Android系统Gps分析(一)【转】
本文转载自:http://blog.csdn.net/xnwyd/article/details/7198728
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1 GPS架构
2 GPS分析
2.1 头文件
头文件定义在:hardware/libhardware/include/hardware/gps.h,定义了GPS底层相关的结构体和接口
GpsLocation
GPS位置信息结构体,包含经纬度,高度,速度,方位角等。
- /** Flags to indicate which values are valid in a GpsLocation. */
- typedef uint16_t GpsLocationFlags;
- // IMPORTANT: Note that the following values must match
- // constants in GpsLocationProvider.java.
- /** GpsLocation has valid latitude and longitude. */
- #define GPS_LOCATION_HAS_LAT_LONG 0x0001
- /** GpsLocation has valid altitude. */
- #define GPS_LOCATION_HAS_ALTITUDE 0x0002
- /** GpsLocation has valid speed. */
- #define GPS_LOCATION_HAS_SPEED 0x0004
- /** GpsLocation has valid bearing. */
- #define GPS_LOCATION_HAS_BEARING 0x0008
- /** GpsLocation has valid accuracy. */
- #define GPS_LOCATION_HAS_ACCURACY 0x0010
- /** Represents a location. */
- typedef struct {
- /** set to sizeof(GpsLocation) */
- size_t size;
- /** Contains GpsLocationFlags bits. */
- uint16_t flags;
- /** Represents latitude in degrees. */
- double latitude;
- /** Represents longitude in degrees. */
- double longitude;
- /** Represents altitude in meters above the WGS 84 reference
- * ellipsoid. */
- double altitude;
- /** Represents speed in meters per second. */
- float speed;
- /** Represents heading in degrees. */
- float bearing;
- /** Represents expected accuracy in meters. */
- float accuracy;
- /** Timestamp for the location fix. */
- GpsUtcTime timestamp;
- } GpsLocation;
GpsStatus
GPS状态包括5种状态,分别为未知,正在定位,停止定位,启动未定义,未启动。
- /** GPS status event values. */
- typedef uint16_t GpsStatusValue;
- // IMPORTANT: Note that the following values must match
- // constants in GpsLocationProvider.java.
- /** GPS status unknown. */
- #define GPS_STATUS_NONE 0
- /** GPS has begun navigating. */
- #define GPS_STATUS_SESSION_BEGIN 1
- /** GPS has stopped navigating. */
- #define GPS_STATUS_SESSION_END 2
- /** GPS has powered on but is not navigating. */
- #define GPS_STATUS_ENGINE_ON 3
- /** GPS is powered off. */AgpsCallbacks
- AgpsInterface
- #define GPS_STATUS_ENGINE_OFF 4
- /** Represents the status. */
- typedef struct {
- /** set to sizeof(GpsStatus) */
- size_t size;
- GpsStatusValue status;
- } GpsStatus;
GpsSvInfo
GPS卫星信息,包含卫星编号,信号强度,卫星仰望角,方位角等。
- /** Represents SV information. */
- typedef struct {
- /** set to sizeof(GpsSvInfo) */
- size_t size;
- /** Pseudo-random number for the SV. */
- int prn;
- /** Signal to noise ratio. */
- float snr;
- /** Elevation of SV in degrees. */
- float elevation;
- /** Azimuth of SV in degrees. */
- float azimuth;
- } GpsSvInfo;
GpsSvStatus
GPS卫星状态,包含可见卫星数和信息,星历时间,年历时间等。
- /** Represents SV status. */
- typedef struct {
- /** set to sizeof(GpsSvStatus) */
- size_t size;
- /** Number of SVs currently visible. */
- int num_svs;
- /** Contains an array of SV information. */
- GpsSvInfo sv_list[GPS_MAX_SVS];
- /** Represents a bit mask indicating which SVs
- * have ephemeris data.
- */
- uint32_t ephemeris_mask;
- /** Represents a bit mask indicating which SVs
- * have almanac data.
- */
- uint32_t almanac_mask;
- /**
- * Represents a bit mask indicating which SVs
- * were used for computing the most recent position fix.
- */
- uint32_t used_in_fix_mask;
- } GpsSvStatus;
GpsCallbacks
回调函数定义
- /** Callback with location information. 向上层传递GPS位置信息
- * Can only be called from a thread created by create_thread_cb.
- */
- typedef void (* gps_location_callback)(GpsLocation* location);
- /** Callback with status information. 向上层传递GPS状态信息
- * Can only be called from a thread created by create_thread_cb.
- */
- typedef void (* gps_status_callback)(GpsStatus* status);
- /** Callback with SV status information. 向上层传递GPS卫星信息
- * Can only be called from a thread created by create_thread_cb.
- */
- typedef void (* gps_sv_status_callback)(GpsSvStatus* sv_info);
- /** Callback for reporting NMEA sentences. 向上层传递MEMA数据
- * Can only be called from a thread created by create_thread_cb.
- */
- typedef void (* gps_nmea_callback)(GpsUtcTime timestamp, const char* nmea, int length);
- /** Callback to inform framework of the GPS engine's capabilities.告知GPS模块可以实现的功能
- * Capability parameter is a bit field of GPS_CAPABILITY_* flags.
- */
- typedef void (* gps_set_capabilities)(uint32_t capabilities);
- /** Callback utility for acquiring the GPS wakelock.上锁,防止处理GPS事件时中止。
- * This can be used to prevent the CPU from suspending while handling GPS events.
- */
- typedef void (* gps_acquire_wakelock)();
- /** Callback utility for releasing the GPS wakelock. */释放锁
- typedef void (* gps_release_wakelock)();
- /** Callback for creating a thread that can call into the Java framework code.等待上层请求
- * This must be used to create any threads that report events up to the framework.
- */
- typedef pthread_t (* gps_create_thread)(const char* name, void (*start)(void *), void* arg);
- /** GPS callback structure. */
- typedef struct {
- /** set to sizeof(GpsCallbacks) */
- size_t size;
- gps_location_callback location_cb;
- gps_status_callback status_cb;
- gps_sv_status_callback sv_status_cb;
- gps_nmea_callback nmea_cb;
- gps_set_capabilities set_capabilities_cb;
- gps_acquire_wakelock acquire_wakelock_cb;
- gps_release_wakelock release_wakelock_cb;
- gps_create_thread create_thread_cb;
- } GpsCallbacks;
GpsInterface
GPS接口是最重要的结构体,上层是通过此接口与硬件适配层交互的。
- /** Represents the standard GPS interface. */
- typedef struct {
- /** set to sizeof(GpsInterface) */
- size_t size;
- /**
- * Opens the interface and provides the callback routines
- * to the implemenation of this interface.
- */
- int (*init)( GpsCallbacks* callbacks );
- /** Starts navigating. 启动定位*/
- int (*start)( void );
- /** Stops navigating. 取消定位*/
- int (*stop)( void );
- /** Closes the interface. 关闭GPS接口*/
- void (*cleanup)( void );
- /** Injects the current time.填入时间 */
- int (*inject_time)(GpsUtcTime time, int64_t timeReference,
- int uncertainty);
- /** Injects current location from another location provider填入位置
- * (typically cell ID).
- * latitude and longitude are measured in degrees
- * expected accuracy is measured in meters
- */
- int (*inject_location)(double latitude, double longitude, float accuracy);
- /**
- * Specifies that the next call to start will not use the删除全部或部分辅助数据,在性能测试时使用
- * information defined in the flags. GPS_DELETE_ALL is passed for
- * a cold start.
- */
- void (*delete_aiding_data)(GpsAidingData flags);
- /**设置定位模式和GPS工作模式等
- * min_interval represents the time between fixes in milliseconds.
- * preferred_accuracy represents the requested fix accuracy in meters.
- * preferred_time represents the requested time to first fix in milliseconds.
- */
- int (*set_position_mode)(GpsPositionMode mode, GpsPositionRecurrence recurrence,
- uint32_t min_interval, uint32_t preferred_accuracy, uint32_t preferred_time);
- /** Get a pointer to extension information. 自定义的接口*/
- const void* (*get_extension)(const char* name);
- } GpsInterface;
gps_device_t
GPS设备结构体,继承自hw_device_tcommon,硬件适配接口,向上层提供了重要的get_gps_interface接口。
- struct gps_device_t {
- struct hw_device_t common;
- /**
- * Set the provided lights to the provided values.
- *
- * Returns: 0 on succes, error code on failure.
- */
- const GpsInterface* (*get_gps_interface)(struct gps_device_t* dev);
- };
2.2硬件适配层
GPS硬件适配层的源码位于:hardware/qcom/gps目录下。
我们看gps/loc_api/llibloc_api/gps.c,首先定义了gps设备模块实例:
- const struct hw_module_t HAL_MODULE_INFO_SYM = {
- .tag = HARDWARE_MODULE_TAG,
- .version_major = 1,
- .version_minor = 0,
- .id = GPS_HARDWARE_MODULE_ID,
- .name = "loc_api GPS Module",
- .author = "Qualcomm USA, Inc.",
- .methods = &gps_module_methods,
- };
这里的methods指向gps.c文件中的gps_module_methods
- static struct hw_module_methods_t gps_module_methods = {
- .open = open_gps
- };
gps_module_methods定义了设备的open函数为open_gps,我们看open_gps函数:
- static int open_gps(const struct hw_module_t* module, char const* name,
- struct hw_device_t** device)
- {
- struct gps_device_t *dev = malloc(sizeof(struct gps_device_t));
- memset(dev, 0, sizeof(*dev));
- dev->common.tag = HARDWARE_DEVICE_TAG;
- dev->common.version = 0;
- dev->common.module = (struct hw_module_t*)module;
- dev->get_gps_interface = gps__get_gps_interface;
- *device = (struct hw_device_t*)dev;
- return 0;
- }
此处可以看作是GPS设备的初始化函数,在使用设备前必须执行此函数。函数里面指定了hw_device_t的module成员,以及gps_device_t的get_gps_interface成员。上层可通过gps_device_t的get_gps_interface调用gps__get_gps_interface函数。gps__get_gps_interface的定义如下:
- const GpsInterface* gps__get_gps_interface(struct gps_device_t* dev)
- {
- return get_gps_interface();
- }
用代码跟踪可看到,此函数返回了gps/loc_eng.cpp文件的sLocEngInterface变量,sLocEngInterface定义如下:
- // Defines the GpsInterface in gps.h
- static const GpsInterface sLocEngInterface =
- {
- sizeof(GpsInterface),
- loc_eng_init,
- loc_eng_start,
- loc_eng_stop,
- loc_eng_cleanup,
- loc_eng_inject_time,
- loc_eng_inject_location,
- loc_eng_delete_aiding_data,
- loc_eng_set_position_mode,
- loc_eng_get_extension,
- };
sLocEngInterface指定了GpsInterface结构体的各个回调函数,如启动定位/取消定位等,这些回调函数的实现均在loc_eng.cpp中实现。
2.2 JNI适配层
GPSJNI适配层的源码位于:frameworks/base/services/jni/com_android_server_location_GpsLocationProvider.cpp
首先看注册JNI方法的函数定义:
- int register_android_server_location_GpsLocationProvider(JNIEnv* env)
- {
- return jniRegisterNativeMethods(env, "com/android/server/location/GpsLocationProvider", sMethods, NELEM(sMethods));
- }
此函数被同目录下onload.cpp文件调用,调用地方在:
- extern "C" jint JNI_OnLoad(JavaVM* vm, void* reserved)
- {
- JNIEnv* env = NULL;
- jint result = -1;
- if (vm->GetEnv((void**) &env, JNI_VERSION_1_4) != JNI_OK) {
- LOGE("GetEnv failed!");
- return result;
- }
- LOG_ASSERT(env, "Could not retrieve the env!");
- //...省略其他注册代码
- register_android_server_location_GpsLocationProvider(env);
- return JNI_VERSION_1_4;
- }
从这里可以看到,JNI初始化的时候,即会进行JNI方法的注册,从而使上层应用能通过JNI调用c/c++本地方法。
回到register_android_server_location_GpsLocationProvider函数,变量sMethods定义如下:
- static JNINativeMethod sMethods[] = {
- /* name, signature, funcPtr */
- {"class_init_native", "()V", (void *)android_location_GpsLocationProvider_class_init_native},
- {"native_is_supported", "()Z", (void*)android_location_GpsLocationProvider_is_supported},
- {"native_init", "()Z", (void*)android_location_GpsLocationProvider_init},
- {"native_cleanup", "()V", (void*)android_location_GpsLocationProvider_cleanup},
- {"native_set_position_mode", "(IIIII)Z", (void*)android_location_GpsLocationProvider_set_position_mode},
- {"native_start", "()Z", (void*)android_location_GpsLocationProvider_start},
- {"native_stop", "()Z", (void*)android_location_GpsLocationProvider_stop},
- {"native_delete_aiding_data", "(I)V", (void*)android_location_GpsLocationProvider_delete_aiding_data},
- {"native_read_sv_status", "([I[F[F[F[I)I", (void*)android_location_GpsLocationProvider_read_sv_status},
- {"native_read_nmea", "([BI)I", (void*)android_location_GpsLocationProvider_read_nmea},
- {"native_inject_time", "(JJI)V", (void*)android_location_GpsLocationProvider_inject_time},
- {"native_inject_location", "(DDF)V", (void*)android_location_GpsLocationProvider_inject_location},
- {"native_supports_xtra", "()Z", (void*)android_location_GpsLocationProvider_supports_xtra},
- {"native_inject_xtra_data", "([BI)V", (void*)android_location_GpsLocationProvider_inject_xtra_data},
- {"native_agps_data_conn_open", "(Ljava/lang/String;)V", (void*)android_location_GpsLocationProvider_agps_data_conn_open},
- {"native_agps_data_conn_closed", "()V", (void*)android_location_GpsLocationProvider_agps_data_conn_closed},
- {"native_agps_data_conn_failed", "()V", (void*)android_location_GpsLocationProvider_agps_data_conn_failed},
- {"native_agps_set_id","(ILjava/lang/String;)V",(void*)android_location_GpsLocationProvider_agps_set_id},
- {"native_agps_set_ref_location_cellid","(IIIII)V",(void*)android_location_GpsLocationProvider_agps_set_reference_location_cellid},
- {"native_set_agps_server", "(ILjava/lang/String;I)V", (void*)android_location_GpsLocationProvider_set_agps_server},
- {"native_send_ni_response", "(II)V", (void*)android_location_GpsLocationProvider_send_ni_response},
- {"native_agps_ni_message", "([BI)V", (void *)android_location_GpsLocationProvider_agps_send_ni_message},
- {"native_get_internal_state", "()Ljava/lang/String;", (void*)android_location_GpsLocationProvider_get_internal_state},
- {"native_update_network_state", "(ZIZLjava/lang/String;)V", (void*)android_location_GpsLocationProvider_update_network_state },
- };
这里定义了GPS所有向上层提供的JNI本地方法,这些本地方法是如何与硬件适配层交互的呢?我们看其中一个本地方法android_location_GpsLocationProvider_start:
- static jboolean android_location_GpsLocationProvider_start(JNIEnv* env, jobject obj)
- {
- const GpsInterface* interface = GetGpsInterface(env, obj);
- if (interface)
- return (interface->start() == 0);
- else
- return false;
- }
它调用了GetGpsInterface获得GpsInterface接口,然后直接调用该接口的start回调函数。GetGpsInterface方法定义如下:
- static const GpsInterface* GetGpsInterface(JNIEnv* env, jobject obj) {
- // this must be set before calling into the HAL library
- if (!mCallbacksObj)
- mCallbacksObj = env->NewGlobalRef(obj);
- if (!sGpsInterface) {
- sGpsInterface = get_gps_interface();
- if (!sGpsInterface || sGpsInterface->init(&sGpsCallbacks) != 0) {
- sGpsInterface = NULL;
- return NULL;
- }
- }
- return sGpsInterface;
- }
这个函数返回了sGpsInterface,而sGpsInterface又是从get_gps_interface()获得的,我们继续查看get_gps_interface()函数的实现:
- static const GpsInterface* get_gps_interface() {
- int err;
- hw_module_t* module;
- const GpsInterface* interface = NULL;
- err = hw_get_module(GPS_HARDWARE_MODULE_ID, (hw_module_t const**)&module);
- if (err == 0) {
- hw_device_t* device;
- err = module->methods->open(module, GPS_HARDWARE_MODULE_ID, &device);
- if (err == 0) {
- gps_device_t* gps_device = (gps_device_t *)device;
- interface = gps_device->get_gps_interface(gps_device);
- }
- }
- return interface;
- }
这里面调用hw_get_module加载硬件适配模块.so文件,接着通过hw_device_t接口调用open()函数,实际执行gps/loc_api/llibloc_api/gps.c定义的open_gps函数,而后调用gps_device_t接口的get_gps_interface函数,此函数也是在gps.c中定义的,最后返回硬件适配层中loc_eng.cpp文件的sLocEngInterface,从而打通了上层到底层的通道。
2.3 Java Framework
GPSFramework源码位于:frameworks/base/location
2.3.1接口和类简介
首先对GPSFramework重要的接口和类作一个简单的介绍
接口
用于当Gps状态发生变化时接收通知 |
|
用于接收Gps的NMEA数据 |
|
用于接收当位置信息发生变化时,LocationManager发出的通知 |
类
地址信息类 |
|
用于根据设备情况动态选择provider |
|
用于处理地理编码信息 |
|
用于获取当前卫星状态 |
|
用于获取当前Gps状态 |
|
地理位置信息类 |
|
用于获取和操作gps系统服务 |
|
抽象类,用于提供位置提供者(Locationprovider) |
2.3.2 使用Gps编程接口
下面,我们用一个代码示例说明如何在应用层写一个简单的gps程序。
首先在AndroidManifest.xml中添加位置服务权限:
- <uses-permission android:name="android.permission.INTERNET" />
- <uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION" />
- <uses-permission android:name="android.permission.ACCESS_FIND_LOCATION" />
- <uses-permission android:name="android.permission.ACCESS_FINE_LOCATION"></uses-permission>
接着获取位置信息:
- //获取位置服务
- LocationManager locationManager = (LocationManager) getSystemService(Context.LOCATION_SERVICE);
- Criteria criteria = new Criteria();
- // 获得最好的定位效果
- criteria.setAccuracy(Criteria.ACCURACY_FINE); //设置为最大精度
- criteria.setAltitudeRequired(false); //不获取海拔信息
- criteria.setBearingRequired(false); //不获取方位信息
- criteria.setCostAllowed(false); //是否允许付费
- criteria.setPowerRequirement(Criteria.POWER_LOW); // 使用省电模式
- // 获得当前的位置提供者
- String provider = locationManager.getBestProvider(criteria, true);
- // 获得当前的位置
- Location location = locationManager.getLastKnownLocation(provider);
- Geocoder gc = new Geocoder(this);
- List<Address> addresses = null;
- try {
- //根据经纬度获得地址信息
- addresses = gc.getFromLocation(location.getLatitude(), location.getLongitude(), 1);
- } catch (IOException e) {
- e.printStackTrace();
- } if (addresses.size() > 0) {
- //获取address类的成员信息
- Sring msg = “”;
- msg += "AddressLine:" + addresses.get(0).getAddressLine(0)+ "\n";
- msg += "CountryName:" + addresses.get(0).getCountryName()+ "\n";
- msg += "Locality:" + addresses.get(0).getLocality() + "\n";
- msg += "FeatureName:" + addresses.get(0).getFeatureName();
- }
设置侦听,当位置信息发生变化时,自动更新相关信息
- //匿名类,继承自LocationListener接口
- private final LocationListener locationListener = new LocationListener() {
- public void onLocationChanged(Location location) {
- updateWithNewLocation(location);//更新位置信息
- }
- public void onProviderDisabled(String provider){
- updateWithNewLocation(null);//更新位置信息
- }
- public void onProviderEnabled(String provider){ }
- public void onStatusChanged(String provider, int status,Bundle extras){ }
- };
- //更新位置信息
- private void updateWithNewLocation(Location location) {
- if (location != null) {
- //获取经纬度
- double lat = location.getLatitude();
- double lng = location.getLongitude();
- }
- //添加侦听
- locationManager.requestLocationUpdates(provider, 2000, 10,locationListener);
2.3.3接口和类分析
下面对相关的类或接口进行分析,LocationManager的代码文件位于: frameworks/base/location/Java/location/LocationManager.java
我们看其构造函数:
- public LocationManager(ILocationManager service) {
- mService = service;
- }
其中mService为ILocationManager接口类型,构造函数的参数为service,外部调用时传入LocationManagerService实例。LocationManager是Android系统的gps位置信息系统服务,在稍后将会对其进行分析。由带参构造函数实例化LocationManager类的方式用得不多,一般用的方式是由getSystemService获得LocationManagerService服务,再强制转换为LocationManager。例如在2.3.2中的代码示例中是这样获取gps服务的:
- LocationManager locationManager = (LocationManager) getSystemService(Context.LOCATION_SERVICE);
这里的Context.LOCATION_SERVICE为”location”,标识gps服务。
LocationManagerService服务是整个GpsFramework的核心,首先看它是如何加载的,代码文件位于:frameworks/base/services/java/com/android/server/systemserver.java
- …//省略其他代码
- LocationManagerService location = null;
- …//省略其他代码
- try {
- Slog.i(TAG, "Location Manager");
- location = new LocationManagerService(context);
- ServiceManager.addService(Context.LOCATION_SERVICE, location);
- } catch (Throwable e) {
- Slog.e(TAG, "Failure starting Location Manager", e);
- }
此处向ServiceManger系统服务管理器注册了新的服务,其名称为”location”,类型为LocationManagerService。注册此服务后,Java应用程序可通过ServiceManager获得LocationManagerService的代理接口ILocationManager.Stub,从而调用LocationManagerService提供的接口函数。ILocationManager位于:
frameworks/base/location/java/location/ILocationManager.aidl,其代码如下:
- /**
- * System private API for talking with the location service.
- *
- * {@hide}
- */
- interface ILocationManager
- {
- List<String> getAllProviders();
- List<String> getProviders(in Criteria criteria, boolean enabledOnly);
- String getBestProvider(in Criteria criteria, boolean enabledOnly);
- boolean providerMeetsCriteria(String provider, in Criteria criteria);
- void requestLocationUpdates(String provider, in Criteria criteria, long minTime, float minDistance,
- boolean singleShot, in ILocationListener listener);
- void requestLocationUpdatesPI(String provider, in Criteria criteria, long minTime, float minDistance,
- boolean singleShot, in PendingIntent intent);
- void removeUpdates(in ILocationListener listener);
- void removeUpdatesPI(in PendingIntent intent);
- boolean addGpsStatusListener(IGpsStatusListener listener);
- void removeGpsStatusListener(IGpsStatusListener listener);
- // for reporting callback completion
- void locationCallbackFinished(ILocationListener listener);
- boolean sendExtraCommand(String provider, String command, inout Bundle extras);
- void addProximityAlert(double latitude, double longitude, float distance,
- long expiration, in PendingIntent intent);
- void removeProximityAlert(in PendingIntent intent);
- Bundle getProviderInfo(String provider);
- boolean isProviderEnabled(String provider);
- Location getLastKnownLocation(String provider);
- // Used by location providers to tell the location manager when it has a new location.
- // Passive is true if the location is coming from the passive provider, in which case
- // it need not be shared with other providers.
- void reportLocation(in Location location, boolean passive);
- boolean geocoderIsPresent();
- String getFromLocation(double latitude, double longitude, int maxResults,
- in GeocoderParams params, out List<Address> addrs);
- String getFromLocationName(String locationName,
- double lowerLeftLatitude, double lowerLeftLongitude,
- double upperRightLatitude, double upperRightLongitude, int maxResults,
- in GeocoderParams params, out List<Address> addrs);
- void addTestProvider(String name, boolean requiresNetwork, boolean requiresSatellite,
- boolean requiresCell, boolean hasMonetaryCost, boolean supportsAltitude,
- boolean supportsSpeed, boolean supportsBearing, int powerRequirement, int accuracy);
- void removeTestProvider(String provider);
- void setTestProviderLocation(String provider, in Location loc);
- void clearTestProviderLocation(String provider);
- void setTestProviderEnabled(String provider, boolean enabled);
- void clearTestProviderEnabled(String provider);
- void setTestProviderStatus(String provider, int status, in Bundle extras, long updateTime);
- void clearTestProviderStatus(String provider);
- // for NI support
- boolean sendNiResponse(int notifId, int userResponse);
- }
android系统通过ILocationManager.aidl文件自动生成IlocationManager.Stub代理接口,在Java客户端获取LocationManagerService的方式如下:
- ILocationManager mLocationManager;
- IBinder b = ServiceManager.getService(Context.LOCATION_SERVICE);
- mLocationManager = IlocationManager.Stub.asInterface(b);
客户端通过mLocationManager即可操作LocationMangerService继承自ILocationManager.Stub的的公共接口。之前提到了通过getSystemSerivice方式也可以获得LocationManagerService,但getSystemService()返回的是Object,必须转换为其他接口,我们可以看到之前的是强制转换为LocationManager类型,而此处由ServiceManager.getService返回IBinder接口,再通过ILocationManager.Stub转换为ILocationManager类型,是更加规范的做法。
LocationMangerService的代码文件位于:
frameworks/base/services/java/com/android/server/LocationMangerService.java
我们首先看其中的systemReady()函数
- void systemReady() {
- // we defer starting up the service until the system is ready
- Thread thread = new Thread(null, this, "LocationManagerService");
- thread.start();
- }
此处启动自身服务线程,因LocationMangerService继承自Runnable接口,当启动此线程后,会执行继承自Runnable接口的run()函数,我们看run()函数的定义:
- public void run()
- {
- Process.setThreadPriority(Process.THREAD_PRIORITY_BACKGROUND);
- Looper.prepare();
- mLocationHandler = new LocationWorkerHandler();
- initialize();
- Looper.loop();
- }
此处调用了initialize()进行初始化,initialize()函数定义如下:
- private void initialize() {
- //...省略其他代码
- loadProviders();
- //...省略其他代码
- }
此处调用了loadProviders()函数,loadProviders()函数调用了_loadProvidersLocked(),其代码如下:
- private void _loadProvidersLocked() {
- // Attempt to load "real" providers first
- if (GpsLocationProvider.isSupported()) {
- // Create a gps location provider
- GpsLocationProvider gpsProvider = new GpsLocationProvider(mContext, this);
- mGpsStatusProvider = gpsProvider.getGpsStatusProvider();
- mNetInitiatedListener = gpsProvider.getNetInitiatedListener();
- addProvider(gpsProvider);
- mGpsLocationProvider = gpsProvider;
- }
- // create a passive location provider, which is always enabled
- PassiveProvider passiveProvider = new PassiveProvider(this);
- addProvider(passiveProvider);
- mEnabledProviders.add(passiveProvider.getName());
- // initialize external network location and geocoder services
- if (mNetworkLocationProviderPackageName != null) {
- mNetworkLocationProvider =
- new LocationProviderProxy(mContext, LocationManager.NETWORK_PROVIDER,
- mNetworkLocationProviderPackageName, mLocationHandler);
- addProvider(mNetworkLocationProvider);
- }
- if (mGeocodeProviderPackageName != null) {
- mGeocodeProvider = new GeocoderProxy(mContext, mGeocodeProviderPackageName);
- }
- updateProvidersLocked();
- }
在这里对GpsLocationProvider和NetworkLocationProvider类作了初始化,并添加到provider集合中。GpsLocationProvider和NetworkLocationProvider继承自LocationProviderInterface接口,分别代表两种位置提供者(LocationProvider):
(1)LocationManager.GPS_PROVIDER:GPS模式,精度比较高,但是慢而且消耗电力,而且可能因为天气原因或者障碍物而无法获取卫星信息,另外设备可能没有GPS模块(2)LocationManager.NETWORK_PROVIDER:通过网络获取定位信息,精度低,耗电少,获取信息速度较快,不依赖GPS模块。
Android提供criteria类,可根据当前设备情况动态选择位置提供者。我们在之前2.3.2的代码示例中,有这样一句代码:
- // 获得当前的位置提供者
- String provider = locationManager.getBestProvider(criteria, true);
getBestProvider其实是根据Criteria的条件遍历mProviders集合,返回符合条件的provider名称。我们再看GpsLocationProvider的实现,其代码文件位于:
frameworks/base/services/java/com/android/server/location/GpsLocationProvider.java
在GpsLocationProvider的构造函数中:
- public GpsLocationProvider(Context context, ILocationManager locationManager) {
- //...省略部分代码
- IntentFilter intentFilter = new IntentFilter();
- intentFilter.addAction(Intents.DATA_SMS_RECEIVED_ACTION);
- intentFilter.addDataScheme("sms");
- intentFilter.addDataAuthority("localhost","7275");
- context.registerReceiver(mBroadcastReciever, intentFilter);
- intentFilter = new IntentFilter();
- intentFilter.addAction(Intents.WAP_PUSH_RECEIVED_ACTION);
- try {
- intentFilter.addDataType("application/vnd.omaloc-supl-init");
- } catch (IntentFilter.MalformedMimeTypeException e) {
- Log.w(TAG, "Malformed SUPL init mime type");
- }
- context.registerReceiver(mBroadcastReciever, intentFilter);
- //...省略部分代码
- // wait until we are fully initialized before returning
- mThread = new GpsLocationProviderThread();
- mThread.start();
- while (true) {
- try {
- mInitializedLatch.await();
- break;
- } catch (InterruptedException e) {
- Thread.currentThread().interrupt();
- }
- }
- }
这里注册了广播接受者mBroadcastReciever,用于接收广播消息,消息过滤在intentFilter中定义。下面看它接收广播消息时的动作:
- private final BroadcastReceiver mBroadcastReciever = new BroadcastReceiver() {
- @Override public void onReceive(Context context, Intent intent) {
- String action = intent.getAction();
- if (action.equals(ALARM_WAKEUP)) {
- if (DEBUG) Log.d(TAG, "ALARM_WAKEUP");
- startNavigating(false);
- } else if (action.equals(ALARM_TIMEOUT)) {
- if (DEBUG) Log.d(TAG, "ALARM_TIMEOUT");
- hibernate();
- } else if (action.equals(Intents.DATA_SMS_RECEIVED_ACTION)) {
- checkSmsSuplInit(intent);
- } else if (action.equals(Intents.WAP_PUSH_RECEIVED_ACTION)) {
- checkWapSuplInit(intent);
- }
- }
- };
当接收ALARM_EAKEUP时,执行startNavigating函数,当接收到ALARM_TIMEOUT广播时,执行hibernate函数。这两个函数很关键,下面看他们的实现:
- private void startNavigating(boolean singleShot) {
- //...省略部分代码
- if (!native_set_position_mode(mPositionMode, GPS_POSITION_RECURRENCE_PERIODIC,
- interval, 0, 0)) {
- mStarted = false;
- Log.e(TAG, "set_position_mode failed in startNavigating()");
- return;
- }
- if (!native_start()) {
- mStarted = false;
- Log.e(TAG, "native_start failed in startNavigating()");
- return;
- }
- //...省略部分代码
- }
看到没有,这里调用了native_set_position_mode和native_start方法,而这些方法正是我们之前在JNI适配层提到的注册的本地方法。同样的,hibernate函数调用了JNI提供的native_stop方法。我们再看GpsLocationProvider的内部私有函数:
可以看到所有这些本地方法,都是在JNI层注册的,GpsLocationProvider类是从JNI层到Framework层的通道。
下面回到LocationManagerService,分析如何获取最新的位置信息(Location),获取最新的location的函数是getLastKnownLocation,其实现如下:
- private Location _getLastKnownLocationLocked(String provider) {
- checkPermissionsSafe(provider);
- LocationProviderInterface p = mProvidersByName.get(provider);
- if (p == null) {
- return null;
- }
- if (!isAllowedBySettingsLocked(provider)) {
- return null;
- }
- return mLastKnownLocation.get(provider);
- }
这里mLastKnownLocation类型为HashMap<String,Location>,所以mLastKnownLocation.get(provider)表示通过provider的名称在哈希字典中获取相应的location,那么这些location是什么时候被存入到哈希字典中的呢?
我们回到LocationManagerService的run函数:
- public void run()
- {
- Process.setThreadPriority(Process.THREAD_PRIORITY_BACKGROUND);
- Looper.prepare();
- mLocationHandler = new LocationWorkerHandler();
- initialize();
- Looper.loop();
- }
这里对类型为LocationWorkerHandler的变量进行初始化,LocationWorkerHandler是在LocationManagerService的一个内部类,它继承自Handler类,Handler是Android系统用于应用程序内部通信的组件,内部通信指同个进程的主线程与其他线程间的通信,Handler通过Message或Runnable对象进行通信。我们继续看LocationWorkerHandler的实现:
- private class LocationWorkerHandler extends Handler {
- @Override
- public void handleMessage(Message msg) {
- try {
- if (msg.what == MESSAGE_LOCATION_CHANGED) {
- // log("LocationWorkerHandler: MESSAGE_LOCATION_CHANGED!");
- synchronized (mLock) {
- Location location = (Location) msg.obj;
- String provider = location.getProvider();
- boolean passive = (msg.arg1 == 1);
- if (!passive) {
- // notify other providers of the new location
- for (int i = mProviders.size() - 1; i >= 0; i--) {
- LocationProviderInterface p = mProviders.get(i);
- if (!provider.equals(p.getName())) {
- p.updateLocation(location);
- }
- }
- }
- if (isAllowedBySettingsLocked(provider)) {
- handleLocationChangedLocked(location, passive);
- }
- }
- } else if (msg.what == MESSAGE_PACKAGE_UPDATED) {
- //...省略部分代码
- }
- }
- } catch (Exception e) {
- // Log, don't crash!
- Slog.e(TAG, "Exception in LocationWorkerHandler.handleMessage:", e);
- }
- }
- }
这里重写Handle类的handleMessage方法,处理用Handle接收的Message对象消息。当接受到位置信息变化的消息MESSAGE_LOCATION_CHANGED时,调用p.updateLocationhandleLocationChangedLocked方法,其实现如下:
- private void handleLocationChangedLocked(Location location, boolean passive) {
- //...省略部分代码
- // Update last known location for provider
- Location lastLocation = mLastKnownLocation.get(provider);
- if (lastLocation == null) {
- mLastKnownLocation.put(provider, new Location(location));
- } else {
- lastLocation.set(location);
- }
- //...省略部分代码
- }
可以看到是在handleLocationChangedLocked函数中实现对lastknownlocation的更新的,那么在LocationWorkerHandler类中处理的MESSAGE_LOCATION_CHANGED消息是谁发送出来的呢?答案是在LocationManagerService类的reportLocation函数中:
- public void reportLocation(Location location, boolean passive) {
- if (mContext.checkCallingOrSelfPermission(INSTALL_LOCATION_PROVIDER)
- != PackageManager.PERMISSION_GRANTED) {
- throw new SecurityException("Requires INSTALL_LOCATION_PROVIDER permission");
- }
- mLocationHandler.removeMessages(MESSAGE_LOCATION_CHANGED, location);
- Message m = Message.obtain(mLocationHandler, MESSAGE_LOCATION_CHANGED, location);
- m.arg1 = (passive ? 1 : 0);
- mLocationHandler.sendMessageAtFrontOfQueue(m);
- }
此处构造了新的Message对象,然后发送到消息队列的首位置。在GpsLocationProvider类的reportLocation函数中,有这样一段代码:
- try {
- mLocationManager.reportLocation(mLocation, false);
- } catch (RemoteException e) {
- Log.e(TAG, "RemoteException calling reportLocation");
- }
所以实际是由GpsLocationProvider主动调用LocationManagerService的reportLocation方法,从而更新最新的位置信息。
实际上,GpsLocationoProvider的reportLocation对应了硬件适配层中的GpsCallbacks结构体中的回调函数gps_location_callback
- /** Callback with location information. 向上层传递GPS位置信息
- * Can only be called from a thread created by create_thread_cb.
- */
- typedef void (* gps_location_callback)(GpsLocation* location);
那么GpsLocationProvider中的reportLocation函数是如何与GpsCallbacks的gps_location_callback挂钩的呢?我们回到JNI适配层的代码文件:
frameworks/base/services/jni/com_android_server_location_GpsLocationProvider.cpp
其中定义的GetGpsInterface函数:
- static const GpsInterface* GetGpsInterface(JNIEnv* env, jobject obj) {
- // this must be set before calling into the HAL library
- if (!mCallbacksObj)
- mCallbacksObj = env->NewGlobalRef(obj);
- if (!sGpsInterface) {
- sGpsInterface = get_gps_interface();
- if (!sGpsInterface || sGpsInterface->init(&sGpsCallbacks) != 0) {
- sGpsInterface = NULL;
- return NULL;
- }
- }
- return sGpsInterface;
- }
这里面的sGpsInterface->init(&sGpsCallbacks)调用了GpsInterface的init回调函数,即初始化GpsCallbacks结构体变量sGpsCallbacks,sGpsCallbacks定义如下:
- GpsCallbacks sGpsCallbacks = {
- sizeof(GpsCallbacks),
- location_callback,
- status_callback,
- sv_status_callback,
- nmea_callback,
- set_capabilities_callback,
- acquire_wakelock_callback,
- release_wakelock_callback,
- create_thread_callback,
- };
我们再次看GpsCallbacks的定义(其代码文件在硬件适配层的头文件gps.h中):
- typedef struct {
- size_t size;
- gps_location_callback location_cb;
- gps_status_callback status_cb;
- gps_sv_status_callback sv_status_cb;
- gps_nmea_callback nmea_cb;
- gps_set_capabilities set_capabilities_cb;
- gps_acquire_wakelock acquire_wakelock_cb;
- gps_release_wakelock release_wakelock_cb;
- gps_create_thread create_thread_cb;
- } GpsCallbacks;
比较sGpsCallbacks与GpsCallbacks,可以看到location_callback与gps_location_callback对应。再看location_callback函数的定义:
- static void location_callback(GpsLocation* location)
- {
- JNIEnv* env = AndroidRuntime::getJNIEnv();
- env->CallVoidMethod(mCallbacksObj, method_reportLocation, location->flags,
- (jdouble)location->latitude, (jdouble)location->longitude,
- (jdouble)location->altitude,
- (jfloat)location->speed, (jfloat)location->bearing,
- (jfloat)location->accuracy, (jlong)location->timestamp);
- checkAndClearExceptionFromCallback(env, __FUNCTION__);
- }
这里面利用JNI调用了Java语言的方法method_reportLocation,method_reportLocation是一个jmethodID变量,表示一个由Java语言定义的方法。下面我们看method_reportLocation的赋值代码:
- static void android_location_GpsLocationProvider_class_init_native(JNIEnv* env, jclass clazz) {
- method_reportLocation = env->GetMethodID(clazz, "reportLocation", "(IDDDFFFJ)V");
- //...省略部分代码
- }
这里表示method_reportLocation指向Java类clazz里的方法reportLocation,那么这个Java类clazz是不是表示GpsLocationProvider呢?我们找到注册JNI方法的方法表:
- tatic JNINativeMethod sMethods[] = {
- /* name, signature, funcPtr */
- {"class_init_native", "()V", (void *)android_location_GpsLocationProvider_class_init_native},
- //...省略部分代码
- }
这里说明_GpsLocationProvider_class_init_native对应的native方法名称是class_init_native,下面我们只要确定在Java中的某个类A调用了class_init_native方法,即可以说明A类的reportLocation函数是GpsCallbacks的回调函数。
我们回到GpsLocationProvider的代码文件:
frameworks/base/services/java/com/android/server/location/GpsLocationProvider.java
其中有一段代码:
- static { class_init_native(); }
说明是在GpsLocationProvider中调用了class_init_native方法,从而说明GpsLocationProvider的reportLocation函数是GpsCallbacks的回调函数,即当Gps设备的位置信息发生变化时,它调用GpsLocationProvider的回调函数reportLocation,继而调用LocationManagerService的reportLocation函数,从而更新应用层的位置信息。
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