Android WIFI 詳解
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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
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