java - 如果我将套接字从主 Activity 中分离出来，为什么它会抛出 IOException？

Question

我在 Android 上编写了一个简单的程序，它使用 Socket 连接到服务器并接收一些数据。当我以这种方式编码时，效果很好:

public class MainActivity extends Activity 
{
    EditText ip_box;
    Button login_button;
    TextView text;
    Handler handler;
    final int port = 12121;
    Socket socket;
    String ip;

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

        init();//omitted

        handler = new Handler()
        {
            public void handleMessage(Message msg)
            {
                String words = (String)msg.obj;
                text.setText((String)msg.obj);
            }
        };

        class GetThread implements Runnable
        {
            public void getMsg()
            {
                try 
                {
                    Scanner in = new Scanner(socket.getInputStream());
                    String gotmsg = in.nextLine();
                    Message msg = new Message();
                    msg.obj = gotmsg;
                    MainActivity.this.handler.sendMessage(msg);

                } catch (UnknownHostException e) 
                {
                    Message msg = new Message();
                    msg.obj = "net error";
                    MainActivity.this.handler.sendMessage(msg);
                } catch (IOException e) 
                {
                    Message msg = new Message();
                    msg.obj = "net error";
                    MainActivity.this.handler.sendMessage(msg);
                }

            }

            @Override
            public void run() 
            {
                try 
                {
                    socket = new Socket();
                    socket.connect(new InetSocketAddress(ip, port) , 5000);
                } catch (UnknownHostException e) 
                {
                    ...
                } catch (IOException e) {
                    ...
                }

                if( socket != null)
                    getMsg();
                else
                {
                    ...
                }
            }
        }

        login_button.setOnClickListener(new OnClickListener()
        {
            @Override
            public void onClick(View arg0) 
            {
                // TODO Auto-generated method stub
                ip = ip_box.getText().toString();
                GetThread g = new GetThread();
                new Thread(g).start();
            }

        });
    }

}

我要做的就是使套接字连接成为一个独立的类。我是这样制作类(class)的:

public class ClientSocketManager
{
    String ip;
    int port;
    Socket socket;
    Handler handler; //use this to send messages

    /**
     * Thread to get message from server
     * @author Zero
     *
     */
    class GetThread implements Runnable
    {
        @Override
        public void run() 
        {
            try 
            {
                BufferedReader in = new BufferedReader(new InputStreamReader(socket.getInputStream()));
                while(true)
                {
                    String input = in.readLine();
                    if(input!=null)
                    {
                        Message msg = new Message();
                        msg.obj = input;
                        handler.sendMessage(msg);
                    }
                } 
            }
            catch (IOException e) 
            {
                System.out.println("NetThreadIOException");
                Message msg = new Message();
                msg.obj = "net error";
                handler.sendMessage(msg);
            }
            catch (NullPointerException e)
            {
                //System.out.println("NetThreadIOException");
                Message msg = new Message();
                msg.obj = "net error";
                handler.sendMessage(msg);
            }
        }
    }

    /**
     * Thread to login to server
     * @author Zero
     *
     */
    class LoginThread implements Runnable
    {
        boolean ok;
        @Override
        public void run() 
        {
            try 
            {
                socket = new Socket();
                socket.connect(new InetSocketAddress(ip, port) , 5000);
            } catch (UnknownHostException e) 
            {
                System.out.println("UnknownHostException");
                Message msg = new Message();
                msg.obj = "did not login";
                handler.sendMessage(msg);
                ok=false;
            } catch (IOException e) {
                System.out.println("IOException");
                Message msg = new Message();
                msg.obj = "did not login";
                handler.sendMessage(msg);
                ok=false;
            }
        }
    }

    public ClientSocketManager(){}

    /**
     * Create a new ClientSocketManager
     * @param _ip
     * @param _port
     * @param _handler
     */
    public ClientSocketManager(String _ip, int _port, Handler _handler)
    {
        ip = _ip;
        port = _port;
        handler = _handler;
    }

    public boolean login()
    {
        LoginThread login_thread = new LoginThread();
        new Thread(login_thread).start();

        return login_thread.ok;

    }

    public void openGetThread()
    {
        GetThread getThread = new GetThread();
        new Thread(getThread).start();
    }
}

在主 Activity 中，我像这样使用 ClientSocketManager:

        login_button.setOnClickListener(new OnClickListener()
        {
            @Override
            public void onClick(View arg0) 
            {
                // TODO Auto-generated method stub
                ip = ip_box.getText().toString();
                client_socket_manager = new ClientSocketManager(ip, port, handler);
                boolean logged = client_socket_manager.login();
                //if(!logged)
                //  return;
                client_socket_manager.openGetThread();
            }

        })

现在它在String input = in.readLine();上抛出IOException。我对此很好奇。可能的原因是什么？

非常感谢!

Answer 1

原因可能是: client_socket_manager.login() 和 client_socket_manager.openGetThread() 启动两个并发运行的线程来执行两个操作 login 和 get。因此，当您尚未登录时，将执行 get 操作。