> 編寫:[naizhengtan](https://github.com/naizhengtan) - 原文:[http://developer.android.com/training/connect-devices-wirelessly/wifi-direct.html](http://developer.android.com/training/connect-devices-wirelessly/wifi-direct.html) Android提供的Wi-Fi點對點（P2P）APIs允許應用程序無需連接到網絡和熱點的情況下連接到附近的設備。（Android Wi-Fi P2P框架遵循[Wi-Fi Direct?](http://www.wi-fi.org/discover-and-learn/wi-fi-direct) 驗證程序）Wi-Fi P2P技術使得應用程序可以快速發現附近的設備并與之交互。相比于藍牙技術，Wi-Fi P2P的優勢是具有較大的連接范圍。 本節主要內容是使用Wi-Fi P2P技術發現并連接到附近的設備。 ### 配置應用權限 使用Wi-Fi P2P技術，需要添加[CHANGE_WIFI_STATE](http://developer.android.com/reference/android/Manifest.permission.html#CHANGE_WIFI_STATE),[ACCESS_WIFI_STATE](http://developer.android.com/reference/android/Manifest.permission.html#ACCESS_WIFI_STATE)以及[INTERNET](http://developer.android.com/reference/android/Manifest.permission.html#INTERNET)三種權限到應用的manifest文件。Wi-Fi P2P技術雖然不需要訪問互聯網，但是它會使用Java中的標準socket。而使用socket需要具有INTERNET權限，這也是Wi-Fi P2P技術需要申請該權限的原因。 ~~~ <manifest xmlns:android="http://schemas.android.com/apk/res/android" package="com.example.android.nsdchat" ... <uses-permission android:required="true" android:name="android.permission.ACCESS_WIFI_STATE"/> <uses-permission android:required="true" android:name="android.permission.CHANGE_WIFI_STATE"/> <uses-permission android:required="true" android:name="android.permission.INTERNET"/> ... ~~~ ### 廣播接收器(BroadCast Receiver)和點對點管理器(Peer-to-peer Manager) 使用Wi-Fi P2P的時候需要偵聽相關的廣播事件（broadcast intent）。所以在應用中需要實例化一個[IntentFilter](http://developer.android.com/reference/android/content/IntentFilter.html)，并將其設置為偵聽下列事件： - [WIFI_P2P_STATE_CHANGED_ACTION](http://developer.android.com/reference/android/net/wifi/p2p/WifiP2pManager.html#WIFI_P2P_STATE_CHANGED_ACTION) 指示Wi-Fi P2P是否開啟 - [WIFI_P2P_PEERS_CHANGED_ACTION](http://developer.android.com/reference/android/net/wifi/p2p/WifiP2pManager.html#WIFI_P2P_PEERS_CHANGED_ACTION) 代表對等節點（peer）列表發生了變化 - [WIFI_P2P_CONNECTION_CHANGED_ACTION](http://developer.android.com/reference/android/net/wifi/p2p/WifiP2pManager.html#WIFI_P2P_CONNECTION_CHANGED_ACTION) 表明Wi-Fi P2P的連接狀態發生了改變 - [WIFI_P2P_THIS_DEVICE_CHANGED_ACTION](http://developer.android.com/reference/android/net/wifi/p2p/WifiP2pManager.html#WIFI_P2P_THIS_DEVICE_CHANGED_ACTION) 指示設備的詳細配置發生了變化 ~~~ private final IntentFilter intentFilter = new IntentFilter(); ... @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); // Indicates a change in the Wi-Fi P2P status. intentFilter.addAction(WifiP2pManager.WIFI_P2P_STATE_CHANGED_ACTION); // Indicates a change in the list of available peers. intentFilter.addAction(WifiP2pManager.WIFI_P2P_PEERS_CHANGED_ACTION); // Indicates the state of Wi-Fi P2P connectivity has changed. intentFilter.addAction(WifiP2pManager.WIFI_P2P_CONNECTION_CHANGED_ACTION); // Indicates this device's details have changed. intentFilter.addAction(WifiP2pManager.WIFI_P2P_THIS_DEVICE_CHANGED_ACTION); ... } ~~~ 在[onCreate()](http://developer.android.com/reference/android/app/Activity.html#onCreate(android.os.Bundle))方法的最后，需要獲得[WifiPpManager](http://developer.android.com/reference/android/net/wifi/p2p/WifiP2pManager.html)的實例，并調用它的[initialize()](http://developer.android.com/reference/android/net/wifi/p2p/WifiP2pManager.html#initialize(android.content.Context, android.os.Looper, android.net.wifi.p2p.WifiP2pManager.ChannelListener))方法。該方法將返回[WifiP2pManager.Channel](http://developer.android.com/reference/android/net/wifi/p2p/WifiP2pManager.Channel.html)對象。你的應用將使用該對象與Wi-Fi P2P框架進行交互。 ~~~ @Override Channel mChannel; public void onCreate(Bundle savedInstanceState) { .... mManager = (WifiP2pManager) getSystemService(Context.WIFI_P2P_SERVICE); mChannel = mManager.initialize(this, getMainLooper(), null); } ~~~ 接下來，創建一個新的[BroadcastReceiver](http://developer.android.com/reference/android/content/BroadcastReceiver.html)類偵聽系統中Wi-Fi P2P的狀態變化。在[onReceive()](http://developer.android.com/reference/android/content/BroadcastReceiver.html#onReceive(android.content.Context, android.content.Intent))方法中，加入對上述四種不同P2P狀態變化的處理。 ~~~ @Override public void onReceive(Context context, Intent intent) { String action = intent.getAction(); if (WifiP2pManager.WIFI_P2P_STATE_CHANGED_ACTION.equals(action)) { // Determine if Wifi P2P mode is enabled or not, alert // the Activity. int state = intent.getIntExtra(WifiP2pManager.EXTRA_WIFI_STATE, -1); if (state == WifiP2pManager.WIFI_P2P_STATE_ENABLED) { activity.setIsWifiP2pEnabled(true); } else { activity.setIsWifiP2pEnabled(false); } } else if (WifiP2pManager.WIFI_P2P_PEERS_CHANGED_ACTION.equals(action)) { // The peer list has changed! We should probably do something about // that. } else if (WifiP2pManager.WIFI_P2P_CONNECTION_CHANGED_ACTION.equals(action)) { // Connection state changed! We should probably do something about // that. } else if (WifiP2pManager.WIFI_P2P_THIS_DEVICE_CHANGED_ACTION.equals(action)) { DeviceListFragment fragment = (DeviceListFragment) activity.getFragmentManager() .findFragmentById(R.id.frag_list); fragment.updateThisDevice((WifiP2pDevice) intent.getParcelableExtra( WifiP2pManager.EXTRA_WIFI_P2P_DEVICE)); } } ~~~ 最后，在主界面開啟時，加入注冊intent filter和broadcast receiver的代碼，并在暫停或關閉時，注銷它們。最好的位置是在onResume()和onPause()方法中。 ~~~ /** register the BroadcastReceiver with the intent values to be matched */ @Override public void onResume() { super.onResume(); receiver = new WiFiDirectBroadcastReceiver(mManager, mChannel, this); registerReceiver(receiver, intentFilter); } @Override public void onPause() { super.onPause(); unregisterReceiver(receiver); } ~~~ ### 初始化對等節點發現（Peer Discovery）過程 在Wi-Fi P2P中，應用通過調用[discoverPeers()](http://developer.android.com/reference/android/net/wifi/p2p/WifiP2pManager.html#discoverPeers(android.net.wifi.p2p.WifiP2pManager.Channel, android.net.wifi.p2p.WifiP2pManager.ActionListener))搜尋附近的設備。該方法需要以下參數： - 上節中調用WifiP2pManager的initialize()函數獲得的[WifiP2pManager.Channel](http://developer.android.com/reference/android/net/wifi/p2p/WifiP2pManager.Channel.html)對象 - 一個對[WifiP2pManager.ActionListener](http://developer.android.com/reference/android/net/wifi/p2p/WifiP2pManager.ActionListener.html)接口的實現，包括了當系統成功/失敗發現所調用的方法 ~~~ mManager.discoverPeers(mChannel, new WifiP2pManager.ActionListener() { @Override public void onSuccess() { // Code for when the discovery initiation is successful goes here. // No services have actually been discovered yet, so this method // can often be left blank. Code for peer discovery goes in the // onReceive method, detailed below. } @Override public void onFailure(int reasonCode) { // Code for when the discovery initiation fails goes here. // Alert the user that something went wrong. } }); ~~~ 需要注意的是，在此的成功僅僅表示對Peer發現（Peer Discovery）的過程完成初始化。方法discoverPeers()開啟了發現過程并且立即返回。系統會通過調用WifiP2pManager.ActionListener中的方法通知應用對等節點發現過程初始化是否正確。同時，對等節點發現過程本身仍然繼續運行，直到一條連接或者一個P2P小組建立。 ### 獲取對等節點列表 在完成對等節點發現過程的初始化后，我們需要進一步獲取附近的對等節點列表。第一步是實現[WifiP2pManager.PeerListListener](http://developer.android.com/reference/android/net/wifi/p2p/WifiP2pManager.PeerListListener.html)接口。該接口提供了Wi-Fi P2P框架發現的對等節點信息。下列代碼實現了相應功能： ~~~ private List peers = new ArrayList(); ... private PeerListListener peerListListener = new PeerListListener() { @Override public void onPeersAvailable(WifiP2pDeviceList peerList) { // Out with the old, in with the new. peers.clear(); peers.addAll(peerList.getDeviceList()); // If an AdapterView is backed by this data, notify it // of the change. For instance, if you have a ListView of available // peers, trigger an update. ((WiFiPeerListAdapter) getListAdapter()).notifyDataSetChanged(); if (peers.size() == 0) { Log.d(WiFiDirectActivity.TAG, "No devices found"); return; } } } ~~~ 接下來，完善上文廣播接收者（Broadcast Receiver）的onReceiver()方法。當收到[WIFI_P2P_PEERS_CHANGED_ACTION](http://developer.android.com/reference/android/net/wifi/p2p/WifiP2pManager.html#WIFI_P2P_PEERS_CHANGED_ACTION)事件時，調用[requestPeer()](http://developer.android.com/reference/android/net/wifi/p2p/WifiP2pManager.html#requestPeers(android.net.wifi.p2p.WifiP2pManager.Channel, android.net.wifi.p2p.WifiP2pManager.PeerListListener))方法獲取對等節點列表。在此，需要將WifiP2pManager.PeerListListener對象傳遞給該方法。一種方法是在廣播接收者構造時，就將對象作為參數傳入。 ~~~ public void onReceive(Context context, Intent intent) { ... else if (WifiP2pManager.WIFI_P2P_PEERS_CHANGED_ACTION.equals(action)) { // Request available peers from the wifi p2p manager. This is an // asynchronous call and the calling activity is notified with a // callback on PeerListListener.onPeersAvailable() if (mManager != null) { mManager.requestPeers(mChannel, peerListListener); } Log.d(WiFiDirectActivity.TAG, "P2P peers changed"); }... } ~~~ 現在，一個[WIFI_P2P_PEERS_CHANGED_ACTION](http://developer.android.com/reference/android/net/wifi/p2p/WifiP2pManager.html#WIFI_P2P_PEERS_CHANGED_ACTION)事件將觸發應用對Peer列表的更新了。 ### 連接一個對等節點 為了連接到一個對等節點，你需要創一個新的[WifiP2pConfig](http://developer.android.com/reference/android/net/wifi/p2p/WifiP2pConfig.html)對象，并將要連接的設備信息從[WifiP2pDevice](http://developer.android.com/reference/android/net/wifi/p2p/WifiP2pDevice.html)拷貝到其中，最后調用[connect()](http://developer.android.com/reference/android/net/wifi/p2p/WifiP2pManager.html#connect(android.net.wifi.p2p.WifiP2pManager.Channel, android.net.wifi.p2p.WifiP2pConfig, android.net.wifi.p2p.WifiP2pManager.ActionListener))方法。 ~~~ @Override public void connect() { // Picking the first device found on the network. WifiP2pDevice device = peers.get(0); WifiP2pConfig config = new WifiP2pConfig(); config.deviceAddress = device.deviceAddress; config.wps.setup = WpsInfo.PBC; mManager.connect(mChannel, config, new ActionListener() { @Override public void onSuccess() { // WiFiDirectBroadcastReceiver will notify us. Ignore for now. } @Override public void onFailure(int reason) { Toast.makeText(WiFiDirectActivity.this, "Connect failed. Retry.", Toast.LENGTH_SHORT).show(); } }); } ~~~ 在本段代碼中的[WifiP2pManager.ActionListener](http://developer.android.com/reference/android/net/wifi/p2p/WifiP2pManager.ActionListener.html)僅能通知你初始化的成功或失敗。想要偵聽連接狀態的變化，需要實現[WifiP2pManager.ConnectionInfoListener](http://developer.android.com/reference/android/net/wifi/p2p/WifiP2pManager.ConnectionInfoListener.html)接口。接口中的[onConnectionInfoAvailable()](http://developer.android.com/reference/android/net/wifi/p2p/WifiP2pManager.ConnectionInfoListener.html#onConnectionInfoAvailable(android.net.wifi.p2p.WifiP2pInfo))回調函數會在連接狀態發生改變時通知應用程序。當有多個設備同時試圖連接到一臺設備時（例如多人游戲或者聊天群），這一臺設備將被指定為“群主”（group owner）。 ~~~ @Override public void onConnectionInfoAvailable(final WifiP2pInfo info) { // InetAddress from WifiP2pInfo struct. InetAddress groupOwnerAddress = info.groupOwnerAddress.getHostAddress()); // After the group negotiation, we can determine the group owner. if (info.groupFormed && info.isGroupOwner) { // Do whatever tasks are specific to the group owner. // One common case is creating a server thread and accepting // incoming connections. } else if (info.groupFormed) { // The other device acts as the client. In this case, // you'll want to create a client thread that connects to the group // owner. } } ~~~ 此時，回頭繼續完善廣播接收者的onReceive()方法，并修改對[WIFI_P2P_CONNECTION_CHANGED_ACTION]()intent的監聽部分的代碼。當該intent接收到后，調用[requestConnectionInfo()](http://developer.android.com/reference/android/net/wifi/p2p/WifiP2pManager.html#WIFI_P2P_CONNECTION_CHANGED_ACTION)方法。此方法為異步，所以結果將會被你提供的[WifiP2pManager.ConnectionInfoListener](http://developer.android.com/reference/android/net/wifi/p2p/WifiP2pManager.html#requestConnectionInfo(android.net.wifi.p2p.WifiP2pManager.Channel, android.net.wifi.p2p.WifiP2pManager.ConnectionInfoListener))所獲取。 ~~~ ... } else if (WifiP2pManager.WIFI_P2P_CONNECTION_CHANGED_ACTION.equals(action)) { if (mManager == null) { return; } NetworkInfo networkInfo = (NetworkInfo) intent .getParcelableExtra(WifiP2pManager.EXTRA_NETWORK_INFO); if (networkInfo.isConnected()) { // We are connected with the other device, request connection // info to find group owner IP mManager.requestConnectionInfo(mChannel, connectionListener); } ... ~~~