本文主要是介绍（一百三十五）Android O探索WLAN扫描(WIFI SCAN ALWAYS)，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！
1.界面信息
小米mix2 WLAN扫描开关位于设置-更多设置-系统安全-位置信息-扫描，截图如下
2.流程梳理
搜索字符串
jiatai@jiatai:~/expand/aosp/aosp/packages/apps/Settings/res/values-zh-rCN$ grep "WLAN.*扫描" ./ -nr
./arrays.xml:250: <item msgid="8281201165558093009">"WLAN扫描"</item>
./strings.xml:738: <string name="wifi_scan_notify_text" msgid="5593805423071186757">"为了提高位置信息的精确度，系统应用和服务仍然会扫描 WLAN 网络。您可以在<xliff:g id="LINK_BEGIN_0">LINK_BEGIN</xliff:g>扫描设置<xliff:g id="LINK_END_1">LINK_END</xliff:g>中更改此设置。"</string>
./strings.xml:739: <string name="wifi_scan_notify_text_scanning_off" msgid="3426075479272242098">"要提高位置信息的精确度，请在<xliff:g id="LINK_BEGIN_0">LINK_BEGIN</xliff:g>扫描设置<xliff:g id="LINK_END_1">LINK_END</xliff:g>中开启 WLAN 扫描功能。"</string>
./strings.xml:827: <string name="wifi_scan_always_turnon_message" msgid="203123538572122989">"为了提高位置信息精确度以及其他目的，“<xliff:g id="APP_NAME">%1$s</xliff:g>”请求启用网络扫描功能（在关闭了WLAN时也可进行扫描）。\n\n是否对所有需要进行扫描的应用批准这项请求？"</string>
./strings.xml:1430: <string name="location_scanning_wifi_always_scanning_title" msgid="6216705505621183645">"WLAN 扫描"</string>jiatai@jiatai:~/expand/aosp/aosp/packages/apps/Settings/res/xml$ grep "location_scanning_wifi_always_scanning_title" ./ -nr
./location_scanning.xml:22: android:title="@string/location_scanning_wifi_always_scanning_title"
jiatai@jiatai:~/expand/aosp/aosp/packages/apps/Settings/res/xml$ vim ./location_scanning.xml
jiatai@jiatai:~/expand/aosp/aosp/packages/apps/Settings/res/xml$ cd ../../src/
jiatai@jiatai:~/expand/aosp/aosp/packages/apps/Settings/src$ grep "wifi_always_scanning" ./ -nr
./com/android/settings/location/ScanningSettings.java:32: private static final String KEY_WIFI_SCAN_ALWAYS_AVAILABLE = "wifi_always_scanning";之后定位到ScanningSettings这个类对应于开关的逻辑处理
2.1 ScanningSettings
68 @Override69 public boolean onPreferenceTreeClick(Preference preference) {70 String key = preference.getKey();71 if (KEY_WIFI_SCAN_ALWAYS_AVAILABLE.equals(key)) {72 Global.putInt(getContentResolver(),73 Global.WIFI_SCAN_ALWAYS_AVAILABLE,74 ((SwitchPreference) preference).isChecked() ? 1 : 0);75 } else if (KEY_BLUETOOTH_SCAN_ALWAYS_AVAILABLE.equals(key)) {76 Global.putInt(getContentResolver(),77 Global.BLE_SCAN_ALWAYS_AVAILABLE,78 ((SwitchPreference) preference).isChecked() ? 1 : 0);79 } else {80 return super.onPreferenceTreeClick(preference);81 }82 return true;83 }
从如上代码可以看到该开关其实就是对应了一个数据库值（Global.WIFI_SCAN_ALWAYS_AVAILABLE）的变化
在framework搜索相关数据库监听
挨个看了下WifiServiceImpl中有对该数据库值（Global.WIFI_SCAN_ALWAYS_AVAILABLE）的监听
2.2 WifiServiceImpl
/*** Observes settings changes to scan always mode.*/private void registerForScanModeChange() {ContentObserver contentObserver = new ContentObserver(null) {@Overridepublic void onChange(boolean selfChange) {mSettingsStore.handleWifiScanAlwaysAvailableToggled();mWifiController.sendMessage(CMD_SCAN_ALWAYS_MODE_CHANGED);}};mFrameworkFacade.registerContentObserver(mContext,Settings.Global.getUriFor(Settings.Global.WIFI_SCAN_ALWAYS_AVAILABLE),false, contentObserver);}数据库值（Global.WIFI_SCAN_ALWAYS_AVAILABLE）的变化会触发
mSettingsStore.handleWifiScanAlwaysAvailableToggled();mWifiController.sendMessage(CMD_SCAN_ALWAYS_MODE_CHANGED);依次看下
2.3 WifiSettingsStore
synchronized void handleWifiScanAlwaysAvailableToggled() {mScanAlwaysAvailable = getPersistedScanAlwaysAvailable();}private boolean getPersistedScanAlwaysAvailable() {return Settings.Global.getInt(mContext.getContentResolver(),Settings.Global.WIFI_SCAN_ALWAYS_AVAILABLE,0) == 1;}WifiSettingsStore就是更新一下自己保存的局部变量mScanAlwaysAvailable与当前开关保存一致。
2.4 WifiController
搜索代码看了下只有三个状态会对消息CMD_SCAN_ALWAYS_MODE_CHANGED进行处理，分别是
DefaultState(不作处理)
ApStaDisabledState（若开关打开，切换到StaDisabledWithScanState）
StaDisabledWithScanState（若开关关闭，切换到ApStaDisabledState）
2.4.1 wifi scan always打开
class ApStaDisabledState extends State {
...case CMD_SCAN_ALWAYS_MODE_CHANGED:if (mSettingsStore.isScanAlwaysAvailable()) {transitionTo(mStaDisabledWithScanState);}break;
class StaDisabledWithScanState extends State {private int mDeferredEnableSerialNumber = 0;private boolean mHaveDeferredEnable = false;private long mDisabledTimestamp;@Overridepublic void enter() {// need to set the mode before starting supplicant because WSM will assume we are going// in to client modemWifiStateMachine.setOperationalMode(WifiStateMachine.SCAN_ONLY_WITH_WIFI_OFF_MODE);mWifiStateMachine.setSupplicantRunning(true);// Supplicant can't restart right away, so not the time we switched offmDisabledTimestamp = SystemClock.elapsedRealtime();mDeferredEnableSerialNumber++;mHaveDeferredEnable = false;mWifiStateMachine.clearANQPCache();}从如上代码及状态之间图示可以看出状态切换只走了StaDisabledWithScanState的enter方法
简单看了就是切换到了SCAN_ONLY_WITH_WIFI_OFF_MODE并且启动了supplicant
WSM
i 切换SCAN_ONLY_WITH_WIFI_OFF_MODE
/*** TODO: doc*/public void setOperationalMode(int mode) {if (mVerboseLoggingEnabled) log("setting operational mode to " + String.valueOf(mode));sendMessage(CMD_SET_OPERATIONAL_MODE, mode, 0);}InitialState
case CMD_SET_OPERATIONAL_MODE:mOperationalMode = message.arg1;if (mOperationalMode != DISABLED_MODE) {sendMessage(CMD_START_SUPPLICANT);}break;ii 启动supplicant
/*** TODO: doc*/public void setSupplicantRunning(boolean enable) {if (enable) {sendMessage(CMD_START_SUPPLICANT);} else {sendMessage(CMD_STOP_SUPPLICANT);}}可以看到两步其实都下发了启动supplicant的命令，简单看起来有冗余，之后WiFi启动流程是差不多的，加载驱动-启动supplicant，从InitialState-SupplicantStartingState-SupplicantStartedState
class SupplicantStartedState extends State {@Overridepublic void enter() {if (mVerboseLoggingEnabled) {logd("SupplicantStartedState enter");}mWifiNative.setExternalSim(true);setRandomMacOui();mCountryCode.setReadyForChange(true);// We can't do this in the constructor because WifiStateMachine is created before the// wifi scanning service is initializedif (mWifiScanner == null) {mWifiScanner = mWifiInjector.getWifiScanner();synchronized (mWifiReqCountLock) {mWifiConnectivityManager =mWifiInjector.makeWifiConnectivityManager(mWifiInfo,hasConnectionRequests());mWifiConnectivityManager.setUntrustedConnectionAllowed(mUntrustedReqCount > 0);mWifiConnectivityManager.handleScreenStateChanged(mScreenOn);}}mWifiDiagnostics.startLogging(mVerboseLoggingEnabled);mIsRunning = true;updateBatteryWorkSource(null);/*** Enable bluetooth coexistence scan mode when bluetooth connection is active.* When this mode is on, some of the low-level scan parameters used by the* driver are changed to reduce interference with bluetooth*/mWifiNative.setBluetoothCoexistenceScanMode(mBluetoothConnectionActive);// Check if there is a voice call on-going and set/reset the tx power limit// appropriately.if (mEnableVoiceCallSarTxPowerLimit) {if (getTelephonyManager().isOffhook()) {sendMessage(CMD_SELECT_TX_POWER_SCENARIO,WifiNative.TX_POWER_SCENARIO_VOICE_CALL);} else {sendMessage(CMD_SELECT_TX_POWER_SCENARIO,WifiNative.TX_POWER_SCENARIO_NORMAL);}}// initialize network statesetNetworkDetailedState(DetailedState.DISCONNECTED);// Disable legacy multicast filtering, which on some chipsets defaults to enabled.// Legacy IPv6 multicast filtering blocks ICMPv6 router advertisements which breaks IPv6// provisioning. Legacy IPv4 multicast filtering may be re-enabled later via// IpClient.Callback.setFallbackMulticastFilter()mWifiNative.stopFilteringMulticastV4Packets();mWifiNative.stopFilteringMulticastV6Packets();if (mOperationalMode == SCAN_ONLY_MODE ||mOperationalMode == SCAN_ONLY_WITH_WIFI_OFF_MODE) {mWifiNative.disconnect();setWifiState(WIFI_STATE_DISABLED);transitionTo(mScanModeState);} else if (mOperationalMode == CONNECT_MODE) {setWifiState(WIFI_STATE_ENABLING);// Transitioning to Disconnected state will trigger a scan and subsequently AutoJointransitionTo(mDisconnectedState);} else if (mOperationalMode == DISABLED_MODE) {transitionTo(mSupplicantStoppingState);}
。。。之前梳理WiFi启动流程的时候OperationalMode都是CONNECT_MODE，之后会切换到DisconnectedState
而这次wifi scan always的OperationalMode是SCAN_ONLY_WITH_WIFI_OFF_MODE，这时会切换到ScanModeState
class ScanModeState extends State {private int mLastOperationMode;@Overridepublic void enter() {mLastOperationMode = mOperationalMode;mWifiStateTracker.updateState(WifiStateTracker.SCAN_MODE);}@Overridepublic boolean processMessage(Message message) {logStateAndMessage(message, this);switch(message.what) {case CMD_SET_OPERATIONAL_MODE:if (message.arg1 == CONNECT_MODE) {mOperationalMode = CONNECT_MODE;setWifiState(WIFI_STATE_ENABLING);transitionTo(mDisconnectedState);} else if (message.arg1 == DISABLED_MODE) {transitionTo(mSupplicantStoppingState);}// Nothing to dobreak;// Handle scan. All the connection related commands are// handled only in ConnectModeStatecase CMD_START_SCAN:handleScanRequest(message);break;default:return NOT_HANDLED;}return HANDLED;}}这个状态很简单，就处理两个消息，CMD_SET_OPERATIONAL_MODE和CMD_START_SCAN，主要看下CMD_START_SCAN的处理
（对比ConnectModeState可以处理CMD_START_CONNECT CMD_START_ROAM CMD_SAVE_CONFIG等等连接相关的命令）
private void handleScanRequest(Message message) {ScanSettings settings = null;WorkSource workSource = null;// unbundle parametersBundle bundle = (Bundle) message.obj;if (bundle != null) {settings = bundle.getParcelable(CUSTOMIZED_SCAN_SETTING);workSource = bundle.getParcelable(CUSTOMIZED_SCAN_WORKSOURCE);}Set<Integer> freqs = null;if (settings != null && settings.channelSet != null) {freqs = new HashSet<>();for (WifiChannel channel : settings.channelSet) {freqs.add(channel.freqMHz);}}// Retrieve the list of hidden network SSIDs to scan for.List<WifiScanner.ScanSettings.HiddenNetwork> hiddenNetworks =mWifiConfigManager.retrieveHiddenNetworkList();// call wifi native to start the scanif (startScanNative(freqs, hiddenNetworks, workSource)) {// a full scan covers everything, clearing scan request bufferif (freqs == null)mBufferedScanMsg.clear();messageHandlingStatus = MESSAGE_HANDLING_STATUS_OK;return;}// if reach here, scan request is rejectedif (!mIsScanOngoing) {// if rejection is NOT due to ongoing scan (e.g. bad scan parameters),// discard this request and pop up the next oneif (mBufferedScanMsg.size() > 0) {sendMessage(mBufferedScanMsg.remove());}messageHandlingStatus = MESSAGE_HANDLING_STATUS_DISCARD;} else if (!mIsFullScanOngoing) {// if rejection is due to an ongoing scan, and the ongoing one is NOT a full scan,// buffer the scan request to make sure specified channels will be scanned eventuallyif (freqs == null)mBufferedScanMsg.clear();if (mBufferedScanMsg.size() < SCAN_REQUEST_BUFFER_MAX_SIZE) {Message msg = obtainMessage(CMD_START_SCAN,message.arg1, message.arg2, bundle);mBufferedScanMsg.add(msg);} else {// if too many requests in buffer, combine them into a single full scanbundle = new Bundle();bundle.putParcelable(CUSTOMIZED_SCAN_SETTING, null);bundle.putParcelable(CUSTOMIZED_SCAN_WORKSOURCE, workSource);Message msg = obtainMessage(CMD_START_SCAN, message.arg1, message.arg2, bundle);mBufferedScanMsg.clear();mBufferedScanMsg.add(msg);}messageHandlingStatus = MESSAGE_HANDLING_STATUS_LOOPED;} else {// mIsScanOngoing and mIsFullScanOngoingmessageHandlingStatus = MESSAGE_HANDLING_STATUS_FAIL;}}这里还可以看到
// Retrieve the list of hidden network SSIDs to scan for.List<WifiScanner.ScanSettings.HiddenNetwork> hiddenNetworks =mWifiConfigManager.retrieveHiddenNetworkList();这边应该是可以让扫描可以扫描到隐藏网络的相关代码，梳理待续
可以理解为ScanModeState主要就处理扫描请求，和其所处模式SCAN_ONLY_WITH_WIFI_OFF_MODE的描述很相符，WiFi关闭情况下只进行扫描。
2.4.1 wifi scan always关闭
WifiController
class ApStaDisabledState extends State {private int mDeferredEnableSerialNumber = 0;private boolean mHaveDeferredEnable = false;private long mDisabledTimestamp;@Overridepublic void enter() {mWifiStateMachine.setSupplicantRunning(false);// Supplicant can't restart right away, so not the time we switched offmDisabledTimestamp = SystemClock.elapsedRealtime();mDeferredEnableSerialNumber++;mHaveDeferredEnable = false;mWifiStateMachine.clearANQPCache();}这边看来就是将supplicant关闭即可
WSM ScanModeState的父状态为SupplicantStartedState，由于ScanModeState无法处理CMD_STOP_SUPPLICANT，由其父状态SupplicantStartedState处理。
class SupplicantStartedState extends State {
...@Overridepublic boolean processMessage(Message message) {logStateAndMessage(message, this);switch(message.what) {case CMD_STOP_SUPPLICANT: /* Supplicant stopped by user */if (mP2pSupported) {transitionTo(mWaitForP2pDisableState);} else {transitionTo(mSupplicantStoppingState);}break;
...@Overridepublic void exit() {mWifiDiagnostics.stopLogging();mIsRunning = false;updateBatteryWorkSource(null);mScanResults = new ArrayList<>();final Intent intent = new Intent(WifiManager.WIFI_SCAN_AVAILABLE);intent.addFlags(Intent.FLAG_RECEIVER_REGISTERED_ONLY_BEFORE_BOOT);intent.putExtra(WifiManager.EXTRA_SCAN_AVAILABLE, WIFI_STATE_DISABLED);mContext.sendStickyBroadcastAsUser(intent, UserHandle.ALL);mBufferedScanMsg.clear();mNetworkInfo.setIsAvailable(false);if (mNetworkAgent != null) mNetworkAgent.sendNetworkInfo(mNetworkInfo);mCountryCode.setReadyForChange(false);}}切换到SupplicantStoppingState
class SupplicantStoppingState extends State {@Overridepublic void enter() {/* Send any reset commands to supplicant before shutting it down */handleNetworkDisconnect();String suppState = System.getProperty("init.svc.wpa_supplicant");if (suppState == null) suppState = "unknown";setWifiState(WIFI_STATE_DISABLING);mSupplicantStateTracker.sendMessage(CMD_RESET_SUPPLICANT_STATE);logd("SupplicantStoppingState: disableSupplicant "+ " init.svc.wpa_supplicant=" + suppState);if (mWifiNative.disableSupplicant()) {mWifiNative.closeSupplicantConnection();sendSupplicantConnectionChangedBroadcast(false);setWifiState(WIFI_STATE_DISABLED);} else {// Failed to disable supplicanthandleSupplicantConnectionLoss(true);}transitionTo(mInitialState);}}关闭supplicant后切换到InitialState状态
class InitialState extends State {private void cleanup() {// Tearing down the client interfaces below is going to stop our supplicant.mWifiMonitor.stopAllMonitoring();mDeathRecipient.unlinkToDeath();mWifiNative.tearDown();}@Overridepublic void enter() {mWifiStateTracker.updateState(WifiStateTracker.INVALID);cleanup();}流程处理完毕。
3.总结
WIFI SCAN ALWAYS对应模式为SCAN_ONLY_WITH_WIFI_OFF_MODE，SCAN_ONLY_WITH_WIFI_OFF_MODE顾名思义WiFi关闭情况下只处理扫描请求。
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