为什么我的 UDP 客户端/服务器数据报没有进行双向通信?

Java Client Side: A button calls a function to send a UDP message, and assign the response into a global variable which then I try to display on the screen via a TextBox

    public class MainActivity extends AppCompatActivity {

    String message;
    String Response;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        // Button Declaration
        final TextView TextOne = (TextView) findViewById(R.id.StatusText);
        Button LftBtn = (Button) findViewById(R.id.LeftButton);
        // ...
        // other code here (button declaration and event handlers
        // ...

        // Left Button Click
        LftBtn.setOnTouchListener(
                new Button.OnTouchListener() {
                    public boolean onTouch(View v, MotionEvent event) {
                        if (event.getAction() == MotionEvent.ACTION_DOWN) {
                            //Button pressed
                            TextOne.setText("Left");
                            message = "Left";
                            SendUdpMsg(message);
                            TextOne.setText(Response);
                            return true;
                        } else if (event.getAction() == MotionEvent.ACTION_UP) {
                            //Button released do nothing
                            return true;
                        }
                        return false;
                    }//onTouch
                });//setOnTouchListener
    }

    // This function is responsible for sending a udp packet to a hardCoded IP below. Returns nothing and takes a string(the message) as a parameter.
    public void SendUdpMsg(final String msg)
    {
        Thread networkThread = new Thread() {

            // No local Host 127.0.0.1 in Android
            String host = "192.168.200.3"; // my actual IP
            int port = 15000;
            DatagramSocket dsocket = null;
            String Response = "1";

            public void run() {
                try {
                    // Get the Internet address of the specified host
                    InetAddress address = InetAddress.getByName(host);

                    // wrap a packet
                    DatagramPacket packet = new DatagramPacket(
                            msg.getBytes(),
                            msg.length(),
                            address, port);

                    // Create a datagram socket, send the packet through it, close it.
                    dsocket = new DatagramSocket();
                    dsocket.send(packet);

                    // Here, I am receiving the response?
                    byte[] buffer = new byte[1024];
                    DatagramPacket packet2 = new DatagramPacket(buffer, buffer.length);
                    dsocket.receive(packet2);
                    Response = new String(buffer, 0, packet2.getLength());
                    runOnUiThread(new Runnable() {
                        @Override
                        public void run()
                        {
                            // I can't use this since TextOne is a local variable in the above function
                            //TextOne.setText(Response);
                        }
                    });
                    dsocket.close();
                } catch (Exception e) {
                    e.printStackTrace();
                }//catch
            }//run
        };// Networkthread
        networkThread.start();//networkThread.start() 
    }       
}

推荐答案

网络代码正常，问题是你没有等待响应，即SendUdpMsg方法无法返回响应立即，它应该由后台线程推送.例如:

dsocket.receive(packet2);
Response = new String(buffer, 0, packet2.getLength());

// we received the response
// but since we are running on a background thread, we can not touch the UI
runOnUiThread(new Runnable() {
    @Override
    public void run() {
        // this is executed on the main (UI) thread
        TextOne.setText(Response);                        }
});

dsocket.close();