Android WIFI 詳解

public class WifiEnabler implementsPreference.OnPreferenceChangeListener {

……

public boolean onPreferenceChange(Preference preference,Object value) {

booleanenable = (Boolean) value;

……

if (mWifiManager.setWifiEnabled(enable)) {

mCheckBox.setEnabled(false);

……

}

……

}

我們都知道Wifimanager只是個服務(wù)代理，所以它會調(diào)用WifiService的setWifiEnabled()函數(shù)，而這個函數(shù)會調(diào)用 sendEnableMessage()函數(shù)，了解android消息處理機制的都知道，這個函數(shù)最終會給自己發(fā)送一個 MESSAGE_ENABLE_WIFI的消息，被WifiService里面定義的handlermessage()函數(shù)處理，會調(diào)用 setWifiEnabledBlocking()函數(shù)。下面是調(diào)用流程：

mWifiEnabler.onpreferencechange()=>mWifiManage.setWifienabled()=>mWifiService.setWifiEnabled()=>mWifiService.sendEnableMessage()=>mWifiService.handleMessage()=>mWifiService.setWifiEnabledBlocking().

在setWifiEnabledBlocking()函數(shù)中主要做如下工作：加載Wifi驅(qū)動，啟動wpa_supplicant，注冊廣播接收器，啟動WifiThread監(jiān)聽線程。代碼如下：

……

if (enable) {

if (!mWifiStateTracker.loadDriver()) {

Slog.e(TAG, Failed toload Wi-Fi driver.);

setWifiEnabledState(WIFI_STATE_UNKNOWN, uid);

return false;

}

if (!mWifiStateTracker.startSupplicant()) {

mWifiStateTracker.unloadDriver();

Slog.e(TAG, Failed tostart supplicant daemon.);

setWifiEnabledState(WIFI_STATE_UNKNOWN, uid);

return false;

}

registerForBroadcasts();

mWifiStateTracker.startEventLoop();

……

至此，Wifi使能結(jié)束，自動進(jìn)入掃描階段。

(2) 掃描AP

當(dāng)驅(qū)動加載成功后，如果配置文件的AP_SCAN = 1，掃描會自動開始，WifiMonitor將會從supplicant收到一個消息EVENT_DRIVER_STATE_CHANGED，調(diào)用 handleDriverEvent()，然后調(diào)用mWifiStateTracker.notifyDriverStarted()，該函數(shù)向消息隊列 添加EVENT_DRIVER_STATE_CHANGED，handlermessage()函數(shù)處理消息時調(diào)用scan()函數(shù)，并通過 WifiNative將掃描命令發(fā)送到wpa_supplicant。

Frameworks/base/wifi/java/android/net/wifi/WifiMonitor.java

private void handleDriverEvent(Stringstate) {

if (state == null) {

return;

}

if (state.equals(STOPPED)) {

mWifiStateTracker.notifyDriverStopped();

} else if (state.equals(STARTED)) {

mWifiStateTracker.notifyDriverStarted();

} else if (state.equals(HANGED)) {

mWifiStateTracker.notifyDriverHung();

}

}

Frameworks/base/wifi/java/android/net/wifi/WifiStateTracker.java

case EVENT_DRIVER_STATE_CHANGED:

switch(msg.arg1) {

case DRIVER_STARTED:

/**

*Set the number of allowed radio channels according

*to the system setting, since it gets reset by the

*driver upon changing to the STARTED state.

*/

setNumAllowedChannels();

synchronized (this) {

if (mRunState == RUN_STATE_STARTING) {

mRunState = RUN_STATE_RUNNING;

if (!mIsScanOnly) {

reconnectCommand();

} else {

// In somesituations, supplicant needs to be kickstarted to

// start thebackground scanning

scan(true);

}

}

}

break;

上面是啟動Wifi時，自動進(jìn)行的AP的掃描，用戶當(dāng)然也可以手動掃描AP，這部分實現(xiàn)在WifiService里面，WifiService通過startScan()接口函數(shù)發(fā)送掃描命令到supplicant。

Frameworks/base/wifi/java/android/net/wifi/WifiStateTracker.java

public boolean startScan(booleanforceActive) {

enforceChangePermission();

switch (mWifiStateTracker.getSupplicantState()) {

case DISCONNECTED:

case INACTIVE:

case SCANNING:

case DORMANT:

break;

default:

mWifiStateTracker.setScanResultHandling(

WifiStateTracker.SUPPL_SCAN_HANDLING_LIST_ONLY);

break;

}

return mWifiStateTracker.scan(forceActive);

}

然后下面的流程同上面的自動掃描，我們來分析一下手動掃描從哪里開始的。我們應(yīng)該知道手動掃描是通過菜單鍵的掃描鍵來響應(yīng)的，而響應(yīng)該動作的應(yīng)該是 WifiSettings類中Scanner類的handlerMessage()函數(shù)，它調(diào)用WifiManager的 startScanActive()，這才調(diào)用WifiService的startScan()。

packages/apps/Settings/src/com/android/settings/wifiwifisettings.java

public boolean onCreateOptionsMenu(Menu menu) {

menu.add(Menu.NONE, MENU_ID_SCAN, 0, R.string.wifi_menu_scan)

.setIcon(R.drawable.ic_menu_scan_network);

menu.add(Menu.NONE, MENU_ID_ADVANCED, 0, R.string.wifi_menu_advanced)

.setIcon(android.R.drawable.ic_menu_manage);

return super.onCreateOptionsMenu(menu);

}

當(dāng)按下菜單鍵時，WifiSettings就會調(diào)用這個函數(shù)繪制菜單。如果選擇掃描按鈕，WifiSettings會調(diào)用onOptionsItemSelected()。

packages/apps/Settings/src/com/android/settings/wifiwifisettings.java