在Android系统启动的时候，会在./frameworks/base/services/java/com/android/server/SystemServer.java类中启动许多服务，其中和Wifi相关的服务就在这里初始化。在SystemServer的main方法中，我们可以看到
thr.initAndLoop();
这里调用了它的内部类对象的initAndLoop方法，在这个方法的作用主要就是初始化系统启动需要加载的服务的，我们在这个方法中可以找到
try { Slog.i(TAG, "Wi-Fi Service"); wifi = new WifiService(context); ServiceManager.addService(Context.WIFI_SERVICE, wifi); } catch (Throwable e) { reportWtf("starting Wi-Fi Service", e); } try { Slog.i(TAG, "Connectivity Service"); connectivity = new ConnectivityService( context, networkManagement, networkStats, networkPolicy); ServiceManager.addService(Context.CONNECTIVITY_SERVICE, connectivity); networkStats.bindConnectivityManager(connectivity); networkPolicy.bindConnectivityManager(connectivity); wifiP2p.connectivityServiceReady(); wifi.checkAndStartWifi(); } catch (Throwable e) { reportWtf("starting Connectivity Service", e); }这里我们可以看到初始化了一个WifiService和ConnectivityService对象，并把这2个对象注册到ServiceManager中，然后通过创建的对象wifi 来调用checkAndStartWifi方法，具体的WifiService的分析我们下一章再做详细介绍，现在我们简单分析下ConnectivityService。
ConnectivityService是管理系统中所有的数据连接服务，其中就包括Wifi，我们来看看它的构造函数，路径：./frameworks/base/services/java/com/android/server/ConnectivityService.java
public ConnectivityService(Context context, INetworkManagementService netd, INetworkStatsService statsService, INetworkPolicyManager policyManager) { // Currently, omitting a NetworkFactory will create one internally // TODO: create here when we have cleaner WiMAX support this(context, netd, statsService, policyManager, null); }public ConnectivityService(Context context, INetworkManagementService netManager, INetworkStatsService statsService, INetworkPolicyManager policyManager, NetworkFactory netFactory) { if (DBG) log("ConnectivityService starting up"); HandlerThread handlerThread = new HandlerThread("ConnectivityServiceThread"); handlerThread.start(); mHandler = new InternalHandler(handlerThread.getLooper()); mTrackerHandler = new NetworkStateTrackerHandler(handlerThread.getLooper());// Create and start trackers for hard-coded networks for (int targetNetworkType : mPriorityList) { final NetworkConfig config = mNetConfigs[targetNetworkType]; final NetworkStateTracker tracker; try { /** M: Hotspot Manager @{*/ if(config.radio == TYPE_USB){ log("new UsbDataStateTracker"); mNetTrackers[targetNetworkType] = new UsbDataStateTracker(targetNetworkType, config.name, mNetd); mNetTrackers[targetNetworkType].startMonitoring(context, mTrackerHandler); continue; } if(true == FeatureOption.MTK_ALPS_BOX_SUPPORT && config.radio == TYPE_ETHERNET){ if (DBG) log("Starting Ethernet Service."); mNetTrackers[TYPE_ETHERNET] = makeEthStateTracker(context); if(mNetTrackers[TYPE_ETHERNET] != null){ if (DBG) log("mNetTrackers[TYPE_ETHERNET] != null"); mNetTrackers[TYPE_ETHERNET].startMonitoring(context, mTrackerHandler); if (config.isDefault()) { mNetTrackers[TYPE_ETHERNET].reconnect(); } } continue; } /*@} */ /*@} */ ///M:new a Teledongle Data Tracker @by mtk94127 @{ if(FeatureOption.MTK_EXTERNAL_DONGLE_SUPPORT && (config.radio == TYPE_TEDONGLE)) { log("new TedongleDataStateTracker"); mNetTrackers[targetNetworkType] = makeTedongleDataTracker(); log("new TedongleDataStateTracker medium!"); mNetTrackers[targetNetworkType].startMonitoring(context, mTrackerHandler); log("new TedongleDataStateTracker end!"); continue; } ///M:@} tracker = netFactory.createTracker(targetNetworkType, config); mNetTrackers[targetNetworkType] = tracker; } catch (IllegalArgumentException e) { Slog.e(TAG, "Problem creating " + getNetworkTypeName(targetNetworkType) + " tracker: " + e); continue; } tracker.startMonitoring(context, mTrackerHandler); if (config.isDefault()) { tracker.reconnect(); } }}这里根据com.android.internal.R.array.networkAttributes配置的属性去创建一个个tracker，并监听其状态，tracker.startMonitoring(context, mTrackerHandler);可以看出tracker可以通过mTrackerHandler向ConnectivityService发送消息，这些消息有
/** * The network state has changed and the NetworkInfo object * contains the new state. * * msg.what = EVENT_STATE_CHANGED * msg.obj = NetworkInfo object */ public static final int EVENT_STATE_CHANGED = BASE_NETWORK_STATE_TRACKER; /** * msg.what = EVENT_CONFIGURATION_CHANGED * msg.obj = NetworkInfo object */ public static final int EVENT_CONFIGURATION_CHANGED = BASE_NETWORK_STATE_TRACKER + 1; /** * msg.what = EVENT_RESTORE_DEFAULT_NETWORK * msg.obj = FeatureUser object */ public static final int EVENT_RESTORE_DEFAULT_NETWORK = BASE_NETWORK_STATE_TRACKER + 2; /** * msg.what = EVENT_NETWORK_SUBTYPE_CHANGED * msg.obj = NetworkInfo object */ public static final int EVENT_NETWORK_SUBTYPE_CHANGED = BASE_NETWORK_STATE_TRACKER + 3; /** * msg.what = EVENT_NETWORK_CONNECTED * msg.obj = LinkProperties object */ public static final int EVENT_NETWORK_CONNECTED = BASE_NETWORK_STATE_TRACKER + 4; /** * msg.what = EVENT_NETWORK_CONNECTION_DISCONNECTED * msg.obj = LinkProperties object, same iface name */ public static final int EVENT_NETWORK_DISCONNECTED = BASE_NETWORK_STATE_TRACKER + 5;
当WiFi的连接AP成功后，就会想 ConnectivityService发送一个EVENT_STATE_CHANGED消息。
接着我们来看创建了哪些tracker，找到createTracker方法
@Override public NetworkStateTracker createTracker(int targetNetworkType, NetworkConfig config) { switch (config.radio) { case TYPE_WIFI: return new WifiStateTracker(targetNetworkType, config.name); case TYPE_MOBILE: return new MobileDataStateTracker(targetNetworkType, config.name); case TYPE_DUMMY: return new DummyDataStateTracker(targetNetworkType, config.name); case TYPE_BLUETOOTH: return BluetoothTetheringDataTracker.getInstance(); case TYPE_WIMAX: return makeWimaxStateTracker(mContext, mTrackerHandler); case TYPE_CSD: return new CsdStateTracker(targetNetworkType, config.name); default: throw new IllegalArgumentException( "Trying to create a NetworkStateTracker for an unknown radio type: " + config.radio); } }这里我们主要关注TYPE_WIFI，创建了一个WifiStateTracker对象，进入到WifiStateTracker的构造方法
public WifiStateTracker(int netType, String networkName) { ///M:@{ mNetType = netType; ///@} mNetworkInfo = new NetworkInfo(netType, 0, networkName, ""); mLinkProperties = new LinkProperties(); mLinkCapabilities = new LinkCapabilities(); mNetworkInfo.setIsAvailable(false); setTeardownRequested(false); }接着调用startMonitoring
/** * Begin monitoring wifi connectivity */ public void startMonitoring(Context context, Handler target) { mCsHandler = target; mContext = context; mWifiManager = (WifiManager) mContext.getSystemService(Context.WIFI_SERVICE); IntentFilter filter = new IntentFilter(); ///M:seperate p2p and wifi @{ if (mNetType == ConnectivityManager.TYPE_WIFI) { filter.addAction(WifiManager.NETWORK_STATE_CHANGED_ACTION); filter.addAction(WifiManager.LINK_CONFIGURATION_CHANGED_ACTION); } ///@} mWifiStateReceiver = new WifiStateReceiver(); mContext.registerReceiver(mWifiStateReceiver, filter); }这里就是注册了一个广播用于接收NETWORK_STATE_CHANGED_ACTION和LINK_CONFIGURATION_CHANGED_ACTION广播，ConnectivityService我们就分析到这里，下一章我们将详细分析WifiService。