文章出處:http://www.limodev.cn/blog
作者連絡方式:李先靜 <xianjimli at hotmail dot com>
Broncho
A1還不支援基站和WIFI定位,Android的老版本裡是有NetworkLocationProvider的,它實現了基站和WIFI定位,但從
android 1.5之後就被移除了。本來想在broncho
A1裡自己實現NetworkLocationProvider的,但一直沒有時間去研究。我知道
gears(http://code.google.com/p/gears/)是有提供類似的功能,昨天研究了一下Gears的代碼,看能不能移植到
android中來。
1.下載原始碼
svn checkout http://gears.googlecode.com/svn/trunk/ gears-read-only
定位相關的原始碼在gears/geolocation目錄中。
2.關注android平台中的基站位置變化。
JAVA類AndroidRadioDataProvider是PhoneStateListener的子類,用來監聽Android電話的狀態變化。當服務狀態、訊號強度和基站變化時,就會用下面代碼擷取小區資訊:
RadioData radioData = new RadioData();
GsmCellLocation gsmCellLocation = (GsmCellLocation) cellLocation;
// Extract the cell id, LAC, and signal strength.
radioData.cellId = gsmCellLocation.getCid();
radioData.locationAreaCode = gsmCellLocation.getLac();
radioData.signalStrength = signalStrength;
// Extract the home MCC and home MNC.
String operator = telephonyManager.getSimOperator();
radioData.setMobileCodes(operator, true);
if (serviceState != null) {
// Extract the carrier name.
radioData.carrierName = serviceState.getOperatorAlphaLong();
// Extract the MCC and MNC.
operator = serviceState.getOperatorNumeric();
radioData.setMobileCodes(operator, false);
}
// Finally get the radio type.
int type = telephonyManager.getNetworkType();
if (type == TelephonyManager.NETWORK_TYPE_UMTS) {
radioData.radioType = RADIO_TYPE_WCDMA;
} else if (type == TelephonyManager.NETWORK_TYPE_GPRS
|| type == TelephonyManager.NETWORK_TYPE_EDGE) {
radioData.radioType = RADIO_TYPE_GSM;
}
然後調用用C代碼實現的onUpdateAvailable函數。
2.Native函數onUpdateAvailable是在radio_data_provider_android.cc裡實現的。
聲明Native函數
JNINativeMethod AndroidRadioDataProvider::native_methods_[] = {
{"onUpdateAvailable",
"(L" GEARS_JAVA_PACKAGE "/AndroidRadioDataProvider$RadioData;J)V",
reinterpret_cast<void*>(AndroidRadioDataProvider::OnUpdateAvailable)
},
};
JNI調用好像只能調用靜態成員函數,把對象本身用一個參數傳進來,然後再調用對象的成員函數。
void AndroidRadioDataProvider::OnUpdateAvailable(JNIEnv* env,
jclass cls,
jobject radio_data,
jlong self) {
assert(radio_data);
assert(self);
AndroidRadioDataProvider *self_ptr =
reinterpret_cast<AndroidRadioDataProvider*>(self);
RadioData new_radio_data;
if (InitFromJavaRadioData(env, radio_data, &new_radio_data)) {
self_ptr->NewRadioDataAvailable(&new_radio_data);
}
}
先判斷基站資訊有沒有變化,如果有變化則通知相關的監聽者。
void AndroidRadioDataProvider::NewRadioDataAvailable(
RadioData* new_radio_data) {
bool is_update_available = false;
data_mutex_.Lock();
if (new_radio_data && !radio_data_.Matches(*new_radio_data)) {
radio_data_ = *new_radio_data;
is_update_available = true;
}
// Avoid holding the mutex locked while notifying observers.
data_mutex_.Unlock();
if (is_update_available) {
NotifyListeners();
}
}
接下來的過程,基站定位和WIFI定位是一樣的,後面我們再來介紹。下面我們先看WIFI定位。
3.關注android平台中的WIFI變化。
JAVA類AndroidWifiDataProvider擴充了BroadcastReceiver類,它關注WIFI掃描結果:
IntentFilter filter = new IntentFilter();
filter.addAction(mWifiManager.SCAN_RESULTS_AVAILABLE_ACTION);
mContext.registerReceiver(this, filter, null, handler);
當收到WIFI掃描結果後,調用Native函數onUpdateAvailable,並把WIFI的掃描結果傳遞過去。
public void onReceive(Context context, Intent intent) {
if (intent.getAction().equals(
mWifiManager.SCAN_RESULTS_AVAILABLE_ACTION)) {
if (Config.LOGV) {
Log.v(TAG, "Wifi scan resulst available");
}
onUpdateAvailable(mWifiManager.getScanResults(), mNativeObject);
}
}
4.Native函數onUpdateAvailable是在wifi_data_provider_android.cc裡實現的。
JNINativeMethod AndroidWifiDataProvider::native_methods_[] = {
{"onUpdateAvailable",
"(Ljava/util/List;J)V",
reinterpret_cast<void*>(AndroidWifiDataProvider::OnUpdateAvailable)
},
};
void AndroidWifiDataProvider::OnUpdateAvailable(JNIEnv* /* env */,
jclass /* cls */,
jobject wifi_data,
jlong self) {
assert(self);
AndroidWifiDataProvider *self_ptr =
reinterpret_cast<AndroidWifiDataProvider*>(self);
WifiData new_wifi_data;
if (wifi_data) {
InitFromJava(wifi_data, &new_wifi_data);
}
// We notify regardless of whether new_wifi_data is empty
// or not. The arbitrator will decide what to do with an empty
// WifiData object.
self_ptr->NewWifiDataAvailable(&new_wifi_data);
}
void AndroidWifiDataProvider::NewWifiDataAvailable(WifiData* new_wifi_data) {
assert(supported_);
assert(new_wifi_data);
bool is_update_available = false;
data_mutex_.Lock();
is_update_available = wifi_data_.DiffersSignificantly(*new_wifi_data);
wifi_data_ = *new_wifi_data;
// Avoid holding the mutex locked while notifying observers.
data_mutex_.Unlock();
if (is_update_available) {
is_first_scan_complete_ = true;
NotifyListeners();
}
#if USING_CCTESTS
// This is needed for running the WiFi test on the emulator.
// See wifi_data_provider_android.h for details.
if (!first_callback_made_ && wifi_data_.access_point_data.empty()) {
first_callback_made_ = true;
NotifyListeners();
}
#endif
}
從以上代碼可以看出,WIFI定位和基站定位的邏輯差不多,只是前者擷取的WIFI的掃描結果,而後者擷取的基站資訊。後面代碼的基本上就統一起來了,接下來我們繼續看。
5.把變化(WIFI/基站)通知給相應的監聽者。
AndroidWifiDataProvider和AndroidRadioDataProvider都是繼承了DeviceDataProviderImplBase,DeviceDataProviderImplBase的主要功能就是管理所有Listeners。
static DeviceDataProvider *Register(ListenerInterface *listener) {
MutexLock mutex(&instance_mutex_);
if (!instance_) {
instance_ = new DeviceDataProvider();
}
assert(instance_);
instance_->Ref();
instance_->AddListener(listener);
return instance_;
}
static bool Unregister(ListenerInterface *listener) {
MutexLock mutex(&instance_mutex_);
if (!instance_->RemoveListener(listener)) {
return false;
}
if (instance_->Unref()) {
delete instance_;
instance_ = NULL;
}
return true;
}
6.誰在監聽變化(WIFI/基站)
NetworkLocationProvider在監聽變化(WIFI/基站):
radio_data_provider_ = RadioDataProvider::Register(this);
wifi_data_provider_ = WifiDataProvider::Register(this);
當有變化時,會調用函數DeviceDataUpdateAvailable:
// DeviceDataProviderInterface::ListenerInterface implementation.
void NetworkLocationProvider::DeviceDataUpdateAvailable(
RadioDataProvider *provider) {
MutexLock lock(&data_mutex_);
assert(provider == radio_data_provider_);
is_radio_data_complete_ = radio_data_provider_->GetData(&radio_data_);
DeviceDataUpdateAvailableImpl();
}
void NetworkLocationProvider::DeviceDataUpdateAvailable(
WifiDataProvider *provider) {
assert(provider == wifi_data_provider_);
MutexLock lock(&data_mutex_);
is_wifi_data_complete_ = wifi_data_provider_->GetData(&wifi_data_);
DeviceDataUpdateAvailableImpl();
}
無論是WIFI還是基站變化,最後都會調用DeviceDataUpdateAvailableImpl:
void NetworkLocationProvider::DeviceDataUpdateAvailableImpl() {
timestamp_ = GetCurrentTimeMillis();
// Signal to the worker thread that new data is available.
is_new_data_available_ = true;
thread_notification_event_.Signal();
}
這裡面只是發了一個signal,通知另外一個線程去處理。
7.誰在等待thread_notification_event_
線程函數NetworkLocationProvider::Run在一個迴圈中等待thread_notification_event,當有變化(WIFI/基站)時,就準備請求伺服器查詢位置。
先等待:
if (remaining_time > 0) {
thread_notification_event_.WaitWithTimeout(
static_cast<int>(remaining_time));
} else {
thread_notification_event_.Wait();
}
準備請求:
if (make_request) {
MakeRequest();
remaining_time = 1;
}
再來看MakeRequest的實現:
先從cache中尋找位置:
const Position *cached_position =
position_cache_->FindPosition(radio_data_, wifi_data_);
data_mutex_.Unlock();
if (cached_position) {
assert(cached_position->IsGoodFix());
// Record the position and update its timestamp.
position_mutex_.Lock();
position_ = *cached_position;
position_.timestamp = timestamp_;
position_mutex_.Unlock();
// Let listeners know that we now have a position available.
UpdateListeners();
return true;
}
如果找不到,再做實際的請求
return request_->MakeRequest(access_token,
radio_data_,
wifi_data_,
request_address_,
address_language_,
kBadLatLng, // We don't have a position to pass
kBadLatLng, // to the server.
timestamp_);
7.用戶端協議封裝
前面的request_是NetworkLocationRequest執行個體,先看MakeRequest的實現:
先對參數進行打包:
if (!FormRequestBody(host_name_, access_token, radio_data, wifi_data,
request_address, address_language, latitude, longitude,
is_reverse_geocode_, &post_body_)) {
return false;
}
通知負責收發的線程
thread_event_.Signal();
8.負責收發的線程
void NetworkLocationRequest::Run() {
while (true) {
thread_event_.Wait();
if (is_shutting_down_) {
break;
}
MakeRequestImpl();
}
}
void NetworkLocationRequest::MakeRequestImpl() {
WebCacheDB::PayloadInfo payload;
把打包好的資料通過HTTP請求,發送給伺服器
scoped_refptr<BlobInterface> payload_data;
bool result = HttpPost(url_.c_str(),
false, // Not capturing, so follow redirects
NULL, // reason_header_value
HttpConstants::kMimeApplicationJson, // Content-Type
NULL, // mod_since_date
NULL, // required_cookie
true, // disable_browser_cookies
post_body_.get(),
&payload,
&payload_data,
NULL, // was_redirected
NULL, // full_redirect_url
NULL); // error_message
MutexLock lock(&is_processing_response_mutex_);
// is_aborted_ may be true even if HttpPost succeeded.
if (is_aborted_) {
LOG(("NetworkLocationRequest::Run() : HttpPost request was cancelled.\n"));
return;
}
if (listener_) {
Position position;
std::string response_body;
if (result) {
// If HttpPost succeeded, payload_data is guaranteed to be non-NULL.
assert(payload_data.get());
if (!payload_data->Length() ||
!BlobToString(payload_data.get(), &response_body)) {
LOG(("NetworkLocationRequest::Run() : Failed to get response body.\n"));
}
}
解析出位置資訊
std::string16 access_token;
GetLocationFromResponse(result, payload.status_code, response_body,
timestamp_, url_, is_reverse_geocode_,
&position, &access_token);
通知位置資訊的監聽者。
bool server_error =
!result || (payload.status_code >= 500 && payload.status_code < 600);
listener_->LocationResponseAvailable(position, server_error, access_token);
}
}
有人會問,請求是發哪個伺服器的?當然是google了,預設的URL是:
static const char16 *kDefaultLocationProviderUrl =
STRING16(L"https://www.google.com/loc/json");
回過頭來,我們再總結一下:
1.WIFI和基站定位過程如下:
2.NetworkLocationProvider和NetworkLocationRequest各有一個線程來非同步處理請求。
3.這裡的NetworkLocationProvider與android中的NetworkLocationProvider並不是同一個東西,這裡
是給gears用的,要在android的google
map中使用,還得封裝成android中的NetworkLocationProvider的介面。
4.WIFI和基站定位與平台無關,只要你能拿到WIFI掃描結果或基站資訊,而且能訪問google的定位服務器,不管你是Android平台,Windows Mobile平台還是傳統的feature phone,你都可以實現WIFI和基站定位。
附: WIFI和基站定位原理
無論是WIFI的存取點,還是移動網路的基站裝置,它們的位置基本上都是固定的。裝置端(如手機)可以找到它們的ID,現在的問題就是如何通過這些ID找到對應的位置。網上的流行的說法是開車把所有每個位置都跑一遍,把這些裝置的位置與GPS測試的位置關聯起來。
參考資料:
Gears: http://gears.googlecode.com/
Google 地圖 API: http://code.google.com/intl/zh-CN/apis/maps/documentation/reference.html
wifi定位技術: http://blog.csdn.net/NewMap/archive/2009/03/17/3999337.aspx