;); sensorOffsets.version = _env-GetFieldID(sensorClass, mVersion, I); sensorOffsets.handle = _env-GetFieldID(sensorClass, mHandle, I); sensorOffsets.type = _env-GetFieldID(sensorClass, mType, I); sensorOffsets.range = _env-GetFieldID(sensorClass, mMaxRange, F); sensorOffsets.resolution = _env-GetFieldID(sensorClass, mResolution,F); sensorOffsets.power = _env-GetFieldID(sensorClass, mPower, F);這個函數(shù)只是獲取和設(shè)置一些信息吧，我們不關(guān)心。接著 sensors_module_init();我們看這函數(shù)static jintsensors_module_init(JNIEnv *env, jclass clazz) int err = 0; sensors_module_t const* module; err = hw_get_module(SENSORS_HARDWARE_MODULE_ID, (const hw_module_t *)&module); if (err = 0) sSensorModule = (sensors_module_t*)module; return err;它獲取了sensor的模塊信息，并把它賦給sSensorModule全局變量，之后傳的modules參數(shù)都為這個。接著在構(gòu)造函數(shù)里 final ArrayList fullList = sFullSensorsList; int i = 0; do Sensor sensor = new Sensor(); i = sensors_module_get_next_sensor(sensor, i); if (i=0) Log.d(TAG, found sensor: + sensor.getName() + , handle= + sensor.getHandle(); sensor.setLegacyType(getLegacySensorType(sensor.getType(); fullList.add(sensor); sHandleToSensor.append(sensor.getHandle(), sensor); while (i0);這里主要是通過jni函數(shù)sensors_module_get_next_sensor(sensor, i);獲取傳感器列表，并把它加入自己的fullList列表中。我們看sensors_module_get_next_sensor()函數(shù)static jintsensors_module_get_next_sensor(JNIEnv *env, jobject clazz, jobject sensor, jint next) if (sSensorModule = NULL) return 0; SensorOffsets& sensorOffsets = gSensorOffsets; const struct sensor_t* list; int count = sSensorModule-get_sensors_list(sSensorModule, &list); if (next = count) return -1; list += next; jstring name = env-NewStringUTF(list-name); jstring vendor = env-NewStringUTF(list-vendor); env-SetObjectField(sensor, sensorO, name); env-SetObjectField(sensor, sensorOffsets.vendor, vendor); env-SetIntField(sensor, sensorOffsets.version, list-version); env-SetIntField(sensor, sensorOffsets.handle, list-handle); env-SetIntField(sensor, sensorOffsets.type, list-type); env-SetFloatField(sensor, sensorOffsets.range, list-maxRange); env-SetFloatField(sensor, sensorOffsets.resolution, list-resolution); env-SetFloatField(sensor, sensorOffsets.power, list-power); next+; return next它主要是調(diào)用HAL層的get_sensors_list()函數(shù)取得傳感器列表信息。接著在sensorManger構(gòu)造函數(shù)最后 sSensorThread = new SensorThread();創(chuàng)建一個SensorThread()線程。但并未運行，但在SensorThread類的構(gòu)造函數(shù)里會執(zhí)行jni函數(shù) sensors_data_init();我們看此函數(shù)static jintsensors_data_init(JNIEnv *env, jclass clazz) if (sSensorModule = NULL) return -1; int err = sensors_data_open(&sSensorModule-common, &sSensorDevice); return err;它調(diào)用了HAL層的sensors_data_open函數(shù)，而這個函數(shù)位于sensor.h中，它調(diào)用的是static inline int sensors_data_open(const struct hw_module_t* module, struct sensors_data_device_t* device) return module-methods-open(module, SENSORS_HARDWARE_DATA, (struct hw_device_t*)device);Modules-methods-open函數(shù)。而在SensorThread類的析構(gòu)函數(shù)finalize()里會調(diào)用 sensors_data_uninit();static jintsensors_data_uninit(JNIEnv *env, jclass clazz) int err = 0; if (sSensorDevice) err = sensors_data_close(sSensorDevice); if (err = 0) sSensorDevice = 0; return err;在sensor.h里static inline int sensors_data_close(struct sensors_data_device_t* device) return device-common.close(&device-common);那什么時候sSensorThread線程會運行呢？我們在下面看registerListener()函數(shù)。（2） public boolean registerListener(SensorEventListener listener, Sensor sensor, int rate) return registerListener(listener, sensor, rate, null);它調(diào)用的是 public boolean registerListener(SensorEventListener listener, Sensor sensor, int rate, Handler handler)在這函數(shù)中，先驗證rate，然后檢測注冊的listener在不在本類的sListeners列表中。 for (ListenerDelegate i : sListeners) if (i.getListener() = listener) l = i; break; 如果不在就申請一個listener，并把它加入全局列表sListener中，并調(diào)用mSensorService的enableSensor()函數(shù)使能傳感器，這個enableSensor()函數(shù)最終會調(diào)用HAL層的active函數(shù)和set_delay()函數(shù)，使用后然后判斷sListener列表是否為空，當然，第一次為空時加入一個新的listener就不為空了，此時就執(zhí)行sSensorThread的startLocked運行sSensorThread線程了 l = new ListenerDelegate(listener, sensor, handler); result = mSensorService.enableSensor(l, name, handle, delay); if (result) sListeners.add(l); sListeners.notify(); if (!sListeners.isEmpty() sSensorThread.startLocked(mSensorService); 另一方面，如果注冊的listener在sListeners列表中，則先調(diào)用mSensorService的enableSensor()函數(shù)使能傳感器，然后把注冊的傳感器加入到已存在的listener中。 result = mSensorService.enableSensor(l, name, handle, delay); if (result) l.addSensor(sensor); 接下來我們看看startLocked函數(shù)，它在SensorThread中， void startLocked(ISensorService service) try if (mThread = null) Bundle dataChannel = service.getDataChannel(); mThread = new Thread(new SensorThreadRunnable(dataChannel), SensorThread.class.getName(); mThread.start(); catch (RemoteException e) Log.e(TAG, RemoteException in startLocked: , e); 第一次mThread為null，然后它調(diào)用了service.getDataChannel()函數(shù)，此函數(shù)在SensorService類中，主要調(diào)用了jni函數(shù)_sensors_control_open()， public Bundle getDataChannel() throws RemoteException / synchronize so we do not require sensor HAL to be thread-safe. synchronized(mListeners) return _sensors_control_open(); SensorService類中調(diào)用的jni函數(shù)主要都在com_android_server_SensorService.cpp文件 中，我們看一下這個函數(shù)static jobjectandroid_open(JNIEnv *env, jclass clazz) native_handle_t* handle = sSensorDevice-open_data_source(sSensorDevice); if (!handle) return NULL; / new Bundle() jobject bundle = env-NewObject( gBundleOffsets.mClass, gBundleOffsets.mConstructor); if (handle-numFds 0) jobjectArray fdArray = env-NewObjectArray(handle-numFds, gParcelFileDescriptorOffsets.mClass, NULL); for (int i = 0; i numFds; i+) / new FileDescriptor() jobject fd = env-NewObject(gFileDescriptorOffsets.mClass, gFileDescriptorOffsets.mConstructor); env-SetIntField(fd, gFileDescriptorOffsets.mDescriptor, handle-datai); / new ParcelFileDescriptor() jobject pfd = env-NewObject(gParcelFileDescriptorOffsets.mClass, gParcelFileDescriptorOffsets.mConstructor, fd); env-SetObjectArrayElement(fdArray, i, pfd); / bundle.putParcelableArray(fds, fdArray); env-CallVoidMethod(bundle, gBundleOffsets.mPutParcelableArray, env-NewStringUTF(fds), fdArray); if (handle-numInts 0) jintArray intArray = env-NewIntArray(handle-numInts); env-SetIntArrayRegion(intArray, 0, handle-numInts, &handle-datahandle-numInts); / bundle.putIntArray(ints, intArray); env-CallVoidMethod(bundle, gBundleOffsets.mPutIntArray, env-NewStringUTF(ints), intArray); / delete the file handle, but dont close any file descriptors native_handle_delete(handle); return bundle;它主要調(diào)用了HAL層的open_data_source()函數(shù)。取得一些文件描述符等信息。接下來SensorThread創(chuàng)建一個線程，調(diào)用start()就進入SensorThreadRunnable類的run()函數(shù)了，所以我們接著去看run()函數(shù)，它首先調(diào)用open()函數(shù) if (!open() return; 在open()函數(shù)中調(diào)用了 jni函數(shù)sensors_data_open(fds, ints);static jintsensors_data_open(JNIEnv *env, jclass clazz, jobjectArray fdArray, jintArray intArray) jclass FileDescriptor = env-FindClass(java/io/FileDescriptor); jfieldID fieldOffset = env-GetFieldID(FileDescriptor, descriptor, I); int numFds = (fdArray ? env-GetArrayLength(fdArray) : 0); int numInts = (intArray ? env-GetArrayLength(intArray) : 0); native_handle_t* handle = native_handle_create(numFds, numInts); int offset = 0; for (int i = 0; i GetObjectArrayElement(fdArray, i); if (fdo) handle-dataoffset+ = env-GetIntField(fdo, fieldOffset); else handle-dataoffset+ = -1; if (numInts 0) jint* ints = env-GetIntArrayElements(intArray, 0); for (int i = 0; i dataoffset+ = intsi; env-ReleaseIntArrayElements(intArray, ints, 0); / doesnt take ownership of the native handle return sSensorDevice-data_open(sSensorDevice, handle);這函數(shù)最終調(diào)用了HAL層的data_open()，之后run()函數(shù)就進入一個while循環(huán)了。 while (true) / wait for an event final int sensor = sensors_data_poll(values, status, timestamp); int accuracy = status0; synchronized (sListeners) if (sensor = -1 | sListeners.isEmpty() if (sensor = -1) / we lost the connection to the event stream. this happens / when the last listener is removed. Log.d(TAG, _sensors_data_poll() failed, we ba