在android中没有收到Udp广播包

Question

我在下面写下了在android中发送和接收udp广播包的代码。当我在模拟器中运行它时，它无法接收数据。什么是问题？

在Eclipse中：

Discoverer.java：

public class Discoverer extends Thread {

    private static final String TAG = "Discovery";
    private static final int DISCOVERY_PORT = 2562;
    private static final int TIMEOUT_MS = 15000;

    private WifiManager mWifi;

    interface DiscoveryReceiver {
        void addAnnouncedServers(InetAddress[] host, int port[]);
    }

    Discoverer(WifiManager wifi) {
        mWifi = wifi;
    }

    public void run() {
        try {
            DatagramSocket socket = new DatagramSocket(DISCOVERY_PORT);
            socket.setBroadcast(true);
            socket.setSoTimeout(TIMEOUT_MS);
            sendDiscoveryRequest(socket);
            listenForResponses(socket);
        } catch (IOException e) {
            Log.e(TAG, "Could not send discovery request", e);
        }
    }

    //Send a broadcast UDP packet

    private void sendDiscoveryRequest(DatagramSocket socket) throws IOException {
        String data = "my data";
        Log.d(TAG, "Sending data " + data);
        DatagramPacket packet = new DatagramPacket(data.getBytes(),
                data.length(), InetAddress.getByName("127.0.0.1") // 'Within' the emulator!/*getBroadcastAddress()*/
                , DISCOVERY_PORT);
        socket.send(packet);
    }

    // Calculate the broadcast IP we need to send the packet along. 
    private InetAddress getBroadcastAddress() throws IOException {
        DhcpInfo dhcp = mWifi.getDhcpInfo();
        if (dhcp == null) {
            Log.d(TAG, "Could not get dhcp info");
            return null;
        }
        int broadcast = (dhcp.ipAddress & dhcp.netmask) | ~dhcp.netmask;
        byte[] quads = new byte[4];
        for (int k = 0; k < 4; k++)
            quads[k] = (byte) ((broadcast >> k * 8) & 0xFF);
        return InetAddress.getByAddress(quads);
    }

    // Listen on socket for responses, timing out after TIMEOUT_MS

    private void listenForResponses(DatagramSocket socket) throws IOException {
        byte[] buf = new byte[1024];
        try {

            while (true) {
                DatagramPacket packet = new DatagramPacket(buf, buf.length);
                socket.receive(packet);
                String s = new String(packet.getData(), 0, packet.getLength());

                Log.d(TAG, "Received response " + s);
            }
        } catch (SocketTimeoutException e) {
            Log.d(TAG, "Receive timed out");
        }
    }


}

Rec_Broadcast.java：

public class Rec_Broadcast extends AsyncTask<Void, Void, Void> {

    @Override
    protected Void doInBackground(Void... urls)
    {
        DatagramSocket socketUDP;

        try
        {
            socketUDP = new DatagramSocket(5050,InetAddress.getByName("127.0.0.1"));
            socketUDP.setSoTimeout(85000);

            // set it to true if you want to receive broadcast packets
            socketUDP.setBroadcast(false); 
        }
        catch (Exception e)
        {
            e.printStackTrace();
            return null;
        }

        byte[] buff = new byte[512];
        DatagramPacket packet = new DatagramPacket(buff, buff.length);
        boolean asyncTask_UDP_is_running;
        try
        {
            asyncTask_UDP_is_running=true;
            boolean aplicationActive = true;
            // Keep running until application gets inactive
            while (aplicationActive)
            {
                 Log.i("my client","Ready to receive broadcast packets!");
                try
                {
                    socketUDP.receive(packet);
                    Log.i("my client", "Packet received from: " + packet.getAddress().getHostAddress());
                    String data = new String(packet.getData()).trim();
                    Log.i("my client", "Packet received data: " + data);
                }
                catch (java.net.SocketTimeoutException ex)
                {
                    // timeout
                }
                catch (Exception e)
                {
                    Log.i("my client", "Oops" + e.getMessage());
                    return null; 
                }
            }
        }
        finally
        {
            asyncTask_UDP_is_running=false;
        }
        return null;
    }
}

主要活动：

WifiManager w = (WifiManager) getSystemService(Context.WIFI_SERVICE);
new Rec_Broadcast().execute();
new Discoverer(w).start();

in Manifest：

 <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE"/>
<uses-permission android:name="android.permission.ACCESS_WIFI_STATE"/><uses-permission android:name="android.permission.CHANGE_WIFI_STATE" />
<uses-permission android:name="android.permission.CHANGE_WIFI_MULTICAST_STATE"/>
<uses-permission android:name="android.permission.INTERNET"/>