Question

我想创建Socket连接，但我有一些问题。我必须在新线程中创建它，但我不能。

public class SocketManager {
    private static SocketManager instance;


    private BufferedReader in;
    private PrintWriter out;
    private Socket mSocket = null;

    public static SocketManager me() {
        if (instance == null) {
            instance = new SocketManager();
        }
        return instance;
    }

    public void connection() {
        new AsyncTask<Void, Void, Void>() {

            @Override
            protected Void doInBackground(Void... params) {
                try {
                    mSocket = new Socket(Constants.CHAT_SERVER_URL, 4444);
                } catch (IOException e) {
                    e.printStackTrace();
                }
                return null;
            }
        }.execute();
    }

    public boolean isConnected() {
        return mSocket.isConnected();
    }

和

@Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        status = (TextView) findViewById(R.id.status);
        button = (Button) findViewById(R.id.button);
        button.setOnClickListener(this);
        SocketManager.me().connection();
        if (SocketManager.me().isConnected()) {
            status.setText("Connected");
        } else {
            status.setText("Disconnected");
        }

我有错误：

java.lang.NullPointerException: Attempt to invoke virtual method 'boolean java.net.Socket.isConnected()' on a null object reference

Becouse mSocket在新线程中创建，当我调用它时== null;如何在新线程中创建mSocket并使用它？

Answer 1

我认为方法＆＃34; isConnected（）＆＃34;正在尝试在初始化之前访问mSocket。

尝试将其更改为：

public boolean isConnected() {
    return mSocket == null ? false : mSocket.isConnected();
}

这将避免此方法的NullPointerException。

但是这里正确的方法是使用回调，这样子线程可以在主线程完成时通知主线程。

public class SocketTask extends AsyncTask<Void, Void, Void> {

    public interface AsyncTaskListener<T> {
        void onTaskCompleted(T t);
    }

    private final AsyncTaskListener<String> listener;

    public SocketTask(AsyncTaskListener<String> listener) {
        this.listener = listener;
    }

    @Override
    protected Void doInBackground(Void... params) {

        try {
                    mSocket = new Socket(Constants.CHAT_SERVER_URL, 4444);
                } catch (IOException e) {
                    e.printStackTrace();
                }
                return null;
    }

    @Override
    protected void onPostExecute() {
        listener.onTaskCompleted();
    }
}

你的类SocketManager需要实现回调：

public class SocketManager implements SocketTask.AsyncTaskListener {

}

Answer 2

最好的方法是使用界面。

在Socketmanager类中创建一个接口

public class SocketManager {
    private static SocketManager instance;
    private SocketListner listner;

    public interface SocketListner {
        void onConnectionSuccess();
        void onConnectionFailed();
    }

    public void connection(SocketListner listner) {
        this.listner = listner;
        new ConnectionTask().execute();
    }

并从doInBackGround()方法返回一个布尔值，以检查连接是否成功

    class ConnectionTask new AsyncTask<Void, Void, Boolean>() {
        @Override
        protected Void doInBackground(Void... params) {
            //...your code

        }
        @Override
        protected void onPostExecute(Boolean result) {
            if(result) {
                listner.onConnectionSuccess();
            } else {
                listner.onConnectionFailed();
            }
        }
    }

在您的活动中实施界面

 public class YourActivity imlpements SocketListner {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
     //your code
      ..
    }
    @Override
    void onConnectionSuccess() {
        //your socket is connected
        status.setText("Connected");
    }

    @Override
    void onConnectionFailed() {
        status.setText("Disconnected");
    }
}

Answer 3

添加布尔值以了解您的asynctask是否完整。

boolean mIsSocketInstanceCreated = false;

public void connection() {
        new AsyncTask<Void, Void, Void>() {
            @Override
            protected Void doInBackground(Void... params) {
                try {
                    mSocket = new Socket(Constants.CHAT_SERVER_URL, 4444);
                    mIsSocketInstanceCreated = true;
                } catch (IOException e) {
                    e.printStackTrace();
                   mIsSocketInstanceCreated = false;
                }
                return null;
            }
        }.execute();
}

    public boolean isConnected() {
        if (mIsSocketInstanceCreated)
          return mSocket.isConnected();
        return false;
    }

如何在新线程中创建Socket

3 个答案: