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。
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2. /** Flags to indicate which values are valid in a GpsLocation. */
3. typedef uint16_t GpsLocationFlags;
4. // IMPORTANT: Note that the following values must match
5. // constants in GpsLocationProvider.java.
6. /** GpsLocation has valid latitude and longitude. */
7. #define GPS_LOCATION_HAS_LAT_LONG 0x0001
8. /** GpsLocation has valid altitude. */
9. #define GPS_LOCATION_HAS_ALTITUDE 0x0002
10. /** GpsLocation has valid speed. */
11. #define GPS_LOCATION_HAS_SPEED 0x0004
12. /** GpsLocation has valid bearing. */
13. #define GPS_LOCATION_HAS_BEARING 0x0008
14. /** GpsLocation has valid accuracy. */
15. #define GPS_LOCATION_HAS_ACCURACY 0x0010
16.
17. /** Represents a location. */
18. typedef struct {
19. /** set to sizeof(GpsLocation) */
20. size_t size;
21. /** Contains GpsLocationFlags bits. */
22. uint16_t flags;
23. /** Represents latitude in degrees. */
24. double latitude;
25. /** Represents longitude in degrees. */
26. double longitude;
27. /** Represents altitude in meters above the WGS 84 reference
28. * ellipsoid. */
29. double altitude;
30. /** Represents speed in meters per second. */
31. float speed;
32. /** Represents heading in degrees. */
33. float bearing;
34. /** Represents expected accuracy in meters. */
35. float accuracy;
36. /** Timestamp for the location fix. */
37. GpsUtcTime timestamp;
38. } 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。
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40. /** GPS status event values. */
41. typedef uint16_t GpsStatusValue;
42. // IMPORTANT: Note that the following values must match
43. // constants in GpsLocationProvider.java.
44. /** GPS status unknown. */
45. #define GPS_STATUS_NONE 0
46. /** GPS has begun navigating. */
47. #define GPS_STATUS_SESSION_BEGIN 1
48. /** GPS has stopped navigating. */
49. #define GPS_STATUS_SESSION_END 2
50. /** GPS has powered on but is not navigating. */
51. #define GPS_STATUS_ENGINE_ON 3
52. /** GPS is powered off. */AgpsCallbacks
53.
54. AgpsInterface
55. #define GPS_STATUS_ENGINE_OFF 4
56.
57. /** Represents the status. */
58. typedef struct {
59. /** set to sizeof(GpsStatus) */
60. size_t size;
61. GpsStatusValue status;
62. } 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。
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64. /** Represents SV information. */
65. typedef struct {
66. /** set to sizeof(GpsSvInfo) */
67. size_t size;
68. /** Pseudo-random number for the SV. */
69. int prn;
70. /** Signal to noise ratio. */
71. float snr;
72. /** Elevation of SV in degrees. */
73. float elevation;
74. /** Azimuth of SV in degrees. */
75. float azimuth;
76. } 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。
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78. /** Represents SV status. */
79. typedef struct {
80. /** set to sizeof(GpsSvStatus) */
81. size_t size;
82.
83. /** Number of SVs currently visible. */
84. int num_svs;
85.
86. /** Contains an array of SV information. */
87. GpsSvInfo sv_list[GPS_MAX_SVS];
88.
89. /** Represents a bit mask indicating which SVs
90. * have ephemeris data.
91. */
92. uint32_t ephemeris_mask;
93.
94. /** Represents a bit mask indicating which SVs
95. * have almanac data.
96. */
97. uint32_t almanac_mask;
98.
99. /**
100. * Represents a bit mask indicating which SVs
101. * were used for computing the most recent position fix.
102. */
103. uint32_t used_in_fix_mask;
104. } GpsSvStatus;
• GpsCallbacks
回调函数定义
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106. /** Callback with location information. 向上层传递GPS位置信息
107. * Can only be called from a thread created by create_thread_cb.
108. */
109. typedef void (* gps_location_callback)(GpsLocation* location);
110.
111. /** Callback with status information. 向上层传递GPS状态信息
112. * Can only be called from a thread created by create_thread_cb.
113. */
114. typedef void (* gps_status_callback)(GpsStatus* status);
115.
116. /** Callback with SV status information. 向上层传递GPS卫星信息
117. * Can only be called from a thread created by create_thread_cb.
118. */
119. typedef void (* gps_sv_status_callback)(GpsSvStatus* sv_info);
120.
121. /** Callback for reporting NMEA sentences. 向上层传递MEMA数据
122. * Can only be called from a thread created by create_thread_cb.
123. */
124. typedef void (* gps_nmea_callback)(GpsUtcTime timestamp, const char* nmea, int length);
125.
126. /** Callback to inform framework of the GPS engine's capabilities.告知GPS模块可以实现的功能
127. * Capability parameter is a bit field of GPS_CAPABILITY_* flags.
128. */
129. typedef void (* gps_set_capabilities)(uint32_t capabilities);
130.
131. /** Callback utility for acquiring the GPS wakelock.上锁，防止处理GPS事件时中止。
132. * This can be used to prevent the CPU from suspending while handling GPS events.
133. */
134. typedef void (* gps_acquire_wakelock)();
135.
136. /** Callback utility for releasing the GPS wakelock. */释放锁
137. typedef void (* gps_release_wakelock)();
138.
139. /** Callback for creating a thread that can call into the Java framework code.等待上层请求
140. * This must be used to create any threads that report events up to the framework.
141. */
142. typedef pthread_t (* gps_create_thread)(const char* name, void (*start)(void *), void* arg);
143.
144. /** GPS callback structure. */
145. typedef struct {
146. /** set to sizeof(GpsCallbacks) */
147. size_t size;
148. gps_location_callback location_cb;
149. gps_status_callback status_cb;
150. gps_sv_status_callback sv_status_cb;
151. gps_nmea_callback nmea_cb;
152. gps_set_capabilities set_capabilities_cb;
153. gps_acquire_wakelock acquire_wakelock_cb;
154. gps_release_wakelock release_wakelock_cb;
155. gps_create_thread create_thread_cb;
156. } 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。
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158. /** Represents the standard GPS interface. */
159. typedef struct {
160. /** set to sizeof(GpsInterface) */
161. size_t size;
162. /**
163. * Opens the interface and provides the callback routines
164. * to the implemenation of this interface.
165. */
166. int (*init)( GpsCallbacks* callbacks );
167.
168. /** Starts navigating. 启动定位*/
169. int (*start)( void );
170.
171. /** Stops navigating. 取消定位*/
172. int (*stop)( void );
173.
174. /** Closes the interface. 关闭GPS接口*/
175. void (*cleanup)( void );
176.
177. /** Injects the current time.填入时间 */
178. int (*inject_time)(GpsUtcTime time, int64_t timeReference,
179. int uncertainty);
180.
181. /** Injects current location from another location provider填入位置
182. * (typically cell ID).
183. * latitude and longitude are measured in degrees
184. * expected accuracy is measured in meters
185. */
186. int (*inject_location)(double latitude, double longitude, float accuracy);
187.
188. /**
189. * 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
190. * information defined in the flags. GPS_DELETE_ALL is passed for
191. * a cold start.
192. */
193. void (*delete_aiding_data)(GpsAidingData flags);
194.
195. /**设置定位模式和GPS工作模式等
196. * min_interval represents the time between fixes in milliseconds.
197. * preferred_accuracy represents the requested fix accuracy in meters.
198. * preferred_time represents the requested time to first fix in milliseconds.
199. */
200. int (*set_position_mode)(GpsPositionMode mode, GpsPositionRecurrence recurrence,
201. uint32_t min_interval, uint32_t preferred_accuracy, uint32_t preferred_time);
202.
203. /** Get a pointer to extension information. 自定义的接口*/
204. const void* (*get_extension)(const char* name);
205. } 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。
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207. struct gps_device_t {
208. struct hw_device_t common;
209.
210. /**
211. * Set the provided lights to the provided values.
212. *
213. * Returns: 0 on succes, error code on failure.
214. */
215. const GpsInterface* (*get_gps_interface)(struct gps_device_t* dev);
216. };
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：
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217. const struct hw_module_t HAL_MODULE_INFO_SYM = {
218. .tag = HARDWARE_MODULE_TAG,
219. .version_major = 1,
220. .version_minor = 0,
221. .id = GPS_HARDWARE_MODULE_ID,
222. .name = "loc_api GPS Module",
223. .author = "Qualcomm USA, Inc.",
224. .methods = &gps_module_methods,
225. };
这里的methods指向gps.c文件中的gps_module_methods
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226. static struct hw_module_methods_t gps_module_methods = {
227. .open = open_gps
228. };
gps_module_methods定义了设备的open函数为open_gps，我们看open_gps函数：
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229. static int open_gps(const struct hw_module_t* module, char const* name,
230. struct hw_device_t** device)
231. {
232. struct gps_device_t *dev = malloc(sizeof(struct gps_device_t));
233. memset(dev, 0, sizeof(*dev));
234.
235. dev->common.tag = HARDWARE_DEVICE_TAG;
236. dev->common.version = 0;
237. dev->common.module = (struct hw_module_t*)module;
238. dev->get_gps_interface = gps__get_gps_interface;
239.
240. *device = (struct hw_device_t*)dev;
241. return 0;
242. }
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：
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243. const GpsInterface* gps__get_gps_interface(struct gps_device_t* dev)
244. {
245. return get_gps_interface();
246. }
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：
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247. // Defines the GpsInterface in gps.h
248. static const GpsInterface sLocEngInterface =
249. {
250. sizeof(GpsInterface),
251. loc_eng_init,
252. loc_eng_start,
253. loc_eng_stop,
254. loc_eng_cleanup,
255. loc_eng_inject_time,
256. loc_eng_inject_location,
257. loc_eng_delete_aiding_data,
258. loc_eng_set_position_mode,
259. loc_eng_get_extension,
260. };
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：
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261. int register_android_server_location_GpsLocationProvider(JNIEnv* env)
262. {
263. return jniRegisterNativeMethods(env, "com/android/server/location/GpsLocationProvider", sMethods, NELEM(sMethods));
264. }
此函数被同目录下onload.cpp文件调用，调用地方在：
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265. extern "C" jint JNI_OnLoad(JavaVM* vm, void* reserved)
266. {
267. JNIEnv* env = NULL;
268. jint result = -1;
269.
270. if (vm->GetEnv((void**) &env, JNI_VERSION_1_4) != JNI_OK) {
271. LOGE("GetEnv failed!");
272. return result;
273. }
274. LOG_ASSERT(env, "Could not retrieve the env!");
275.
276. //...省略其他注册代码
277. register_android_server_location_GpsLocationProvider(env);
278.
279. return JNI_VERSION_1_4;
280. }
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：
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281. static JNINativeMethod sMethods[] = {
282. /* name, signature, funcPtr */
283. {"class_init_native", "()V", (void *)android_location_GpsLocationProvider_class_init_native},
284. {"native_is_supported", "()Z", (void*)android_location_GpsLocationProvider_is_supported},
285. {"native_init", "()Z", (void*)android_location_GpsLocationProvider_init},
286. {"native_cleanup", "()V", (void*)android_location_GpsLocationProvider_cleanup},
287. {"native_set_position_mode", "(IIIII)Z", (void*)android_location_GpsLocationProvider_set_position_mode},
288. {"native_start", "()Z", (void*)android_location_GpsLocationProvider_start},
289. {"native_stop", "()Z", (void*)android_location_GpsLocationProvider_stop},
290. {"native_delete_aiding_data", "(I)V", (void*)android_location_GpsLocationProvider_delete_aiding_data},
291. {"native_read_sv_status", "([I[F[F[F[I)I", (void*)android_location_GpsLocationProvider_read_sv_status},
292. {"native_read_nmea", "([BI)I", (void*)android_location_GpsLocationProvider_read_nmea},
293. {"native_inject_time", "(JJI)V", (void*)android_location_GpsLocationProvider_inject_time},
294. {"native_inject_location", "(DDF)V", (void*)android_location_GpsLocationProvider_inject_location},
295. {"native_supports_xtra", "()Z", (void*)android_location_GpsLocationProvider_supports_xtra},
296. {"native_inject_xtra_data", "([BI)V", (void*)android_location_GpsLocationProvider_inject_xtra_data},
297. {"native_agps_data_conn_open", "(Ljava/lang/String;)V", (void*)android_location_GpsLocationProvider_agps_data_conn_open},
298. {"native_agps_data_conn_closed", "()V", (void*)android_location_GpsLocationProvider_agps_data_conn_closed},
299. {"native_agps_data_conn_failed", "()V", (void*)android_location_GpsLocationProvider_agps_data_conn_failed},
300. {"native_agps_set_id","(ILjava/lang/String;)V",(void*)android_location_GpsLocationProvider_agps_set_id},
301. {"native_agps_set_ref_location_cellid","(IIIII)V",(void*)android_location_GpsLocationProvider_agps_set_reference_location_cellid},
302. {"native_set_agps_server", "(ILjava/lang/String;I)V", (void*)android_location_GpsLocationProvider_set_agps_server},
303. {"native_send_ni_response", "(II)V", (void*)android_location_GpsLocationProvider_send_ni_response},
304. {"native_agps_ni_message", "([BI)V", (void *)android_location_GpsLocationProvider_agps_send_ni_message},
305. {"native_get_internal_state", "()Ljava/lang/String;", (void*)android_location_GpsLocationProvider_get_internal_state},
306. {"native_update_network_state", "(ZIZLjava/lang/String;)V", (void*)android_location_GpsLocationProvider_update_network_state },
307. };
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：
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308. static jboolean android_location_GpsLocationProvider_start(JNIEnv* env, jobject obj)
309. {
310. const GpsInterface* interface = GetGpsInterface(env, obj);
311. if (interface)
312. return (interface->start() == 0);
313. else
314. return false;
315. }
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：
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316. static const GpsInterface* GetGpsInterface(JNIEnv* env, jobject obj) {
317. // this must be set before calling into the HAL library
318. if (!mCallbacksObj)
319. mCallbacksObj = env->NewGlobalRef(obj);
320.
321. if (!sGpsInterface) {
322. sGpsInterface = get_gps_interface();
323. if (!sGpsInterface || sGpsInterface->init(&sGpsCallbacks) != 0) {
324. sGpsInterface = NULL;
325. return NULL;
326. }
327. }
328. return sGpsInterface;
329. }
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：
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330. static const GpsInterface* get_gps_interface() {
331. int err;
332. hw_module_t* module;
333. const GpsInterface* interface = NULL;
334.
335. err = hw_get_module(GPS_HARDWARE_MODULE_ID, (hw_module_t const**)&module);
336. if (err == 0) {
337. hw_device_t* device;
338. err = module->methods->open(module, GPS_HARDWARE_MODULE_ID, &device);
339. if (err == 0) {
340. gps_device_t* gps_device = (gps_device_t *)device;
341. interface = gps_device->get_gps_interface(gps_device);
342. }
343. }
344.
345. return interface;
346. }
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
GpsStatus.Listener
用于当Gps状态发生变化时接收通知
GpsStatus.NmeaListener
用于接收Gps的NMEA数据
LocationListener
用于接收当位置信息发生变化时，LocationManager发出的通知
• 类
Address
地址信息类
Criteria
用于根据设备情况动态选择provider
Geocoder
用于处理地理编码信息
GpsSatellite
用于获取当前卫星状态
GpsStatus
用于获取当前Gps状态
Location
地理位置信息类
LocationManager
用于获取和操作gps系统服务
LocationProvider
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:
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350.
351.
352.
353.
• 接着获取位置信息：
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355. //获取位置服务
356. LocationManager locationManager = (LocationManager) getSystemService(Context.LOCATION_SERVICE);
357. Criteria criteria = new Criteria();
358. // 获得最好的定位效果
359. criteria.setAccuracy(Criteria.ACCURACY_FINE); //设置为最大精度
360. criteria.setAltitudeRequired(false); //不获取海拔信息
361. criteria.setBearingRequired(false); //不获取方位信息
362. criteria.setCostAllowed(false); //是否允许付费
363. criteria.setPowerRequirement(Criteria.POWER_LOW); // 使用省电模式
364. // 获得当前的位置提供者
365. String provider = locationManager.getBestProvider(criteria, true);
366. // 获得当前的位置
367. Location location = locationManager.getLastKnownLocation(provider);
368. Geocoder gc = new Geocoder(this);
369. List addresses = null;
370. try {
371. //根据经纬度获得地址信息
372. addresses = gc.getFromLocation(location.getLatitude(), location.getLongitude(), 1);
373. } catch (IOException e) {
374. e.printStackTrace();
375. } if (addresses.size() > 0) {
376. //获取address类的成员信息
377. Sring msg = “”;
378. msg += "AddressLine：" + addresses.get(0).getAddressLine(0)+ "\n";
379. msg += "CountryName：" + addresses.get(0).getCountryName()+ "\n";
380. msg += "Locality：" + addresses.get(0).getLocality() + "\n";
381. msg += "FeatureName：" + addresses.get(0).getFeatureName();
382. }
• 设置侦听，当位置信息发生变化时，自动更新相关信息
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384. //匿名类，继承自LocationListener接口
385. private final LocationListener locationListener = new LocationListener() {
386. public void onLocationChanged(Location location) {
387. updateWithNewLocation(location);//更新位置信息
388. }
389. public void onProviderDisabled(String provider){
390. updateWithNewLocation(null);//更新位置信息
391. }
392. public void onProviderEnabled(String provider){ }
393. public void onStatusChanged(String provider, int status,Bundle extras){ }
394. };
395. //更新位置信息
396. private void updateWithNewLocation(Location location) {
397.
398.
399. if (location != null) {
400. //获取经纬度
401. double lat = location.getLatitude();
402. double lng = location.getLongitude();
403. }
404. //添加侦听
405. 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：
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406. public LocationManager(ILocationManager service) {
407. mService = service;
408. }
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：
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409. 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
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410. …//省略其他代码
411. LocationManagerService location = null;
412. …//省略其他代码
413. try {
414. Slog.i(TAG, "Location Manager");
415. location = new LocationManagerService(context);
416. ServiceManager.addService(Context.LOCATION_SERVICE, location);
417. } catch (Throwable e) {
418. Slog.e(TAG, "Failure starting Location Manager", e);
419. }
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：
[java] view plaincopy
420. /**
421. * System private API for talking with the location service.
422. *
423. * {@hide}
424. */
425. interface ILocationManager
426. {
427. List getAllProviders();
428. List getProviders(in Criteria criteria, boolean enabledOnly);
429. String getBestProvider(in Criteria criteria, boolean enabledOnly);
430. boolean providerMeetsCriteria(String provider, in Criteria criteria);
431.
432. void requestLocationUpdates(String provider, in Criteria criteria, long minTime, float minDistance,
433. boolean singleShot, in ILocationListener listener);
434. void requestLocationUpdatesPI(String provider, in Criteria criteria, long minTime, float minDistance,
435. boolean singleShot, in PendingIntent intent);
436. void removeUpdates(in ILocationListener listener);
437. void removeUpdatesPI(in PendingIntent intent);
438.
439. boolean addGpsStatusListener(IGpsStatusListener listener);
440. void removeGpsStatusListener(IGpsStatusListener listener);
441.
442. // for reporting callback completion
443. void locationCallbackFinished(ILocationListener listener);
444.
445. boolean sendExtraCommand(String provider, String command, inout Bundle extras);
446.
447. void addProximityAlert(double latitude, double longitude, float distance,
448. long expiration, in PendingIntent intent);
449. void removeProximityAlert(in PendingIntent intent);
450.
451. Bundle getProviderInfo(String provider);
452. boolean isProviderEnabled(String provider);
453.
454. Location getLastKnownLocation(String provider);
455.
456. // Used by location providers to tell the location manager when it has a new location.
457. // Passive is true if the location is coming from the passive provider, in which case
458. // it need not be shared with other providers.
459. void reportLocation(in Location location, boolean passive);
460.
461. boolean geocoderIsPresent();
462. String getFromLocation(double latitude, double longitude, int maxResults,
463. in GeocoderParams params, out List addrs);
464. String getFromLocationName(String locationName,
465. double lowerLeftLatitude, double lowerLeftLongitude,
466. double upperRightLatitude, double upperRightLongitude, int maxResults,
467. in GeocoderParams params, out List addrs);
468.
469. void addTestProvider(String name, boolean requiresNetwork, boolean requiresSatellite,
470. boolean requiresCell, boolean hasMonetaryCost, boolean supportsAltitude,
471. boolean supportsSpeed, boolean supportsBearing, int powerRequirement, int accuracy);
472. void removeTestProvider(String provider);
473. void setTestProviderLocation(String provider, in Location loc);
474. void clearTestProviderLocation(String provider);
475. void setTestProviderEnabled(String provider, boolean enabled);
476. void clearTestProviderEnabled(String provider);
477. void setTestProviderStatus(String provider, int status, in Bundle extras, long updateTime);
478. void clearTestProviderStatus(String provider);
479.
480. // for NI support
481. boolean sendNiResponse(int notifId, int userResponse);
482. }
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：
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483. ILocationManager mLocationManager;
484. IBinder b = ServiceManager.getService(Context.LOCATION_SERVICE);
485. 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
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486. void systemReady() {
487. // we defer starting up the service until the system is ready
488. Thread thread = new Thread(null, this, "LocationManagerService");
489. thread.start();
490. }
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：
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491. public void run()
492. {
493. Process.setThreadPriority(Process.THREAD_PRIORITY_BACKGROUND);
494. Looper.prepare();
495. mLocationHandler = new LocationWorkerHandler();
496. initialize();
497. Looper.loop();
498. }
此处调用了initialize()进行初始化，initialize()函数定义如下：
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499. private void initialize() {
500. //...省略其他代码
501. loadProviders();
502.
503. //...省略其他代码
504.
505. }
此处调用了loadProviders()函数，loadProviders()函数调用了_loadProvidersLocked()，其代码如下：
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506. private void _loadProvidersLocked() {
507. // Attempt to load "real" providers first
508. if (GpsLocationProvider.isSupported()) {
509. // Create a gps location provider
510. GpsLocationProvider gpsProvider = new GpsLocationProvider(mContext, this);
511. mGpsStatusProvider = gpsProvider.getGpsStatusProvider();
512. mNetInitiatedListener = gpsProvider.getNetInitiatedListener();
513. addProvider(gpsProvider);
514. mGpsLocationProvider = gpsProvider;
515. }
516.
517. // create a passive location provider, which is always enabled
518. PassiveProvider passiveProvider = new PassiveProvider(this);
519. addProvider(passiveProvider);
520. mEnabledProviders.add(passiveProvider.getName());
521.
522. // initialize external network location and geocoder services
523. if (mNetworkLocationProviderPackageName != null) {
524. mNetworkLocationProvider =
525. new LocationProviderProxy(mContext, LocationManager.NETWORK_PROVIDER,
526. mNetworkLocationProviderPackageName, mLocationHandler);
527. addProvider(mNetworkLocationProvider);
528. }
529.
530. if (mGeocodeProviderPackageName != null) {
531. mGeocodeProvider = new GeocoderProxy(mContext, mGeocodeProviderPackageName);
532. }
533.
534. updateProvidersLocked();
535. }
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：
[java] view plaincopy
536. // 获得当前的位置提供者
537. 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：
[plain] view plaincopy
538. public GpsLocationProvider(Context context, ILocationManager locationManager) {
539.
540. //...省略部分代码
541. IntentFilter intentFilter = new IntentFilter();
542. intentFilter.addAction(Intents.DATA_SMS_RECEIVED_ACTION);
543. intentFilter.addDataScheme("sms");
544. intentFilter.addDataAuthority("localhost","7275");
545. context.registerReceiver(mBroadcastReciever, intentFilter);
546.
547. intentFilter = new IntentFilter();
548. intentFilter.addAction(Intents.WAP_PUSH_RECEIVED_ACTION);
549. try {
550. intentFilter.addDataType("application/vnd.omaloc-supl-init");
551. } catch (IntentFilter.MalformedMimeTypeException e) {
552. Log.w(TAG, "Malformed SUPL init mime type");
553. }
554. context.registerReceiver(mBroadcastReciever, intentFilter);
555.
556.
557. //...省略部分代码
558. // wait until we are fully initialized before returning
559. mThread = new GpsLocationProviderThread();
560. mThread.start();
561. while (true) {
562. try {
563. mInitializedLatch.await();
564. break;
565. } catch (InterruptedException e) {
566. Thread.currentThread().interrupt();
567. }
568. }
569. }
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：
[java] view plaincopy
570. private final BroadcastReceiver mBroadcastReciever = new BroadcastReceiver() {
571. @Override public void onReceive(Context context, Intent intent) {
572. String action = intent.getAction();
573.
574. if (action.equals(ALARM_WAKEUP)) {
575. if (DEBUG) Log.d(TAG, "ALARM_WAKEUP");
576. startNavigating(false);
577. } else if (action.equals(ALARM_TIMEOUT)) {
578. if (DEBUG) Log.d(TAG, "ALARM_TIMEOUT");
579. hibernate();
580. } else if (action.equals(Intents.DATA_SMS_RECEIVED_ACTION)) {
581. checkSmsSuplInit(intent);
582. } else if (action.equals(Intents.WAP_PUSH_RECEIVED_ACTION)) {
583. checkWapSuplInit(intent);
584. }
585. }
586. };
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：
[java] view plaincopy
587. private void startNavigating(boolean singleShot) {
588.
589. //...省略部分代码
590.
591. if (!native_set_position_mode(mPositionMode, GPS_POSITION_RECURRENCE_PERIODIC,
592. interval, 0, 0)) {
593. mStarted = false;
594. Log.e(TAG, "set_position_mode failed in startNavigating()");
595. return;
596. }
597. if (!native_start()) {
598. mStarted = false;
599. Log.e(TAG, "native_start failed in startNavigating()");
600. return;
601. }
602. //...省略部分代码
603. }
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：
[java] view plaincopy
604. private Location _getLastKnownLocationLocked(String provider) {
605. checkPermissionsSafe(provider);
606.
607. LocationProviderInterface p = mProvidersByName.get(provider);
608. if (p == null) {
609. return null;
610. }
611.
612. if (!isAllowedBySettingsLocked(provider)) {
613. return null;
614. }
615.
616. return mLastKnownLocation.get(provider);
617. }
这里mLastKnownLocation类型为HashMap，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：
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618. public void run()
619. {
620. Process.setThreadPriority(Process.THREAD_PRIORITY_BACKGROUND);
621. Looper.prepare();
622. mLocationHandler = new LocationWorkerHandler();
623. initialize();
624. Looper.loop();
625. }
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：
[java] view plaincopy
626. private class LocationWorkerHandler extends Handler {
627.
628. @Override
629. public void handleMessage(Message msg) {
630. try {
631. if (msg.what == MESSAGE_LOCATION_CHANGED) {
632. // log("LocationWorkerHandler: MESSAGE_LOCATION_CHANGED!");
633.
634. synchronized (mLock) {
635. Location location = (Location) msg.obj;
636. String provider = location.getProvider();
637. boolean passive = (msg.arg1 == 1);
638.
639. if (!passive) {
640. // notify other providers of the new location
641. for (int i = mProviders.size() - 1; i >= 0; i--) {
642. LocationProviderInterface p = mProviders.get(i);
643. if (!provider.equals(p.getName())) {
644. p.updateLocation(location);
645. }
646. }
647. }
648.
649. if (isAllowedBySettingsLocked(provider)) {
650. handleLocationChangedLocked(location, passive);
651. }
652. }
653. } else if (msg.what == MESSAGE_PACKAGE_UPDATED) {
654. //...省略部分代码
655. }
656. }
657. } catch (Exception e) {
658. // Log, don't crash!
659. Slog.e(TAG, "Exception in LocationWorkerHandler.handleMessage:", e);
660. }
661. }
662. }
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：
[java] view plaincopy
663. private void handleLocationChangedLocked(Location location, boolean passive) {
664. //...省略部分代码
665.
666. // Update last known location for provider
667. Location lastLocation = mLastKnownLocation.get(provider);
668. if (lastLocation == null) {
669. mLastKnownLocation.put(provider, new Location(location));
670. } else {
671. lastLocation.set(location);
672. }
673. //...省略部分代码
674. }
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：
[java] view plaincopy
675. public void reportLocation(Location location, boolean passive) {
676. if (mContext.checkCallingOrSelfPermission(INSTALL_LOCATION_PROVIDER)
677. != PackageManager.PERMISSION_GRANTED) {
678. throw new SecurityException("Requires INSTALL_LOCATION_PROVIDER permission");
679. }
680.
681. mLocationHandler.removeMessages(MESSAGE_LOCATION_CHANGED, location);
682. Message m = Message.obtain(mLocationHandler, MESSAGE_LOCATION_CHANGED, location);
683. m.arg1 = (passive ? 1 : 0);
684. mLocationHandler.sendMessageAtFrontOfQueue(m);
685. }
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：
[java] view plaincopy
686. try {
687. mLocationManager.reportLocation(mLocation, false);
688. } catch (RemoteException e) {
689. Log.e(TAG, "RemoteException calling reportLocation");
690. }
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
[cpp] view plaincopy
691. /** Callback with location information. 向上层传递GPS位置信息
692. * Can only be called from a thread created by create_thread_cb.
693. */
694. 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：
[cpp] view plaincopy
695. static const GpsInterface* GetGpsInterface(JNIEnv* env, jobject obj) {
696. // this must be set before calling into the HAL library
697. if (!mCallbacksObj)
698. mCallbacksObj = env->NewGlobalRef(obj);
699.
700. if (!sGpsInterface) {
701. sGpsInterface = get_gps_interface();
702. if (!sGpsInterface || sGpsInterface->init(&sGpsCallbacks) != 0) {
703. sGpsInterface = NULL;
704. return NULL;
705. }
706. }
707. return sGpsInterface;
708. }
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：
[cpp] view plaincopy
709. GpsCallbacks sGpsCallbacks = {
710. sizeof(GpsCallbacks),
711. location_callback,
712. status_callback,
713. sv_status_callback,
714. nmea_callback,
715. set_capabilities_callback,
716. acquire_wakelock_callback,
717. release_wakelock_callback,
718. create_thread_callback,
719. };
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）：
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720. typedef struct {
721. size_t size;
722. gps_location_callback location_cb;
723. gps_status_callback status_cb;
724. gps_sv_status_callback sv_status_cb;
725. gps_nmea_callback nmea_cb;
726. gps_set_capabilities set_capabilities_cb;
727. gps_acquire_wakelock acquire_wakelock_cb;
728. gps_release_wakelock release_wakelock_cb;
729. gps_create_thread create_thread_cb;
730. } 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：
[cpp] view plaincopy
731. static void location_callback(GpsLocation* location)
732. {
733. JNIEnv* env = AndroidRuntime::getJNIEnv();
734. env->CallVoidMethod(mCallbacksObj, method_reportLocation, location->flags,
735. (jdouble)location->latitude, (jdouble)location->longitude,
736. (jdouble)location->altitude,
737. (jfloat)location->speed, (jfloat)location->bearing,
738. (jfloat)location->accuracy, (jlong)location->timestamp);
739. checkAndClearExceptionFromCallback(env, __FUNCTION__);
740. }
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：
[cpp] view plaincopy
741. static void android_location_GpsLocationProvider_class_init_native(JNIEnv* env, jclass clazz) {
742. method_reportLocation = env->GetMethodID(clazz, "reportLocation", "(IDDDFFFJ)V");
743. //...省略部分代码
744. }
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：
[cpp] view plaincopy
745. tatic JNINativeMethod sMethods[] = {
746. /* name, signature, funcPtr */
747. {"class_init_native", "()V", (void *)android_location_GpsLocationProvider_class_init_native},
748. //...省略部分代码
749. }
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：
[java] view plaincopy
750. 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。
