Android系列之Wifi定位

Broncho A1还不支持基站和WIFI定位，Android的老版本里是有NetworkLocationProvider的，它实现了基站和WIFI定位，但从 android 1.5之后就被移除了。本来想在broncho A1里自己实现NetworkLocationProvider的，但一直没有时间去研究。我知道 gears(http://code.google.com/p/gears/)是有提供类似的功能，昨天研究了一下Gears的代码，看能不能移植到 android中来

1.下载源代码 
[url]svn checkout http://gears.googlecode.com/svn/trunk/ gears-read-only[/url] 
定位相关的源代码在gears/geolocation目录中。

2.关注android平台中的基站位置变化

JAVA类AndroidRadioDataProvider是 PhoneStateListener的子类，用来监听Android电话的状态变化。当服务状态、信号强度和基站变化时，

就会用下面代码获取小区信息：

1 RadioData radioData = new RadioData();         
2             GsmCellLocation gsmCellLocation = (GsmCellLocation) cellLocation;         
3             
4             // Extract the cell id, LAC, and signal strength.         
5             radioData.cellId = gsmCellLocation.getCid();         
6             radioData.locationAreaCode = gsmCellLocation.getLac();         
7             radioData.signalStrength = signalStrength;         
8             
9             // Extract the home MCC and home MNC.        
10             String operator = telephonyManager.getSimOperator();        
11             radioData.setMobileCodes(operator, true);        
12            
13             if (serviceState != null) {        
14                 // Extract the carrier name.        
15                 radioData.carrierName = serviceState.getOperatorAlphaLong();        
16            
17                 // Extract the MCC and MNC.        
18                 operator = serviceState.getOperatorNumeric();        
19                 radioData.setMobileCodes(operator, false);        
20             }        
21            
22             // Finally get the radio type.        
23             int type = telephonyManager.getNetworkType();        
24             if (type == TelephonyManager.NETWORK_TYPE_UMTS) {        
25                 radioData.radioType = RADIO_TYPE_WCDMA;        
26             } else if (type == TelephonyManager.NETWORK_TYPE_GPRS        
27                                    || type == TelephonyManager.NETWORK_TYPE_EDGE) {        
28                 radioData.radioType = RADIO_TYPE_GSM;        
29             }     
30

然后再调用用C代码实现的onUpdateAvailable函数。 
2.Native函数onUpdateAvailable是在 radio_data_provider_android.cc里实现的。 
声明Native函数

1 JNINativeMethod AndroidRadioDataProvider::native_methods_[] = {        
2     {"onUpdateAvailable",        
3        "(L" GEARS_JAVA_PACKAGE "/AndroidRadioDataProvider$RadioData;J)V",        
4        reinterpret_cast<void*>(AndroidRadioDataProvider::OnUpdateAvailable)        
5     },        
6 };     
7

 

JNI调用好像只能调用静态成员函数，把对象本身用一个参数传进来，然后再调用对象的成员函数。

 

 

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);            
}        
}    

 

先判断基站信息有没有变化，如果有变化则通知相关的监听者。

 

1 void AndroidRadioDataProvider::NewRadioDataAvailable(         
2         RadioData* new_radio_data) {         
3     bool is_update_available = false;         
4     data_mutex_.Lock();         
5     if (new_radio_data && !radio_data_.Matches(*new_radio_data)) {         
6         radio_data_ = *new_radio_data;         
7         is_update_available = true;         
8     }         
9     // Avoid holding the mutex locked while notifying observers.        
10     data_mutex_.Unlock();        
11            
12     if (is_update_available) {        
13         NotifyListeners();        
14     }        
15 }    

 

接下来的过程，在基站定位和WIFI定位是一样的，后面我们再来介绍。下面我们先看 WIFI定位

3.关注android平台中的WIFI变化。 

JAVA类AndroidWifiDataProvider扩展了 BroadcastReceiver类，它关注WIFI扫描结果:

1 IntentFilter filter = new IntentFilter();        
2         filter.addAction(mWifiManager.SCAN_RESULTS_AVAILABLE_ACTION);        
3         mContext.registerReceiver(this, filter, null, handler);    

当收到WIFI扫描结果后，调用Native函数 onUpdateAvailable，并把WIFI的扫描结果传递过去。

1 public void onReceive(Context context, Intent intent) {        
2        if (intent.getAction().equals(        
3                        mWifiManager.SCAN_RESULTS_AVAILABLE_ACTION)) {        
4            if (Config.LOGV) {        
5                Log.v(TAG, "Wifi scan resulst available");        
6            }        
7            onUpdateAvailable(mWifiManager.getScanResults(), mNativeObject);        
8        }        
9    }    

Native函数onUpdateAvailable是在 wifi_data_provider_android.cc里实现的。

1 JNINativeMethod AndroidWifiDataProvider::native_methods_[] = {    
2 {"onUpdateAvailable",    
3 "(Ljava/util/List;J)V",    
4 reinterpret_cast<void*>(AndroidWifiDataProvider::OnUpdateAvailable)    
5 },    
6 };    
7    
8 void AndroidWifiDataProvider::OnUpdateAvailable(JNIEnv* /* env */,    
9 jclass /* cls */,    
10 jobject wifi_data,    
11 jlong self) {    
12 assert(self);    
13 AndroidWifiDataProvider *self_ptr =    
14 reinterpret_cast<AndroidWifiDataProvider*>(self);    
15 WifiData new_wifi_data;    
16 if (wifi_data) {    
17 InitFromJava(wifi_data, &new_wifi_data);    
18 }    
19 // We notify regardless of whether new_wifi_data is empty    
20 // or not. The arbitrator will decide what to do with an empty    
21 // WifiData object.    
22 self_ptr->NewWifiDataAvailable(&new_wifi_data);    
23 }    
24    
25 void AndroidWifiDataProvider::NewWifiDataAvailable(WifiData* new_wifi_data) {    
26 assert(supported_);    
27 assert(new_wifi_data);    
28 bool is_update_available = false;    
29 data_mutex_.Lock();    
30 is_update_available = wifi_data_.DiffersSignificantly(*new_wifi_data);    
31 wifi_data_ = *new_wifi_data;    
32 // Avoid holding the mutex locked while notifying observers.    
33 data_mutex_.Unlock();    
34    
35 if (is_update_available) {    
36 is_first_scan_complete_ = true;    
37 NotifyListeners();    
38 }    
39    
40 #if USING_CCTESTS    
41 // This is needed for running the WiFi test on the emulator.    
42 // See wifi_data_provider_android.h for details.    
43 if (!first_callback_made_ && wifi_data_.access_point_data.empty()) {    
44 first_callback_made_ = true;    
45 NotifyListeners();    
46 }    
47 #endif    
48 }    
49    
50 JNINativeMethod AndroidWifiDataProvider::native_methods_[] = { 
51 {"onUpdateAvailable", 
52 "(Ljava/util/List;J)V", 
53 reinterpret_cast<void*>(AndroidWifiDataProvider::OnUpdateAvailable) 
54 }, 
55 }; 
56    
57 void AndroidWifiDataProvider::OnUpdateAvailable(JNIEnv* /* env */, 
58 jclass /* cls */, 
59 jobject wifi_data, 
60 jlong self) { 
61 assert(self); 
62 AndroidWifiDataProvider *self_ptr = 
63 reinterpret_cast<AndroidWifiDataProvider*>(self); 
64 WifiData new_wifi_data; 
65 if (wifi_data) { 
66 InitFromJava(wifi_data, &new_wifi_data); 
67 } 
68 // We notify regardless of whether new_wifi_data is empty 
69 // or not. The arbitrator will decide what to do with an empty 
70 // WifiData object. 
71 self_ptr->NewWifiDataAvailable(&new_wifi_data); 
72 } 
73    
74 void AndroidWifiDataProvider::NewWifiDataAvailable(WifiData* new_wifi_data) { 
75 assert(supported_); 
76 assert(new_wifi_data); 
77 bool is_update_available = false; 
78 data_mutex_.Lock(); 
79 is_update_available = wifi_data_.DiffersSignificantly(*new_wifi_data); 
80 wifi_data_ = *new_wifi_data; 
81 // Avoid holding the mutex locked while notifying observers. 
82 data_mutex_.Unlock(); 
83    
84 if (is_update_available) { 
85 is_first_scan_complete_ = true; 
86 NotifyListeners(); 
87 } 
88    
89 #if USING_CCTESTS 
90 // This is needed for running the WiFi test on the emulator. 
91 // See wifi_data_provider_android.h for details. 
92 if (!first_callback_made_ && wifi_data_.access_point_data.empty()) { 
93 first_callback_made_ = true; 
94 NotifyListeners(); 
95 } 
96 #endif 
97 } 
98

从以上代码可以看出，WIFI定位和基站定位的逻辑差不多，只是前者获取的WIFI的扫描结果，而后者获取的基站信息。

后面代码的基本上就统一起来了，接下来我们继续看。 

5.把变化(WIFI/基站）通知给相应的监听者。

1 AndroidWifiDataProvider和AndroidRadioDataProvider都是继承了DeviceDataProviderImplBase，DeviceDataProviderImplBase的主要功能就是管理所有Listeners。         
2             
3     static DeviceDataProvider *Register(ListenerInterface *listener) {         
4         MutexLock mutex(&instance_mutex_);         
5         if (!instance_) {         
6             instance_ = new DeviceDataProvider();         
7         }         
8         assert(instance_);         
9         instance_->Ref();        
10         instance_->AddListener(listener);        
11         return instance_;        
12     }        
13            
14     static bool Unregister(ListenerInterface *listener) {        
15         MutexLock mutex(&instance_mutex_);        
16         if (!instance_->RemoveListener(listener)) {        
17             return false;        
18         }        
19         if (instance_->Unref()) {        
20             delete instance_;        
21             instance_ = NULL;        
22         }        
23         return true;        
24     }     
25

6.谁在监听变化(WIFI/基站） 

NetworkLocationProvider在监听变化(WIFI/基站）: 

1 radio_data_provider_ = RadioDataProvider::Register(this);        
2     wifi_data_provider_ = WifiDataProvider::Register(this);    

 

当有变化时，会调用函数DeviceDataUpdateAvailable：

 

 

 无论是WIFI还是基站变化，最后都会调用 DeviceDataUpdateAvailableImpl：

1 void NetworkLocationProvider::DeviceDataUpdateAvailableImpl() { 
2     timestamp_ = GetCurrentTimeMillis(); 
3     
4     // Signal to the worker thread that new data is available. 
5     is_new_data_available_ = true; 
6     thread_notification_event_.Signal(); 
7 }

 

 

这里面只是发了一个signal，通知另外一个线程去处理。 

7.谁在等待thread_notification_event_ 

线程函数NetworkLocationProvider::Run在一个循环中等待 thread_notification_event，当有变化(WIFI/基站）时，就准备请求服务器查询位置。 

先等待：

1 if (remaining_time > 0) { 
2             thread_notification_event_.WaitWithTimeout( 
3                     static_cast<int>(remaining_time)); 
4         } else { 
5             thread_notification_event_.Wait(); 
6         }

准备请求：

1 if (make_request) {        
2     MakeRequest();        
3     remaining_time = 1;        
4 }    

 

再来看MakeRequest的实现： 

先从cache中查找位置：

1    const Position *cached_position =    
2             position_cache_->FindPosition(radio_data_, wifi_data_);    
3     data_mutex_.Unlock();    
4     if (cached_position) {    
5         assert(cached_position->IsGoodFix());    
6         // Record the position and update its timestamp.    
7         position_mutex_.Lock();    
8         position_ = *cached_position;    
9         position_.timestamp = timestamp_; 
10         position_mutex_.Unlock(); 
11     
12         // Let listeners know that we now have a position available. 
13         UpdateListeners(); 
14         return true; 
15     }

 

如果找不到，再做实际的请求

1     return request_->MakeRequest(access_token, 
2                                                                radio_data_, 
3                                                                wifi_data_, 
4                                                                request_address_, 
5                                                                address_language_, 
6                                                                kBadLatLng,    // We don't have a position to pass 
7                                                                kBadLatLng,    // to the server. 
8                                                                timestamp_);

 

 

7.客户端协议包装 

前面的request_是NetworkLocationRequest实例，先看 MakeRequest的实现： 

先对参数进行打包：

1     if (!FormRequestBody(host_name_, access_token, radio_data, wifi_data, 
2                                                request_address, address_language, latitude, longitude, 
3                                                is_reverse_geocode_, &post_body_)) { 
4         return false; 
5     }

通知负责收发的线程 

1 thread_event_.Signal();

8.负责收发的线程

1 void NetworkLocationRequest::Run() {    
2     while (true) {    
3         thread_event_.Wait();    
4         if (is_shutting_down_) {    
5             break;    
6         }    
7         MakeRequestImpl();    
8     }    
9 } 
10     
11 void NetworkLocationRequest::MakeRequestImpl() { 
12     WebCacheDB::PayloadInfo payload;

 

把打包好的数据通过HTTP请求，发送给服务器
 

1    scoped_refptr<BlobInterface> payload_data;    
2     bool result = HttpPost(url_.c_str(),    
3                                                    false,                        // Not capturing, so follow redirects    
4                                                    NULL,                         // reason_header_value    
5                                                    HttpConstants::kMimeApplicationJson,    // Content-Type    
6                                                    NULL,                         // mod_since_date    
7                                                    NULL,                         // required_cookie    
8                                                    true,                         // disable_browser_cookies    
9                                                    post_body_.get(), 
10                                                    &payload, 
11                                                    &payload_data, 
12                                                    NULL,                         // was_redirected 
13                                                    NULL,                         // full_redirect_url 
14                                                    NULL);                        // error_message 
15     
16     MutexLock lock(&is_processing_response_mutex_); 
17     // is_aborted_ may be true even if HttpPost succeeded. 
18     if (is_aborted_) { 
19         LOG(("NetworkLocationRequest::Run() : HttpPost request was cancelled./n")); 
20         return; 
21     } 
22     if (listener_) { 
23         Position position; 
24         std::string response_body; 
25         if (result) { 
26             // If HttpPost succeeded, payload_data is guaranteed to be non-NULL. 
27             assert(payload_data.get()); 
28             if (!payload_data->Length() || 
29                     !BlobToString(payload_data.get(), &response_body)) { 
30                 LOG(("NetworkLocationRequest::Run() : Failed to get response body./n")); 
31             } 
32         }

 

解析出位置信息

1 std::string16 access_token; 
2         GetLocationFromResponse(result, payload.status_code, response_body, 
3                                                         timestamp_, url_, is_reverse_geocode_, 
4                                                         &position, &access_token);

通知位置信息的监听者

1    bool server_error = 
2                 !result || (payload.status_code >= 500 && payload.status_code < 600); 
3         listener_->LocationResponseAvailable(position, server_error, access_token); 
4     } 
5 }

有人会问，请求是发哪个服务器的？当然是google了，缺省的URL是：

1 static const char16 *kDefaultLocationProviderUrl = 
2         STRING16(L"https://www.google.com/loc/json");

回过头来，我们再总结一下：

1.WIFI和基站定位过程如下：

2.NetworkLocationProvider和 NetworkLocationRequest各有一个线程来异步处理请求。 

3.这里的NetworkLocationProvider与android中的 NetworkLocationProvider并不是同一个东西，这里是给gears用的，要在android的google map中使用，还得包装成android中的NetworkLocationProvider的接口。 

4.WIFI和基站定位与平台无关，只要你能拿到WIFI扫描结果或基站信息，而且能访问google的定位服务器，不管你是Android平台，Windows Mobile平台还是传统的feature phone，你都可以实现WIFI和基站定位。

附: WIFI和基站定位原理 

无论是WIFI的接入点，还是移动网络的基站设备，它们的位置基本上都是固定的。设备端(如手机）可以找到它们的ID，现在的问题就是如何通过这些ID找到对应的位置。网上的流行的说法是开车把所有每个位置都跑一遍，把这些设备的位置与 GPS测试的位置关联起来。  

本文出自 “失落的程序” 博客，请务必保留此出处http://350526.blog.51cto.com/340526/367139