Android的WiFi
我们通常看到WiFi的守护进程wpa_supplicant在我们的ps的进程列表中，这个就是我们的wifi守护进程。wpa_supplicant在external/wpa_supplicant里实现
wpa_supplicant适配层是通用的wpa_supplicant的封装，在Android中作为WIFI部分的硬件抽象层来使用。wpa_supplicant适配层主要用于封装与wpa_supplicant守护进程的通信，以提供给Android框架使用。它实现了加载，控制和消息监控等功能。
wpa_supplicant适配层的头文件如下所示：
hardware/libhardware_legacy/include/hardware_legacy/wifi.h
我们看它的加载过程
Init会在系统启动首先加载init.rc这个文件会加载所有service，这是linux启动的第一个用户空间的应用（属于linux进程，不属于Android应用）。
Service wpa_supplicant /system/bin/wpa_supplicant –Dwext –iwlan0 –d –c /data/misc/wifi/wpa_supplicant.conf
#user wifi
#group wifi system
Socket wpa_eth0 dgram 0660 wifi system
Disabled
Oneshot
Serive dhcpcd /system/bin/dhcpcd –f /system/etc/dhcpcd/dhcpcd.conf –d eth0
Disabled
Onshot
On property:init.svc.wpa_supplicant=stopped
Stop dhcpcd
添加/system/etc/wifi/wpa_supplicant.conf
Update_config=1
Ctrl_interface=/data/system/wpa_supplicant //和IFACE_DIR对应
Eapol_verison=1
Ap_scan=1
Fast_reauth=1
通过linux内核模块/system/lib/modules/wlan.ko 这个wifi模块定义在/hardware/libhardware_legacy/wifi/wifi.c
当SystemServer启动后会加载一系列的Service其中init2启动的就有ConnectivityService。ConnectivityService.java (frameworks/base/services/java/com/android/server)会管理所有的Connectivity相关的比如APN，WiFi。看看是怎么启动WiFi Service的：
if (DBG) Log.v(TAG, "Starting Wifi Service.");
WifiStateTracker wst = new WifiStateTracker(context, mHandler);
WifiService wifiService = new WifiService(context, wst);
ServiceManager.addService(Context.WIFI_SERVICE, wifiService);
WifiStateTracker会创建WifMonitor来接受来自底层的事件。WifiService和WifiMonitor是整个模块的核心部分，WifiService负责启动关闭wpa_supplicant、发命令给wpa_supplicant进程，WiFiMonitor负责从wpa_supplicant接收事件
整个流程是
SystemServer -> ServerThread -> ConnectivityService -> ConnectivityThread -> WifiTracker->WifiService -> WifiMonitor
WiFi 的启动过程
用户在设置界面下开启了WiFi，调用应用程序Settings中的setWifiEnabler的onPerferenceChange,再由WifiEnable调用WifiService，发送MESSAGE_ENABLE_WIFI,首先装载wifi内核模块wlan.ko然后启动wpa_supplicant（用/data/misc/wifi/wpa_supplicant.conf配置），再通过WifiStateTracker来启动WifiMonitor监视线程
WifiSettings.java (packages/apps/settings/src/com/android/settings/wifi)启动
mWifiEnabled = (CheckBoxPreference) preferenceScreen.findPreference(KEY_WIFI_ENABLED);
mWifiEnabler = new WifiEnabler(this, (WifiManager) getSystemService(WIFI_SERVICE),
mWifiEnabled);
这样就启动WifiEnabler
WifiEnabler.java (packages/apps/settings/src/com/android/settings/wifi)通过WifiManager调用WifiManager.java (frameworks/base/wifi/java/android/net/wifi) setWifiEnabled 中的 IWifiManager来启动wifiservice[mService.setWifiEnabled(enabled);]
WifiService.java (frameworks/base/services/java/com/android/server)又setWifiEnabled()这个里面的sendEnableMessage(enable, true, Binder.getCallingUid());来发送一则消息
Message msg = Message.obtain(mWifiHandler,
(enable ? MESSAGE_ENABLE_WIFI : MESSAGE_DISABLE_WIFI),
(persist ? 1 : 0), uid);
msg.sendToTarget();发送给自身的消息。
通过WifiHandler的 handleMessage来维护这些消息，enable的时候会调用setWifiEnabledBlocking这个函数，这个函数会做setWifiEnabledState 然后做两件事： 1. 调用wifi 本地方法JNI的WifiNative.loadDriver
下面说本地方法WifiNative.loadDriver函数 WifiNative.java (frameworks/base/wifi/java/android/net/wifi) Android的WIFI系统的JNI的部分：
frameworks/base/core/jni/android_net_wifi_Wifi.cpp 中的android_net_wifi_loadDriver()可以把wifi驱动模块装载
Wifi.c (hardware/libhardware_legacy/wifi) 内核模块/system/lib/modules/wlan.ko中的wifi_load_driver()
设置wlan.driver.status属性为ok，至此wifi模块加载完毕。
2. 再来看看启动，同样是在WifiService 中的setWifiEnabledBlocking这个函数会调用startSupplicant 通过WifiNative.java (frameworks/base/wifi/java/android/net/wifi)的startSupplicant来启动JNI：frameworks/base/core/jni/android_net_wifi_Wifi.cpp的android_net_wifi_startSupplicant调用驱动模块Wifi.c (hardware/libhardware_legacy/wifi) wlan.ko中的wifi_start_supplicant, Wifi 启动完毕
成功启动wifi之后setWifiEnabledBlocking运行mWifiStateTracker.startEventLoop();事件循环，来监视事件mWifiMonitor.startMonitoring(); à MonitorThread().start();一直在线程里循环调用WifiNative.waitForEvent();最后调用
setWifiEnabledState(eventualWifiState, uid); intent = new Intent(WifiManager.WIFI_STATE_CHANGED_ACTION);广播消息向外界通知wifi已经成功启动了。
查找热点AP
上面说了WifiManager发送广播WIFI_STATE_CHANGED_ACTION，只要Android应用注册了接受该Action的就接受，我们的WifiLayer注册了接收到该Action
WifiSettings.java (packages/apps/settings/src/com/android/settings/wifi)中有mWifiLayer.onCreate();（这个函数创建WifiLayer指定接受的Action）
WifiLayer.java (packages/apps/settings/src/com/android/settings/wifi)中的BroadcastReceiver 有一句话else if (action.equals(WifiManager.WIFI_STATE_CHANGED_ACTION)) {
handleWifiStateChanged(intent.getIntExtra(WifiManager.EXTRA_WIFI_STATE,
WifiManager.WIFI_STATE_UNKNOWN));
这个函数会调用loadConfiguredAccessPoints和attemptScan来开始扫描，调用WifiManager的mWifiManager.startScanActive，WifiManager.java中的mService.startScan通过WifiService中的startScan通过本地方法WifiNative.setScanResultHandlingCommand启动JNI android_net_wifi_Wifi.cpp (frameworks/base/core/jni) 中的android_net_wifi_setScanResultHandlingCommand的命令“AP_SCAN 模式” Wifi.c ::wifi_command(cmd)开始扫描wifi_send_command发出SCAN命令调用wpa_supplicant开始扫描
扫描完成之后会发送SCAN_RESULT 在WifiMonitor的HandleEvent里处理调用mWifiStateTracker.notifyScanResultsAvailable(); à sendEmptyMessage(EVENT_SCAN_RESULTS_AVAILABLE); mWifiStateTracker中的 handleMessage接收到case EVENT_SCAN_RESULTS_AVAILABLE:之后发送广播mContext.sendBroadcast(new Intent(WifiManager.SCAN_RESULTS_AVAILABLE_ACTION));
WiFiLayer接收到这个消息在mReceiver = new BroadcastReceiver()中处理handleScanResultsAvailable();
WiFi 连接流程
用户在AccessPointDialog中输入密码之后点击连接按钮，Android调用顺序如下：
AccessPointDialog.java (packages/apps/settings/src/com/android/settings/wifi) -> onClick -> handleConnect(); -> mWifiLayer.connectToNetwork ->通过WifiConfiguration config = findConfiguredNetwork(state);查看是不是配置过的，如果是就直接使用了，如果不是config = addConfiguration(state, 0); -> managerEnableNetwork -> mWifiManager.enableNetwork -> mService.enableNetwork -> WifiService. enableNetwork -> WifiNative.enableNetworkCommand -> JNI: android_net_wifi_Wifi.cpp android_net_wifi_enableNetworkCommand 调用wpa_suppcant发送相关命令返回之后由WiFiMonitor处理跟以前类似，连接的中间流程与查找AP的流程类似，都经过了WifiMonitor对“CONNECTED”消息响应的捕获，以及WifiStateTracker对EVENT_SUPPLICANT_STATE_ CHANGED的处理。还有一个比较重
要的步骤是WifiStateTracker通过对DHCP服务器的申请进行了IP地址分配。最终会广播NETWORK_STATE_CHANGED_ ACTION消息，由WifiLayer响应。
IP地址分配
由上面继续说IP地址分配，因为当wpa_supplicant链接AP成功之后，它会发出事件从而wifi_for_event函数会接收到该事件，由WifiMonitor中的MonitorThread执行执行这个事件handleEvent-> case CONNECTED: handleNetworkStateChange -> mWifiStateTracker.notifyStateChange -> EVENT_NETWORK_STATE_CHANGED -> handleMessage 下的：case EVENT_SUPPLICANT_STATE_CHANGED: -> intent = new Intent(WifiManager.SUPPLICANT_STATE_CHANGED_ACTION); Wi-Fi supplicant state changed:
èSettingsObserver专门是观察该类变化的
if (changed) {
resetInterface(true);
configureInterface();
if (mUseStaticIp) {
mTarget.sendEmptyMessage(EVENT_CONFIGURATION_CHANGED);
}
}
è
mDhcpTarget.sendEmptyMessage(EVENT_DHCP_START);
->
DhcpHandler的handleMessage函数case EVENT_DHCP_START: NetworkUtils.runDhcp获取DHCP的IP地址，成功之后发送EVENT_INTERFACE_CONFIGURATION_SUCCEEDED:
event通过WifiStateTracker的HandleMessage函数case EVENT_INTERFACE_CONFIGURATION_SUCCEEDED:会调用sendNetworkStateChangeBroadcast Intent intent = new Intent(WifiManager.NETWORK_STATE_CHANGED_ACTION);发送全局Intent Action 完成网络切换。
-------------------------------------------------------------------WIFI启动 代码流程走读
初始化
在 SystemServer 启动的时候,会生成一个 ConnectivityService 的实例 ,try { Log.i(TAG, "Starting Connectivity Service.");ServiceManager.addService(Context.CONNECTIVITY_SERVICE, newConnectivityService(context));} catch (Throwable e) { Log.e(TAG, "Failure starting Connectivity Service", e);}ConnectivityService 的构造函数 会创建 WifiService,if (DBG) Log.v(TAG, "Starting Wifi Service.");mWifiStateTracker = new WifiStateTracker(context, handler);WifiService wifiService = new WifiService(context, mWifiStateTracker);ServiceManager.addService(Context.WIFI_SERVICE, wifiService);WifiStateTracker 会创建 WifiMonitor 接收来自底层的事件,WifiService 和 WifiMonitor 是整个模块的核心 。WifiService 负责启动关闭 wpa_supplicant、启动关闭 WifiMonitor 监视线程和把命令 下发给 wpa_supplicant,而 WifiMonitor 则负责从 wpa_supplicant 接收事件通知。连接 AP1. 使能 WIFIWirelessSettings 在初始化的时候配置了由 WifiEnabler 来处理 Wifi 按钮,private void initToggles() { mWifiEnabler = new WifiEnabler(this,(WifiManager) getSystemService(WIFI_SERVICE),(CheckBoxPreference) findPreference(KEY_TOGGLE_WIFI));当用户按下 Wifi 按钮后, Android 会调用 WifiEnabler 的 onPreferenceChange, 再由 WifiEnabler调用 WifiManager 的 setWifiEnabled 接口 函数,通过 AIDL,实际调用的是 WifiService 的setWifiEnabled 函数,WifiService 接着向自身发送一条 MESSAGE_ENABLE_WIFI 消息,在处理该消息的代码 中做真正的使能工作:首先装载 WIFI 内核模块(该模块的位置硬编码为"/system/lib/modules/wlan.ko" ), 然 后 启 动 wpa_supplicant ( 配 置 文 件 硬 编 码 为"/data/misc/wifi/wpa_supplicant.conf") 再通过 WifiStateTracker 来启动 WifiMonitor 中的监视,线程。private boolean setWifiEnabledBlocking(boolean enable) { final int eventualWifiState = enable ? WIFI_STATE_ENABLED :WIFI_STATE_DISABLED;updateWifiState(enable ? WIFI_STATE_ENABLING : WIFI_STATE_DISABLING);if (enable) { if (!WifiNative.loadDriver()) { Log.e(TAG, "Failed to load Wi-Fi driver.");updateWifiState(WIFI_STATE_UNKNOWN);return false;}if (!WifiNative.startSupplicant()) { WifiNative.unloadDriver();Log.e(TAG, "Failed to start supplicant daemon.");updateWifiState(WIFI_STATE_UNKNOWN);return false;}mWifiStateTracker.startEventLoop();}// Success!persistWifiEnabled(enable);updateWifiState(eventualWifiState);return true;}当使能成功后,会广播发送 WIFI_STATE_CHANGED_ACTION 这个 Intent 通知外界 WIFI已 经 成 功 使 能 了 。 WifiEnabler 创 建 的 时 候 就 会 向 Android 注 册 接 收WIFI_STATE_CHANGED_ACTION,因此它会收到该 Intent,从而开始扫描。private void handleWifiStateChanged(int wifiState) { if (wifiState == WIFI_STATE_ENABLED) { loadConfiguredAccessPoints();attemptScan();}2. 查找 AP扫描的入口函数是 WifiService 的 startScan,它其实也就是往 wpa_supplicant 发送 SCAN 命令。static jboolean android_net_wifi_scanCommand(JNIEnv* env, jobject clazz){ jboolean result;// Ignore any error from setting the scan mode.// The scan will still work.(void)doBooleanCommand("DRIVER SCAN-ACTIVE", "OK");result = doBooleanCommand("SCAN", "OK");(void)doBooleanCommand("DRIVER SCAN-PASSIVE", "OK");return result;}当 wpa_supplicant 处理完 SCAN 命令后,它会向控制通道发送事件通知扫描完成,从而wifi_wait_for_event 函数会接收到该事件,由此 WifiMonitor 中的 MonitorThread 会被执行来出来这个事件,void handleEvent(int event, String remainder) { case SCAN_RESULTS:mWifiStateTracker.notifyScanResultsAvailable();break;WifiStateTracker 则接着广播发送 SCAN_RESULTS_AVAILABLE_ACTION 这个 Intentcase EVENT_SCAN_RESULTS_AVAILABLE:mContext.sendBroadcast(newIntent(WifiManager.SCAN_RESULTS_AVAILABLE_ACTION));WifiLayer 注册了接收 SCAN_RESULTS_AVAILABLE_ACTION 这个 Intent,所以它的相关处理函数 handleScanResultsAvailable 会被调用,在该函数中,先会去拿到 SCAN 的结果(最终是往 wpa_supplicant 发送 SCAN_RESULT 命令并读取返回值来实现的) ,List<ScanResult> list = mWifiManager.getScanResults();对每一个扫描返回的 AP,WifiLayer 会调用 WifiSettings 的 onAccessPointSetChanged 函数,从而最终把该 AP 加到 GUI 显示列表中。public void onAccessPointSetChanged(AccessPointState ap, boolean added) { AccessPointPreference pref = mAps.get(ap);if (added) { if (pref == null) { pref = new AccessPointPreference(this, ap);mAps.put(ap, pref);} else { pref.setEnabled(true);}mApCategory.addPreference(pref);}}3. 配置 AP 参数当用户在 WifiSettings 界面上选择了一个 AP 后,会显示配置 AP 参数的一个对话框,public boolean onPreferenceTreeClick(PreferenceScreen preferenceScreen, Preferencepreference) { if (preference instanceof AccessPointPreference) { AccessPointState state = ((AccessPointPreference)preference).getAccessPointState();showAccessPointDialog(state, AccessPointDialog.MODE_INFO);}}4. 连接当用户在 AcessPointDialog 中选择好加密方式和输入密钥之后,再点击连接按钮,Android就会去连接这个 AP。private void handleConnect() { String password = getEnteredPassword();if (!TextUtils.isEmpty(password)) { mState.setPassword(password);}mWifiLayer.connectToNetwork(mState);}WifiLayer 会先检测这个 AP 是不是之前被配置过,这个是通过向 wpa_supplicant 发送LIST_NETWORK 命令并且比较返回值来实现的,// Need WifiConfiguration for the APWifiConfiguration config = findConfiguredNetwork(state);如果 wpa_supplicant 没有这个 AP 的配置信息, 则会向 wpa_supplicant 发送 ADD_NETWORK命令来添加该 AP,if (config == null) { // Connecting for the first time, need to create itconfig = addConfiguration(state,ADD_CONFIGURATION_ENABLE|ADD_CONFIGURATION_SAVE);}ADD_NETWORK 命 令 会 返 回 一 个 ID , WifiLayer 再 用 这 个 返 回 的 ID 作 为 参 数 向wpa_supplicant 发送 ENABLE_NETWORK 命令,从而让 wpa_supplicant 去连接该 AP。// Make sure that network is enabled, and disable othersmReenableApsOnNetworkStateChange = true;if (!mWifiManager.enableNetwork(state.networkId, true)) { Log.e(TAG, "Could not enable network ID " + state.networkId);error(R.string.error_connecting);return false;}5. 配置 IP 地址当 wpa_supplicant 成功连接上 AP 之后,它会向控制通道发送事件通知连接上 AP 了,从而wifi_wait_for_event 函数会接收到该事件,由此 WifiMonitor 中的 MonitorThread 会被执行来出来这个事件,void handleEvent(int event, String remainder) { case CONNECTED:handleNetworkStateChange(NetworkInfo.DetailedState.CONNECTED,remainder);break;WifiMonitor 再调用 WifiStateTracker 的 notifyStateChange,WifiStateTracker 则接着会往自身发送 EVENT_DHCP_START 消息来启动 DHCP 去获取 IP 地址,private void handleConnectedState() { setPollTimer();mLastSignalLevel = -1;if (!mHaveIPAddress & !mObtainingIPAddress) { mObtainingIPAddress = true;mDhcpTarget.obtainMessage(EVENT_DHCP_START).sendToTarget();}}然后再广播发送 NETWORK_STATE_CHANGED_ACTION 这个 Intentcase EVENT_NETWORK_STATE_CHANGED:if (result.state != DetailedState.DISCONNECTED || !mDisconnectPending) { intent = newIntent(WifiManager.NETWORK_STATE_CHANGED_ACTION);intent.putExt ra(WifiManager.EXTRA_NETWORK_INFO,mNetworkInfo);if (result.BSSID != null)intent.putExtra(WifiManager.EXTRA_BSSID, result.BSSID);mContext.sendStickyBroadcast(intent);}break;WifiLayer 注册了接收 NETWORK_STATE_CHANGED_ACTION 这个 Intent,所以它的相关处理函数 handleNetworkStateChanged 会被调用,当 DHCP 拿到 IP 地址之后,会再发送 EVENT_DHCP_SUCCEEDED 消息,private class DhcpHandler extends Handler { public void handleMessage(Message msg) { switch (msg.what) { case EVENT_DHCP_START:if (NetworkUtils.runDhcp(mInterfaceName, mDhcpInfo)) { event = EVENT_DHCP_SUCCEEDED;}WifiLayer 处 理 EVENT_DHCP_SUCCEEDED 消 息 , 会 再 次 广 播 发 送NETWORK_STATE_CHANGED_ACTION 这个 Intent,这次带上完整的 IP 地址信息。case EVENT_DHCP_SUCCEEDED:mWifiInfo.setIpAddress(mDhcpInfo.ipAddress);setDetailedState(DetailedState.CONNECTED);intent = newIntent(WifiManager.NETWORK_STATE_CHANGED_ACTION);intent.putExtra(WifiManager.EXTRA_NETWORK_INFO, mNetworkInfo);mContext.sendStickyBroadcast(intent);break;至此为止,整个连接过程完成。问题:目前的实现不支持 Ad-hoc 方式。<!--++ plugin_code qcomic begin--> <!--++ plugin_code qcomic end-->---------------------------------------------------------------------------------android 网络连接管理
系统中对网络的判断和选在是在Connectivityervice这个服务中来处理的，在系统启动的时候会启动这个系统服务：
系统启动完毕后，ConnectivityService在系统启动的时候就启动了。在android内部，用framework/base/core/res/res/values/config.xml中定义了网络的类型：<string-array translatable="false" name="networkAttributes"><item>"default,wifi,0"</item><item>"default,mobile,0"</item><item>"mms,mobile,1"</item><item>"supl,mobile,1"</item><item>"dun,mobile,1"</item><item>"hipri,mobile,2"</item></string-array><string-array translatable="false" name="radioAttributes"><item>"wifi,1,1"</item><item>"mobile,0,1"</item></string-array>ConnectivityManager定义了向对应的字符串常量：public static final int TYPE_MOBILE = 0;/*** The Default WIFI data connection. When active, all data traffic* will use this connection by default. Should not coexist with other* default connections.*/public static final int TYPE_WIFI = 1;/*** An MMS-specific Mobile data connection. This connection may be the* same as {@link #TYPEMOBILE} but it may be different. This is used* by applications needing to talk to the carrier's Multimedia Messaging* Service servers. It may coexist with default data connections.* {@hide}*/public static final int TYPE_MOBILE_MMS = 2;/*** A SUPL-specific Mobile data connection. This connection may be the* same as {@link #TYPEMOBILE} but it may be different. This is used* by applications needing to talk to the carrier's Secure User Plane* Location servers for help locating the device. It may coexist with* default data connections.* {@hide}*/public static final int TYPE_MOBILE_SUPL = 3;/*** A DUN-specific Mobile data connection. This connection may be the* same as {@link #TYPEMOBILE} but it may be different. This is used* by applicaitons performing a Dial Up Networking bridge so that* the carrier is aware of DUN traffic. It may coexist with default data* connections.* {@hide}*/public static final int TYPE_MOBILE_DUN = 4;/*** A High Priority Mobile data connection. This connection is typically* the same as {@link #TYPEMOBILE} but the routing setup is different.* Only requesting processes will have access to the Mobile DNS servers* and only IP's explicitly requested via {@link #requestRouteToHost}* will route over this interface.*{@hide}*/public static final int TYPE_MOBILE_HIPRI = 5;/** {@hide} */public static final int MAX_RADIO_TYPE = TYPE_WIFI;/** {@hide} */public static final int MAX_NETWORK_TYPE = TYPE_MOBILE_HIPRI;public static final int DEFAULT_NETWORK_PREFERENCE = TYPE_WIFI;并设置了默认的网络连接是TYPE_WIFI.ConnectivityManager的方法是通过AIDL的使用，调用ConnectivityService中的方法来实现的。ConnectivityService继承了IConnectivityManage.stub.在ConnectivityService内部，定义了两个类来解析xml中的网络类型，类的代码如下：private class NetworkAttributes { /*** Class for holding settings read from resources.*/public String mName;public int mType;public int mRadio;public int mPriority;public NetworkInfo.State mLastState;public NetworkAttributes(String init) { String fragments[] = init.split(",");mName = fragments[0].toLowerCase();if (fragments[1].toLowerCase().equals("wifi")) { mRadio = ConnectivityManager.TYPE_WIFI;} else { mRadio = ConnectivityManager.TYPE_MOBILE;}if (mName.equals("default")) { mType = mRadio;} else if (mName.equals("mms")) { mType = ConnectivityManager.TYPE_MOBILE_MMS;} else if (mName.equals("supl")) { mType = ConnectivityManager.TYPE_MOBILE_SUPL;} else if (mName.equals("dun")) { mType = ConnectivityManager.TYPE_MOBILE_DUN;} else if (mName.equals("hipri")) { mType = ConnectivityManager.TYPE_MOBILE_HIPRI;}mPriority = Integer.parseInt(fragments[2]);mLastState = NetworkInfo.State.UNKNOWN;}public boolean isDefault() { return (mType == mRadio);}}private class RadioAttributes { public String mName;public int mPriority;public int mSimultaneity;public int mType;public RadioAttributes(String init) { String fragments[] = init.split(",");mName = fragments[0].toLowerCase();mPriority = Integer.parseInt(fragments[1]);mSimultaneity = Integer.parseInt(fragments[2]);if (mName.equals("wifi")) { mType = ConnectivityManager.TYPE_WIFI;} else { mType = ConnectivityManager.TYPE_MOBILE;}}}并通过一下代码，来给网络分配优先级，mPriorityList = new int[naStrings.length];{ int priority = 0; //lowestint nextPos = naStrings.length-1;while (nextPos>-1) { for (int i = 0; i < mNetAttributes.length; i++) { if(mNetAttributes[i].mPriority == priority) { mPriorityList[nextPos--] = i;}}priority++;}}mNetRequestersPids =new ArrayList[ConnectivityManager.MAX_NETWORK_TYPE+1];for (int i=0; i<=ConnectivityManager.MAX_NETWORK_TYPE; i++) { mNetRequestersPids[i] = new ArrayList();}其中，TYPE_MOBILE_HIPRI的优先级最高，其次为TYPE_MOBILE_MMS，TYPE_MOBILE_SUPL，TYPE_MOBILE_DUN，优先级最低的为TYPE_WIFI，TYPE_MOBILE。TYPE_WIFI，TYPE_MOBILE两个网络类型中，TYPE_WIFI大于TYPE_MOBILE的优先级，在打开wifi的连接后，mobile网络会被关闭。wifi网络连接关闭后，mobile网络会重新连接。在处理网络连接的Handler的代码中有处理：private void handleConnect(NetworkInfo info) { int type = info.getType();Log.d(TAG, "Got Network Connection Succ from Driver nwtype="+type);// snapshot isFailover, because sendConnectedBroadcast() resets itboolean isFailover = info.isFailover();NetworkStateTracker thisNet = mNetTrackers[type];// if this is a default net and other default is running// kill the one not preferredif (mNetAttributes[type].isDefault()) { if (mActiveDefaultNetwork != -1 && mActiveDefaultNetwork != type) { if ((type != mNetworkPreference &&mNetAttributes[mActiveDefaultNetwork].mPriority >mNetAttributes[type].mPriority) ||mNetworkPreference == mActiveDefaultNetwork) { if(!((SystemProperties.get(CNE.UseCne,"false").equals("true") ||SystemProperties.get(CNE.UseCne,"false").equals("TRUE"))&&CNE.isCndUp)) { // don't accept this oneif (DBG) Log.v(TAG, "Not broadcasting CONNECT_ACTION " +"to torn down network " + info.getTypeName());teardown(thisNet);}return;} else { // tear down the otherNetworkStateTracker otherNet =mNetTrackers[mActiveDefaultNetwork];if (DBG) Log.v(TAG, "Policy requires " +otherNet.getNetworkInfo().getTypeName() +" teardown");if(!((SystemProperties.get(CNE.UseCne,"false").equals("true") ||SystemProperties.get(CNE.UseCne,"false").equals("TRUE"))&&CNE.isCndUp)) { if (DBG) Log.i(TAG, "CNE To support Simultaneous Nws we"+" will not tear down other nw");if (!teardown(otherNet)) { Log.e(TAG, "Network declined teardown request");return;}}if (isFailover) { otherNet.releaseWakeLock();}}}mActiveDefaultNetwork = type;}thisNet.setTeardownRequested(false);thisNet.updateNetworkSettings();handleConnectivityChange();sendConnectedBroadcast(info);}SystemServer启动ConnectivityService，ConnectivityService启动对网络的监视器。在SystemServer的run()函数中，启动ConnectivityService的代码：try { Log.i(TAG, "Connectivity Service");connectivity = ConnectivityService.getInstance(context);ServiceManager.addService(Context.CONNECTIVITY_SERVICE, connectivity);connectivity.startCne();} catch (Throwable e) { Log.e(TAG, "Failure starting Connectivity Service", e);}在ConnectivityService的构造函数中启动网络监视器的代码：if (DBG) Log.v(TAG, "Starting Wifi Service.");WifiStateTracker wst = new WifiStateTracker(context, mHandler);WifiService wifiService = new WifiService(context, wst);ServiceManager.addService(Context.WIFI_SERVICE, wifiService);mNetTrackers[ConnectivityManager.TYPE_WIFI] = wst;mNetTrackers[ConnectivityManager.TYPE_MOBILE] =new MobileDataStateTracker(context, mHandler,ConnectivityManager.TYPE_MOBILE, Phone.APN_TYPE_DEFAULT,"MOBILE");mNetTrackers[ConnectivityManager.TYPE_MOBILE_MMS] =new MobileDataStateTracker(context, mHandler,ConnectivityManager.TYPE_MOBILE_MMS, Phone.APN_TYPE_MMS,"MOBILE_MMS");mNetTrackers[ConnectivityManager.TYPE_MOBILE_SUPL] =new MobileDataStateTracker(context, mHandler,ConnectivityManager.TYPE_MOBILE_SUPL, Phone.APN_TYPE_SUPL,"MOBILE_SUPL");mNetTrackers[ConnectivityManager.TYPE_MOBILE_DUN] =new MobileDataStateTracker(context, mHandler,ConnectivityManager.TYPE_MOBILE_DUN, Phone.APN_TYPE_DUN,"MOBILE_DUN");mNetTrackers[ConnectivityManager.TYPE_MOBILE_HIPRI] =new MobileDataStateTracker(context, mHandler,ConnectivityManager.TYPE_MOBILE_HIPRI, Phone.APN_TYPE_HIPRI,"MOBILE_HIPRI");mNumDnsEntries = 0;mTestMode = SystemProperties.get("cm.test.mode").equals("true")&& SystemProperties.get("ro.build.type").equals("eng");for (NetworkStateTracker t : mNetTrackers)t.startMonitoring();// Constructing this starts it toomWifiWatchdogService = new WifiWatchdogService(context, wst);在settings中可以设置网络连接，比如打开wifi，打开bluetooth,设置apn的连接等等，在设置完成后，设置的消息会存在一个数据库中保存，并发送系统消息来广播网络设置的变化。在网络监视器中捕捉了settings中发出的相应的网络广播信息，网络监视器中注册了settings中网络变化的信息，有变化会做相应的处理，并将处理的结果存储在NetworkInfo类的一个对象中，在ConnectivityService中通过public NetworkInfo getNetworkInfo(int networkType)方法可以得知当前networkType类型网络的连接情况。在app中，我们可以通过ConnectivityManager来获取当前的网络信息，并能指定当前程序需要的网络类型：ConnectivityManager mCnn = context.getSystemService(context.NONNECTIVITY_SERVICE);NetworkInfo mNetinfo = mCnn.getActiveNetworkInfo();mCnn.setNetworkPreference(int preference);//设定首选网络类型。假如没有设定，网络类型为系统默认。在wifi，3G网络同时存在的情况下，系统会默认的调用wifi网络，加载wifi的驱动，走wifi网络。