Android WIFI 分析(二)

本文介绍Wifi 分析线路二：在Setting中打开WiFi功能、扫描网络以及连接网络的流程。

WifiSettings 无线网络设置界面

WifiEnabler 相当于无线网络设置开关

WifiDialog 显示的无线网络配置信息由WifiConfigController 来控制和管理

Scanner 用于处理和无线网络扫描相关的工作

1、Settings 操作

无线网络设置界面UI 初始化过程中，WifiSettings 的onActivityCreated() 方法被调用：

    public void onActivityCreated(Bundle savedInstanceState) {
        super.onActivityCreated(savedInstanceState);

        mWifiTracker =
                new WifiTracker(getActivity(), this, mBgThread.getLooper(), true, true, false);
        mWifiManager = mWifiTracker.getManager();
    }

WifiTracker 构造函数调用：

    WifiTracker(Context context, WifiListener wifiListener, Looper workerLooper,
            boolean includeSaved, boolean includeScans, boolean includePasspoints,
            WifiManager wifiManager, ConnectivityManager connectivityManager,
            Looper currentLooper) {
 　　　　//添加多个广播事件，在startTracker() 方法中进行注册
        mFilter = new IntentFilter();
        mFilter.addAction(WifiManager.WIFI_STATE_CHANGED_ACTION);
        mFilter.addAction(WifiManager.SCAN_RESULTS_AVAILABLE_ACTION);
        mFilter.addAction(WifiManager.NETWORK_IDS_CHANGED_ACTION);
        mFilter.addAction(WifiManager.SUPPLICANT_STATE_CHANGED_ACTION);
        mFilter.addAction(WifiManager.CONFIGURED_NETWORKS_CHANGED_ACTION);
        mFilter.addAction(WifiManager.LINK_CONFIGURATION_CHANGED_ACTION);
        mFilter.addAction(WifiManager.NETWORK_STATE_CHANGED_ACTION);

        mNetworkRequest = new NetworkRequest.Builder()
                .clearCapabilities()
                .addTransportType(NetworkCapabilities.TRANSPORT_WIFI)
                .build();
    }

WifiSettings 的onStart() 方法创建WifiEnabler：

    public void onStart() {
        // On/off switch is hidden for Setup Wizard (returns null)
        mWifiEnabler = createWifiEnabler();
    }

     WifiEnabler createWifiEnabler() {
        final SettingsActivity activity = (SettingsActivity) getActivity();
        return new WifiEnabler(activity, activity.getSwitchBar());
    }

WifiEnabler 的构造函数，添加广播事件：

    public WifiEnabler(Context context, SwitchBar switchBar) {
        mWifiManager = (WifiManager) context.getSystemService(Context.WIFI_SERVICE);
　　　　 //添加三个广播事件
        mIntentFilter = new IntentFilter(WifiManager.WIFI_STATE_CHANGED_ACTION);
        // The order matters! We really should not depend on this. :(
        mIntentFilter.addAction(WifiManager.SUPPLICANT_STATE_CHANGED_ACTION);
        mIntentFilter.addAction(WifiManager.NETWORK_STATE_CHANGED_ACTION);

        setupSwitchBar();
    }

WIFI_STATE_CHANGED_ACTION：反映WiFi 功能所对应的状态，包括WIFI_STATE_DISABLED(Wifi 功能已被关闭)、WIFI_STATE_DISABLING(Wifi 功能正在关闭中)、WIFI_STATE_ENABLED(Wifi 功能已被打开)、WIFI_STATE_ENABLING(Wifi 功能正在打开中)、WIFI_STATE_UNKNOWN(Wifi 功能状态未知)。

SUPPLICANT_STATE_CHANGED_ACTION：表示WPAS 的状态发生了变化。

NETWORK_STATE_CHANGED_ACTION：表示WIFI 连接状态发生变化，其携带的信息一般是NetworkInfo 对象。

WifiSettings 和 WifiEnabler 的设置的广播接收对象在onResume() 的方法中被注册：

    public void onResume() {
        final Activity activity = getActivity();
        if (mWifiEnabler != null) {
            mWifiEnabler.resume(activity); //调用WifiEnabler 类
        }

        mWifiTracker.startTracking(); //调用framework WifiTracker 类
        activity.invalidateOptionsMenu();
    }

WifiEnabler 类的resume() 方法如下：

    public void resume(Context context) {
        mContext = context;
        // Wi-Fi state is sticky, so just let the receiver update UI
        mContext.registerReceiver(mReceiver, mIntentFilter); //注册构造函数中添加的三个广播事件
        if (!mListeningToOnSwitchChange) {
            mSwitchBar.addOnSwitchChangeListener(this);
            mListeningToOnSwitchChange = true;
        }
    }

WifiTracker 类的startTracking() 方法如下：

    /**
     * Start tracking wifi networks.
     * Registers listeners and starts scanning for wifi networks. If this is not called
     * then forceUpdate() must be called to populate getAccessPoints().
     */
    public void startTracking() {
        resumeScanning();
        if (!mRegistered) {
            mContext.registerReceiver(mReceiver, mFilter); //注册构造函数中添加的广播事件
            // NetworkCallback objects cannot be reused. http://b/20701525 .
            mNetworkCallback = new WifiTrackerNetworkCallback();
            mConnectivityManager.registerNetworkCallback(mNetworkRequest, mNetworkCallback);
        }
    }

WifiEnabler 处理较多的及时WIFI_STATE_CHANGED_ACTION 广播，根据此广播信息更新Switch 的界面。

2、启用WIFI 功能

WifiEnabler 实现了SwitchBar 的onSwitchChangeListener 接口，故用户点击事件将触发WifiEnabler 的onSwitchChanged() 方法：

    public void onSwitchChanged(Switch switchView, boolean isChecked) {
        // Disable tethering if enabling Wifi
        if (mayDisableTethering(isChecked)) {
            mWifiManager.setWifiApEnabled(null, false);
        }
    }

WifiManager 的setWifiApEnabled() 方法将触发WifiService 开展一系列的动作，在此过程中，WifiManager 会通过发送广播的方法向外界发布一些信息，所以需重点关注广播事件的处理。

WifiTracker 的广播接收对象的处理：

    final BroadcastReceiver mReceiver = new BroadcastReceiver() {
        @Override
        public void onReceive(Context context, Intent intent) {
            String action = intent.getAction();
            if (WifiManager.WIFI_STATE_CHANGED_ACTION.equals(action)) {
                updateWifiState(intent.getIntExtra(WifiManager.EXTRA_WIFI_STATE,
                        WifiManager.WIFI_STATE_UNKNOWN));
            } 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); //发送更新无线网络列表消息
            } else if (WifiManager.NETWORK_STATE_CHANGED_ACTION.equals(action)) {
                NetworkInfo info = (NetworkInfo) intent.getParcelableExtra(
                        WifiManager.EXTRA_NETWORK_INFO);
                mConnected.set(info.isConnected());
                mMainHandler.sendEmptyMessage(MainHandler.MSG_CONNECTED_CHANGED);
                mWorkHandler.sendEmptyMessage(WorkHandler.MSG_UPDATE_ACCESS_POINTS);
                mWorkHandler.obtainMessage(WorkHandler.MSG_UPDATE_NETWORK_INFO, info)
                        .sendToTarget();
            }
        }
    };

WifiEnabler 的广播接收对象的处理：

    private final BroadcastReceiver mReceiver = new BroadcastReceiver() {
        @Override
        public void onReceive(Context context, Intent intent) {
            String action = intent.getAction();
            if (WifiManager.WIFI_STATE_CHANGED_ACTION.equals(action)) {
                handleWifiStateChanged(intent.getIntExtra(
                        WifiManager.EXTRA_WIFI_STATE, WifiManager.WIFI_STATE_UNKNOWN));
            } else if (WifiManager.SUPPLICANT_STATE_CHANGED_ACTION.equals(action)) {
                if (!mConnected.get()) {
                    handleStateChanged(WifiInfo.getDetailedStateOf((SupplicantState)
                            intent.getParcelableExtra(WifiManager.EXTRA_NEW_STATE)));
                }
            } else if (WifiManager.NETWORK_STATE_CHANGED_ACTION.equals(action)) {
                NetworkInfo info = (NetworkInfo) intent.getParcelableExtra(
                        WifiManager.EXTRA_NETWORK_INFO);
                mConnected.set(info.isConnected());
                handleStateChanged(info.getDetailedState());
            }
        }
    };

1) 触发扫描

当WIFI 功能被启用时，将收到WIFI_STATE_CHANGED_ACTION 广播，该广播的处理函数是WifiTracker 的updateWifiState() 方法：

    private void updateWifiState(int state) {
        mWorkHandler.obtainMessage(WorkHandler.MSG_UPDATE_WIFI_STATE, state, 0).sendToTarget();
    } //向内部WrokHandler 对象发送消息

MSG_UPDATE_WIFI_STATE 的处理：

                case MSG_UPDATE_WIFI_STATE:
                    if (msg.arg1 == WifiManager.WIFI_STATE_ENABLED) {
                        if (mScanner != null) {
                            // We only need to resume if mScanner isn't null because
                            // that means we want to be scanning.
                            mScanner.resume(); //启动扫描
                        }
                    } else {
                        mLastInfo = null;
                        mLastNetworkInfo = null;
                        if (mScanner != null) {
                            mScanner.pause();
                        }
                    }
                    mMainHandler.obtainMessage(MainHandler.MSG_WIFI_STATE_CHANGED, msg.arg1, 0)
                            .sendToTarget(); //向内部MainHandler 对象发送消息
                    break;

Scanner 也是WifiTracker 内部定义的一个Handler：

    class Scanner extends Handler {
        static final int MSG_SCAN = 0;

        void resume() {
            if (!hasMessages(MSG_SCAN)) {
                sendEmptyMessage(MSG_SCAN);
            }
        }

        @Override
        public void handleMessage(Message message) {
            if (message.what != MSG_SCAN) return;
            if (mWifiManager.startScan()) { //发起扫描
                mRetry = 0;
            } else if (++mRetry >= 3) { //扫描失败
                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); //每1秒发起一次扫描
        }
    }

2) 更新AP 列表

如果WPAS 扫描完毕，则WifiTracker 将收到SCAN_RESULTS_AVAILABLE_ACTION 广播，发送消息MSG_UPDATE_ACCESS_POINTS，WorkHandler 对此消息的处理如下：

                case MSG_UPDATE_ACCESS_POINTS:
                    updateAccessPoints();
                    break;

继而调用updateAccessPoints() 方法：

    private void updateAccessPoints() {
        final Collection<ScanResult> results = fetchScanResults(); //获取扫描结果
        final List<WifiConfiguration> configs = mWifiManager.getConfiguredNetworks();
        // Pre-sort accessPoints to speed preference insertion
        Collections.sort(accessPoints); //创建AP 列表
        mMainHandler.sendEmptyMessage(MainHandler.MSG_ACCESS_POINT_CHANGED); //向MainHandler 发送MSG_ACCESS_POINT_CHANGED

3) 加入目标无线网络

从列表中选择加入某个无线网络，处理用户选择AP 事件的方法是WifiSettings 的onPreferenceTreeClick() 方法：

    public boolean onPreferenceTreeClick(Preference preference) {
        if (preference instanceof LongPressAccessPointPreference) {
            mSelectedAccessPoint = ((LongPressAccessPointPreference) preference).getAccessPoint();
            /** Bypass dialog for unsecured, unsaved, and inactive networks */
            if (mSelectedAccessPoint.getSecurity() == AccessPoint.SECURITY_NONE &&
                    !mSelectedAccessPoint.isSaved() && !mSelectedAccessPoint.isActive()) { //对于没有安全设置的无线网络，直接连接它即可
                mSelectedAccessPoint.generateOpenNetworkConfig();
                connect(mSelectedAccessPoint.getConfig());
            } else if (mSelectedAccessPoint.isSaved()) {
                showDialog(mSelectedAccessPoint, WifiConfigUiBase.MODE_VIEW); //弹出无线密码输入框
            } else {
                showDialog(mSelectedAccessPoint, WifiConfigUiBase.MODE_CONNECT);
            }
        } else if (preference == mAddPreference) {
            onAddNetworkPressed();
        }
    }

当用户设置完目标无线网络(例如设置密码)后，点击“连接”按钮，将触发WifiSettings 的submit() 方法被调用：

    /* package */ void submit(WifiConfigController configController) {
        final WifiConfiguration config = configController.getConfig();
        if (config == null) {
        ......
        } else if (configController.getMode() == WifiConfigUiBase.MODE_MODIFY) {
            mWifiManager.save(config, mSaveListener);
        } else {
            mWifiManager.save(config, mSaveListener);
            if (mSelectedAccessPoint != null) { // Not an "Add network"
                connect(config); //连接目标无线网络
            }
        }
        mWifiTracker.resumeScanning();
    }

至此，后续的工作就是等待并处理广播事件，如果一切顺利，将接收一个NETWORK_STATE_CHANGED_ACTION 广播事件以告知手机成功加入目标无线网络。

和WifiManager 交互的几个重要函数以作下面分析重点：

setWifiEnabled()：启用WIFI 功能

startScanActive()：启动AP 扫描

connect()：连接至目标AP