Android4.4.2源碼分析之WiFi模組（二）

標籤：

接著上一篇繼續對WiFi源碼的分析

Android4.4.2源碼分析之WiFi模組（一）

onResume方法中

6>，首先是調用WiFiEnabler的resume方法對switch進行管理

接下來註冊廣播

getActivity().registerReceiver(mReceiver, mFilter);

廣播監聽的action如下

       //wifi狀態改變的action        mFilter.addAction(WifiManager.WIFI_STATE_CHANGED_ACTION);              //WiFi掃描到附近可用WiFi時的廣播        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);        mFilter.addAction(WifiManager.RSSI_CHANGED_ACTION);

查看WiFiManager發現各action定義如下，以及在監聽到對應廣播後各處理如下

i>

 /**     * Broadcast intent action indicating that Wi-Fi has been enabled, disabled,     * enabling, disabling, or unknown. One extra provides this state as an int.     * Another extra provides the previous state, if available.     *     * @see #EXTRA_WIFI_STATE     * @see #EXTRA_PREVIOUS_WIFI_STATE     */    @SdkConstant(SdkConstantType.BROADCAST_INTENT_ACTION)    public static final String WIFI_STATE_CHANGED_ACTION =        "android.net.wifi.WIFI_STATE_CHANGED";

WIFI_STATE_CHANGED_ACTION：當WiFi被開啟、關閉、正在開啟、正在關閉或者位置狀態即wifi狀態發生改變時系統會自動發送該廣播，該廣播會附帶有兩個值，一個是int型表示改變後的state，可通過欄位EXTRA_WIFI_STATE擷取，還有一個是int型的改變前的state（如果有的話）可通過欄位EXTRA_PREVIOUS_WIFI_STATE擷取

當監聽到該廣播後會進行如下處理：更新WiFi狀態（在WiFiEnbabler中也監聽了該廣播，用於當WiFi狀態改變時對switch進行更新）

 if (WifiManager.WIFI_STATE_CHANGED_ACTION.equals(action)) {            updateWifiState(intent.getIntExtra(WifiManager.EXTRA_WIFI_STATE,                    WifiManager.WIFI_STATE_UNKNOWN));

updateWifiState方法如下

private void updateWifiState(int state) {        Activity activity = getActivity();        if (activity != null) {        //重新載入菜單  ，該方法會調用activity中的onCreateOptionsMenu載入actionbar         activity.invalidateOptionsMenu();        }        switch (state) {            case WifiManager.WIFI_STATE_ENABLED://開啟WiFi              mScanner.resume();//從下面的方法中可以看到，該方法是用於開啟WiFi的掃描，並記錄掃描次數                return; // not break, to avoid the call to pause() below            case WifiManager.WIFI_STATE_ENABLING://正在開啟WiFi                addMessagePreference(R.string.wifi_starting);                break;            case WifiManager.WIFI_STATE_DISABLED://關閉WiFi              //使用者可以在wlan-->進階選項中去設定時是否隨時都可以掃描（關閉WiFi後也可以掃描），根據使用者的選擇，               //設定在關閉WLAN後顯示介面上的文本              setOffMessage();                break;        }        mLastInfo = null;        mLastState = null;        mScanner.pause();//移除message通知    }

因為更新的方法中涉及到了Scanner，這裡的Scanner是自訂的內部類，繼承自handler，代碼如下

private class Scanner extends Handler {        private int mRetry = 0;        void resume() {            if (!hasMessages(0)) {                sendEmptyMessage(0);            }        }        void forceScan() {            removeMessages(0);            sendEmptyMessage(0);        }        void pause() {            mRetry = 0;            removeMessages(0);        }        @Override        public void handleMessage(Message message) {            if (mWifiManager.startScan()) {                mRetry = 0;            } else if (++mRetry >= 3) {                mRetry = 0;                Activity activity = getActivity();                if (activity != null) {                    Toast.makeText(activity, R.string.wifi_fail_to_scan,                            Toast.LENGTH_LONG).show();                }                return;            }            sendEmptyMessageDelayed(0, 10*1000);//10s後再次發送message        }    }

可以看到，掃描附近可用WiFi的方法為mWifiManager.startScan（）該方法對使用者可見，可直接調用

ii>

/**     * An access point scan has completed, and results are available from the supplicant.     * Call {@link #getScanResults()} to obtain the results.     */    @SdkConstant(SdkConstantType.BROADCAST_INTENT_ACTION)    public static final String SCAN_RESULTS_AVAILABLE_ACTION = "android.net.wifi.SCAN_RESULTS";

SCAN_RESULT_AVAILABLE_ACTION：WiFi掃描結束時系統會發送該廣播，使用者可以監聽該廣播通過調用WifiManager的getScanResults方法來擷取到掃描結果

else if (WifiManager.SCAN_RESULTS_AVAILABLE_ACTION.equals(action) ||                WifiManager.CONFIGURED_NETWORKS_CHANGED_ACTION.equals(action) ||                WifiManager.LINK_CONFIGURATION_CHANGED_ACTION.equals(action)) {                updateAccessPoints();

當使用者掃描到WiFi或者WiFi資訊發生改變時都需要去更新WiFi列表，更新WiFi列表的方法為updateAccessPoints(），掃描載入列表這塊感覺相當複雜，慢慢分析

首先在掃描結束後可以通過getScanResult（）擷取到掃描後的WiFi列表，返回值為List<ScanResult>，所返回的每個WiFi會攜帶如下資訊

各欄位分別代表什麼含義呢？

BSSID：The address of the access point，存取點地址（String值）

SSID：The network name，WiFi名字（String值）

capabilities：Describes the authentication,key management,and encryption schemes supported by the access point，描述存取點的身分識別驗證，密鑰管理和加密方案（String值）

wifiSsid：ASCII encode SSID，This will replace SSID when we deprecate it ，SSID的ASCII碼編碼，當不支援它時我們可以用它來代替ssid（WifiSsid值）

timestamp：timestamp in microseconds （since boot）when this result was last seen，距離上一次的更改的微秒數

level：對於level的定義從源碼中可以看到，表示訊號的強度，屬於int型數值，

 /**     * The detected signal level in dBm, also known as the RSSI.     *     * <p>Use {@link android.net.wifi.WifiManager#calculateSignalLevel} to convert this number into     * an absolute signal level which can be displayed to a user.     */    public int level;

對於訊號強度的顯示可以通過如下代碼

mWifiLevel.setImageLevel(WifiManager.calculateSignalLevel(mList.get(position).level,4));

frequency：The primary 20 MHz frequency (in MHz) of the channel over which the client is communicating with the access point.用戶端與存取點通訊的頻率

我們一般顯示WiFi列表用到的是SSID、level和capabilities

Android源碼中掃描到WiFi後就需要去載入列表，在接收到SCAN_RESULT_AVAILABLE_ACTION廣播後調用updateAccessPoints方法進行更新列表，在該方法中會根據WiFi的開關狀態來對UI進行更新，只有在WiFi開啟時 才會去更新列表，這裡不再對其他情況進行贅述，在WiFi開啟時會通過如下代碼載入

 private void updateAccessPoints() {        // Safeguard from some delayed event handling        if (getActivity() == null) return;        if (isRestrictedAndNotPinProtected()) {            addMessagePreference(R.string.wifi_empty_list_user_restricted);            return;        }        final int wifiState = mWifiManager.getWifiState();        switch (wifiState) {            case WifiManager.WIFI_STATE_ENABLED:                // AccessPoints are automatically sorted with TreeSet.                //擷取到存取點列表               final Collection<AccessPoint> accessPoints = constructAccessPoints();                if (!getResources().getBoolean(R.bool.set_wifi_priority)) {                    getPreferenceScreen().removeAll();                }                if(accessPoints.size() == 0) {                    addMessagePreference(R.string.wifi_empty_list_wifi_on);                }                if (!getResources().getBoolean(R.bool.set_wifi_priority)) {                   for (AccessPoint accessPoint : accessPoints) {                       <pre name="code" class="java">                        //WiFisettings的xml檔案的根節點為preferencescreen，所以通過如下方法添加      preferencegetPreferenceScreen().addPreference(accessPoint); } } if (accessPoints.isEmpty()){ addMessagePreference(R.string.wifi_empty_list_wifi_on); } break; case WifiManager.WIFI_STATE_ENABLING://如果WiFi處於正在開啟的狀態，則清除列表 。。。。。。。。。 } }

那麼存取點列表的擷取是如何進行的呢？

 private List<AccessPoint> constructAccessPoints() {        ArrayList<AccessPoint> accessPoints = new ArrayList<AccessPoint>();        /** Lookup table to more quickly update AccessPoints by only considering objects with the         * correct SSID.  Maps SSID -> List of AccessPoints with the given SSID.  */          //key為ssid,value為存取點ScanResult      Multimap<String, AccessPoint> apMap = new Multimap<String, AccessPoint>();        if (getResources().getBoolean(R.bool.set_wifi_priority)) {            emptyCategory();        }      //getConfiguredNetwors可以返回一個配置列表，擷取到配置好的網路連接，該列表存放了關於已經串連過的存取點WiFi的資訊，          //返回的列表中包括如下欄位，當WiFi 關閉時會返回null           <pre name="code" class="java">         /** <ul>          * <li>networkId</li>          * <li>SSID</li>          * <li>BSSID</li>          * <li>priority</li>          * <li>allowedProtocols</li>          * <li>allowedKeyManagement</li>          * <li>allowedAuthAlgorithms</li>          * <li>allowedPairwiseCiphers</li>          * <li>allowedGroupCiphers</li>          * </ul>          */final List<WifiConfiguration> configs = mWifiManager.getConfiguredNetworks();        if (configs != null) {            for (WifiConfiguration config : configs) {                if (config.SSID != null) {                    AccessPoint accessPoint = new AccessPoint(getActivity(), config);                    accessPoint.update(mLastInfo, mLastState);                    accessPoints.add(accessPoint);                    apMap.put(accessPoint.ssid, accessPoint);                    if (getResources().getBoolean(R.bool.set_wifi_priority)) {                        SetAPCategory(accessPoint, mConfigedAP);                    }                }            }            if (getResources().getBoolean(R.bool.set_wifi_priority)) {                if (mConfigedAP != null && mConfigedAP.getPreferenceCount() == 0) {                    getPreferenceScreen().removePreference(mConfigedAP);                }            }        }         //擷取到WiFi掃描結果，返回附近可用WiFi，包括已經串連的或者已經儲存的WiFi        final List<ScanResult> results = mWifiManager.getScanResults();        if (results != null) {            for (ScanResult result : results) {                // Ignore hidden and ad-hoc networks.                if (result.SSID == null || result.SSID.length() == 0 ||                        result.capabilities.contains("[IBSS]")) {                    continue;                }                boolean found = false;                for (AccessPoint accessPoint : apMap.getAll(result.SSID)) {                    if (accessPoint.update(result))                        found = true;                }                if (!found) {                    AccessPoint accessPoint = new AccessPoint(getActivity(), result);                    accessPoints.add(accessPoint);                    apMap.put(accessPoint.ssid, accessPoint);                    if (getResources().getBoolean(R.bool.set_wifi_priority)) {                        SetAPCategory(accessPoint, mUnKnownAP);                    }                }            }            if (getResources().getBoolean(R.bool.set_wifi_priority)) {                if(mUnKnownAP !=null && mUnKnownAP.getPreferenceCount() == 0){                    getPreferenceScreen().removePreference(mUnKnownAP);                }            }        }        // Pre-sort accessPoints to speed preference insertion        Collections.sort(accessPoints);        return accessPoints;    }

調用mWifiManager.getConfigureNetworks()方法擷取到的是已經配置過串連過的WiFi列表，列表包含下列值

對於掃描到的WiFi的保護方式通過判斷scanresult的capabilities欄位是否包含對應的string來判斷屬於何種保護方式

 boolean wpa = result.capabilities.contains("WPA-PSK");        boolean wpa2 = result.capabilities.contains("WPA2-PSK")

iii>

/**     * The network IDs of the configured networks could have changed.     */    @SdkConstant(SdkConstantType.BROADCAST_INTENT_ACTION)    public static final String NETWORK_IDS_CHANGED_ACTION = "android.net.wifi.NETWORK_IDS_CHANGED";

NETWORK_IDS_CHANGED：所配置的網路的網路ID可能已經改變

iv>

  /**     * Broadcast intent action indicating that the state of establishing a connection to     * an access point has changed.One extra provides the new     * {@link SupplicantState}. Note that the supplicant state is Wi-Fi specific, and     * is not generally the most useful thing to look at if you are just interested in     * the overall state of connectivity.     * @see #EXTRA_NEW_STATE     * @see #EXTRA_SUPPLICANT_ERROR     */    @SdkConstant(SdkConstantType.BROADCAST_INTENT_ACTION)    public static final String SUPPLICANT_STATE_CHANGED_ACTION =        "android.net.wifi.supplicant.STATE_CHANGE";

SUPPLICANT_STATE_CHANGED_ACTION：正在建立的串連狀態已經改變，該廣播會攜帶兩個值

v>

 /**     * Broadcast intent action indicating that the configured networks changed.     * This can be as a result of adding/updating/deleting a network. If     * {@link #EXTRA_MULTIPLE_NETWORKS_CHANGED} is set to true the new configuration     * can be retreived with the {@link #EXTRA_WIFI_CONFIGURATION} extra. If multiple     * Wi-Fi configurations changed, {@link #EXTRA_WIFI_CONFIGURATION} will not be present.     * @hide     */    public static final String CONFIGURED_NETWORKS_CHANGED_ACTION =        "android.net.wifi.CONFIGURED_NETWORKS_CHANGE";

CONFIGURED_NETWORKS_CHANGED_ACTION：當WiFi列表中的網路添加、更新或者刪除時系統會發送該廣播，但是該廣播對使用者隱藏，無法調用

vi>

/**     * Broadcast intent action indicating that the state of Wi-Fi connectivity     * has changed. One extra provides the new state     * in the form of a {@link android.net.NetworkInfo} object. If the new     * state is CONNECTED, additional extras may provide the BSSID and WifiInfo of     * the access point.     * as a {@code String}.     * @see #EXTRA_NETWORK_INFO     * @see #EXTRA_BSSID     * @see #EXTRA_WIFI_INFO     */    @SdkConstant(SdkConstantType.BROADCAST_INTENT_ACTION)    public static final String NETWORK_STATE_CHANGED_ACTION = "android.net.wifi.STATE_CHANGE";

NETWORK_STATE_CHANGED_ACTION：WiFi串連發生改變時系統會發送該廣播，通過欄位EXTRA_NETWORK_INFO可以擷取到WiFi串連的狀態，如果是已串連的狀態，則會有額外的兩個欄位，欄位EXTRA_BSSID可以擷取到所串連的WiFi的bssid，欄位EXTRA_WIFI_INFO可以擷取到所串連的WiFi的資訊擷取到wifiinfo執行個體

vii>

 /**     * The RSSI (signal strength) has changed.     * @see #EXTRA_NEW_RSSI     */    @SdkConstant(SdkConstantType.BROADCAST_INTENT_ACTION)    public static final String RSSI_CHANGED_ACTION = "android.net.wifi.RSSI_CHANGED";

WIFI_RSSI_CHANGED：當WiFi訊號強度發生改變時系統會發送該廣播，通過欄位EXTRA_NEW_RSSI可以擷取到改變後的wifi訊號強度，當然也需要去更新WiFi列表

Android4.4.2源碼分析之WiFi模組（二）