Android Error with Websocket

Question

Im working on Websocket android application. I want to create Register and Login application with websocket. I am able to connect to websocket server with websocket android project. I have created Register,Login activity with online reference.In register Activity, when I'm storing Registered data to Server using "send" method of websocketclient Java Class I'm getting "java.lang.NullPointerException: Attempt to invoke virtual method 'void org.java_websocket.client.WebSocketClient.send(java.lang.String)' on a null object reference" Error on my Log-cat window.

here is my Main Activity:

package org.asperohgedgetws.a7.hgadgetws;
import android.app.Activity;
import android.app.Fragment;
import android.os.Build;
import android.os.Bundle;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;
import android.widget.EditText;
import android.widget.TextView;
import org.java_websocket.client.WebSocketClient;
import org.java_websocket.handshake.ServerHandshake;
import java.net.URI;
import java.net.URISyntaxException;
import android.widget.Button;
import android.widget.Toast;
import android.content.Intent;

public class MainActivity extends Activity implements View.OnClickListener {
Button bLogout;
UserLocalStore userLocalStore;
private WebSocketClient mWebSocketClient;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    bLogout = (Button) findViewById(R.id.bLogout);
    bLogout.setOnClickListener(this);
    userLocalStore = new UserLocalStore(this);
    connectWebSocket();
}
@Override
protected void onStart() {
    super.onStart();
    if (authenticate()== true){
        displayUserDetails();
    } else{
        Toast.makeText(getApplicationContext(), "Not Registered User :(", Toast.LENGTH_SHORT).show();
        startActivity(new Intent(MainActivity.this,Login.class));
    }
}

private boolean authenticate(){
    return userLocalStore.getUserLoggedIn();
}

private void displayUserDetails(){
    User user = userLocalStore.getLoggedInUser();
}

@Override
public void onClick(View v) {
    switch(v.getId()){
        case R.id.bLogout:
            startActivity(new Intent(this,Login.class));
            userLocalStore.clearUserData();
            userLocalStore.setUserLoggedIn(false);
            Toast.makeText(getApplicationContext(), "Logout :)", Toast.LENGTH_SHORT).show();
            break;

    }
}

private void connectWebSocket() {
    URI uri;
    try {
        uri = new URI("ws://xxx.xxx.xxx.xxx:xxxx");
    } catch (URISyntaxException e) {
        e.printStackTrace();
        return;
    }

    mWebSocketClient = new WebSocketClient(uri) {
        @Override
        public void onOpen(ServerHandshake serverHandshake) {
            Log.i("Websocket", "Opened");
            //mWebSocketClient.send("Hello from " + Build.MANUFACTURER + " " + Build.MODEL);
            mWebSocketClient.send("{\"1512BD002\":\"SO@0\":\"2\"}");
        }

        @Override
        public void onMessage(String s) {
            final String message = s;
            runOnUiThread(new Runnable() {
                @Override
                public void run() {
                    //TextView textView = (TextView)findViewById(R.id.messages);
                    //textView.setText(textView.getText() + "\n" + message);
                }
            });
        }

        @Override
        public void onClose(int i, String s, boolean b) {
            Log.i("Websocket", "Closed " + s);
        }

        @Override
        public void onError(Exception e) {
            Log.i("Websocket", "Error " + e.getMessage());
        }
    };
    mWebSocketClient.connect();
}

public void sendMessage(View view) {
 //   EditText editText = (EditText)findViewById(R.id.message);
   // mWebSocketClient.send(editText.getText().toString());
    //editText.setText("");
}
}

RegisterActivity

package org.asperohgedgetws.a7.hgadgetws;

import android.content.Intent;
import android.os.Bundle;
import android.support.design.widget.FloatingActionButton;
import android.support.design.widget.Snackbar;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;

import org.java_websocket.handshake.ServerHandshake;
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;

import org.java_websocket.client.WebSocketClient;

public class Register extends AppCompatActivity implements View.OnClickListener {

Button bRegister;
EditText etName, etAge, etUsername, etPassword;
WebSocketClient nwebsocket;

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

    etName = (EditText) findViewById(R.id.etName);
    etAge = (EditText) findViewById(R.id.etAge);
    etUsername = (EditText) findViewById(R.id.etUsername);
    etPassword = (EditText) findViewById(R.id.etPassword);
    bRegister = (Button) findViewById(R.id.bRegister);
    bRegister.setOnClickListener(this);
}

@Override
public void onClick(View v) {
    switch (v.getId()) {
        case R.id.bRegister:
            // Toast.makeText(getApplicationContext(), "Register", Toast.LENGTH_SHORT).show();

            String name = etName.getText().toString();
            int age = Integer.parseInt(etAge.getText().toString());
            String username = etUsername.getText().toString();
            String password = etPassword.getText().toString();

            User user = new User(name, age, username, password);
            registerUser(user);

            break;
    }
}

private void registerUser(User user) {
    String strtosend = "";
    JSONObject object = new JSONObject();
    try {
        // Add the id to the json
        object.put("name", user.name);
        object.put("age", user.age);
        object.put("username", user.username);
        object.put("password", user.password);
        strtosend = object.toString();

    } catch (JSONException e) {
        // Handle impossible error
        e.printStackTrace();
    }
    Toast.makeText(getApplicationContext(), strtosend, Toast.LENGTH_SHORT).show();
    nwebsocket.send("Hi!");
    Intent loginIntent = new Intent(Register.this, Login.class);
    startActivity(loginIntent);
}
}

Logcat Output:

05-27 11:49:54.331 19459-19459/org.asperohgedgetws.a7.hgadgetws       E/AndroidRuntime: FATAL EXCEPTION: main
                                                                                 Process: org.asperohgedgetws.a7.hgadgetws, PID: 19459
                                                                              java.lang.NullPointerException: Attempt to invoke virtual method 'void org.java_websocket.client.WebSocketClient.send(java.lang.String)' on a null object reference
                                                                                   at org.asperohgedgetws.a7.hgadgetws.Register.registerUser(Register.java:73)
                                                                                  at org.asperohgedgetws.a7.hgadgetws.Register.onClick(Register.java:51)
                                                                                  at android.view.View.performClick(View.java:4780)
                                                                                  at android.view.View$PerformClick.run(View.java:19866)
                                                                                  at android.os.Handler.handleCallback(Handler.java:739)
                                                                                  at android.os.Handler.dispatchMessage(Handler.java:95)
                                                                                  at android.os.Looper.loop(Looper.java:135)
                                                                                  at android.app.ActivityThread.main(ActivityThread.java:5254)
                                                                                  at java.lang.reflect.Method.invoke(Native Method)
                                                                                  at java.lang.reflect.Method.invoke(Method.java:372)
                                                                                  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:903)
                                                                                  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698)

Do I have to use again below code in Registered activity?

private void connectWebSocket() {
    URI uri;
    try {
        uri = new URI("ws://xxx.xxx.xxx.xxx:xxxx");
    } catch (URISyntaxException e) {
        e.printStackTrace();
        return;
    }

    nWebsocketClient = new WebSocketClient(uri) {
        @Override
        public void onOpen(ServerHandshake serverHandshake) {
            Log.i("Websocket", "Opened");
        }

        @Override
        public void onMessage(String s) {
            final String message = s;
            runOnUiThread(new Runnable() {
                @Override
                public void run() {
                }
            });
        }

        @Override
        public void onClose(int i, String s, boolean b) {
            Log.i("Websocket", "Closed " + s);
        }

        @Override
        public void onError(Exception e) {
            Log.i("Websocket", "Error " + e.getMessage());
        }
    };
    nWebsocketClient.connect();
}

Possible duplicate of [What is a NullPointerException, and how do I fix it?](http://stackoverflow.com/questions/218384/what-is-a-nullpointerexception-and-how-do-i-fix-it) — 1615903, May 27 '16 at 09:13
I got that what is NPE, but in my case3 how can I solve it? I am opening websocket Connection in mainActivity, How can I use send function to send Registered Data in registered Activity. I'm newbie to the Android/Java coding so need to understand. please dont mind. — Taher Kawantwala, May 27 '16 at 09:20

sdabet · Accepted Answer · 2016-05-27T11:10:29.387

2

The problem is that your nwebsocket is never initialized, its value is null and that's why you get this error when trying to execute the send method.

You need to initialize it somewhere:

nwebsocket = new WebSocketClient(...);

NB: If you want to share the same instance of WebSocketClient between MainActivity and Register activity, you could make it public static in MainActivity

public static WebSocketClient mWebSocketClient;

Then remove your WebSocketClient nwebsocket from Register and use MainActivity.mWebSocketClient instead.

edited May 27 '16 at 11:10

answered May 27 '16 at 09:14

sdabet

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Yes I got your Point. in Main Activity, I'm opening a Websocket Connection. now in registered activity Why should i initiate thw connection again? I want to send Data over currently opened Socket Connection. So thatas why I want to use send mathod only. – Taher Kawantwala May 27 '16 at 09:44
Thanks fiddler,your editted answer worked for me. Thank you very much. By making it public, its accesible to other classes. Now I have an abstract method in main Activity which reads incoming messages from server "public void onMessage(String s)". I need to read message from this method and want to use in Login Activity as well as Register Activity. – Taher Kawantwala May 27 '16 at 12:34
Hey Fiddler, Do i need to make a different Class who take care of incomiing data. and whenever any of my activity need to have received data , will get from that class member function? Am I on the right track? – Taher Kawantwala May 27 '16 at 12:54
I'm using Kotlin, and your answer, solved my problem. I forgot to call connect(), ex:'webSocketClient.connect()' – QuartZ Sep 03 '21 at 19:52

Android Error with Websocket

1 Answers1