Android系统Gps分析

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

• GpsLocation

GPS位置信息结构体，包含经纬度，高度，速度，方位角等。

/** Flags to indicate which values are valid in a GpsLocation. */
typedef uint16_t GpsLocationFlags;
// IMPORTANT: Note that the following values must match
// constants in GpsLocationProvider.java.
/** GpsLocation has valid latitude and longitude. */
#define GPS_LOCATION_HAS_LAT_LONG   0x0001
/** GpsLocation has valid altitude. */
#define GPS_LOCATION_HAS_ALTITUDE   0x0002
/** GpsLocation has valid speed. */
#define GPS_LOCATION_HAS_SPEED      0x0004
/** GpsLocation has valid bearing. */
#define GPS_LOCATION_HAS_BEARING    0x0008
/** GpsLocation has valid accuracy. */
#define GPS_LOCATION_HAS_ACCURACY   0x0010

/** Represents a location. */
typedef struct {
    /** set to sizeof(GpsLocation) */
    size_t          size;
    /** Contains GpsLocationFlags bits. */
    uint16_t        flags;
    /** Represents latitude in degrees. */
    double          latitude;
    /** Represents longitude in degrees. */
    double          longitude;
    /** Represents altitude in meters above the WGS 84 reference
     * ellipsoid. */
    double          altitude;
    /** Represents speed in meters per second. */
    float           speed;
    /** Represents heading in degrees. */
    float           bearing;
    /** Represents expected accuracy in meters. */
    float           accuracy;
    /** Timestamp for the location fix. */
    GpsUtcTime      timestamp;
} GpsLocation;

/** Flags to indicate which values are valid in a GpsLocation. */ typedef uint16_t GpsLocationFlags; // IMPORTANT: Note that the following values must match // constants in GpsLocationProvider.java. /** GpsLocation has valid latitude and longitude. */ #define GPS_LOCATION_HAS_LAT_LONG 0x0001 /** GpsLocation has valid altitude. */ #define GPS_LOCATION_HAS_ALTITUDE 0x0002 /** GpsLocation has valid speed. */ #define GPS_LOCATION_HAS_SPEED 0x0004 /** GpsLocation has valid bearing. */ #define GPS_LOCATION_HAS_BEARING 0x0008 /** GpsLocation has valid accuracy. */ #define GPS_LOCATION_HAS_ACCURACY 0x0010 /** Represents a location. */ typedef struct { /** set to sizeof(GpsLocation) */ size_t size; /** Contains GpsLocationFlags bits. */ uint16_t flags; /** Represents latitude in degrees. */ double latitude; /** Represents longitude in degrees. */ double longitude; /** Represents altitude in meters above the WGS 84 reference * ellipsoid. */ double altitude; /** Represents speed in meters per second. */ float speed; /** Represents heading in degrees. */ float bearing; /** Represents expected accuracy in meters. */ float accuracy; /** Timestamp for the location fix. */ GpsUtcTime timestamp; } GpsLocation;

• GpsStatus

GPS状态包括5种状态，分别为未知，正在定位，停止定位，启动未定义，未启动。

/** GPS status event values. */
typedef uint16_t GpsStatusValue;
// IMPORTANT: Note that the following values must match
// constants in GpsLocationProvider.java.
/** GPS status unknown. */
#define GPS_STATUS_NONE             0
/** GPS has begun navigating. */
#define GPS_STATUS_SESSION_BEGIN    1
/** GPS has stopped navigating. */
#define GPS_STATUS_SESSION_END      2
/** GPS has powered on but is not navigating. */
#define GPS_STATUS_ENGINE_ON        3
/** GPS is powered off. */AgpsCallbacks

AgpsInterface
#define GPS_STATUS_ENGINE_OFF       4

/** Represents the status. */
typedef struct {
    /** set to sizeof(GpsStatus) */
    size_t          size;
    GpsStatusValue status;
} GpsStatus;

/** GPS status event values. */ typedef uint16_t GpsStatusValue; // IMPORTANT: Note that the following values must match // constants in GpsLocationProvider.java. /** GPS status unknown. */ #define GPS_STATUS_NONE 0 /** GPS has begun navigating. */ #define GPS_STATUS_SESSION_BEGIN 1 /** GPS has stopped navigating. */ #define GPS_STATUS_SESSION_END 2 /** GPS has powered on but is not navigating. */ #define GPS_STATUS_ENGINE_ON 3 /** GPS is powered off. */AgpsCallbacks AgpsInterface #define GPS_STATUS_ENGINE_OFF 4 /** Represents the status. */ typedef struct { /** set to sizeof(GpsStatus) */ size_t size; GpsStatusValue status; } GpsStatus;

• GpsSvInfo

GPS卫星信息，包含卫星编号，信号强度，卫星仰望角，方位角等。

/** Represents SV information. */
typedef struct {
    /** set to sizeof(GpsSvInfo) */
    size_t          size;
    /** Pseudo-random number for the SV. */
    int     prn;
    /** Signal to noise ratio. */
    float   snr;
    /** Elevation of SV in degrees. */
    float   elevation;
    /** Azimuth of SV in degrees. */
    float   azimuth;
} GpsSvInfo;

/** Represents SV information. */ typedef struct { /** set to sizeof(GpsSvInfo) */ size_t size; /** Pseudo-random number for the SV. */ int prn; /** Signal to noise ratio. */ float snr; /** Elevation of SV in degrees. */ float elevation; /** Azimuth of SV in degrees. */ float azimuth; } GpsSvInfo;

• GpsSvStatus

GPS卫星状态，包含可见卫星数和信息，星历时间，年历时间等。

/** Represents SV status. */
typedef struct {
    /** set to sizeof(GpsSvStatus) */
    size_t          size;

    /** Number of SVs currently visible. */
    int         num_svs;

    /** Contains an array of SV information. */
    GpsSvInfo   sv_list[GPS_MAX_SVS];

    /** Represents a bit mask indicating which SVs
     * have ephemeris data.
     */
    uint32_t    ephemeris_mask;

    /** Represents a bit mask indicating which SVs
     * have almanac data.
     */
    uint32_t    almanac_mask;

    /**
     * Represents a bit mask indicating which SVs
     * were used for computing the most recent position fix.
     */
    uint32_t    used_in_fix_mask;
} GpsSvStatus;

/** Represents SV status. */ typedef struct { /** set to sizeof(GpsSvStatus) */ size_t size; /** Number of SVs currently visible. */ int num_svs; /** Contains an array of SV information. */ GpsSvInfo sv_list[GPS_MAX_SVS]; /** Represents a bit mask indicating which SVs * have ephemeris data. */ uint32_t ephemeris_mask; /** Represents a bit mask indicating which SVs * have almanac data. */ uint32_t almanac_mask; /** * Represents a bit mask indicating which SVs * were used for computing the most recent position fix. */ uint32_t used_in_fix_mask; } GpsSvStatus;

• GpsCallbacks

回调函数定义

/** Callback with location information. 向上层传递GPS位置信息
 *  Can only be called from a thread created by create_thread_cb.
 */
typedef void (* gps_location_callback)(GpsLocation* location);

/** Callback with status information. 向上层传递GPS状态信息
 *  Can only be called from a thread created by create_thread_cb.
 */
typedef void (* gps_status_callback)(GpsStatus* status);

/** Callback with SV status information. 向上层传递GPS卫星信息
 *  Can only be called from a thread created by create_thread_cb.
 */
typedef void (* gps_sv_status_callback)(GpsSvStatus* sv_info);

/** Callback for reporting NMEA sentences. 向上层传递MEMA数据
 *  Can only be called from a thread created by create_thread_cb.
 */
typedef void (* gps_nmea_callback)(GpsUtcTime timestamp, const char* nmea, int length);

/** Callback to inform framework of the GPS engine's capabilities.告知GPS模块可以实现的功能
 *  Capability parameter is a bit field of GPS_CAPABILITY_* flags.
 */
typedef void (* gps_set_capabilities)(uint32_t capabilities);

/** Callback utility for acquiring the GPS wakelock.上锁，防止处理GPS事件时中止。
 *  This can be used to prevent the CPU from suspending while handling GPS events.
 */
typedef void (* gps_acquire_wakelock)();

/** Callback utility for releasing the GPS wakelock. */释放锁
typedef void (* gps_release_wakelock)();

/** Callback for creating a thread that can call into the Java framework code.等待上层请求
 *  This must be used to create any threads that report events up to the framework.
 */
typedef pthread_t (* gps_create_thread)(const char* name, void (*start)(void *), void* arg);

/** GPS callback structure. */
typedef struct {
    /** set to sizeof(GpsCallbacks) */
    size_t      size;
    gps_location_callback location_cb;
    gps_status_callback status_cb;
    gps_sv_status_callback sv_status_cb;
    gps_nmea_callback nmea_cb;
    gps_set_capabilities set_capabilities_cb;
    gps_acquire_wakelock acquire_wakelock_cb;
    gps_release_wakelock release_wakelock_cb;
    gps_create_thread create_thread_cb;
} GpsCallbacks;

/** Callback with location information. 向上层传递GPS位置信息 * Can only be called from a thread created by create_thread_cb. */ typedef void (* gps_location_callback)(GpsLocation* location); /** Callback with status information. 向上层传递GPS状态信息 * Can only be called from a thread created by create_thread_cb. */ typedef void (* gps_status_callback)(GpsStatus* status); /** Callback with SV status information. 向上层传递GPS卫星信息 * Can only be called from a thread created by create_thread_cb. */ typedef void (* gps_sv_status_callback)(GpsSvStatus* sv_info); /** Callback for reporting NMEA sentences. 向上层传递MEMA数据 * Can only be called from a thread created by create_thread_cb. */ typedef void (* gps_nmea_callback)(GpsUtcTime timestamp, const char* nmea, int length); /** Callback to inform framework of the GPS engine's capabilities.告知GPS模块可以实现的功能 * Capability parameter is a bit field of GPS_CAPABILITY_* flags. */ typedef void (* gps_set_capabilities)(uint32_t capabilities); /** Callback utility for acquiring the GPS wakelock.上锁，防止处理GPS事件时中止。 * This can be used to prevent the CPU from suspending while handling GPS events. */ typedef void (* gps_acquire_wakelock)(); /** Callback utility for releasing the GPS wakelock. */释放锁 typedef void (* gps_release_wakelock)(); /** Callback for creating a thread that can call into the Java framework code.等待上层请求 * This must be used to create any threads that report events up to the framework. */ typedef pthread_t (* gps_create_thread)(const char* name, void (*start)(void *), void* arg); /** GPS callback structure. */ typedef struct { /** set to sizeof(GpsCallbacks) */ size_t size; gps_location_callback location_cb; gps_status_callback status_cb; gps_sv_status_callback sv_status_cb; gps_nmea_callback nmea_cb; gps_set_capabilities set_capabilities_cb; gps_acquire_wakelock acquire_wakelock_cb; gps_release_wakelock release_wakelock_cb; gps_create_thread create_thread_cb; } GpsCallbacks;

• GpsInterface

GPS接口是最重要的结构体，上层是通过此接口与硬件适配层交互的。

/** Represents the standard GPS interface. */
typedef struct {
    /** set to sizeof(GpsInterface) */
    size_t          size;
    /**
     * Opens the interface and provides the callback routines
     * to the implemenation of this interface.
     */
    int   (*init)( GpsCallbacks* callbacks );

    /** Starts navigating. 启动定位*/
    int   (*start)( void );

    /** Stops navigating. 取消定位*/
    int   (*stop)( void );

    /** Closes the interface. 关闭GPS接口*/
    void  (*cleanup)( void );

    /** Injects the current time.填入时间 */
    int   (*inject_time)(GpsUtcTime time, int64_t timeReference,
                         int uncertainty);

    /** Injects current location from another location provider填入位置
     *  (typically cell ID).
     *  latitude and longitude are measured in degrees
     *  expected accuracy is measured in meters
     */
    int  (*inject_location)(double latitude, double longitude, float accuracy);

    /**
     * Specifies that the next call to start will not use the删除全部或部分辅助数据，在性能测试时使用
     * information defined in the flags. GPS_DELETE_ALL is passed for
     * a cold start.
     */
    void  (*delete_aiding_data)(GpsAidingData flags);

    /**设置定位模式和GPS工作模式等
     * min_interval represents the time between fixes in milliseconds.
     * preferred_accuracy represents the requested fix accuracy in meters.
     * preferred_time represents the requested time to first fix in milliseconds.
     */
    int   (*set_position_mode)(GpsPositionMode mode, GpsPositionRecurrence recurrence,
            uint32_t min_interval, uint32_t preferred_accuracy, uint32_t preferred_time);

    /** Get a pointer to extension information. 自定义的接口*/
    const void* (*get_extension)(const char* name);
} GpsInterface;

/** Represents the standard GPS interface. */ typedef struct { /** set to sizeof(GpsInterface) */ size_t size; /** * Opens the interface and provides the callback routines * to the implemenation of this interface. */ int (*init)( GpsCallbacks* callbacks ); /** Starts navigating. 启动定位*/ int (*start)( void ); /** Stops navigating. 取消定位*/ int (*stop)( void ); /** Closes the interface. 关闭GPS接口*/ void (*cleanup)( void ); /** Injects the current time.填入时间 */ int (*inject_time)(GpsUtcTime time, int64_t timeReference, int uncertainty); /** Injects current location from another location provider填入位置 * (typically cell ID). * latitude and longitude are measured in degrees * expected accuracy is measured in meters */ int (*inject_location)(double latitude, double longitude, float accuracy); /** * Specifies that the next call to start will not use the删除全部或部分辅助数据，在性能测试时使用 * information defined in the flags. GPS_DELETE_ALL is passed for * a cold start. */ void (*delete_aiding_data)(GpsAidingData flags); /**设置定位模式和GPS工作模式等 * min_interval represents the time between fixes in milliseconds. * preferred_accuracy represents the requested fix accuracy in meters. * preferred_time represents the requested time to first fix in milliseconds. */ int (*set_position_mode)(GpsPositionMode mode, GpsPositionRecurrence recurrence, uint32_t min_interval, uint32_t preferred_accuracy, uint32_t preferred_time); /** Get a pointer to extension information. 自定义的接口*/ const void* (*get_extension)(const char* name); } GpsInterface;

• gps_device_t

GPS设备结构体，继承自hw_device_tcommon，硬件适配接口，向上层提供了重要的get_gps_interface接口。

struct gps_device_t {
    struct hw_device_t common;

    /**
     * Set the provided lights to the provided values.
     *
     * Returns: 0 on succes, error code on failure.
     */
    const GpsInterface* (*get_gps_interface)(struct gps_device_t* dev);
};

struct gps_device_t { struct hw_device_t common; /** * Set the provided lights to the provided values. * * Returns: 0 on succes, error code on failure. */ const GpsInterface* (*get_gps_interface)(struct gps_device_t* dev); };

2.2硬件适配层

GPS硬件适配层的源码位于：hardware/qcom/gps目录下。

我们看gps/loc_api/llibloc_api/gps.c，首先定义了gps设备模块实例：

const struct hw_module_t HAL_MODULE_INFO_SYM = {
    .tag = HARDWARE_MODULE_TAG,
    .version_major = 1,
    .version_minor = 0,
    .id = GPS_HARDWARE_MODULE_ID,
    .name = "loc_api GPS Module",
    .author = "Qualcomm USA, Inc.",
    .methods = &gps_module_methods,
};

const struct hw_module_t HAL_MODULE_INFO_SYM = { .tag = HARDWARE_MODULE_TAG, .version_major = 1, .version_minor = 0, .id = GPS_HARDWARE_MODULE_ID, .name = "loc_api GPS Module", .author = "Qualcomm USA, Inc.", .methods = &gps_module_methods, };

这里的methods指向gps.c文件中的gps_module_methods

static struct hw_module_methods_t gps_module_methods = {
    .open = open_gps
};

static struct hw_module_methods_t gps_module_methods = { .open = open_gps };

gps_module_methods定义了设备的open函数为open_gps，我们看open_gps函数：

static int open_gps(const struct hw_module_t* module, char const* name,
        struct hw_device_t** device)
{
    struct gps_device_t *dev = malloc(sizeof(struct gps_device_t));
    memset(dev, 0, sizeof(*dev));

    dev->common.tag = HARDWARE_DEVICE_TAG;
    dev->common.version = 0;
    dev->common.module = (struct hw_module_t*)module;
    dev->get_gps_interface = gps__get_gps_interface;

    *device = (struct hw_device_t*)dev;
    return 0;
}

static int open_gps(const struct hw_module_t* module, char const* name, struct hw_device_t** device) { struct gps_device_t *dev = malloc(sizeof(struct gps_device_t)); memset(dev, 0, sizeof(*dev)); dev->common.tag = HARDWARE_DEVICE_TAG; dev->common.version = 0; dev->common.module = (struct hw_module_t*)module; dev->get_gps_interface = gps__get_gps_interface; *device = (struct hw_device_t*)dev; return 0; }

此处可以看作是GPS设备的初始化函数，在使用设备前必须执行此函数。函数里面指定了hw_device_t的module成员，以及gps_device_t的get_gps_interface成员。上层可通过gps_device_t的get_gps_interface调用gps__get_gps_interface函数。gps__get_gps_interface的定义如下：

const GpsInterface* gps__get_gps_interface(struct gps_device_t* dev)
{
    return get_gps_interface();
}

const GpsInterface* gps__get_gps_interface(struct gps_device_t* dev) { return get_gps_interface(); }

用代码跟踪可看到，此函数返回了gps/loc_eng.cpp文件的sLocEngInterface变量，sLocEngInterface定义如下：

// Defines the GpsInterface in gps.h
static const GpsInterface sLocEngInterface =
{
    sizeof(GpsInterface),
    loc_eng_init,
    loc_eng_start,
    loc_eng_stop,
    loc_eng_cleanup,
    loc_eng_inject_time,
    loc_eng_inject_location,
    loc_eng_delete_aiding_data,
    loc_eng_set_position_mode,
    loc_eng_get_extension,
};

// 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：

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：

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;
}

extern "C" jint JNI_OnLoad(JavaVM* vm, void* reserved) { JNIEnv* env = NULL; jint result = -1; if (vm->GetEnv((void**) &env, JNI_VERSION_1_4) != JNI_OK) { LOGE("GetEnv failed!"); return result; } LOG_ASSERT(env, "Could not retrieve the env!"); //...省略其他注册代码 register_android_server_location_GpsLocationProvider(env); return JNI_VERSION_1_4; }

从这里可以看到，JNI初始化的时候，即会进行JNI方法的注册，从而使上层应用能通过JNI调用c/c++本地方法。

回到register_android_server_location_GpsLocationProvider函数，变量sMethods定义如下：

static JNINativeMethod sMethods[] = {
     /* name, signature, funcPtr */
    {"class_init_native", "()V", (void *)android_location_GpsLocationProvider_class_init_native},
    {"native_is_supported", "()Z", (void*)android_location_GpsLocationProvider_is_supported},
    {"native_init", "()Z", (void*)android_location_GpsLocationProvider_init},
    {"native_cleanup", "()V", (void*)android_location_GpsLocationProvider_cleanup},
    {"native_set_position_mode", "(IIIII)Z", (void*)android_location_GpsLocationProvider_set_position_mode},
    {"native_start", "()Z", (void*)android_location_GpsLocationProvider_start},
    {"native_stop", "()Z", (void*)android_location_GpsLocationProvider_stop},
    {"native_delete_aiding_data", "(I)V", (void*)android_location_GpsLocationProvider_delete_aiding_data},
    {"native_read_sv_status", "([I[F[F[F[I)I", (void*)android_location_GpsLocationProvider_read_sv_status},
    {"native_read_nmea", "([BI)I", (void*)android_location_GpsLocationProvider_read_nmea},
    {"native_inject_time", "(JJI)V", (void*)android_location_GpsLocationProvider_inject_time},
    {"native_inject_location", "(DDF)V", (void*)android_location_GpsLocationProvider_inject_location},
    {"native_supports_xtra", "()Z", (void*)android_location_GpsLocationProvider_supports_xtra},
    {"native_inject_xtra_data", "([BI)V", (void*)android_location_GpsLocationProvider_inject_xtra_data},
    {"native_agps_data_conn_open", "(Ljava/lang/String;)V", (void*)android_location_GpsLocationProvider_agps_data_conn_open},
    {"native_agps_data_conn_closed", "()V", (void*)android_location_GpsLocationProvider_agps_data_conn_closed},
    {"native_agps_data_conn_failed", "()V", (void*)android_location_GpsLocationProvider_agps_data_conn_failed},
    {"native_agps_set_id","(ILjava/lang/String;)V",(void*)android_location_GpsLocationProvider_agps_set_id},
    {"native_agps_set_ref_location_cellid","(IIIII)V",(void*)android_location_GpsLocationProvider_agps_set_reference_location_cellid},
    {"native_set_agps_server", "(ILjava/lang/String;I)V", (void*)android_location_GpsLocationProvider_set_agps_server},
    {"native_send_ni_response", "(II)V", (void*)android_location_GpsLocationProvider_send_ni_response},
    {"native_agps_ni_message", "([BI)V", (void *)android_location_GpsLocationProvider_agps_send_ni_message},
    {"native_get_internal_state", "()Ljava/lang/String;", (void*)android_location_GpsLocationProvider_get_internal_state},
    {"native_update_network_state", "(ZIZLjava/lang/String;)V", (void*)android_location_GpsLocationProvider_update_network_state },
};

static JNINativeMethod sMethods[] = { /* name, signature, funcPtr */ {"class_init_native", "()V", (void *)android_location_GpsLocationProvider_class_init_native}, {"native_is_supported", "()Z", (void*)android_location_GpsLocationProvider_is_supported}, {"native_init", "()Z", (void*)android_location_GpsLocationProvider_init}, {"native_cleanup", "()V", (void*)android_location_GpsLocationProvider_cleanup}, {"native_set_position_mode", "(IIIII)Z", (void*)android_location_GpsLocationProvider_set_position_mode}, {"native_start", "()Z", (void*)android_location_GpsLocationProvider_start}, {"native_stop", "()Z", (void*)android_location_GpsLocationProvider_stop}, {"native_delete_aiding_data", "(I)V", (void*)android_location_GpsLocationProvider_delete_aiding_data}, {"native_read_sv_status", "([I[F[F[F[I)I", (void*)android_location_GpsLocationProvider_read_sv_status}, {"native_read_nmea", "([BI)I", (void*)android_location_GpsLocationProvider_read_nmea}, {"native_inject_time", "(JJI)V", (void*)android_location_GpsLocationProvider_inject_time}, {"native_inject_location", "(DDF)V", (void*)android_location_GpsLocationProvider_inject_location}, {"native_supports_xtra", "()Z", (void*)android_location_GpsLocationProvider_supports_xtra}, {"native_inject_xtra_data", "([BI)V", (void*)android_location_GpsLocationProvider_inject_xtra_data}, {"native_agps_data_conn_open", "(Ljava/lang/String;)V", (void*)android_location_GpsLocationProvider_agps_data_conn_open}, {"native_agps_data_conn_closed", "()V", (void*)android_location_GpsLocationProvider_agps_data_conn_closed}, {"native_agps_data_conn_failed", "()V", (void*)android_location_GpsLocationProvider_agps_data_conn_failed}, {"native_agps_set_id","(ILjava/lang/String;)V",(void*)android_location_GpsLocationProvider_agps_set_id}, {"native_agps_set_ref_location_cellid","(IIIII)V",(void*)android_location_GpsLocationProvider_agps_set_reference_location_cellid}, {"native_set_agps_server", "(ILjava/lang/String;I)V", (void*)android_location_GpsLocationProvider_set_agps_server}, {"native_send_ni_response", "(II)V", (void*)android_location_GpsLocationProvider_send_ni_response}, {"native_agps_ni_message", "([BI)V", (void *)android_location_GpsLocationProvider_agps_send_ni_message}, {"native_get_internal_state", "()Ljava/lang/String;", (void*)android_location_GpsLocationProvider_get_internal_state}, {"native_update_network_state", "(ZIZLjava/lang/String;)V", (void*)android_location_GpsLocationProvider_update_network_state }, };

这里定义了GPS所有向上层提供的JNI本地方法，这些本地方法是如何与硬件适配层交互的呢？我们看其中一个本地方法android_location_GpsLocationProvider_start：

static jboolean android_location_GpsLocationProvider_start(JNIEnv* env, jobject obj)
{
    const GpsInterface* interface = GetGpsInterface(env, obj);
    if (interface)
        return (interface->start() == 0);
    else
        return false;
}

static jboolean android_location_GpsLocationProvider_start(JNIEnv* env, jobject obj) { const GpsInterface* interface = GetGpsInterface(env, obj); if (interface) return (interface->start() == 0); else return false; }

它调用了GetGpsInterface获得GpsInterface接口，然后直接调用该接口的start回调函数。GetGpsInterface方法定义如下：

static const GpsInterface* GetGpsInterface(JNIEnv* env, jobject obj) {
    // this must be set before calling into the HAL library
    if (!mCallbacksObj)
        mCallbacksObj = env->NewGlobalRef(obj);

    if (!sGpsInterface) {
        sGpsInterface = get_gps_interface();
        if (!sGpsInterface || sGpsInterface->init(&sGpsCallbacks) != 0) {
            sGpsInterface = NULL;
            return NULL;
        }
    }
    return sGpsInterface;
}

static const GpsInterface* GetGpsInterface(JNIEnv* env, jobject obj) { // this must be set before calling into the HAL library if (!mCallbacksObj) mCallbacksObj = env->NewGlobalRef(obj); if (!sGpsInterface) { sGpsInterface = get_gps_interface(); if (!sGpsInterface || sGpsInterface->init(&sGpsCallbacks) != 0) { sGpsInterface = NULL; return NULL; } } return sGpsInterface; }

这个函数返回了sGpsInterface，而sGpsInterface又是从get_gps_interface()获得的，我们继续查看get_gps_interface()函数的实现：

static const GpsInterface* get_gps_interface() {
    int err;
    hw_module_t* module;
    const GpsInterface* interface = NULL;

    err = hw_get_module(GPS_HARDWARE_MODULE_ID, (hw_module_t const**)&module);
    if (err == 0) {
        hw_device_t* device;
        err = module->methods->open(module, GPS_HARDWARE_MODULE_ID, &device);
        if (err == 0) {
            gps_device_t* gps_device = (gps_device_t *)device;
            interface = gps_device->get_gps_interface(gps_device);
        }
    }

    return interface;
}

static const GpsInterface* get_gps_interface() { int err; hw_module_t* module; const GpsInterface* interface = NULL; err = hw_get_module(GPS_HARDWARE_MODULE_ID, (hw_module_t const**)&module); if (err == 0) { hw_device_t* device; err = module->methods->open(module, GPS_HARDWARE_MODULE_ID, &device); if (err == 0) { gps_device_t* gps_device = (gps_device_t *)device; interface = gps_device->get_gps_interface(gps_device); } } return interface; }

这里面调用hw_get_module加载硬件适配模块.so文件，接着通过hw_device_t接口调用open()函数，实际执行gps/loc_api/llibloc_api/gps.c定义的open_gps函数，而后调用gps_device_t接口的get_gps_interface函数，此函数也是在gps.c中定义的，最后返回硬件适配层中loc_eng.cpp文件的sLocEngInterface，从而打通了上层到底层的通道。

2.3 Java Framework

GPSFramework源码位于：frameworks/base/location

2.3.1接口和类简介

首先对GPSFramework重要的接口和类作一个简单的介绍

• 接口

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:

1.      
2.      
3.     
4.     

             

• 接着获取位置信息：

        //获取位置服务
 LocationManager locationManager = (LocationManager) getSystemService(Context.LOCATION_SERVICE);
       Criteria criteria = new Criteria();
       // 获得最好的定位效果
       criteria.setAccuracy(Criteria.ACCURACY_FINE);  //设置为最大精度
       criteria.setAltitudeRequired(false);  //不获取海拔信息
       criteria.setBearingRequired(false);  //不获取方位信息
       criteria.setCostAllowed(false);  //是否允许付费
       criteria.setPowerRequirement(Criteria.POWER_LOW);  // 使用省电模式
       // 获得当前的位置提供者
       String provider = locationManager.getBestProvider(criteria, true);
       // 获得当前的位置
       Location location = locationManager.getLastKnownLocation(provider);
Geocoder gc = new Geocoder(this);
       List 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();
       }

//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

      //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);

//匿名类，继承自LocationListener接口 private final LocationListener locationListener = new LocationListener() { public void onLocationChanged(Location location) { updateWithNewLocation(location);//更新位置信息 } public void onProviderDisabled(String provider){ updateWithNewLocation(null);//更新位置信息 } public void onProviderEnabled(String provider){ } public void onStatusChanged(String provider, int status,Bundle extras){ } }; //更新位置信息 private void updateWithNewLocation(Location location) { if (location != null) { //获取经纬度 double lat = location.getLatitude(); double lng = location.getLongitude(); } //添加侦听 locationManager.requestLocationUpdates(provider, 2000, 10,locationListener);

2.3.3接口和类分析

下面对相关的类或接口进行分析，LocationManager的代码文件位于： frameworks/base/location/java/location/LocationManager.java 

我们看其构造函数：

public LocationManager(ILocationManager service) {
        mService = service;
    }

public LocationManager(ILocationManager service) { mService = service; }

其中mService为ILocationManager接口类型，构造函数的参数为service，外部调用时传入LocationManagerService实例。LocationManager是android系统的gps位置信息系统服务，在稍后将会对其进行分析。由带参构造函数实例化LocationManager类的方式用得不多，一般用的方式是由getSystemService获得LocationManagerService服务，再强制转换为LocationManager。例如在2.3.2中的代码示例中是这样获取gps服务的：

LocationManager locationManager = (LocationManager) getSystemService(Context.LOCATION_SERVICE);

LocationManager locationManager = (LocationManager) getSystemService(Context.LOCATION_SERVICE);

这里的Context.LOCATION_SERVICE为”location”，标识gps服务。

LocationManagerService服务是整个GpsFramework的核心，首先看它是如何加载的，代码文件位于：frameworks/base/services/java/com/android/server/systemserver.java

…//省略其他代码
LocationManagerService location = null;
…//省略其他代码
try {
                Slog.i(TAG, "Location Manager");
                location = new LocationManagerService(context);
                ServiceManager.addService(Context.LOCATION_SERVICE, location);
            } catch (Throwable e) {
                Slog.e(TAG, "Failure starting Location Manager", e);
            }

…//省略其他代码 LocationManagerService location = null; …//省略其他代码 try { Slog.i(TAG, "Location Manager"); location = new LocationManagerService(context); ServiceManager.addService(Context.LOCATION_SERVICE, location); } catch (Throwable e) { Slog.e(TAG, "Failure starting Location Manager", e); }

此处向ServiceManger系统服务管理器注册了新的服务，其名称为”location”，类型为LocationManagerService。注册此服务后，Java应用程序可通过ServiceManager获得LocationManagerService的代理接口ILocationManager.Stub，从而调用LocationManagerService提供的接口函数。ILocationManager位于：

frameworks/base/location/java/location/ILocationManager.aidl，其代码如下：

/**
 * System private API for talking with the location service.
 *
 * {@hide}
 */
interface ILocationManager
{
    List 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);
}

/** * 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：

ILocationManager mLocationManager;
IBinder b = ServiceManager.getService(Context.LOCATION_SERVICE);
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

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

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

此处启动自身服务线程，因LocationMangerService继承自Runnable接口，当启动此线程后，会执行继承自Runnable接口的run()函数，我们看run()函数的定义：

public void run()
    {
        Process.setThreadPriority(Process.THREAD_PRIORITY_BACKGROUND);
        Looper.prepare();
        mLocationHandler = new LocationWorkerHandler();
        initialize();
        Looper.loop();
    }

public void run() { Process.setThreadPriority(Process.THREAD_PRIORITY_BACKGROUND); Looper.prepare(); mLocationHandler = new LocationWorkerHandler(); initialize(); Looper.loop(); }

此处调用了initialize()进行初始化，initialize()函数定义如下：

private void initialize() {
       //...省略其他代码
        loadProviders();

    //...省略其他代码

    }

private void initialize() { //...省略其他代码 loadProviders(); //...省略其他代码 }

此处调用了loadProviders()函数，loadProviders()函数调用了_loadProvidersLocked()，其代码如下：

private void _loadProvidersLocked() {
        // Attempt to load "real" providers first
        if (GpsLocationProvider.isSupported()) {
            // Create a gps location provider
            GpsLocationProvider gpsProvider = new GpsLocationProvider(mContext, this);
            mGpsStatusProvider = gpsProvider.getGpsStatusProvider();
            mNetInitiatedListener = gpsProvider.getNetInitiatedListener();
            addProvider(gpsProvider);
            mGpsLocationProvider = gpsProvider;
        }

        // create a passive location provider, which is always enabled
        PassiveProvider passiveProvider = new PassiveProvider(this);
        addProvider(passiveProvider);
        mEnabledProviders.add(passiveProvider.getName());

        // initialize external network location and geocoder services
        if (mNetworkLocationProviderPackageName != null) {
            mNetworkLocationProvider =
                new LocationProviderProxy(mContext, LocationManager.NETWORK_PROVIDER,
                        mNetworkLocationProviderPackageName, mLocationHandler);
            addProvider(mNetworkLocationProvider);
        }

        if (mGeocodeProviderPackageName != null) {
            mGeocodeProvider = new GeocoderProxy(mContext, mGeocodeProviderPackageName);
        }

        updateProvidersLocked();
    }

private void _loadProvidersLocked() { // Attempt to load "real" providers first if (GpsLocationProvider.isSupported()) { // Create a gps location provider GpsLocationProvider gpsProvider = new GpsLocationProvider(mContext, this); mGpsStatusProvider = gpsProvider.getGpsStatusProvider(); mNetInitiatedListener = gpsProvider.getNetInitiatedListener(); addProvider(gpsProvider); mGpsLocationProvider = gpsProvider; } // create a passive location provider, which is always enabled PassiveProvider passiveProvider = new PassiveProvider(this); addProvider(passiveProvider); mEnabledProviders.add(passiveProvider.getName()); // initialize external network location and geocoder services if (mNetworkLocationProviderPackageName != null) { mNetworkLocationProvider = new LocationProviderProxy(mContext, LocationManager.NETWORK_PROVIDER, mNetworkLocationProviderPackageName, mLocationHandler); addProvider(mNetworkLocationProvider); } if (mGeocodeProviderPackageName != null) { mGeocodeProvider = new GeocoderProxy(mContext, mGeocodeProviderPackageName); } updateProvidersLocked(); }

在这里对GpsLocationProvider和NetworkLocationProvider类作了初始化，并添加到provider集合中。GpsLocationProvider和NetworkLocationProvider继承自LocationProviderInterface接口，分别代表两种位置提供者(LocationProvider)：

（1）LocationManager.GPS_PROVIDER：GPS模式，精度比较高，但是慢而且消耗电力，而且可能因为天气原因或者障碍物而无法获取卫星信息，另外设备可能没有GPS模块（2）LocationManager.NETWORK_PROVIDER：通过网络获取定位信息，精度低，耗电少，获取信息速度较快，不依赖GPS模块。

Android提供criteria类，可根据当前设备情况动态选择位置提供者。我们在之前2.3.2的代码示例中，有这样一句代码：

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

// 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：

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：

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);
             }
        }
    };

private final BroadcastReceiver mBroadcastReciever = new BroadcastReceiver() { @Override public void onReceive(Context context, Intent intent) { String action = intent.getAction(); if (action.equals(ALARM_WAKEUP)) { if (DEBUG) Log.d(TAG, "ALARM_WAKEUP"); startNavigating(false); } else if (action.equals(ALARM_TIMEOUT)) { if (DEBUG) Log.d(TAG, "ALARM_TIMEOUT"); hibernate(); } else if (action.equals(Intents.DATA_SMS_RECEIVED_ACTION)) { checkSmsSuplInit(intent); } else if (action.equals(Intents.WAP_PUSH_RECEIVED_ACTION)) { checkWapSuplInit(intent); } } };

当接收ALARM_EAKEUP时，执行startNavigating函数，当接收到ALARM_TIMEOUT广播时，执行hibernate函数。这两个函数很关键，下面看他们的实现：

private void startNavigating(boolean singleShot) {

        //...省略部分代码

            if (!native_set_position_mode(mPositionMode, GPS_POSITION_RECURRENCE_PERIODIC,
                    interval, 0, 0)) {
                mStarted = false;
                Log.e(TAG, "set_position_mode failed in startNavigating()");
                return;
            }
            if (!native_start()) {
                mStarted = false;
                Log.e(TAG, "native_start failed in startNavigating()");
                return;
            }
        //...省略部分代码
    }

private void startNavigating(boolean singleShot) { //...省略部分代码 if (!native_set_position_mode(mPositionMode, GPS_POSITION_RECURRENCE_PERIODIC, interval, 0, 0)) { mStarted = false; Log.e(TAG, "set_position_mode failed in startNavigating()"); return; } if (!native_start()) { mStarted = false; Log.e(TAG, "native_start failed in startNavigating()"); return; } //...省略部分代码 }

看到没有，这里调用了native_set_position_mode和native_start方法，而这些方法正是我们之前在JNI适配层提到的注册的本地方法。同样的，hibernate函数调用了JNI提供的native_stop方法。我们再看GpsLocationProvider的内部私有函数：

可以看到所有这些本地方法，都是在JNI层注册的，GpsLocationProvider类是从JNI层到Framework层的通道。

下面回到LocationManagerService，分析如何获取最新的位置信息(Location)，获取最新的location的函数是getLastKnownLocation，其实现如下：

private Location _getLastKnownLocationLocked(String provider) {
        checkPermissionsSafe(provider);

        LocationProviderInterface p = mProvidersByName.get(provider);
        if (p == null) {
            return null;
        }

        if (!isAllowedBySettingsLocked(provider)) {
            return null;
        }

        return mLastKnownLocation.get(provider);
    }

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：

public void run()
    {
        Process.setThreadPriority(Process.THREAD_PRIORITY_BACKGROUND);
        Looper.prepare();
        mLocationHandler = new LocationWorkerHandler();
        initialize();
        Looper.loop();
    }

public void run() { Process.setThreadPriority(Process.THREAD_PRIORITY_BACKGROUND); Looper.prepare(); mLocationHandler = new LocationWorkerHandler(); initialize(); Looper.loop(); }

这里对类型为LocationWorkerHandler的变量进行初始化，LocationWorkerHandler是在LocationManagerService的一个内部类，它继承自Handler类，Handler是Android系统用于应用程序内部通信的组件，内部通信指同个进程的主线程与其他线程间的通信，Handler通过Message或Runnable对象进行通信。我们继续看LocationWorkerHandler的实现：

private class LocationWorkerHandler extends Handler {

        @Override
        public void handleMessage(Message msg) {
            try {
                if (msg.what == MESSAGE_LOCATION_CHANGED) {
                    // log("LocationWorkerHandler: MESSAGE_LOCATION_CHANGED!");

                    synchronized (mLock) {
                        Location location = (Location) msg.obj;
                        String provider = location.getProvider();
                        boolean passive = (msg.arg1 == 1);

                        if (!passive) {
                            // notify other providers of the new location
                            for (int i = mProviders.size() - 1; i >= 0; i--) {
                                LocationProviderInterface p = mProviders.get(i);
                                if (!provider.equals(p.getName())) {
                                    p.updateLocation(location);
                                }
                            }
                        }

                        if (isAllowedBySettingsLocked(provider)) {
                            handleLocationChangedLocked(location, passive);
                        }
                    }
                } else if (msg.what == MESSAGE_PACKAGE_UPDATED) {
                    //...省略部分代码
                    }
                }
            } catch (Exception e) {
                // Log, don't crash!
                Slog.e(TAG, "Exception in LocationWorkerHandler.handleMessage:", e);
            }
        }
    }

private class LocationWorkerHandler extends Handler { @Override public void handleMessage(Message msg) { try { if (msg.what == MESSAGE_LOCATION_CHANGED) { // log("LocationWorkerHandler: MESSAGE_LOCATION_CHANGED!"); synchronized (mLock) { Location location = (Location) msg.obj; String provider = location.getProvider(); boolean passive = (msg.arg1 == 1); if (!passive) { // notify other providers of the new location for (int i = mProviders.size() - 1; i >= 0; i--) { LocationProviderInterface p = mProviders.get(i); if (!provider.equals(p.getName())) { p.updateLocation(location); } } } if (isAllowedBySettingsLocked(provider)) { handleLocationChangedLocked(location, passive); } } } else if (msg.what == MESSAGE_PACKAGE_UPDATED) { //...省略部分代码 } } } catch (Exception e) { // Log, don't crash! Slog.e(TAG, "Exception in LocationWorkerHandler.handleMessage:", e); } } }

这里重写Handle类的handleMessage方法，处理用Handle接收的Message对象消息。当接受到位置信息变化的消息MESSAGE_LOCATION_CHANGED时，调用p.updateLocationhandleLocationChangedLocked方法，其实现如下：

private void handleLocationChangedLocked(Location location, boolean passive) {
       //...省略部分代码

        // Update last known location for provider
        Location lastLocation = mLastKnownLocation.get(provider);
        if (lastLocation == null) {
            mLastKnownLocation.put(provider, new Location(location));
        } else {
            lastLocation.set(location);
        }
    //...省略部分代码
}

private void handleLocationChangedLocked(Location location, boolean passive) { //...省略部分代码 // Update last known location for provider Location lastLocation = mLastKnownLocation.get(provider); if (lastLocation == null) { mLastKnownLocation.put(provider, new Location(location)); } else { lastLocation.set(location); } //...省略部分代码 }

可以看到是在handleLocationChangedLocked函数中实现对lastknownlocation的更新的，那么在LocationWorkerHandler类中处理的MESSAGE_LOCATION_CHANGED消息是谁发送出来的呢？答案是在LocationManagerService类的reportLocation函数中：

public void reportLocation(Location location, boolean passive) {
        if (mContext.checkCallingOrSelfPermission(INSTALL_LOCATION_PROVIDER)
                != PackageManager.PERMISSION_GRANTED) {
            throw new SecurityException("Requires INSTALL_LOCATION_PROVIDER permission");
        }

        mLocationHandler.removeMessages(MESSAGE_LOCATION_CHANGED, location);
        Message m = Message.obtain(mLocationHandler, MESSAGE_LOCATION_CHANGED, location);
        m.arg1 = (passive ? 1 : 0);
        mLocationHandler.sendMessageAtFrontOfQueue(m);
    }

public void reportLocation(Location location, boolean passive) { if (mContext.checkCallingOrSelfPermission(INSTALL_LOCATION_PROVIDER) != PackageManager.PERMISSION_GRANTED) { throw new SecurityException("Requires INSTALL_LOCATION_PROVIDER permission"); } mLocationHandler.removeMessages(MESSAGE_LOCATION_CHANGED, location); Message m = Message.obtain(mLocationHandler, MESSAGE_LOCATION_CHANGED, location); m.arg1 = (passive ? 1 : 0); mLocationHandler.sendMessageAtFrontOfQueue(m); }

此处构造了新的Message对象，然后发送到消息队列的首位置。在GpsLocationProvider类的reportLocation函数中，有这样一段代码：

try     {
                mLocationManager.reportLocation(mLocation, false);
            } catch (RemoteException e) {
                Log.e(TAG, "RemoteException calling reportLocation");
           }

try { mLocationManager.reportLocation(mLocation, false); } catch (RemoteException e) { Log.e(TAG, "RemoteException calling reportLocation"); }

所以实际是由GpsLocationProvider主动调用LocationManagerService的reportLocation方法，从而更新最新的位置信息。

实际上，GpsLocationoProvider的reportLocation对应了硬件适配层中的GpsCallbacks结构体中的回调函数gps_location_callback

/** Callback with location information. 向上层传递GPS位置信息
 *  Can only be called from a thread created by create_thread_cb.
 */
typedef void (* gps_location_callback)(GpsLocation* location);

/** Callback with location information. 向上层传递GPS位置信息 * Can only be called from a thread created by create_thread_cb. */ typedef void (* gps_location_callback)(GpsLocation* location);

那么GpsLocationProvider中的reportLocation函数是如何与GpsCallbacks的gps_location_callback挂钩的呢？我们回到JNI适配层的代码文件：

frameworks/base/services/jni/com_android_server_location_GpsLocationProvider.cpp

其中定义的GetGpsInterface函数：

static const GpsInterface* GetGpsInterface(JNIEnv* env, jobject obj) {
    // this must be set before calling into the HAL library
    if (!mCallbacksObj)
        mCallbacksObj = env->NewGlobalRef(obj);

    if (!sGpsInterface) {
        sGpsInterface = get_gps_interface();
        if (!sGpsInterface || sGpsInterface->init(&sGpsCallbacks) != 0) {
            sGpsInterface = NULL;
            return NULL;
        }
    }
    return sGpsInterface;
}

static const GpsInterface* GetGpsInterface(JNIEnv* env, jobject obj) { // this must be set before calling into the HAL library if (!mCallbacksObj) mCallbacksObj = env->NewGlobalRef(obj); if (!sGpsInterface) { sGpsInterface = get_gps_interface(); if (!sGpsInterface || sGpsInterface->init(&sGpsCallbacks) != 0) { sGpsInterface = NULL; return NULL; } } return sGpsInterface; }

这里面的sGpsInterface->init(&sGpsCallbacks)调用了GpsInterface的init回调函数，即初始化GpsCallbacks结构体变量sGpsCallbacks，sGpsCallbacks定义如下：

GpsCallbacks sGpsCallbacks = {
    sizeof(GpsCallbacks),
    location_callback,
    status_callback,
    sv_status_callback,
    nmea_callback,
    set_capabilities_callback,
    acquire_wakelock_callback,
    release_wakelock_callback,
    create_thread_callback,
};

GpsCallbacks sGpsCallbacks = { sizeof(GpsCallbacks), location_callback, status_callback, sv_status_callback, nmea_callback, set_capabilities_callback, acquire_wakelock_callback, release_wakelock_callback, create_thread_callback, };

我们再次看GpsCallbacks的定义（其代码文件在硬件适配层的头文件gps.h中）：

typedef struct {
    size_t      size;
    gps_location_callback location_cb;
    gps_status_callback status_cb;
    gps_sv_status_callback sv_status_cb;
    gps_nmea_callback nmea_cb;
    gps_set_capabilities set_capabilities_cb;
    gps_acquire_wakelock acquire_wakelock_cb;
    gps_release_wakelock release_wakelock_cb;
    gps_create_thread create_thread_cb;
} GpsCallbacks;

typedef struct { size_t size; gps_location_callback location_cb; gps_status_callback status_cb; gps_sv_status_callback sv_status_cb; gps_nmea_callback nmea_cb; gps_set_capabilities set_capabilities_cb; gps_acquire_wakelock acquire_wakelock_cb; gps_release_wakelock release_wakelock_cb; gps_create_thread create_thread_cb; } GpsCallbacks;

比较sGpsCallbacks与GpsCallbacks，可以看到location_callback与gps_location_callback对应。再看location_callback函数的定义：

static void location_callback(GpsLocation* location)
{
    JNIEnv* env = AndroidRuntime::getJNIEnv();
    env->CallVoidMethod(mCallbacksObj, method_reportLocation, location->flags,
            (jdouble)location->latitude, (jdouble)location->longitude,
            (jdouble)location->altitude,
            (jfloat)location->speed, (jfloat)location->bearing,
            (jfloat)location->accuracy, (jlong)location->timestamp);
    checkAndClearExceptionFromCallback(env, __FUNCTION__);
}

static void location_callback(GpsLocation* location) { JNIEnv* env = AndroidRuntime::getJNIEnv(); env->CallVoidMethod(mCallbacksObj, method_reportLocation, location->flags, (jdouble)location->latitude, (jdouble)location->longitude, (jdouble)location->altitude, (jfloat)location->speed, (jfloat)location->bearing, (jfloat)location->accuracy, (jlong)location->timestamp); checkAndClearExceptionFromCallback(env, __FUNCTION__); }

这里面利用JNI调用了Java语言的方法method_reportLocation，method_reportLocation是一个jmethodID变量，表示一个由Java语言定义的方法。下面我们看method_reportLocation的赋值代码：

static void android_location_GpsLocationProvider_class_init_native(JNIEnv* env, jclass clazz) {
    method_reportLocation = env->GetMethodID(clazz, "reportLocation", "(IDDDFFFJ)V");
    //...省略部分代码
}

static void android_location_GpsLocationProvider_class_init_native(JNIEnv* env, jclass clazz) { method_reportLocation = env->GetMethodID(clazz, "reportLocation", "(IDDDFFFJ)V"); //...省略部分代码 }

这里表示method_reportLocation指向Java类clazz里的方法reportLocation，那么这个Java类clazz是不是表示GpsLocationProvider呢？我们找到注册JNI方法的方法表：

tatic JNINativeMethod sMethods[] = {
     /* name, signature, funcPtr */
    {"class_init_native", "()V", (void *)android_location_GpsLocationProvider_class_init_native},
    //...省略部分代码
}

tatic JNINativeMethod sMethods[] = { /* name, signature, funcPtr */ {"class_init_native", "()V", (void *)android_location_GpsLocationProvider_class_init_native}, //...省略部分代码 }

这里说明_GpsLocationProvider_class_init_native对应的native方法名称是class_init_native，下面我们只要确定在Java中的某个类A调用了class_init_native方法，即可以说明A类的reportLocation函数是GpsCallbacks的回调函数。

我们回到GpsLocationProvider的代码文件：

frameworks/base/services/java/com/android/server/location/GpsLocationProvider.java

其中有一段代码：

static { class_init_native(); }

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