i am trying to login a user after the user registers but i keep getting java.lang.NullPointerException

Question

I am trying to use Volley and send POST request to check data after login.

What I am trying to do is after checking validation in DonatorLogin I want to create API instance in DonatorLogin and send POSTrequest to server.

Here is my AppController class

package ng.edu.saveasoul.app;
import android.app.Application;
import android.text.TextUtils;

import com.android.volley.Request;
import com.android.volley.RequestQueue;
import com.android.volley.toolbox.Volley;

public class AppController extends Application {

    public static final String TAG = AppController.class.getSimpleName();

    private RequestQueue mRequestQueue;

    private static AppController mInstance;

    @Override
    public void onCreate() {
        super.onCreate();
        mInstance = this;
    }

    public static synchronized AppController getInstance() {
        return mInstance;
    }

    public RequestQueue getRequestQueue() {
        if (mRequestQueue == null) {
            mRequestQueue = Volley.newRequestQueue(getApplicationContext());
        }

        return mRequestQueue;
    }

    public <T> void addToRequestQueue(Request<T> req, String tag) {
        req.setTag(TextUtils.isEmpty(tag) ? TAG : tag);
        getRequestQueue().add(req);
    }

    public <T> void addToRequestQueue(Request<T> req) {
        req.setTag(TAG);
        getRequestQueue().add(req);
    }

    public void cancelPendingRequests(Object tag) {
        if (mRequestQueue != null) {
            mRequestQueue.cancelAll(tag);
        }
    }
}

here is my session manager

package ng.edu.saveasoul.Helper;

import android.content.Context;
import android.content.SharedPreferences;
import android.content.SharedPreferences.Editor;
import android.util.Log;

public class SessionManager {
    // LogCat tag
    private static String TAG = SessionManager.class.getSimpleName();

    // Shared Preferences
    SharedPreferences pref;

    Editor editor;
    Context _context;

    // Shared pref mode
    int PRIVATE_MODE = 0;

    // Shared preferences file name
    private static final String PREF_NAME = "SOS";

    private static final String KEY_IS_LOGGEDIN = "isLoggedIn";
    private static final String KEY_USER_ID = "userId";

    public SessionManager(Context context) {
        this._context = context;
        pref = _context.getSharedPreferences(PREF_NAME, PRIVATE_MODE);
        editor = pref.edit();
    }

    public void setLogin(boolean isLoggedIn) {
        editor.putBoolean(KEY_IS_LOGGEDIN, isLoggedIn);
        // commit changes
        editor.commit();
        Log.d(TAG, "User login session modified!");
    }

    public boolean isLoggedIn(){
        return pref.getBoolean(KEY_IS_LOGGEDIN, false);
    }

    public void saveUserId(String userIdValue) {
        editor.putString(KEY_USER_ID, userIdValue);
        // commit changes
        editor.commit();
        Log.d(TAG, "User login session modified!");
    }

    public String getUserId(){
        return pref.getString(KEY_USER_ID, "");
    }
}

here is my donator login

package ng.edu.saveasoul;

import androidx.appcompat.app.AppCompatActivity;

import android.app.ProgressDialog;
import android.content.Intent;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import java.util.HashMap;
import java.util.Map;
import org.json.JSONException;
import org.json.JSONObject;
import android.widget.Toast;
import com.android.volley.Request;
import com.android.volley.Response;
import com.android.volley.VolleyError;
import com.android.volley.toolbox.StringRequest;
import ng.edu.saveasoul.Helper.SessionManager;
import ng.edu.saveasoul.app.AppConfig;
import ng.edu.saveasoul.app.AppController;


public class DonatorLogin extends AppCompatActivity {


    private static final String TAG = DonatorLogin.class.getSimpleName();

    //initialize variable
    EditText eMail, pword;
    Button btnSubmit, btnSubmit2;
    private ProgressDialog pDialog;
    private SessionManager session;


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

        //assign variable
        eMail = (EditText) findViewById(R.id.text1);
        pword = (EditText) findViewById(R.id.text2);
        btnSubmit = (Button) findViewById(R.id.b1);
        btnSubmit2 = (Button) findViewById(R.id.b2);
        pDialog = new ProgressDialog(this);
        pDialog.setCancelable(false);

        // Session manager
        session = new SessionManager(getApplicationContext());


        // Check if user is already logged in or not
        if (session.isLoggedIn()) {
            // User is already logged in. Take him to main activity
            Intent intent = new Intent(DonatorLogin.this, DonatorProfile.class);
            startActivity(intent);
            finish();
        }


        //second button
        btnSubmit2.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                //call activity page
                openDonatorRegister();
            }
        });

        //first button
        btnSubmit.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                String email = eMail.getText().toString().trim();
                String password = pword.getText().toString().trim();

                // Check for empty data in the form
                if (!email.isEmpty() && !password.isEmpty()) {
                    // login user
                    checkLogin(email, password);
                } else {
                    // Prompt user to enter credentials
                    Toast.makeText(getApplicationContext(),
                            "Please enter the credentials!", Toast.LENGTH_LONG)
                            .show();
                }
            }


        });


    }


    private void checkLogin(String email, String password) {
        // Tag used to cancel the request
        String tag_string_req = "req_register";

        pDialog.setMessage("Registering ...");
        showDialog();

        StringRequest strReq = new StringRequest(Request.Method.POST,
                AppConfig.URL_API, new Response.Listener<String>() {
            @Override
            public void onResponse(String response) {
                Log.d(TAG, "Register Response: " + response.toString());
                hideDialog();

                try {
                    JSONObject jObj = new JSONObject(response);
                    boolean error = jObj.getBoolean("error");

                    if (!error) {
                        // User successfully stored in MySQL
                        String uid = jObj.getString("data");
                        String message = jObj.getString("message");

                        session.saveUserId(uid);
                        Toast.makeText(getApplicationContext(), message, Toast.LENGTH_LONG).show();

                        // Launch login activity
                        Intent intent = new Intent(
                                DonatorLogin.this, DonatorProfile.class);
                        startActivity(intent);
                        finish();
                    } else {

                        // Error occurred in registration. Get the error
                        // message
                        String errorMsg = jObj.getString("message");
                        Toast.makeText(getApplicationContext(),
                                errorMsg, Toast.LENGTH_LONG).show();
                    }

                } catch (JSONException e)
                {
                    e.printStackTrace();
                }
            }

        }, new Response.ErrorListener()
        {

            @Override
            public void onErrorResponse(VolleyError error)
            {
                Log.e(TAG, "Registration Error: " + error.getMessage());
                Toast.makeText(getApplicationContext(),
                        error.getMessage(), Toast.LENGTH_LONG).show();
                hideDialog();
            }
        }) {   //api file //sending data to api
            @Override
            protected Map<String, String> getParams()
            {
                // Posting params to login url
                Map<String, String> params = new HashMap<String, String>();
                params.put("login", "login");//api action call
                params.put("email", email);
                params.put("password", password);
                return params;
            }

        };

        // Adding request to request queue
        AppController.getInstance().addToRequestQueue(strReq, tag_string_req);
    }

    private void showDialog() {
        if (!pDialog.isShowing())
            pDialog.show();
    }

    private void hideDialog() {
        if (pDialog.isShowing())
            pDialog.dismiss();
    }


    //create method
    public void openDonatorRegister()
    {
        //open the class you want to
        Intent intent = new Intent(this, DonatorRegister.class);
        startActivity(intent);
    }

}

here is the error code

Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference at ng.edu.saveasoul.DonatorLogin.onCreate(DonatorLogin.java:74) at android.app.Activity.performCreate(Activity.java:7136) at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:78) at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:108) at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:68) at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1808) at android.os.Handler.dispatchMessage(Handler.java:106) at android.os.Looper.loop(Looper.java:193) at android.app.ActivityThread.main(ActivityThread.java:6669) at java.lang.reflect.Method.invoke(Native Method) at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858)

Does this answer your question? [What is a NullPointerException, and how do I fix it?](https://stackoverflow.com/questions/218384/what-is-a-nullpointerexception-and-how-do-i-fix-it) — a_local_nobody, Sep 05 '20 at 14:02

score 0 · Accepted Answer · answered Sep 05 '20 at 15:07

0

Check if these two buttons points to correct id:

        btnSubmit = (Button) findViewById(R.id.b1);
        btnSubmit2 = (Button) findViewById(R.id.b2);

According to the error, the buttons are null.

answered Sep 05 '20 at 15:07

Basu

763
8
27

i am trying to login a user after the user registers but i keep getting java.lang.NullPointerException

1 Answers1