Android(安卓)Wifi获取组播

Android的Wifi，默认情况下是不接受组播的，见：http://developer.android.com/reference/android/net/wifi/WifiManager.MulticastLock.html

默认情况下，应用是不接收组播信息的，这样要接收处理的报文太多，很快就会把电池用尽。要知道移动设备（特指电话一类的，平板要好得多）目前最重要的因素是电量。

要想打开组播功能，有以下几个步骤：

在Manifest文件中加入：android.permission.CHANGE_WIFI_MULTICAST_STATE，这个权限
获取到MulticastLock对象，这个对象不能直接实例化，要通过WifiManager间接得到，工厂模式
调用MulticastLock对象的acquire方法，获取到组播锁
相应的，用完组播，为了不浪费电力，要调用MulticastLock的release方法释放锁

下面写了个简单示例，通过组播发现服务器。

Activity写的比较简单：

public class MulticastDemoActivity extends Activity {         MulticastLock multicastLock;         /** Called when the activity is first created. */     @Override     public void onCreate(Bundle savedInstanceState) {         super.onCreate(savedInstanceState);         setContentView(R.layout.main);                 allowMulticast();                 try {             NetUtil.findServerIpAddress();         } catch (IOException e) {             throw new RuntimeException(e);         }                 Log.d("multicast.demo", "find ip ok.");                 multicastLock.release();     }         private void allowMulticast(){         WifiManager wifiManager=(WifiManager)getSystemService(Context.WIFI_SERVICE);         multicastLock=wifiManager.createMulticastLock("multicast.test");         multicastLock.acquire();     } }

在Activity中打开和释放组播锁。

使用组播发送报文和接收ip地址信息的工具类代码

public class NetUtil {         private static final String TAG="Net.Utils";     private static final int MULTICAST_PORT=5111;     private static final String GROUP_IP="224.5.0.7";     private static byte[] sendData;         static{         sendData=new byte[4];         // 0xEE78F1FB         sendData[3] = (byte) 0xEE;         sendData[2] = (byte) 0×78;         sendData[1] = (byte) 0xF1;         sendData[0] = (byte) 0xFB;     }         public static String findServerIpAddress() throws IOException{         String ip=null;        MulticastSocket multicastSocket=new MulticastSocket(MULTICAST_PORT);         multicastSocket.setLoopbackMode(true);         InetAddress group = InetAddress.getByName(GROUP_IP);         multicastSocket.joinGroup(group);                 DatagramPacket packet=new DatagramPacket(sendData, sendData.length,group,MULTICAST_PORT);                 for(;;){             multicastSocket.send(packet);             Log.d(TAG,">>>send packet ok");                         byte[] receiveData=new byte[256];             packet=new DatagramPacket(receiveData, receiveData.length);             multicastSocket.receive(packet);                         String packetIpAddress=packet.getAddress().toString();             packetIpAddress=packetIpAddress.substring(1, packetIpAddress.length());             Log.d(TAG,"packet ip address: "+packetIpAddress);                         StringBuilder packetContent=new StringBuilder();             for(int i=0;i<receiveData.length;i++){                 if(receiveData[i]==0){                     break;                 }                 packetContent.append((char)receiveData[i]);             }             ip=packetContent.toString();             Log.d(TAG,"packet content ip is: "+ip);                         if(ip.equals(packetIpAddress)){                 Log.d(TAG,"find server ip address: "+ip);                 break;             }else{                 Log.d(TAG,"not find server ip address, continue …");                 try {                     Thread.sleep(1000);                 } catch (InterruptedException e) {                 }             }         }                 return ip;     } }

转自： http://marshal.easymorse.com/archives/4461

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