Android GPS架构分析（二）
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initialize函数
LocationManagerService.java[php?mod=tag&id=6090" target="_blank" class="relatedlink">Frameworks\base\services\java\com\android\server]
private void initialize() {
// Create a wake lock, needs to be donebefore calling loadProviders() below
powerManager powerManager = (PowerManager)mContext.getSystEMService(Context.POWER_SERVICE);
mWakeLock =powerManager.newWakeLock(PowerManager.PARTIAL_WAKE_LOCK, WAKELOCK_KEY);
// Load providers
loadProviders();
...
initialize函数中最重要的就是loadProviders函数了，该函数调用loadProvidersLocked，然后loadProvidersLocked函数又调用_loadProvidersLocked函数。为什么要这么折腾呢?
先来看一部分的_loadProvidersLocked函数：
private void _loadProvidersLocked() {
// Attempt to load "real"providers first
if (gpsLocationProvider.isSupported()) {
// Create a gps location provider
GpsLocationProvider gpsProvider = newGpsLocationProvider(mContext, this);
mGpsStatusProvider =gpsProvider.getGpsStatusProvider();
mNetInitiatedListener =gpsProvider.getNetInitiatedListener();
addProvider(gpsProvider);
mGpsLocationProvider = gpsProvider;
}
...
注意这个if语句，狠重要，因为在这个语句中得到了HAL层的GPS接口GpsInterface。就是通过调用GpsLocationProvider的isSupported()函数才调用到gps.cpp[hardware/libhardware_legacy/gps]中的gps_get_interface()。这个isSupported函数才是第一个吃螃蟹的人。（而不是JNI层的init函数，这个下面会提到)。
GpsLocationProvider.cpp[frameworks\base\location\java\com\android\internal\location]
public static boolean isSupported() {
return native_is_supported();
}
然而isSupported只有一句话，果然是高手，一击必中。然后就调用native方法，也就是JNI层定义的方法。native_is_supported函数对于JNI层是android_location_GpsLocationProvider_is_supported方法。
android_location_GpsLocationProvider.cpp[frameworks\base\core\jni]
static jbooleanandroid_location_GpsLocationProvider_is_supported(JNIEnv* env, jclass clazz) {
if (！sGpsInterface)
sGpsInterface = gps_get_interface();
return (sGpsInterface ！= NULL);
}
frameworks/base/services/jni/com_android_server_location_GpsLocationProvider.cpp
前面已经提到JNI起到承上启下的作用，gps_get_interface函数属于HAL层的调用，在文件gps.cpp中。
gps.cpp [hardware\libhardware_legacy\gps]
const GpsInterface*
gps_get_interface()
{
if (sGpsInterface == NULL)
gps_find_hardware();
return sGpsInterface;
}
然后通过gps_find_hardware函数去得到gps接口，下面只模拟器中的gpsinterface。
static void
gps_find_hardware( void )
{
#ifdef HAVE_QEMU_GPS_HARDWARE
if (qemu_check()) {
sGpsInterface = gps_get_qemu_interface();
if (sGpsInterface) {
LOGD("using QEMU GPS Hardwareemulation\n");
return;
}
}
#endif
#ifdef HAVE_GPS_HARDWARE
sGpsInterface =gps_get_hardware_interface();
#endif
if (！sGpsInterface)
LOGD("no GPS hardware on thisdevice\n");
}
gps_qemu.c[hardware\libhardware_legacy\gps]
const GpsInterface*gps_get_qemu_interface()
{
return &qemuGpsInterface;
}
qemuGpsInterface的整体实现就在文件gps_qemu.c中。
static const GpsInterface qemuGpsInterface= {
qemu_gps_init,
qemu_gps_start,
qemu_gps_stop,
qemu_gps_cleanup,
qemu_gps_inject_time,
qemu_gps_inject_location,
qemu_gps_delete_aiding_data,
qemu_gps_set_position_mode,
qemu_gps_get_extension,
};
本文来自CSDN博客，转载请标明出处：http://blog.csdn.net/hellolwl/archive/2011/04/06/6305689.aspx