WifiP2pSettings工作流程

本文为《深入理解Android Wi-Fi、NFC和GPS卷》读书笔记，Android源码为Android 5.1

Android平台中，P2P操作用户只需执行如下三个步骤：
1)进入WifiP2pSettings界面；
2)搜索周围的P2P设备。搜索到的设备将显示在WifiP2pSettings中。
3)用户选择其中的某个设备以发起连接。
首先来看WifiP2pSettings的onActivityCreate函数。
1.WifiP2pSettings创建

android-5.1/packages/apps/Settings/src/com/android/settings/wifi/p2p/WifiP2pSettings.java

    public void onActivityCreated(Bundle savedInstanceState) {addPreferencesFromResource(R.xml.wifi_p2p_settings);//加载界面元素/*WifiP2pSettings也是通过监听广播的方式来了解系统中Wi-Fi P2P相关的信息及变化情况。下面这几个广播属于P2P特有的，其作用如下：WIFI_P2P_STATE_CHANGED_ACTION:用于通知系统中P2P功能的启用情况，如该功能是enable还是disable。WIFI_P2P_PEERS_CHANGED_ACTION:系统内部将保存搜索到的其他P2P设备信息，如果这些信息有变化，则系统将发送该广播。接收者需要通过WifiP2PManager的requestPeers函数重新获取这些P2P设备的信息。WIFI_P2P_CONNECTION_CHANGED_ACTION:用于通知P2P连接情况，该广播可携带WifiP2pInfo和NetworkInfo两个对象。相关信息可从这两个对象中获取。WIFI_P2P_THIS_DEVICE_CHANGED_ACTION:用于通知本机P2P设备信息发生了变化。WIFI_P2P_DISCOVERY_CHANGED_ACTION:用于通知P2P Device Discovery的工作状态，如启动或停止。WIFI_P2P_PERSISTENT_GROUPS_CHANGED_ACTION:用于通知persistent group信息发生了变化。mIntentFilter.addAction(WifiP2pManager.WIFI_P2P_STATE_CHANGED_ACTION);mIntentFilter.addAction(WifiP2pManager.WIFI_P2P_PEERS_CHANGED_ACTION);mIntentFilter.addAction(WifiP2pManager.WIFI_P2P_CONNECTION_CHANGED_ACTION);mIntentFilter.addAction(WifiP2pManager.WIFI_P2P_THIS_DEVICE_CHANGED_ACTION);mIntentFilter.addAction(WifiP2pManager.WIFI_P2P_DISCOVERY_CHANGED_ACTION);mIntentFilter.addAction(WifiP2pManager.WIFI_P2P_PERSISTENT_GROUPS_CHANGED_ACTION);final Activity activity = getActivity();//创建WifiP2pManager对象，它将和WifiP2pService交互mWifiP2pManager = (WifiP2pManager) getSystemService(Context.WIFI_P2P_SERVICE);if (mWifiP2pManager != null) {//初始化WifiManager并建立和WiFiService的联系mChannel = mWifiP2pManager.initialize(activity, getActivity().getMainLooper(), null);if (mChannel == null) {//Failure to set up connectionLog.e(TAG, "Failed to set up connection with wifi p2p service");mWifiP2pManager = null;}} else {Log.e(TAG, "mWifiP2pManager is null !");}if (savedInstanceState != null && savedInstanceState.containsKey(SAVE_DIALOG_PEER)) {WifiP2pDevice device = savedInstanceState.getParcelable(SAVE_DIALOG_PEER);mSelectedWifiPeer = new WifiP2pPeer(getActivity(), device);}if (savedInstanceState != null && savedInstanceState.containsKey(SAVE_DEVICE_NAME)) {mSavedDeviceName = savedInstanceState.getString(SAVE_DEVICE_NAME);}if (savedInstanceState != null && savedInstanceState.containsKey(SAVE_SELECTED_GROUP)) {mSelectedGroupName = savedInstanceState.getString(SAVE_SELECTED_GROUP);}//创建UI中按钮对应的onClickListenermRenameListener = new OnClickListener() {@Overridepublic void onClick(DialogInterface dialog, int which) {if (which == DialogInterface.BUTTON_POSITIVE) {if (mWifiP2pManager != null) {mWifiP2pManager.setDeviceName(mChannel,mDeviceNameText.getText().toString(),new WifiP2pManager.ActionListener() {public void onSuccess() {if (DBG) Log.d(TAG, " device rename success");}public void onFailure(int reason) {Toast.makeText(getActivity(),R.string.wifi_p2p_failed_rename_message,Toast.LENGTH_LONG).show();}});}}}};//disconnect dialog listenermDisconnectListener = new OnClickListener() {@Overridepublic void onClick(DialogInterface dialog, int which) {if (which == DialogInterface.BUTTON_POSITIVE) {if (mWifiP2pManager != null) {mWifiP2pManager.removeGroup(mChannel, new WifiP2pManager.ActionListener() {public void onSuccess() {if (DBG) Log.d(TAG, " remove group success");}public void onFailure(int reason) {if (DBG) Log.d(TAG, " remove group fail " + reason);}});}}}};//cancel connect dialog listenermCancelConnectListener = new OnClickListener() {@Overridepublic void onClick(DialogInterface dialog, int which) {if (which == DialogInterface.BUTTON_POSITIVE) {if (mWifiP2pManager != null) {mWifiP2pManager.cancelConnect(mChannel,new WifiP2pManager.ActionListener() {public void onSuccess() {if (DBG) Log.d(TAG, " cancel connect success");}public void onFailure(int reason) {if (DBG) Log.d(TAG, " cancel connect fail " + reason);}});}}}};//delete persistent group dialog listenermDeleteGroupListener = new OnClickListener() {@Overridepublic void onClick(DialogInterface dialog, int which) {if (which == DialogInterface.BUTTON_POSITIVE) {if (mWifiP2pManager != null) {if (mSelectedGroup != null) {if (DBG) Log.d(TAG, " deleting group " + mSelectedGroup.getGroupName());mWifiP2pManager.deletePersistentGroup(mChannel,mSelectedGroup.getNetworkId(),new WifiP2pManager.ActionListener() {public void onSuccess() {if (DBG) Log.d(TAG, " delete group success");}public void onFailure(int reason) {if (DBG) Log.d(TAG, " delete group fail " + reason);}});mSelectedGroup = null;} else {if (DBG) Log.w(TAG, " No selected group to delete!" );}}} else if (which == DialogInterface.BUTTON_NEGATIVE) {if (DBG) {Log.d(TAG, " forgetting selected group " + mSelectedGroup.getGroupName());}mSelectedGroup = null;}}};setHasOptionsMenu(true);final PreferenceScreen preferenceScreen = getPreferenceScreen();preferenceScreen.removeAll();preferenceScreen.setOrderingAsAdded(true);mThisDevicePref = new Preference(getActivity());mThisDevicePref.setPersistent(false);mThisDevicePref.setSelectable(false);preferenceScreen.addPreference(mThisDevicePref);mPeersGroup = new PreferenceCategory(getActivity());mPeersGroup.setTitle(R.string.wifi_p2p_peer_devices);preferenceScreen.addPreference(mPeersGroup);mPersistentGroup = new PreferenceCategory(getActivity());mPersistentGroup.setTitle(R.string.wifi_p2p_remembered_groups);preferenceScreen.addPreference(mPersistentGroup);super.onActivityCreated(savedInstanceState);}

2.WifiP2pSettings工作流程
1)WIFI_P2P_STATE_CHANGED_ACTION处理流程
打开WifiP2pSettings后，首先要等待 WIFI_P2P_STATE_CHANGED_ACTION广播以判断P2P功能是否正常启动。相应的处理函数如下所示：
android-5.1/packages/apps/Settings/src/com/android/settings/wifi/p2p/WifiP2pSettings.java

    private final BroadcastReceiver mReceiver = new BroadcastReceiver() {@Overridepublic void onReceive(Context context, Intent intent) {String action = intent.getAction();if (WifiP2pManager.WIFI_P2P_STATE_CHANGED_ACTION.equals(action)) {//从 WIFI_P2P_STATE_CHANGED_ACTION广播中获取相关状态信息以判断P2P功能是否打开mWifiP2pEnabled = intent.getIntExtra(WifiP2pManager.EXTRA_WIFI_STATE,WifiP2pManager.WIFI_P2P_STATE_DISABLED) == WifiP2pManager.WIFI_P2P_STATE_ENABLED;handleP2pStateChanged();//如果搜索到新的P2P设备，则WIFI_P2P_PEERS_CHANGED_ACTION将被发送} else if (WifiP2pManager.WIFI_P2P_PEERS_CHANGED_ACTION.equals(action)) {mPeers = (WifiP2pDeviceList) intent.getParcelableExtra(WifiP2pManager.EXTRA_P2P_DEVICE_LIST);handlePeersChanged();} else if (WifiP2pManager.WIFI_P2P_CONNECTION_CHANGED_ACTION.equals(action)) {if (mWifiP2pManager == null) return;NetworkInfo networkInfo = (NetworkInfo) intent.getParcelableExtra(WifiP2pManager.EXTRA_NETWORK_INFO);WifiP2pInfo wifip2pinfo = (WifiP2pInfo) intent.getParcelableExtra(WifiP2pManager.EXTRA_WIFI_P2P_INFO);if (networkInfo.isConnected()) {if (DBG) Log.d(TAG, "Connected");} else if (mLastGroupFormed != true) {//start a search when we are disconnected//but not on group removed broadcast eventstartSearch();   //如果没有加入某个P2P组，则重新发起设备扫描}mLastGroupFormed = wifip2pinfo.groupFormed;} else if (WifiP2pManager.WIFI_P2P_THIS_DEVICE_CHANGED_ACTION.equals(action)) {mThisDevice = (WifiP2pDevice) intent.getParcelableExtra(WifiP2pManager.EXTRA_WIFI_P2P_DEVICE);if (DBG) Log.d(TAG, "Update device info: " + mThisDevice);updateDevicePref();} else if (WifiP2pManager.WIFI_P2P_DISCOVERY_CHANGED_ACTION.equals(action)) {int discoveryState = intent.getIntExtra(WifiP2pManager.EXTRA_DISCOVERY_STATE,WifiP2pManager.WIFI_P2P_DISCOVERY_STOPPED);if (DBG) Log.d(TAG, "Discovery state changed: " + discoveryState);if (discoveryState == WifiP2pManager.WIFI_P2P_DISCOVERY_STARTED) {updateSearchMenu(true);//更新SEARCH按钮显示的名称} else {updateSearchMenu(false);}} else if (WifiP2pManager.WIFI_P2P_PERSISTENT_GROUPS_CHANGED_ACTION.equals(action)) {if (mWifiP2pManager != null) {mWifiP2pManager.requestPersistentGroupInfo(mChannel, WifiP2pSettings.this);}}}};

    private void handleP2pStateChanged() {updateSearchMenu(false);//该函数将触发WifiP2pSettings的onCreateOptionsMenu被调用mThisDevicePref.setEnabled(mWifiP2pEnabled);mPeersGroup.setEnabled(mWifiP2pEnabled);mPersistentGroup.setEnabled(mWifiP2pEnabled);}

用户下一步要做的事情就是主动搜索周围的P2P设备。Android原生代码中的WifiP2pSettings界面下方有两个按钮，分别是SEARCH和RENAME，分别用于搜索周围的P2P Device和更改本机的P2P设备名。
当P2P功能正常启用后(即上述代码中的mWifiP2pEnabled为true时)，这两个按钮将被使能。此后，用户就可单击SEARCH按钮以搜索周围的P2P设备。该按钮对应的函数是startSearch。

    private void startSearch() {if (mWifiP2pManager != null && !mWifiP2pSearching) {//discoverPeers将搜索周围的P2P设备mWifiP2pManager.discoverPeers(mChannel, new WifiP2pManager.ActionListener() {public void onSuccess() {}public void onFailure(int reason) {if (DBG) Log.d(TAG, " discover fail " + reason);}});}}

当WPAS完成搜索后， WIFI_P2P_PEERS_CHANGED_ACTION广播将被发送。对该广播的处理参考onReceive函数。startSearch还将触发系统发送 WIFI_P2P_DISCOVERY_CHANGED_ACTION广播，WifiP2pSettings将根据该广播携带的信息来更新SEARCH按钮的界面:如果P2P Discovery启动成功(即状态变为 WIFI_P2P_DISCOVERY_STARTED)，则SEARCH按钮名称显示为Searching，否则该按钮显示为Search For Devices。
当系统搜索到新的P2P设备后，WIFI_P2P_PEERS_CHANGED_ACTION广播将被发送，而WifiP2pSettings对于该广播的处理就是调用WifiP2pManager的requestPeers来获取系统保存的P2P设备信息列表
系统中所有的P2P设备信息将通过PeerListener接口类的onPeersAvailable函数返回给WifiP2pSettings：

    public void onPeersAvailable(WifiP2pDeviceList peers) {if (DBG) Log.d(TAG, "Requested peers are available");//系统中所有的P2P设备信息都保存在这个类型为WifiP2pDeviceList的peers对象中mPeers = peers;handlePeersChanged();}

    private void handlePeersChanged() {mPeersGroup.removeAll();//mPeersGroup类型为PreferenceGroup，属于UI相关的类mConnectedDevices = 0;if (DBG) Log.d(TAG, "List of available peers");for (WifiP2pDevice peer: mPeers.getDeviceList()) {if (DBG) Log.d(TAG, "-> " + peer);//WifiP2pPeer是Preference的子类，它和UI相关mPeersGroup.addPreference(new WifiP2pPeer(getActivity(), peer));if (peer.status == WifiP2pDevice.CONNECTED) mConnectedDevices++;}if (DBG) Log.d(TAG, " mConnectedDevices " + mConnectedDevices);}

在该函数中，WifiP2pDeviceList中保存的每一个WifiP2pDevice信息将作为一个Preference项添加到mPeersGroup中并显示在UI界面上。
接下来用户就可在界面中选择某个P2P设备并与之连接，这个步骤由onPreferenceTreeClick函数来完成。

    public boolean onPreferenceTreeClick(PreferenceScreen screen, Preference preference) {if (preference instanceof WifiP2pPeer) {mSelectedWifiPeer = (WifiP2pPeer) preference;//获取用户指定的那一个WifiP2pPeer项if (mSelectedWifiPeer.device.status == WifiP2pDevice.CONNECTED) {showDialog(DIALOG_DISCONNECT);//如果已经和该设备连接，则判断是否需要与之断开连接} else if (mSelectedWifiPeer.device.status == WifiP2pDevice.INVITED) {showDialog(DIALOG_CANCEL_CONNECT);} else {//向对端P2P设备发起连接WifiP2pConfig config = new WifiP2pConfig();config.deviceAddress = mSelectedWifiPeer.device.deviceAddress;//判断系统是否强制使用了某种WSC配置方法int forceWps = SystemProperties.getInt("wifidirect.wps", -1);if (forceWps != -1) {config.wps.setup = forceWps;} else {//获取对端P2P设备支持的WSC配置方法，优先考虑PBCif (mSelectedWifiPeer.device.wpsPbcSupported()) {config.wps.setup = WpsInfo.PBC;} else if (mSelectedWifiPeer.device.wpsKeypadSupported()) {config.wps.setup = WpsInfo.KEYPAD;} else {config.wps.setup = WpsInfo.DISPLAY;}}//通过WifiP2pManager的connect函数向对端P2P设备发起连接。注意，目标设备信息保存在config对象中mWifiP2pManager.connect(mChannel, config,new WifiP2pManager.ActionListener() {public void onSuccess() {if (DBG) Log.d(TAG, " connect success");}public void onFailure(int reason) {Log.e(TAG, " connect fail " + reason);Toast.makeText(getActivity(),R.string.wifi_p2p_failed_connect_message,Toast.LENGTH_SHORT).show();}});}} else if (preference instanceof WifiP2pPersistentGroup) {mSelectedGroup = (WifiP2pPersistentGroup) preference;showDialog(DIALOG_DELETE_GROUP);}return super.onPreferenceTreeClick(screen, preference);}

当系统完成和P2P设备的连接后，WifiP2pSettings将收到 WIFI_P2P_CONNECTION_CHANGED_ACTION 广播，对应的代码见onReceive

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