Android 中的WiFi剖析

Android的WiFi

咱们一般看到WiFi的守护进程wpa_supplicant在咱们的ps的进程列表中，这个就是咱们的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中做为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守护进程的通讯，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适配层的头文件以下所示：

hardware/libhardware_legacy/include/hardware_legacy/wifi.h

咱们看它的加载过程

Init会在系统启动首先加载init.rc这个文件会加载全部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

经过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)会管理全部的Connectivity相关的好比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会建立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而后启动wpa_supplicant（用/data/misc/wifi/wpa_supplicant.conf配置），再经过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)经过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。

经过WifiHandler的 handleMessage来维护这些消息，enable的时候会调用setWifiEnabledBlocking这个函数，这个函数会作setWifiEnabledState 而后作两件事： 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()能够把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，一样是在WifiService 中的setWifiEnabledBlocking这个函数会调用startSupplicant 经过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以后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，咱们的WifiLayer注册了接收到该Action

WifiSettings.java (packages/apps/settings/src/com/android/settings/wifi)中有mWifiLayer.onCreate();（这个函数建立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经过WifiService中的startScan经过本地方法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

扫描完成以后会发送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:以后发送广播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 链接流程

用户在AccessPointDialog中输入密码以后点击链接按钮，Android调用顺序以下：

AccessPointDialog.java (packages/apps/settings/src/com/android/settings/wifi) -> onClick -> handleConnect(); -> mWifiLayer.connectToNetwork ->经过WifiConfiguration config = findConfiguredNetwork(state);查看是否是配置过的，若是是就直接使用了，若是不是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发送相关命令返回以后由WiFiMonitor处理跟之前相似，链接的中间流程与查找AP的流程相似，都通过了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经过对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，由于当wpa_supplicant连接AP成功以后，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，成功以后发送EVENT_INTERFACE_CONFIGURATION_SUCCEEDED:

event经过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, new
ConnectivityService(context));
} catch (Throwable e) {
Log.e(TAG, "Failure starting Connectivity Service", e);
}
ConnectivityService 的构造函数 会建立 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 会建立 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。
链接 AP
1. 使能 WIFI
WirelessSettings 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,经过 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 中作真正的使能工做: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") 再经过 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,所以它会收到该 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 Intent
case EVENT_SCAN_RESULTS_AVAILABLE:
mContext.sendBroadcast(new
Intent(WifiManager.SCAN_RESULTS_AVAILABLE_ACTION));
WifiLayer 注册了接收 SCAN_RESULTS_AVAILABLE_ACTION 这个 Intent,因此它的相关
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, Preference
preference) {
if (preference instanceof AccessPointPreference) {
AccessPointState state = ((AccessPointPreference)
preference).getAccessPointState();
showAccessPointDialog(state, AccessPointDialog.MODE_INFO);
}
}
4. 链接
当用户在 AcessPointDialog 中选择好加密方式和输入密钥以后,再点击链接按钮,Android
就会去链接这个 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 是否是以前被配置过,这个是经过向 wpa_supplicant 发送
LIST_NETWORK 命令而且比较返回值来实现的,
// Need WifiConfiguration for the AP
WifiConfiguration config = findConfiguredNetwork(state);
若是 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 it
config = 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 做 为 参 数 向
wpa_supplicant 发送 ENABLE_NETWORK 命令,从而让 wpa_supplicant 去链接该 AP。
// Make sure that network is enabled, and disable others
mReenableApsOnNetworkStateChange = 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 成功链接上 AP 以后,它会向控制通道发送事件通知链接上 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();
}
}
而后再广播发送 NETWORK_STATE_CHANGED_ACTION 这个 Intent
case EVENT_NETWORK_STATE_CHANGED:
if (result.state != DetailedState.DISCONNECTED || !mDisconnectPending) {
intent = new
Intent(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,因此它的相关
处理函数 handleNetworkStateChanged 会被调用,
当 DHCP 拿到 IP 地址以后,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,此次带上完整的 IP 地址信息。
case EVENT_DHCP_SUCCEEDED:
mWifiInfo.setIpAddress(mDhcpInfo.ipAddress);
setDetailedState(DetailedState.CONNECTED);
intent = new
Intent(WifiManager.NETWORK_STATE_CHANGED_ACTION);
intent.putExtra(WifiManager.EXTRA_NETWORK_INFO, mNetworkInfo);
mContext.sendStickyBroadcast(intent);
break;
至此为止,整个链接过程完成。
问题:
目前的实现不支持 Ad-hoc 方式。<!--++ plugin_code qcomic begin--> <!--++ plugin_code qcomic end-->

---------------------------------------------------------------------------------android 网络链接管理

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链接是TYPE_WIFI.ConnectivityManager的方法是经过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，类的代码以下：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;}}}并经过一下代码，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的链接后，mobile网络会被关闭。wifi网络链接关闭后，mobile网络会从新链接。在处理网络链接的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中能够设置网络链接，好比打开wifi，打开bluetooth,设置apn的链接等等，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，有变化会作相应的处理，并将处理的结果存储在NetworkInfo类的一个对象中，在ConnectivityService中经过public NetworkInfo getNetworkInfo(int networkType)方法能够得知当前networkType类型网络的链接状况。在app中，咱们能够经过ConnectivityManager来获取当前的网络信息，并能指定当前程序须要的网络类型：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网络同时存在的状况下，系统会默认的调用wifi网络，加载wifi的驱动，走wifi网络。