Question

我正在创建一个Android应用程序，用它的IP响应UDP广播。这是代码：

 byte[] buf = new byte[128];
 final DatagramPacket packet = new DatagramPacket(buf, buf.length);
 listenSocket.receive(packet);

 Toast.makeText(network, "UDP connection detected.", Toast.LENGTH_LONG).show();
 if (packet.getData()[0] == 0x1 && packet.getData()[1] == 0x42) { //respond to broadcast:
      String ip = Utils.getIP() + ":" + COMM_PORT + "\r\n";
      final byte[] send = new byte[32];
      send[0] = 0x1;
      send[1] = 0x43;
      System.arraycopy(ip.getBytes(), 0, send, 2, 20);
      Toast.makeText(network, Arrays.toString(send), Toast.LENGTH_LONG).show();
      Toast.makeText(network, "IP address is null?" + (listenSocket.getInetAddress() == null), Toast.LENGTH_LONG).show(); // this prints IP address is null?true to the console

      DatagramPacket confirm = new DatagramPacket(send, send.length, listenSocket.getRemoteSocketAddress()); //FAILS HERE
      listenSocket.send(confirm);
      listenSocket.close();
 }

而不是DatagramPacket confirm = new DatagramPacket(send, send.length, listenSocket.getRemoteSocketAddress());我尝试过：

DatagramPacket confirm = new DatagramPacket(send, send.length, listenSocket.getInetAddress(), listenSocket.getPort());

但getPort()给出-1（表示套接字未连接），getInetAddress（）给出null，也表示它没有连接。

如何响应UDP广播连接？

由于

Answer 1

我有解决方案！

您必须从收到的DatagramPacket获取IP地址和端口;

DatagramPacket confirm = new DatagramPacket(send, send.length, receivedPacket.getAddress(), receivedPacket.getPort());

响应UDP广播

1 个答案: