Question

我使用以下代码将UDP数据包发送到服务器。这个代码在PC上工作正常。但是当谈到Android设备时...方法test()不打印任何东西......我是什么意思做错了？请指教。

import java.io.IOException;
import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.InetAddress;
import java.net.InterfaceAddress;
import java.net.NetworkInterface;
import java.util.Enumeration;

import android.support.v7.app.ActionBarActivity;
import android.support.v7.app.ActionBar;
import android.support.v4.app.Fragment;
import android.annotation.SuppressLint;
import android.os.Bundle;
import android.os.StrictMode;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.View.OnClickListener;
import android.view.ViewGroup;
import android.widget.Button;
import android.widget.Toast;
import android.os.Build;

@SuppressLint("NewApi") public class MainActivity extends ActionBarActivity {
    StrictMode.ThreadPolicy policy = new StrictMode.ThreadPolicy.Builder().permitAll().build();
    @Override
    protected void onCreate(Bundle savedInstanceState) {

         StrictMode.setThreadPolicy(policy); 
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Button button = (Button) findViewById(R.id.button1);

        button.setOnClickListener(new OnClickListener() {

            @Override
            public void onClick(View view) {


            test();

            }

        });

    }
    void test()
    {


        // Find the server using UDP broadcast
        try {
          //Open a random port to send the package
            DatagramSocket  c = new DatagramSocket();
          c.setBroadcast(true);

          byte[] sendData = "DISCOVER_FUIFSERVER_REQUEST".getBytes();

          //Try the 255.255.255.255 first
          try {
            DatagramPacket sendPacket = new DatagramPacket(sendData, sendData.length, InetAddress.getByName("255.255.255.255"), 8888);
            c.send(sendPacket);
          //  Log.d("MyApp",getClass().getName() + ">>> Request packet sent to: 255.255.255.255 (DEFAULT)");
          } catch (Exception e) {
             // Log.d("MyApp",e.getMessage());
          }

          // Broadcast the message over all the network interfaces
          Enumeration<NetworkInterface>  interfaces = NetworkInterface.getNetworkInterfaces();
          while (interfaces.hasMoreElements()) {
            NetworkInterface networkInterface = interfaces.nextElement();

            if (networkInterface.isLoopback() || !networkInterface.isUp()) {
              continue; // Don't want to broadcast to the loopback interface
            }

            for (InterfaceAddress interfaceAddress : networkInterface.getInterfaceAddresses()) {
              InetAddress broadcast = interfaceAddress.getBroadcast();
              if (broadcast == null) {
                continue;
              }

              // Send the broadcast package!
              try {
                DatagramPacket sendPacket = new DatagramPacket(sendData, sendData.length, broadcast, 8888);
                c.send(sendPacket);
              } catch (Exception e) {
                  //Log.d("MyApp",e.getMessage());
              }

           //   Log.d("MyApp",getClass().getName() + ">>> Request packet sent to: " + broadcast.getHostAddress() + "; Interface: " + networkInterface.getDisplayName());
            }
          }

         //  Log.d("MyApp",getClass().getName() + ">>> Done looping over all network interfaces. Now waiting for a reply!");

          //Wait for a response
          byte[] recvBuf = new byte[15000];
          DatagramPacket receivePacket = new DatagramPacket(recvBuf, recvBuf.length);
          c.receive(receivePacket);

          //We have a response

          //Check if the message is correct
          String message = new String(receivePacket.getData()).trim();
          if (message.equals("DISCOVER_FUIFSERVER_RESPONSE")) {
            //DO SOMETHING WITH THE SERVER'S IP (for example, store it in your controller)
        //    Controller_Base.setServerIp(receivePacket.getAddress());
          }

          //Close the port!
          c.close();
        } catch (IOException ex) {
             //  Log.d("MyApp",ex.getMessage());
        }
    }



}

更新：

错误：

06-03 14:50:35.038: E/AndroidRuntime(31361): FATAL EXCEPTION: main
06-03 14:50:35.038: E/AndroidRuntime(31361): Process: com.example.project, PID: 31361
06-03 14:50:35.038: E/AndroidRuntime(31361): java.lang.NullPointerException: println needs a message
06-03 14:50:35.038: E/AndroidRuntime(31361):    at android.util.Log.println_native(Native Method)
06-03 14:50:35.038: E/AndroidRuntime(31361):    at android.util.Log.d(Log.java:139)
06-03 14:50:35.038: E/AndroidRuntime(31361):    at com.example.project.MainActivity.test(MainActivity.java:64)
06-03 14:50:35.038: E/AndroidRuntime(31361):    at com.example.project.MainActivity$1.onClick(MainActivity.java:39)
06-03 14:50:35.038: E/AndroidRuntime(31361):    at android.view.View.performClick(View.java:4756)
06-03 14:50:35.038: E/AndroidRuntime(31361):    at android.view.View$PerformClick.run(View.java:19761)
06-03 14:50:35.038: E/AndroidRuntime(31361):    at android.os.Handler.handleCallback(Handler.java:739)
06-03 14:50:35.038: E/AndroidRuntime(31361):    at android.os.Handler.dispatchMessage(Handler.java:95)
06-03 14:50:35.038: E/AndroidRuntime(31361):    at android.os.Looper.loop(Looper.java:135)
06-03 14:50:35.038: E/AndroidRuntime(31361):    at android.app.ActivityThread.main(ActivityThread.java:5253)
06-03 14:50:35.038: E/AndroidRuntime(31361):    at java.lang.reflect.Method.invoke(Native Method)
06-03 14:50:35.038: E/AndroidRuntime(31361):    at java.lang.reflect.Method.invoke(Method.java:372)
06-03 14:50:35.038: E/AndroidRuntime(31361):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:900)
06-03 14:50:35.038: E/AndroidRuntime(31361):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:695)

Answer 1

尝试使用＆＃39; Log.d＆＃39;而不是System.out.println＆＃39;

修改并且在concanation之前检查字符串的空值。也就是说，对所有Log.d方法都这样做：

if ( broadcast! = null && broadcast.getHostAddress() && networkInterface! =null&&networkInterface.getDisplayName()!=null) { Log.d("MyApp",getClass().getName() + ">>> Request packet sent to: " + broadcast.getHostAddress() + "; Interface: " + networkInterface.getDisplayName()); }

修改通过test()包裹Thread功能：

new Thread(new Runnable() { @Override public void run() { test(); } }).start();

UDP数据包发现不起作用

1 个答案: