Android WIFI框架分析（2）

上文讲到WIFI的启动流程，当然接着便扫描热点（AP），然后显示扫描到的AP、配置AP（填写IP地址等信息）、连接AP、获取IP地址、最后就是想要的上网咯！

一、扫描热点（AP）

上文启动WIFI成功后：// Success!        
        setWifiEnabledState(eventualWifiState, uid);
private void setWifiEnabledState(int wifiState, int uid) {
 // Broadcast
        final Intent intent = new Intent(WifiManager.WIFI_STATE_CHANGED_ACTION);
}

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。WifiLayer 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。

WifiSetting.java:

protected void onCreate(Bundle savedInstanceState) {
    mWifiLayer.onCreate();
}

-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

WifiLayer.java:
public void onCreate() {
        mWifiManager = (WifiManager) mContext.getSystemService(Context.WIFI_SERVICE);
        
        mIntentFilter = new IntentFilter();
        mIntentFilter.addAction(WifiManager.NETWORK_STATE_CHANGED_ACTION);
        mIntentFilter.addAction(WifiManager.SCAN_RESULTS_AVAILABLE_ACTION);
        mIntentFilter.addAction(WifiManager.WIFI_STATE_CHANGED_ACTION);        
    }
public void onResume() {
        mContext.registerReceiver(mReceiver, mIntentFilter);        
        if (isWifiEnabled()) {
            // Kick start the continual scan
            queueContinuousScan();
        }
    }

以上就是WifiLayer.java注册接收的部分事件。接收部分事件处理有：
private BroadcastReceiver mReceiver = new BroadcastReceiver() {
private BroadcastReceiver mReceiver = new BroadcastReceiver() {
        public void onReceive(Context context, Intent intent) {
            final String action = intent.getAction();
            if (action.equals(WifiManager.NETWORK_STATE_CHANGED_ACTION)) {
                handleNetworkStateChanged(
                        (NetworkInfo) intent.getParcelableExtra(WifiManager.EXTRA_NETWORK_INFO),
                        intent.getStringExtra(WifiManager.EXTRA_BSSID));
            } else if (action.equals(WifiManager.SCAN_RESULTS_AVAILABLE_ACTION)) {
                handleScanResultsAvailable();
            } ……

           else if (action.equals(WifiManager.WIFI_STATE_CHANGED_ACTION)) {
                handleWifiStateChanged(intent.getIntExtra(WifiManager.EXTRA_WIFI_STATE,
                        WifiManager.WIFI_STATE_UNKNOWN));
            }           
        }
    };

从可接受的事件看，当WIFI_STATE_CHANGED_ACTION时，对应的处理函数有：

handleWifiStateChanged(intent.getIntExtra(WifiManager.EXTRA_WIFI_STATE,
                        WifiManager.WIFI_STATE_UNKNOWN));

private void handleWifiStateChanged(int wifiState) {
   attemptScan();
   …………
 }

public void attemptScan() {
  if (!mWifiManager.startScanActive()) {
            postAttemptScan();
        } 
}

WifiManager.java:
public boolean startScanActive() {
 return mService.startScan(true);
}

-------AIDL-------------------------------------------------------------------------------------------------------------------------------------------------------------------------

WifiService.java:
public boolean startScan(boolean forceActive) {
 …………
 return WifiNative.scanCommand(forceActive);
}

---------JNI---------------------------------------------------------------------------------------------------------------------------------------------------------------------------

android_net_wifi_wifi.cpp:
{ "scanCommand", "(Z)Z", (void*) android_net_wifi_scanCommand },
static jboolean android_net_wifi_scanCommand(JNIEnv* env, jobject clazz, jboolean forceActive)
{
 …………
 result = doBooleanCommand("SCAN", "OK");
}
static jboolean doBooleanCommand(const char *cmd, const char *expect)
{
 if (doCommand(cmd, reply, sizeof(reply)) != 0) {
        return (jboolean)JNI_FALSE;
    } 
}
static int doCommand(const char *cmd, char *replybuf, int replybuflen)
{
 if (::wifi_command(cmd, replybuf, &reply_len) != 0)
        return -1;
 …………
}

-------HAL------------------------------------------------------------------------------------------------------------------------------------------------------------------------

wifi.c:
int wifi_command(const char *command, char *reply, size_t *reply_len)
{
    return wifi_send_command(ctrl_conn, command, reply, reply_len);
}
int wifi_send_command(struct wpa_ctrl *ctrl, const char *cmd, char *reply, size_t *reply_len)
{
 ret = wpa_ctrl_request(ctrl, cmd, strlen(cmd), reply, reply_len, NULL);
 …………
}
wpa_ctrl.c:
int wpa_ctrl_request()在wpa_ctrl.c中其实就是执行SCAN命令。

二、显示扫描的AP

当扫描成后，WifiMonitor 中的MonitorThread 会被执行来出来这个事件：

  void handleEvent(int event, String remainder) {
            switch (event) {   
                case SCAN_RESULTS:
                    mWifiStateTracker.notifyScanResultsAvailable();
->sendEmptyMessage(EVENT_SCAN_RESULTS_AVAILABLE);
    break;
}

 WifiStateTracker.java 
public void handleMessage(Message msg) {               
  switch (msg.what) {
               case EVENT_SCAN_RESULTS_AVAILABLE:
                        if (ActivityManagerNative.isSystemReady()) {
                                mContext.sendBroadcast(new   Intent(WifiManager.SCAN_RESULTS_AVAILABLE_ACTION));        
                     }
}

WifiLayer注册接收SCAN_RESULTS_AVAILABLE_ACTION这个Intent：

private BroadcastReceiver mReceiver = new BroadcastReceiver() {
        @Override
        public void onReceive(Context context, Intent intent) {
 else if (action.equals(WifiManager.SCAN_RESULTS_AVAILABLE_ACTION)) 
       {             

             handleScanResultsAvailable();     

     }
 handleScanResultsAvailable();
       -> list = mWifiManager.getScanResults();
        -> mCallback.onAccessPointSetChanged(ap, true);

handleScanResultsAvailable()中首先会去拿到SCAN的结果（最终是往wpa_supplicant中发送SCAN_RESULT命令并读取返回值来实现的），对每一个扫描返回的AP，WifiLayer会回调WifiSetting的onAccessPointSetChanged函数，从而最终把该AP加到GUI显示列表中。

三、配置AP

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()
          ->showAccessPointDialog(state, AccessPointDialog.MODE_INFO);
                    ->AccessPointDialog dialog   = 
                                            new AccessPointDialog(this,    mWifiLayer);
                                     showDialog(dialog);

当用户在AccessPointDialog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。

四、连接AP

在AccessPointDialog.java中点击连接后会执行：

public void onClick(DialogInterface dialog, int which) {
           handleConnect();
   -> mWifiLayer.connectToNetwork(mState);
    ->  // Need WifiConfiguration for the AP
                               WifiConfiguration config = findConfiguredNetwork(state);
                                config = addConfiguration(state, 0);
                                managerEnableNetwork(state, false)
          ->mWifiManager.enableNetwork()
                                         ->mService.enalbeNetwork()
                     ->WifiNative.enableNetworkCommand() 

接下去就JNI { "enableNetworkCommand", "(IZ)Z", (void*) android_net_wifi_enableNetworkCommand },最终就是向wpa_supplicant发送连接命令
五、获取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) {
       switch (event) {   
              case CONNECTED:
                  handleNetworkStateChange();
                  -> mWifiStateTracker.notifyStateChange(newState, BSSID, networkId);
  ->msg.sendToTarget();
                  break;
}

WifiStateTracker.java 
public void handleMessage(Message msg) {          
  switch (msg.what) {               
            case EVENT_NETWORK_STATE_CHANGED:
                       sendNetworkStateChangeBroadcast(mWifiInfo.getBSSID());       
                     }
}
WifiStateTracker中注册的对Wifi相关数据库的观察者if(changed)   则启动：
 private void configureInterface() 
   ->  mDhcpTarget.sendEmptyMessage();
 private class DhcpHandler extends Handler 
          handleMessage()
              ->switch (msg.what) {
                      case EVENT_DHCP_START:
                              Target.sendEmptyMessage(event);

DhcpHandler会发送EVENT_DHCP_START消息启动DHCP去获取IP地址，当DHCP拿到IP地址之后，会发送EVENT_INTERFACE_CONFIGURATION_SUCCEEDED的消息，然后WifiStateTacker中的handleMessage会处理这样的消息 

case EVENT_INTERFACE_CONFIGURATION_SUCCEEDED:
     sendNetworkStateChangeBroadcast(mWifiInfo.getBSSID());
            ->  Intent intent = new Intent(WifiManager.NETWORK_STATE_CHANGED_ACTION);
            -> mContext.sendStickyBroadcast(intent);

这次带上完整的IP地址信息。WifiLayer中注册了此Intent的接受者，会调用handleNetworkStateChanged进行处理。最后就可以自由的上网了