Android GPS架构分析（五）

最新推荐文章于 2024-08-12 03:25:40 发布

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最新推荐文章于 2024-08-12 03:25:40 发布

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文章出处：http://danielwood.cublog.cn

言归正传，分析sGpsInterface->init方法。

gps_qume.c

static int
qemu_gps_init(GpsCallbacks* callbacks)
{
GpsState* s = _gps_state;
if (!s->init)
gps_state_init(s);
if (s->fd < 0)
return -1;
s->callbacks = *callbacks;
return 0;
}

在sGpsInterface->init中，也就是在qemu_gps_init方法，首先调用了gps_state_init，其次注册了回调函数，再说一次，这个回调函数就是在JNI层实现的，而且有JNI层传下来的函数。

static void
gps_state_init( GpsState* state )
{
state->init = 1;
state->control[0] = -1;
state->control[1] = -1;
state->fd = -1;
state->fd = qemu_channel_open( &state->channel,
QEMU_CHANNEL_NAME,
O_RDONLY );
if (state->fd < 0) {
D("no gps emulation detected");
return;
}
D("gps emulation will read from '%s' qemud channel", QEMU_CHANNEL_NAME );
if ( socketpair( AF_LOCAL, SOCK_STREAM, 0, state->control ) < 0 ) {
LOGE("could not create thread control socket pair: %s", strerror(errno));
goto Fail;
}
if ( pthread_create( &state->thread, NULL, gps_state_thread, state ) != 0 ) {
LOGE("could not create gps thread: %s", strerror(errno));
goto Fail;
}
D("gps state initialized");
return;
Fail:
gps_state_done( state );
}

在这个gps_state_init函数中，首先打开串口，然后建立socket通信，然后建立线程监听底层数据上报，分别对应于代码中黄低部分。

3）建立线程监听事件

mEventThread = new GpsEventThread();
mEventThread.start();

来看看GpsEventThread的run函数。

public void run() {
if (DEBUG) Log.d(TAG, "GpsEventThread starting");
// Exit as soon as disable() is called instead of waiting for the GPS to stop.
while (mEnabled) {
// this will wait for an event from the GPS,
// which will be reported via reportLocation or reportStatus
native_wait_for_event();
}
if (DEBUG) Log.d(TAG, "GpsEventThread exiting");
}
}

run函数中还是需要调用native函数：JNI：android_location_GpsLocationProvider_wait_for_event函数。这个函数就是在一个while循环里面等待事件的触发（由回调函数触发），然后调用GpsLocationProvider类的数据上报函数（Location数据）。这个在后面还会讲到。

static void android_location_GpsLocationProvider_wait_for_event(JNIEnv* env, jobject obj)
{
pthread_mutex_lock(&sEventMutex);
while (sPendingCallbacks == 0) {
pthread_cond_wait(&sEventCond, &sEventMutex);
}
...
}

分析完了enable函数以后就轮到enableLocationTracking函数了。

GpsLocationProvider.java

public void enableLocationTracking(boolean enable) { synchronized (mHandler) { mHandler.removeMessages(ENABLE_TRACKING); Message m = Message.obtain(mHandler, ENABLE_TRACKING); m.arg1 = (enable ? 1 : 0); mHandler.sendMessage(m); } }

同样地，也采取Handler的方式。调用的是handleEnableLocationTracking函数。

private void handleEnableLocationTracking(boolean enable) { if (enable) { mTTFF = 0; mLastFixTime = 0; startNavigating(); } else { mAlarmManager.cancel(mWakeupIntent); mAlarmManager.cancel(mTimeoutIntent); stopNavigating(); } }

调用startNavigating函数。

private void startNavigating() { if (!mStarted) { if (DEBUG) Log.d(TAG, "startNavigating"); mStarted = true; int positionMode; if (Settings.Secure.getInt(mContext.getContentResolver(), Settings.Secure.ASSISTED_GPS_ENABLED, 1) != 0) { positionMode = GPS_POSITION_MODE_MS_BASED; } else { positionMode = GPS_POSITION_MODE_STANDALONE; } if (!native_start(positionMode, false, 1)) { mStarted = false; Log.e(TAG, "native_start failed in startNavigating()"); return; }