在安卓中通过MulticastSocket接收数据出现问题

Question

我最近一直在构建一个Android应用程序，我在网络部分遇到了一些问题。首先，我得到了this错误，现在我已经升级了程序，但现在我有另一个问题。我有一个单独的类，它启动自己的发送线程和另一个接收线程。下面是要发送的内容：

import java.io.IOException;
import java.net.DatagramPacket;
import java.net.InetAddress;
import java.net.MulticastSocket;

import android.widget.EditText;

public class Sender implements Runnable {

    private MulticastSocket so;
    private InetAddress serverAddress;
    private int port;
    private EditText messageBoard;
    private EditText eText1;
    private EditText eText2;
    private EditText eText3;
    private Thread myActivity = new Thread(this);

    public Sender(EditText etHost, EditText etPort, EditText messageBoard, EditText etSend) {
        eText1 = etHost;
        eText2 = etPort;
        eText3 = etSend;
        this.messageBoard = messageBoard;
        myActivity.start();
    }

    @Override
    public void run() {

        // convert the host name to InetAddress
        try {
            //serverAddress = InetAddress.getByName(eText1.getText().toString());
            serverAddress = InetAddress.getByName("atlas.dsv.su.se");
        } catch (Exception e) {}

        //convert the port to an int
        //port = Integer.parseInt(eText2.getText().toString());
        port = 4456;

        // create socket and start communicating
        try {
            so = new MulticastSocket(port);
            so.joinGroup(serverAddress);
        } catch (IOException e) {}

        // start listening for incoming messages
        new Receiver(so, messageBoard);
    }

    /**
     * This method copies the text from the input text field to the conversation text field and
     * cleans the input text field
     */
    public void sendMessage() {

        // get the text that they contain and add the new messages to the old ones
        String message = eText3.getText().toString();
        String conversation = messageBoard.getText().toString();
        String newConverstion = conversation.concat("\n[You] ").concat(message);

        // make the messages text view editable
        messageBoard.setFocusable(true);
        messageBoard.setText(newConverstion);   // add the new message to the text view
        messageBoard.setFocusable(false);   // make the messages text view not editable

        // erase the text on the second text view that has just been sent
        eText3.setText("");

        // Send message to server

        // convert message to bytes array
        byte[] data = (message).getBytes();

        // create and send a datagram
        DatagramPacket packet = new DatagramPacket(data, data.length, serverAddress, port);

        try {
            so.send(packet);
        } catch (IOException e) {}


    }   // end of sendMessage

}

下面是用于接收的代码：

import java.io.IOException;
import java.net.DatagramPacket;
import java.net.MulticastSocket;

import android.widget.EditText;

public class Receiver implements Runnable {

    private Thread myActivity = new Thread(this);
    private MulticastSocket so;
    private EditText messageBoard;

    public Receiver(MulticastSocket sock, EditText messBo) {
        so = sock;
        messageBoard = messBo; 
        myActivity.start();
    }

    @Override
    public void run() {
        byte[] data = new byte[1024];   // received data container

        while (true) {
            try {
                // create a datagram for receiving
                DatagramPacket packet = new DatagramPacket(data, data.length);

                // wait for the next message
                so.receive(packet);

                String message = new String(data, 0, packet.getLength());

                // add the new messages to the old ones
                String conversation = messageBoard.getText().toString();
                String newConverstion = conversation.concat("\n[Remote] ").concat(message);

                // make the messages text view editable
                messageBoard.setFocusable(true);
                messageBoard.setText(newConverstion);   // add the new message to the text view
                messageBoard.setFocusable(false);   // make the messages text view not editable


            } catch (IOException ioe) {}
        }
    }

}

当我运行它时，我得到：

01-25 00:23:27.281: W/dalvikvm(582): threadid=12: thread exiting with uncaught exception (group=0x409c01f8)
01-25 00:23:27.281: E/AndroidRuntime(582): FATAL EXCEPTION: Thread-80
01-25 00:23:27.281: E/AndroidRuntime(582): java.lang.NullPointerException
01-25 00:23:27.281: E/AndroidRuntime(582):  at com.regeduser00x.proj1.Receiver.run(Receiver.java:31)
01-25 00:23:27.281: E/AndroidRuntime(582):  at java.lang.Thread.run(Thread.java:856)

第31行是so.receive(packet);，它的问题是什么？

Answer 1

我最好的猜测是你的套接字进入了你的接收器构造函数null。但是如果看不到你是如何尝试使用它的，我就不能确定了。

但是我可以说，您可能会发现使用AsyncTask实现您的类会更简单。它们是专门为了简化线程的创建和交互而创建的。

这里有一些需要检查的东西，它们将帮助你实现你想要实现的目标。

这两个是开发人员文档的一部分：

http://developer.android.com/resources/articles/painless-threading.html

http://developer.android.com/reference/android/os/AsyncTask.html

这里有一个使用AsyncTask的很好的例子：

http://www.screaming-penguin.com/node/7746