Wi-Fi PNO扫描流程（Android P）

article/2025/11/6 6:25:00

简介：当手机灭屏情况下，有保存网络时，若已连接，不扫描，否则，PNO扫描，即只扫描已保存的网络。最小间隔min=20s，最大间隔max=20s*3=60s

PNO 即Preferred Network Offload，用于系统在休眠的时候连接WiFi

Wi-Fi PNO扫描流程

WifiConnectivityManager.java
灭屏时，WifiConnectivityManager中handleScreenStateChanged函数会判断是否触发PNO扫描。并且进行PNO扫描列表设置、PNO扫描间隔(20s)设置等PNO扫描的参数设置。所以先从处理屏幕状态改变开始。

public void handleScreenStateChanged(boolean screenOn) {localLog("handleScreenStateChanged: screenOn=" + screenOn);mScreenOn = screenOn;mOpenNetworkNotifier.handleScreenStateChanged(screenOn);mCarrierNetworkNotifier.handleScreenStateChanged(screenOn);startConnectivityScan(SCAN_ON_SCHEDULE);
}

开始连接扫描。扫描方式根据当前的屏幕状态和WiFi状态选择。这里会选择PNO扫描。

private void startConnectivityScan(boolean scanImmediately) {localLog("startConnectivityScan: screenOn=" + mScreenOn+ " wifiState=" + stateToString(mWifiState)+ " scanImmediately=" + scanImmediately+ " wifiEnabled=" + mWifiEnabled+ " wifiConnectivityManagerEnabled="+ mWifiConnectivityManagerEnabled);if (!mWifiEnabled || !mWifiConnectivityManagerEnabled) {return;}if (mWifiState != WIFI_STATE_CONNECTED && mWifiState != WIFI_STATE_DISCONNECTED) {return;}if (mScreenOn) {startPeriodicScan(scanImmediately);} else {if (mWifiState == WIFI_STATE_DISCONNECTED && !mPnoScanStarted) {startDisconnectedPnoScan();}}}

当屏幕关闭且WiFI未连接时，开启PNO扫描，初始化scan的设置。
可以看到扫描间隔为20s：scanSettings.periodInMs = DISCONNECTED_PNO_SCAN_INTERVAL_MS

private static final int DISCONNECTED_PNO_SCAN_INTERVAL_MS = 20 * 1000; // 20 seconds

private void startDisconnectedPnoScan() {// Initialize PNO settingsPnoSettings pnoSettings = new PnoSettings();List<PnoSettings.PnoNetwork> pnoNetworkList = mConfigManager.retrievePnoNetworkList();int listSize = pnoNetworkList.size();pnoSettings.networkList = new PnoSettings.PnoNetwork[listSize];pnoSettings.networkList = pnoNetworkList.toArray(pnoSettings.networkList);pnoSettings.min5GHzRssi = mMin5GHzRssi;pnoSettings.min24GHzRssi = mMin24GHzRssi;pnoSettings.initialScoreMax = mInitialScoreMax;pnoSettings.currentConnectionBonus = mCurrentConnectionBonus;pnoSettings.sameNetworkBonus = mSameNetworkBonus;pnoSettings.secureBonus = mSecureBonus;pnoSettings.band5GHzBonus = mBand5GHzBonus;// Initialize scan settingsScanSettings scanSettings = new ScanSettings();scanSettings.band = getScanBand();scanSettings.reportEvents = WifiScanner.REPORT_EVENT_NO_BATCH;scanSettings.numBssidsPerScan = 0;scanSettings.periodInMs = DISCONNECTED_PNO_SCAN_INTERVAL_MS;mPnoScanListener.clearScanDetails();mScanner.startDisconnectedPnoScan(scanSettings, pnoSettings, mPnoScanListener);mPnoScanStarted = true;
}

WifiScanner.java
startDisconnectedPnoScan --> startPnoScan 开启PNO扫描

public void startDisconnectedPnoScan(ScanSettings scanSettings, PnoSettings pnoSettings,PnoScanListener listener) {Preconditions.checkNotNull(listener, "listener cannot be null");Preconditions.checkNotNull(pnoSettings, "pnoSettings cannot be null");int key = addListener(listener);if (key == INVALID_KEY) return;validateChannel();pnoSettings.isConnected = false;startPnoScan(scanSettings, pnoSettings, key);
}

startPnoScan发送PNO扫描（CMD_START_PNO_SCAN）的消息，由WifiScanningServiceImpl处理。

private void startPnoScan(ScanSettings scanSettings, PnoSettings pnoSettings, int key) {// Bundle up both the settings and send it across.Bundle pnoParams = new Bundle();// Set the PNO scan flag.scanSettings.isPnoScan = true;pnoParams.putParcelable(PNO_PARAMS_SCAN_SETTINGS_KEY, scanSettings);pnoParams.putParcelable(PNO_PARAMS_PNO_SETTINGS_KEY, pnoSettings);mAsyncChannel.sendMessage(CMD_START_PNO_SCAN, 0, key, pnoParams);
}

WifiScanningServiceImpl.java
从StartedState状态开始，获取到PNO扫描的设置以后，进入HwPnoScanState状态。

class StartedState extends State {.......@Overridepublic boolean processMessage(Message msg) {ClientInfo ci = mClients.get(msg.replyTo);switch (msg.what) {case WifiScanner.CMD_START_PNO_SCAN:........pnoParams.setDefusable(true);PnoSettings pnoSettings =pnoParams.getParcelable(WifiScanner.PNO_PARAMS_PNO_SETTINGS_KEY);if (mScannerImpl.isHwPnoSupported(pnoSettings.isConnected)) {deferMessage(msg);transitionTo(mHwPnoScanState);} else {replyFailed(msg, WifiScanner.REASON_INVALID_REQUEST, "not supported");}.................}return HANDLED;}
}

如果已经有PNO扫描，则进入StartedState。如果没有，则addHwPnoScanRequest。
注意：这里的StartedState是WifiBackgroundScanStateMachine中的StartedState。

class HwPnoScanState extends State {@Overridepublic boolean processMessage(Message msg) {ClientInfo ci = mClients.get(msg.replyTo);switch (msg.what) {case WifiScanner.CMD_START_PNO_SCAN:Bundle pnoParams = (Bundle) msg.obj;if (pnoParams == null) {replyFailed(msg, WifiScanner.REASON_INVALID_REQUEST, "params null");return HANDLED;}pnoParams.setDefusable(true);PnoSettings pnoSettings =pnoParams.getParcelable(WifiScanner.PNO_PARAMS_PNO_SETTINGS_KEY);ScanSettings scanSettings =pnoParams.getParcelable(WifiScanner.PNO_PARAMS_SCAN_SETTINGS_KEY);if (addHwPnoScanRequest(ci, msg.arg2, scanSettings, pnoSettings)) {replySucceeded(msg);} else {replyFailed(msg, WifiScanner.REASON_INVALID_REQUEST, "bad request");transitionTo(mStartedState);}break;...........return HANDLED;}
}

addHwPnoScanRequest --> addPnoScanRequest

private boolean addHwPnoScanRequest(ClientInfo ci, int handler, ScanSettings scanSettings,PnoSettings pnoSettings) {if (ci == null) {Log.d(TAG, "Failing scan request ClientInfo not found " + handler);return false;}if (!mActivePnoScans.isEmpty()) {loge("Failing scan request because there is already an active scan");return false;}WifiNative.PnoSettings nativePnoSettings =convertSettingsToPnoNative(scanSettings, pnoSettings);if (!mScannerImpl.setHwPnoList(nativePnoSettings, mPnoScanStateMachine)) {return false;}logScanRequest("addHwPnoScanRequest", ci, handler, null, scanSettings, pnoSettings);addPnoScanRequest(ci, handler, scanSettings, pnoSettings);return true;
}

private void addPnoScanRequest(ClientInfo ci, int handler, ScanSettings scanSettings,PnoSettings pnoSettings) {mActivePnoScans.addRequest(ci, handler, WifiStateMachine.WIFI_WORK_SOURCE,Pair.create(pnoSettings, scanSettings));addInternalClient(ci);
}