Android系统Gps分析

6610阅读　0评论2013-06-09　conceptcon
分类：嵌入式

http://blog.csdn.net/xnwyd/article/details/7198728
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

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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  1. /** Flags to indicate which values are valid in a GpsLocation. */  
  2. typedef uint16_t GpsLocationFlags;  
  3. // IMPORTANT: Note that the following values must match   
  4. // constants in GpsLocationProvider.java.   
  5. /** GpsLocation has valid latitude and longitude. */  
  6. #define GPS_LOCATION_HAS_LAT_LONG   0x0001   
  7. /** GpsLocation has valid altitude. */  
  8. #define GPS_LOCATION_HAS_ALTITUDE   0x0002   
  9. /** GpsLocation has valid speed. */  
  10. #define GPS_LOCATION_HAS_SPEED      0x0004   
  11. /** GpsLocation has valid bearing. */  
  12. #define GPS_LOCATION_HAS_BEARING    0x0008   
  13. /** GpsLocation has valid accuracy. */  
  14. #define GPS_LOCATION_HAS_ACCURACY   0x0010   
  15.   
  16. /** Represents a location. */  
  17. typedef struct {  
  18.     /** set to sizeof(GpsLocation) */  
  19.     size_t          size;  
  20.     /** Contains GpsLocationFlags bits. */  
  21.     uint16_t        flags;  
  22.     /** Represents latitude in degrees. */  
  23.     double          latitude;  
  24.     /** Represents longitude in degrees. */  
  25.     double          longitude;  
  26.     /** Represents altitude in meters above the WGS 84 reference 
  27.      * ellipsoid. */  
  28.     double          altitude;  
  29.     /** Represents speed in meters per second. */  
  30.     float           speed;  
  31.     /** Represents heading in degrees. */  
  32.     float           bearing;  
  33.     /** Represents expected accuracy in meters. */  
  34.     float           accuracy;  
  35.     /** Timestamp for the location fix. */  
  36.     GpsUtcTime      timestamp;  
  37. } GpsLocation;  
/** 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;

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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  1. /** GPS status event values. */  
  2. typedef uint16_t GpsStatusValue;  
  3. // IMPORTANT: Note that the following values must match   
  4. // constants in GpsLocationProvider.java.   
  5. /** GPS status unknown. */  
  6. #define GPS_STATUS_NONE             0   
  7. /** GPS has begun navigating. */  
  8. #define GPS_STATUS_SESSION_BEGIN    1   
  9. /** GPS has stopped navigating. */  
  10. #define GPS_STATUS_SESSION_END      2   
  11. /** GPS has powered on but is not navigating. */  
  12. #define GPS_STATUS_ENGINE_ON        3   
  13. /** GPS is powered off. */AgpsCallbacks  
  14.   
  15. AgpsInterface  
  16. #define GPS_STATUS_ENGINE_OFF       4   
  17.   
  18. /** Represents the status. */  
  19. typedef struct {  
  20.     /** set to sizeof(GpsStatus) */  
  21.     size_t          size;  
  22.     GpsStatusValue status;  
  23. } GpsStatus;  
/** 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;


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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  1. /** Represents SV information. */  
  2. typedef struct {  
  3.     /** set to sizeof(GpsSvInfo) */  
  4.     size_t          size;  
  5.     /** Pseudo-random number for the SV. */  
  6.     int     prn;  
  7.     /** Signal to noise ratio. */  
  8.     float   snr;  
  9.     /** Elevation of SV in degrees. */  
  10.     float   elevation;  
  11.     /** Azimuth of SV in degrees. */  
  12.     float   azimuth;  
  13. } GpsSvInfo;  
/** 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;

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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  1. /** Represents SV status. */  
  2. typedef struct {  
  3.     /** set to sizeof(GpsSvStatus) */  
  4.     size_t          size;  
  5.   
  6.     /** Number of SVs currently visible. */  
  7.     int         num_svs;  
  8.   
  9.     /** Contains an array of SV information. */  
  10.     GpsSvInfo   sv_list[GPS_MAX_SVS];  
  11.   
  12.     /** Represents a bit mask indicating which SVs 
  13.      * have ephemeris data. 
  14.      */  
  15.     uint32_t    ephemeris_mask;  
  16.   
  17.     /** Represents a bit mask indicating which SVs 
  18.      * have almanac data. 
  19.      */  
  20.     uint32_t    almanac_mask;  
  21.   
  22.     /** 
  23.      * Represents a bit mask indicating which SVs 
  24.      * were used for computing the most recent position fix. 
  25.      */  
  26.     uint32_t    used_in_fix_mask;  
  27. } GpsSvStatus;  
/** 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;

回调函数定义

[cpp] view plaincopyprint?
  1. /** Callback with location information. 向上层传递GPS位置信息 
  2.  *  Can only be called from a thread created by create_thread_cb. 
  3.  */  
  4. typedef void (* gps_location_callback)(GpsLocation* location);  
  5.   
  6. /** Callback with status information. 向上层传递GPS状态信息 
  7.  *  Can only be called from a thread created by create_thread_cb. 
  8.  */  
  9. typedef void (* gps_status_callback)(GpsStatus* status);  
  10.   
  11. /** Callback with SV status information. 向上层传递GPS卫星信息 
  12.  *  Can only be called from a thread created by create_thread_cb. 
  13.  */  
  14. typedef void (* gps_sv_status_callback)(GpsSvStatus* sv_info);  
  15.   
  16. /** Callback for reporting NMEA sentences. 向上层传递MEMA数据 
  17.  *  Can only be called from a thread created by create_thread_cb. 
  18.  */  
  19. typedef void (* gps_nmea_callback)(GpsUtcTime timestamp, const char* nmea, int length);  
  20.   
  21. /** Callback to inform framework of the GPS engine's capabilities.告知GPS模块可以实现的功能 
  22.  *  Capability parameter is a bit field of GPS_CAPABILITY_* flags. 
  23.  */  
  24. typedef void (* gps_set_capabilities)(uint32_t capabilities);  
  25.   
  26. /** Callback utility for acquiring the GPS wakelock.上锁，防止处理GPS事件时中止。 
  27.  *  This can be used to prevent the CPU from suspending while handling GPS events. 
  28.  */  
  29. typedef void (* gps_acquire_wakelock)();  
  30.   
  31. /** Callback utility for releasing the GPS wakelock. */释放锁  
  32. typedef void (* gps_release_wakelock)();  
  33.   
  34. /** Callback for creating a thread that can call into the Java framework code.等待上层请求 
  35.  *  This must be used to create any threads that report events up to the framework. 
  36.  */  
  37. typedef pthread_t (* gps_create_thread)(const char* name, void (*start)(void *), void* arg);  
  38.   
  39. /** GPS callback structure. */  
  40. typedef struct {  
  41.     /** set to sizeof(GpsCallbacks) */  
  42.     size_t      size;  
  43.     gps_location_callback location_cb;  
  44.     gps_status_callback status_cb;  
  45.     gps_sv_status_callback sv_status_cb;  
  46.     gps_nmea_callback nmea_cb;  
  47.     gps_set_capabilities set_capabilities_cb;  
  48.     gps_acquire_wakelock acquire_wakelock_cb;  
  49.     gps_release_wakelock release_wakelock_cb;  
  50.     gps_create_thread create_thread_cb;  
  51. } GpsCallbacks;  
/** 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;

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。


[cpp] view plaincopyprint?
  1. /** Represents the standard GPS interface. */  
  2. typedef struct {  
  3.     /** set to sizeof(GpsInterface) */  
  4.     size_t          size;  
  5.     /** 
  6.      * Opens the interface and provides the callback routines 
  7.      * to the implemenation of this interface. 
  8.      */  
  9.     int   (*init)( GpsCallbacks* callbacks );  
  10.   
  11.     /** Starts navigating. 启动定位*/  
  12.     int   (*start)( void );  
  13.   
  14.     /** Stops navigating. 取消定位*/  
  15.     int   (*stop)( void );  
  16.   
  17.     /** Closes the interface. 关闭GPS接口*/  
  18.     void  (*cleanup)( void );  
  19.   
  20.     /** Injects the current time.填入时间 */  
  21.     int   (*inject_time)(GpsUtcTime time, int64_t timeReference,  
  22.                          int uncertainty);  
  23.   
  24.     /** Injects current location from another location provider填入位置 
  25.      *  (typically cell ID). 
  26.      *  latitude and longitude are measured in degrees 
  27.      *  expected accuracy is measured in meters 
  28.      */  
  29.     int  (*inject_location)(double latitude, double longitude, float accuracy);  
  30.   
  31.     /** 
  32.      * 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 
  33.      * information defined in the flags. GPS_DELETE_ALL is passed for 
  34.      * a cold start. 
  35.      */  
  36.     void  (*delete_aiding_data)(GpsAidingData flags);  
  37.   
  38.     /**设置定位模式和GPS工作模式等 
  39.      * min_interval represents the time between fixes in milliseconds. 
  40.      * preferred_accuracy represents the requested fix accuracy in meters. 
  41.      * preferred_time represents the requested time to first fix in milliseconds. 
  42.      */  
  43.     int   (*set_position_mode)(GpsPositionMode mode, GpsPositionRecurrence recurrence,  
  44.             uint32_t min_interval, uint32_t preferred_accuracy, uint32_t preferred_time);  
  45.   
  46.     /** Get a pointer to extension information. 自定义的接口*/  
  47.     const void* (*get_extension)(const char* name);  
  48. } GpsInterface;  
/** 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。


[cpp] view plaincopyprint?
  1. struct gps_device_t {  
  2.     struct hw_device_t common;  
  3.   
  4.     /** 
  5.      * Set the provided lights to the provided values. 
  6.      * 
  7.      * Returns: 0 on succes, error code on failure. 
  8.      */  
  9.     const GpsInterface* (*get_gps_interface)(struct gps_device_t* dev);  
  10. };  
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：

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  1. const struct hw_module_t HAL_MODULE_INFO_SYM = {  
  2.     .tag = HARDWARE_MODULE_TAG,  
  3.     .version_major = 1,  
  4.     .version_minor = 0,  
  5.     .id = GPS_HARDWARE_MODULE_ID,  
  6.     .name = "loc_api GPS Module",  
  7.     .author = "Qualcomm USA, Inc.",  
  8.     .methods = &gps_module_methods,  
  9. };  
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


[cpp] view plaincopyprint?
  1. static struct hw_module_methods_t gps_module_methods = {  
  2.     .open = open_gps  
  3. };  
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：


[cpp] view plaincopyprint?
  1. static int open_gps(const struct hw_module_t* module, char const* name,  
  2.         struct hw_device_t** device)  
  3. {  
  4.     struct gps_device_t *dev = malloc(sizeof(struct gps_device_t));  
  5.     memset(dev, 0, sizeof(*dev));  
  6.   
  7.     dev->common.tag = HARDWARE_DEVICE_TAG;  
  8.     dev->common.version = 0;  
  9.     dev->common.module = (struct hw_module_t*)module;  
  10.     dev->get_gps_interface = gps__get_gps_interface;  
  11.   
  12.     *device = (struct hw_device_t*)dev;  
  13.     return 0;  
  14. }  
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：

[cpp] view plaincopyprint?
  1. const GpsInterface* gps__get_gps_interface(struct gps_device_t* dev)  
  2. {  
  3.     return get_gps_interface();  
  4. }  
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：

[cpp] view plaincopyprint?
  1. // Defines the GpsInterface in gps.h   
  2. static const GpsInterface sLocEngInterface =  
  3. {  
  4.     sizeof(GpsInterface),  
  5.     loc_eng_init,  
  6.     loc_eng_start,  
  7.     loc_eng_stop,  
  8.     loc_eng_cleanup,  
  9.     loc_eng_inject_time,  
  10.     loc_eng_inject_location,  
  11.     loc_eng_delete_aiding_data,  
  12.     loc_eng_set_position_mode,  
  13.     loc_eng_get_extension,  
  14. };  
// 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：

[plain] view plaincopyprint?
  1. int register_android_server_location_GpsLocationProvider(JNIEnv* env)  
  2. {  
  3.     return jniRegisterNativeMethods(env, "com/android/server/location/GpsLocationProvider", sMethods, NELEM(sMethods));  
  4. }  
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：

[cpp] view plaincopyprint?
  1. extern "C" jint JNI_OnLoad(JavaVM* vm, void* reserved)  
  2. {  
  3.     JNIEnv* env = NULL;  
  4.     jint result = -1;  
  5.   
  6.     if (vm->GetEnv((void**) &env, JNI_VERSION_1_4) != JNI_OK) {  
  7.         LOGE("GetEnv failed!");  
  8.         return result;  
  9.     }  
  10.     LOG_ASSERT(env, "Could not retrieve the env!");  
  11.   
  12.     //...省略其他注册代码   
  13.     register_android_server_location_GpsLocationProvider(env);  
  14.   
  15.     return JNI_VERSION_1_4;  
  16. }  
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：

[cpp] view plaincopyprint?
  1. static JNINativeMethod sMethods[] = {  
  2.      /* name, signature, funcPtr */  
  3.     {"class_init_native", "()V", (void *)android_location_GpsLocationProvider_class_init_native},  
  4.     {"native_is_supported", "()Z", (void*)android_location_GpsLocationProvider_is_supported},  
  5.     {"native_init", "()Z", (void*)android_location_GpsLocationProvider_init},  
  6.     {"native_cleanup", "()V", (void*)android_location_GpsLocationProvider_cleanup},  
  7.     {"native_set_position_mode", "(IIIII)Z", (void*)android_location_GpsLocationProvider_set_position_mode},  
  8.     {"native_start", "()Z", (void*)android_location_GpsLocationProvider_start},  
  9.     {"native_stop", "()Z", (void*)android_location_GpsLocationProvider_stop},  
  10.     {"native_delete_aiding_data", "(I)V", (void*)android_location_GpsLocationProvider_delete_aiding_data},  
  11.     {"native_read_sv_status", "([I[F[F[F[I)I", (void*)android_location_GpsLocationProvider_read_sv_status},  
  12.     {"native_read_nmea", "([BI)I", (void*)android_location_GpsLocationProvider_read_nmea},  
  13.     {"native_inject_time", "(JJI)V", (void*)android_location_GpsLocationProvider_inject_time},  
  14.     {"native_inject_location", "(DDF)V", (void*)android_location_GpsLocationProvider_inject_location},  
  15.     {"native_supports_xtra", "()Z", (void*)android_location_GpsLocationProvider_supports_xtra},  
  16.     {"native_inject_xtra_data", "([BI)V", (void*)android_location_GpsLocationProvider_inject_xtra_data},  
  17.     {"native_agps_data_conn_open", "(Ljava/lang/String;)V", (void*)android_location_GpsLocationProvider_agps_data_conn_open},  
  18.     {"native_agps_data_conn_closed", "()V", (void*)android_location_GpsLocationProvider_agps_data_conn_closed},  
  19.     {"native_agps_data_conn_failed", "()V", (void*)android_location_GpsLocationProvider_agps_data_conn_failed},  
  20.     {"native_agps_set_id","(ILjava/lang/String;)V",(void*)android_location_GpsLocationProvider_agps_set_id},  
  21.     {"native_agps_set_ref_location_cellid","(IIIII)V",(void*)android_location_GpsLocationProvider_agps_set_reference_location_cellid},  
  22.     {"native_set_agps_server", "(ILjava/lang/String;I)V", (void*)android_location_GpsLocationProvider_set_agps_server},  
  23.     {"native_send_ni_response", "(II)V", (void*)android_location_GpsLocationProvider_send_ni_response},  
  24.     {"native_agps_ni_message", "([BI)V", (void *)android_location_GpsLocationProvider_agps_send_ni_message},  
  25.     {"native_get_internal_state", "()Ljava/lang/String;", (void*)android_location_GpsLocationProvider_get_internal_state},  
  26.     {"native_update_network_state", "(ZIZLjava/lang/String;)V", (void*)android_location_GpsLocationProvider_update_network_state },  
  27. };  
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：

[cpp] view plaincopyprint?
  1. static jboolean android_location_GpsLocationProvider_start(JNIEnv* env, jobject obj)  
  2. {  
  3.     const GpsInterface* interface = GetGpsInterface(env, obj);  
  4.     if (interface)  
  5.         return (interface->start() == 0);  
  6.     else  
  7.         return false;  
  8. }  
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：

[cpp] view plaincopyprint?
  1. static const GpsInterface* GetGpsInterface(JNIEnv* env, jobject obj) {  
  2.     // this must be set before calling into the HAL library   
  3.     if (!mCallbacksObj)  
  4.         mCallbacksObj = env->NewGlobalRef(obj);  
  5.   
  6.     if (!sGpsInterface) {  
  7.         sGpsInterface = get_gps_interface();  
  8.         if (!sGpsInterface || sGpsInterface->init(&sGpsCallbacks) != 0) {  
  9.             sGpsInterface = NULL;  
  10.             return NULL;  
  11.         }  
  12.     }  
  13.     return sGpsInterface;  
  14. }  
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：

[cpp] view plaincopyprint?
  1. static const GpsInterface* get_gps_interface() {  
  2.     int err;  
  3.     hw_module_t* module;  
  4.     const GpsInterface* interface = NULL;  
  5.   
  6.     err = hw_get_module(GPS_HARDWARE_MODULE_ID, (hw_module_t const**)&module);  
  7.     if (err == 0) {  
  8.         hw_device_t* device;  
  9.         err = module->methods->open(module, GPS_HARDWARE_MODULE_ID, &device);  
  10.         if (err == 0) {  
  11.             gps_device_t* gps_device = (gps_device_t *)device;  
  12.             interface = gps_device->get_gps_interface(gps_device);  
  13.         }  
  14.     }  
  15.   
  16.     return interface;  
  17. }  
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



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



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。

[plain] view plaincopyprint?
  1.      
  2.      
  3.     
  4.     
             

  • 接着获取位置信息：

[java] view plaincopyprint?
  1.         //获取位置服务   
  2.  LocationManager locationManager = (LocationManager) getSystemService(Context.LOCATION_SERVICE);    
  3.        Criteria criteria = new Criteria();    
  4.        // 获得最好的定位效果     
  5.        criteria.setAccuracy(Criteria.ACCURACY_FINE);  //设置为最大精度   
  6.        criteria.setAltitudeRequired(false);  //不获取海拔信息   
  7.        criteria.setBearingRequired(false);  //不获取方位信息   
  8.        criteria.setCostAllowed(false);  //是否允许付费   
  9.        criteria.setPowerRequirement(Criteria.POWER_LOW);  // 使用省电模式   
  10.        // 获得当前的位置提供者     
  11.        String provider = locationManager.getBestProvider(criteria, true);    
  12.        // 获得当前的位置     
  13.        Location location = locationManager.getLastKnownLocation(provider);    
  14. Geocoder gc = new Geocoder(this);     
  15.        List
     addresses = null;    
  16.        try {  
  17.     //根据经纬度获得地址信息     
  18.            addresses = gc.getFromLocation(location.getLatitude(), location.getLongitude(), 1);    
  19.        } catch (IOException e) {    
  20.            e.printStackTrace();    
  21.        } if (addresses.size() > 0) {  
  22. //获取address类的成员信息   
  23. Sring msg = “”;     
  24.        msg += "AddressLine：" + addresses.get(0).getAddressLine(0)+ "\n";     
  25.        msg += "CountryName：" + addresses.get(0).getCountryName()+ "\n";     
  26.        msg += "Locality：" + addresses.get(0).getLocality() + "\n";     
  27.        msg += "FeatureName：" + addresses.get(0).getFeatureName();     
  28.        }     
//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
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

[java] view plaincopyprint?
  1.       //匿名类，继承自LocationListener接口   
  2. private final LocationListener locationListener = new LocationListener() {  
  3.            public void onLocationChanged(Location location) {  
  4.            updateWithNewLocation(location);//更新位置信息   
  5.            }  
  6.            public void onProviderDisabled(String provider){  
  7.            updateWithNewLocation(null);//更新位置信息   
  8.            }  
  9.            public void onProviderEnabled(String provider){ }  
  10.            public void onStatusChanged(String provider, int status,Bundle extras){ }  
  11.    };  
  12. //更新位置信息   
  13. private void updateWithNewLocation(Location location) {  
  14.          
  15.   
  16.            if (location != null) {  
  17.     //获取经纬度   
  18.            double lat = location.getLatitude();  
  19.            double lng = location.getLongitude();  
  20.    }  
  21. //添加侦听   
  22.  locationManager.requestLocationUpdates(provider, 2000, 10,locationListener);  
//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：

[java] view plaincopyprint?
  1. public LocationManager(ILocationManager service) {  
  2.         mService = service;  
  3.     }  
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：

[java] view plaincopyprint?
  1. LocationManager locationManager = (LocationManager) getSystemService(Context.LOCATION_SERVICE);    
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

[java] view plaincopyprint?
  1. …//省略其他代码   
  2. LocationManagerService location = null;  
  3. …//省略其他代码   
  4. try {  
  5.                 Slog.i(TAG, "Location Manager");  
  6.                 location = new LocationManagerService(context);  
  7.                 ServiceManager.addService(Context.LOCATION_SERVICE, location);  
  8.             } catch (Throwable e) {  
  9.                 Slog.e(TAG, "Failure starting Location Manager", e);  
  10.             }  
…//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：

[java] view plaincopyprint?
  1. /** 
  2.  * System private API for talking with the location service. 
  3.  * 
  4.  * {@hide} 
  5.  */  
  6. interface ILocationManager  
  7. {  
  8.     List getAllProviders();  
  9.     List getProviders(in Criteria criteria, boolean enabledOnly);  
  10.     String getBestProvider(in Criteria criteria, boolean enabledOnly);  
  11.     boolean providerMeetsCriteria(String provider, in Criteria criteria);  
  12.   
  13.     void requestLocationUpdates(String provider, in Criteria criteria, long minTime, float minDistance,  
  14.         boolean singleShot, in ILocationListener listener);  
  15.     void requestLocationUpdatesPI(String provider, in Criteria criteria, long minTime, float minDistance,  
  16.         boolean singleShot, in PendingIntent intent);  
  17.     void removeUpdates(in ILocationListener listener);  
  18.     void removeUpdatesPI(in PendingIntent intent);  
  19.   
  20.     boolean addGpsStatusListener(IGpsStatusListener listener);  
  21.     void removeGpsStatusListener(IGpsStatusListener listener);  
  22.   
  23.     // for reporting callback completion   
  24.     void locationCallbackFinished(ILocationListener listener);  
  25.   
  26.     boolean sendExtraCommand(String provider, String command, inout Bundle extras);  
  27.   
  28.     void addProximityAlert(double latitude, double longitude, float distance,  
  29.         long expiration, in PendingIntent intent);  
  30.     void removeProximityAlert(in PendingIntent intent);  
  31.   
  32.     Bundle getProviderInfo(String provider);  
  33.     boolean isProviderEnabled(String provider);  
  34.   
  35.     Location getLastKnownLocation(String provider);  
  36.   
  37.     // Used by location providers to tell the location manager when it has a new location.   
  38.     // Passive is true if the location is coming from the passive provider, in which case   
  39.     // it need not be shared with other providers.   
  40.     void reportLocation(in Location location, boolean passive);  
  41.   
  42.     boolean geocoderIsPresent();  
  43.     String getFromLocation(double latitude, double longitude, int maxResults,  
  44.         in GeocoderParams params, out List
     addrs);  
  45.     String getFromLocationName(String locationName,  
  46.         double lowerLeftLatitude, double lowerLeftLongitude,  
  47.         double upperRightLatitude, double upperRightLongitude, int maxResults,  
  48.         in GeocoderParams params, out List
     addrs);  
  49.   
  50.     void addTestProvider(String name, boolean requiresNetwork, boolean requiresSatellite,  
  51.         boolean requiresCell, boolean hasMonetaryCost, boolean supportsAltitude,  
  52.         boolean supportsSpeed, boolean supportsBearing, int powerRequirement, int accuracy);  
  53.     void removeTestProvider(String provider);  
  54.     void setTestProviderLocation(String provider, in Location loc);  
  55.     void clearTestProviderLocation(String provider);  
  56.     void setTestProviderEnabled(String provider, boolean enabled);  
  57.     void clearTestProviderEnabled(String provider);  
  58.     void setTestProviderStatus(String provider, int status, in Bundle extras, long updateTime);  
  59.     void clearTestProviderStatus(String provider);  
  60.   
  61.     // for NI support   
  62.     boolean sendNiResponse(int notifId, int userResponse);  
  63. }  
/** * System private API for talking with the location service. * * {@hide} */ interface ILocationManager { List getAllProviders(); List 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
addrs); String getFromLocationName(String locationName, double lowerLeftLatitude, double lowerLeftLongitude, double upperRightLatitude, double upperRightLongitude, int maxResults, in GeocoderParams params, out List
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：

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  1. ILocationManager mLocationManager;  
  2. IBinder b = ServiceManager.getService(Context.LOCATION_SERVICE);  
  3. mLocationManager = IlocationManager.Stub.asInterface(b);  
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

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  1. void systemReady() {  
  2.         // we defer starting up the service until the system is ready    
  3.         Thread thread = new Thread(null, this, "LocationManagerService");  
  4.         thread.start();  
  5.     }  
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：

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  1. public void run()  
  2.     {  
  3.         Process.setThreadPriority(Process.THREAD_PRIORITY_BACKGROUND);  
  4.         Looper.prepare();  
  5.         mLocationHandler = new LocationWorkerHandler();  
  6.         initialize();  
  7.         Looper.loop();  
  8.     }  
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：

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  1. private void initialize() {  
  2.        //...省略其他代码   
  3.         loadProviders();  
  4.       
  5.     //...省略其他代码   
  6.           
  7.     }  
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：

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  1. private void _loadProvidersLocked() {  
  2.         // Attempt to load "real" providers first   
  3.         if (GpsLocationProvider.isSupported()) {  
  4.             // Create a gps location provider   
  5.             GpsLocationProvider gpsProvider = new GpsLocationProvider(mContext, this);  
  6.             mGpsStatusProvider = gpsProvider.getGpsStatusProvider();  
  7.             mNetInitiatedListener = gpsProvider.getNetInitiatedListener();  
  8.             addProvider(gpsProvider);  
  9.             mGpsLocationProvider = gpsProvider;  
  10.         }  
  11.   
  12.         // create a passive location provider, which is always enabled   
  13.         PassiveProvider passiveProvider = new PassiveProvider(this);  
  14.         addProvider(passiveProvider);  
  15.         mEnabledProviders.add(passiveProvider.getName());  
  16.   
  17.         // initialize external network location and geocoder services   
  18.         if (mNetworkLocationProviderPackageName != null) {  
  19.             mNetworkLocationProvider =  
  20.                 new LocationProviderProxy(mContext, LocationManager.NETWORK_PROVIDER,  
  21.                         mNetworkLocationProviderPackageName, mLocationHandler);  
  22.             addProvider(mNetworkLocationProvider);  
  23.         }  
  24.   
  25.         if (mGeocodeProviderPackageName != null) {  
  26.             mGeocodeProvider = new GeocoderProxy(mContext, mGeocodeProviderPackageName);  
  27.         }  
  28.   
  29.         updateProvidersLocked();  
  30.     }  
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：

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  1. // 获得当前的位置提供者     
  2. String provider = locationManager.getBestProvider(criteria, true);    
// 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：

[plain] view plaincopyprint?
  1. public GpsLocationProvider(Context context, ILocationManager locationManager) {  
  2.          
  3.     //...省略部分代码  
  4.         IntentFilter intentFilter = new IntentFilter();  
  5.         intentFilter.addAction(Intents.DATA_SMS_RECEIVED_ACTION);  
  6.         intentFilter.addDataScheme("sms");  
  7.         intentFilter.addDataAuthority("localhost","7275");  
  8.         context.registerReceiver(mBroadcastReciever, intentFilter);  
  9.   
  10.         intentFilter = new IntentFilter();  
  11.         intentFilter.addAction(Intents.WAP_PUSH_RECEIVED_ACTION);  
  12.         try {  
  13.             intentFilter.addDataType("application/vnd.omaloc-supl-init");  
  14.         } catch (IntentFilter.MalformedMimeTypeException e) {  
  15.             Log.w(TAG, "Malformed SUPL init mime type");  
  16.         }  
  17.         context.registerReceiver(mBroadcastReciever, intentFilter);  
  18.   
  19.           
  20.         //...省略部分代码  
  21.         // wait until we are fully initialized before returning  
  22.         mThread = new GpsLocationProviderThread();  
  23.         mThread.start();  
  24.         while (true) {  
  25.             try {  
  26.                 mInitializedLatch.await();  
  27.                 break;  
  28.             } catch (InterruptedException e) {  
  29.                 Thread.currentThread().interrupt();  
  30.             }  
  31.         }  
  32.     }  
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：

[java] view plaincopyprint?
  1. private final BroadcastReceiver mBroadcastReciever = new BroadcastReceiver() {  
  2.         @Override public void onReceive(Context context, Intent intent) {  
  3.             String action = intent.getAction();  
  4.   
  5.             if (action.equals(ALARM_WAKEUP)) {  
  6.                 if (DEBUG) Log.d(TAG, "ALARM_WAKEUP");  
  7.                 startNavigating(false);  
  8.             } else if (action.equals(ALARM_TIMEOUT)) {  
  9.                 if (DEBUG) Log.d(TAG, "ALARM_TIMEOUT");  
  10.                 hibernate();  
  11.             } else if (action.equals(Intents.DATA_SMS_RECEIVED_ACTION)) {  
  12.                 checkSmsSuplInit(intent);  
  13.             } else if (action.equals(Intents.WAP_PUSH_RECEIVED_ACTION)) {  
  14.                 checkWapSuplInit(intent);  
  15.              }  
  16.         }  
  17.     };  
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：

[java] view plaincopyprint?
  1. private void startNavigating(boolean singleShot) {  
  2.           
  3.         //...省略部分代码   
  4.               
  5.             if (!native_set_position_mode(mPositionMode, GPS_POSITION_RECURRENCE_PERIODIC,  
  6.                     interval, 0, 0)) {  
  7.                 mStarted = false;  
  8.                 Log.e(TAG, "set_position_mode failed in startNavigating()");  
  9.                 return;  
  10.             }  
  11.             if (!native_start()) {  
  12.                 mStarted = false;  
  13.                 Log.e(TAG, "native_start failed in startNavigating()");  
  14.                 return;  
  15.             }  
  16.         //...省略部分代码   
  17.     }  
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：

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  1. private Location _getLastKnownLocationLocked(String provider) {  
  2.         checkPermissionsSafe(provider);  
  3.   
  4.         LocationProviderInterface p = mProvidersByName.get(provider);  
  5.         if (p == null) {  
  6.             return null;  
  7.         }  
  8.   
  9.         if (!isAllowedBySettingsLocked(provider)) {  
  10.             return null;  
  11.         }  
  12.   
  13.         return mLastKnownLocation.get(provider);  
  14.     }  
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，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：

[java] view plaincopyprint?
  1. public void run()  
  2.     {  
  3.         Process.setThreadPriority(Process.THREAD_PRIORITY_BACKGROUND);  
  4.         Looper.prepare();  
  5.         mLocationHandler = new LocationWorkerHandler();  
  6.         initialize();  
  7.         Looper.loop();  
  8.     }  
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：

[java] view plaincopyprint?
  1. private class LocationWorkerHandler extends Handler {  
  2.   
  3.         @Override  
  4.         public void handleMessage(Message msg) {  
  5.             try {  
  6.                 if (msg.what == MESSAGE_LOCATION_CHANGED) {  
  7.                     // log("LocationWorkerHandler: MESSAGE_LOCATION_CHANGED!");   
  8.   
  9.                     synchronized (mLock) {  
  10.                         Location location = (Location) msg.obj;  
  11.                         String provider = location.getProvider();  
  12.                         boolean passive = (msg.arg1 == 1);  
  13.   
  14.                         if (!passive) {  
  15.                             // notify other providers of the new location   
  16.                             for (int i = mProviders.size() - 1; i >= 0; i--) {  
  17.                                 LocationProviderInterface p = mProviders.get(i);  
  18.                                 if (!provider.equals(p.getName())) {  
  19.                                     p.updateLocation(location);  
  20.                                 }  
  21.                             }  
  22.                         }  
  23.   
  24.                         if (isAllowedBySettingsLocked(provider)) {  
  25.                             handleLocationChangedLocked(location, passive);  
  26.                         }  
  27.                     }  
  28.                 } else if (msg.what == MESSAGE_PACKAGE_UPDATED) {  
  29.                     //...省略部分代码   
  30.                     }  
  31.                 }  
  32.             } catch (Exception e) {  
  33.                 // Log, don't crash!   
  34.                 Slog.e(TAG, "Exception in LocationWorkerHandler.handleMessage:", e);  
  35.             }  
  36.         }  
  37.     }  
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：

[java] view plaincopyprint?
  1. private void handleLocationChangedLocked(Location location, boolean passive) {  
  2.        //...省略部分代码   
  3.   
  4.         // Update last known location for provider   
  5.         Location lastLocation = mLastKnownLocation.get(provider);  
  6.         if (lastLocation == null) {  
  7.             mLastKnownLocation.put(provider, new Location(location));  
  8.         } else {  
  9.             lastLocation.set(location);  
  10.         }  
  11.     //...省略部分代码   
  12. }  
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：

[java] view plaincopyprint?
  1. public void reportLocation(Location location, boolean passive) {  
  2.         if (mContext.checkCallingOrSelfPermission(INSTALL_LOCATION_PROVIDER)  
  3.                 != PackageManager.PERMISSION_GRANTED) {  
  4.             throw new SecurityException("Requires INSTALL_LOCATION_PROVIDER permission");  
  5.         }  
  6.   
  7.         mLocationHandler.removeMessages(MESSAGE_LOCATION_CHANGED, location);  
  8.         Message m = Message.obtain(mLocationHandler, MESSAGE_LOCATION_CHANGED, location);  
  9.         m.arg1 = (passive ? 1 : 0);  
  10.         mLocationHandler.sendMessageAtFrontOfQueue(m);  
  11.     }  
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：

[java] view plaincopyprint?
  1. try     {  
  2.                 mLocationManager.reportLocation(mLocation, false);  
  3.             } catch (RemoteException e) {  
  4.                 Log.e(TAG, "RemoteException calling reportLocation");  
  5.            }  
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

[cpp] view plaincopyprint?
  1. /** Callback with location information. 向上层传递GPS位置信息 
  2.  *  Can only be called from a thread created by create_thread_cb. 
  3.  */  
  4. typedef void (* gps_location_callback)(GpsLocation* location);  
/** 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：

[cpp] view plaincopyprint?
  1. static const GpsInterface* GetGpsInterface(JNIEnv* env, jobject obj) {  
  2.     // this must be set before calling into the HAL library   
  3.     if (!mCallbacksObj)  
  4.         mCallbacksObj = env->NewGlobalRef(obj);  
  5.   
  6.     if (!sGpsInterface) {  
  7.         sGpsInterface = get_gps_interface();  
  8.         if (!sGpsInterface || sGpsInterface->init(&sGpsCallbacks) != 0) {  
  9.             sGpsInterface = NULL;  
  10.             return NULL;  
  11.         }  
  12.     }  
  13.     return sGpsInterface;  
  14. }  
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：

[cpp] view plaincopyprint?
  1. GpsCallbacks sGpsCallbacks = {  
  2.     sizeof(GpsCallbacks),  
  3.     location_callback,  
  4.     status_callback,  
  5.     sv_status_callback,  
  6.     nmea_callback,  
  7.     set_capabilities_callback,  
  8.     acquire_wakelock_callback,  
  9.     release_wakelock_callback,  
  10.     create_thread_callback,  
  11. };  
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）：

[cpp] view plaincopyprint?
  1. typedef struct {  
  2.     size_t      size;  
  3.     gps_location_callback location_cb;  
  4.     gps_status_callback status_cb;  
  5.     gps_sv_status_callback sv_status_cb;  
  6.     gps_nmea_callback nmea_cb;  
  7.     gps_set_capabilities set_capabilities_cb;  
  8.     gps_acquire_wakelock acquire_wakelock_cb;  
  9.     gps_release_wakelock release_wakelock_cb;  
  10.     gps_create_thread create_thread_cb;  
  11. } GpsCallbacks;  
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：

[cpp] view plaincopyprint?
  1. static void location_callback(GpsLocation* location)  
  2. {  
  3.     JNIEnv* env = AndroidRuntime::getJNIEnv();  
  4.     env->CallVoidMethod(mCallbacksObj, method_reportLocation, location->flags,  
  5.             (jdouble)location->latitude, (jdouble)location->longitude,  
  6.             (jdouble)location->altitude,  
  7.             (jfloat)location->speed, (jfloat)location->bearing,  
  8.             (jfloat)location->accuracy, (jlong)location->timestamp);  
  9.     checkAndClearExceptionFromCallback(env, __FUNCTION__);  
  10. }  
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：

[cpp] view plaincopyprint?
  1. static void android_location_GpsLocationProvider_class_init_native(JNIEnv* env, jclass clazz) {  
  2.     method_reportLocation = env->GetMethodID(clazz, "reportLocation", "(IDDDFFFJ)V");  
  3.     //...省略部分代码   
  4. }  
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：

[cpp] view plaincopyprint?
  1. tatic JNINativeMethod sMethods[] = {  
  2.      /* name, signature, funcPtr */  
  3.     {"class_init_native", "()V", (void *)android_location_GpsLocationProvider_class_init_native},  
  4.     //...省略部分代码   
  5. }  
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：

[java] view plaincopyprint?
  1. static { class_init_native(); }  
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。


3 参考文章

基于android的GPS移植——主要结构体及接口介绍

androidGPS定位，定位城市称，经纬度


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