Wifi Scan in Settings - 小破孩的博客

从点击 Settings Wifi界面中”refresh” 开始追代码流程 :

####packages Settings

            case MENU_ID_SCAN:
                MetricsLogger.action(getActivity(), MetricsLogger.ACTION_WIFI_FORCE_SCAN);
                mWifiTracker.forceScan();
                return true;

####frameworks settingslib WifiTracker

    public void forceScan() {
        if (mWifiManager.isWifiEnabled() && mScanner != null) {
            mScanner.forceScan();
        }
    }
    class Scanner extends Handler {
        static final int MSG_SCAN = 0;

        void forceScan() {
            removeMessages(MSG_SCAN);
            sendEmptyMessage(MSG_SCAN);
        }

        public void handleMessage(Message message) {
            if (mWifiManager.startScan()) {
                mRetry = 0;
            } else if (++mRetry >= 3) {
                mRetry = 0;
                if (mContext != null) {
                    Toast.makeText(mContext, R.string.wifi_fail_to_scan, Toast.LENGTH_LONG).show();
                }
                return;
            }
            sendEmptyMessageDelayed(0, WIFI_RESCAN_INTERVAL_MS);	//WIFI_RESCAN_INTERVAL_MS = 10 * 1000
        }
    }

开始10s一次的循环扫描，3次扫描失败则停止扫描。 ####WifiManager -> WifiService startScan(null, null)

    public void startScan(ScanSettings settings, WorkSource workSource) {
        enforceChangePermission();  
        ......
        mWifiStateMachine.startScan(Binder.getCallingUid(), scanRequestCounter++,
                settings, workSource);
    }

->WifiStateMachine

    sendMessage(CMD_START_SCAN, callingUid, scanCounter, bundle);

    handleScanRequest(WifiNative.SCAN_WITHOUT_CONNECTION_SETUP, message);

    private void handleScanRequest(int type, Message message) {
        ScanSettings settings = null;
        WorkSource workSource = null;

        ......

        // call wifi native to start the scan
        if (startScanNative(type, freqs)) {
            ......
            return;
        }

        // if reach here, scan request is rejected
        ......
    }

->WifiNative

    doBooleanCommand("SCAN");	//向wpa_supplicant下 "SCAN" command

到这里上层scan 结束，下面看搜到 event 的处理

wpa_supplicant 发出 CTRL-EVENT-SCAN-RESULTS 给 WifiMonito , 在 dispatchEvent 中向 WifiStateMachine 发送 SCAN_RESULTS_EVENT ,处理的地方是 SupplicantStartedState

                case WifiMonitor.SCAN_FAILED_EVENT:
                    maybeRegisterNetworkFactory(); // Make sure our NetworkFactory is registered
                    noteScanEnd();
                    setScanResults();	//获取scanResults
                    if (mIsFullScanOngoing || mSendScanResultsBroadcast) {
                        /* Just updated results from full scan, let apps know about this */
                        boolean scanSucceeded = message.what == WifiMonitor.SCAN_RESULTS_EVENT;
                        sendScanResultsAvailableBroadcast(scanSucceeded);	//通知其他app wifi scan result
                    }
                    mSendScanResultsBroadcast = false;
                    mIsScanOngoing = false;
                    mIsFullScanOngoing = false;
                    if (mBufferedScanMsg.size() > 0)
                        sendMessage(mBufferedScanMsg.remove());
                    break;

在 setScanResults 中先向 wpas 下 “BSS RANGE=0- MASK=0x21987” 获取搜索结果,获取到的结果如下，每个AP之间用”====”分割，末尾以“####”来表示结束

	id=8730
	bssid=38:83:45:0d:54:42
	freq=2472
	level=-75
	tsf=0000207703501464
	flags=[WPA2-PSK-CCMP+TKIP-preauth][ESS]
	ssid=POWER-NB
	====
	id=8731
	bssid=c8:60:00:93:f2:5a
	freq=2467
	level=-76
	tsf=0000207703501484
	flags=[WPA2-PSK-CCMP][ESS]
	ssid=ASUS 2.4G
	####

搜索结构先保存在 mScanResults 这个 List 中，将新搜索到的ap 加入到 mScanResultCache 中。

而在 sendScanResultsAvailableBroadcast 中会发送 WifiManager.SCAN_RESULTS_AVAILABLE_ACTION 的 broadcast, Settings 中由 frameworks 中的 WifiTracker 中处理该事件

            } else if (WifiManager.SCAN_RESULTS_AVAILABLE_ACTION.equals(action) ||
                    WifiManager.CONFIGURED_NETWORKS_CHANGED_ACTION.equals(action) ||
                    WifiManager.LINK_CONFIGURATION_CHANGED_ACTION.equals(action)) {
                mWorkHandler.sendEmptyMessage(WorkHandler.MSG_UPDATE_ACCESS_POINTS);

最后都是在 updateAccessPoints 中处理 , 主要是将搜索结果解析之后保存到 mAccessPoints ,并发 MSG_ACCESS_POINT_CHANGED 。
这个 event 的处理会调用到上层注册的 mListener.onConnectedChanged() , 这样回到 Settings 中的 WifiSettings 中重绘搜索列表。