Regarding Login and Sign Up Activity

Question

I am getting an error while running the code. I am creating a login page and sign up page. i am not able to identify what errors are.

public class MainActivity extends ActionBarActivity {

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


        Intent intent = new Intent(this, LoginActivity.class);
        startActivity(intent);
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.menu_main, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();

        //noinspection SimplifiableIfStatement
        if (id == R.id.action_settings) {
            return true;
        }

        return super.onOptionsItemSelected(item);
    }
}

the login activity where user enters the password and username

public class LoginActivity extends AppCompatActivity {
    private static final String TAG = "LoginActivity";
    private static final int REQUEST_SIGNUP = 0;


    EditText _emailText;
     EditText _passwordText;
    Button _loginButton;

    TextView _signupLink;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        //ButterKnife.bind(this);

        _loginButton.setOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View v) {
                login();
            }
        });

        _signupLink.setOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View v) {
                // Start the Signup activity
                Intent intent = new Intent(getApplicationContext(), SignupActivity.class);
                startActivityForResult(intent, REQUEST_SIGNUP);
            }
        });
    }

    public void login() {
        Log.d(TAG, "Login");

        if (!validate()) {
            onLoginFailed();
            return;
        }

        _loginButton.setEnabled(false);

        final ProgressDialog progressDialog = new ProgressDialog(LoginActivity.this,
                R.style.AppTheme_Dark_Dialog);
        progressDialog.setIndeterminate(true);
        progressDialog.setMessage("Authenticating...");
        progressDialog.show();

        String email = _emailText.getText().toString();
        String password = _passwordText.getText().toString();

        // TODO: Implement your own authentication logic here.

        new android.os.Handler().postDelayed(
                new Runnable() {
                    public void run() {
                        // On complete call either onLoginSuccess or onLoginFailed
                        onLoginSuccess();
                        // onLoginFailed();
                        progressDialog.dismiss();
                    }
                }, 3000);
    }


    @Override
    protected void onActivityResult(int requestCode, int resultCode, Intent data) {
        if (requestCode == REQUEST_SIGNUP) {
            if (resultCode == RESULT_OK) {

                // TODO: Implement successful signup logic here
                // By default we just finish the Activity and log them in automatically
                this.finish();
            }
        }
    }

    @Override
    public void onBackPressed() {
        // Disable going back to the MainActivity
        moveTaskToBack(true);
    }

    public void onLoginSuccess() {
        _loginButton.setEnabled(true);
        finish();
    }

    public void onLoginFailed() {
        Toast.makeText(getBaseContext(), "Login failed", Toast.LENGTH_LONG).show();

        _loginButton.setEnabled(true);
    }

    public boolean validate() {
        boolean valid = true;

        String email = _emailText.getText().toString();
        String password = _passwordText.getText().toString();

        if (email.isEmpty() || !android.util.Patterns.EMAIL_ADDRESS.matcher(email).matches()) {
            _emailText.setError("enter a valid email address");
            valid = false;
        } else {
            _emailText.setError(null);
        }

        if (password.isEmpty() || password.length() < 4 || password.length() > 10) {
            _passwordText.setError("between 4 and 10 alphanumeric characters");
            valid = false;
        } else {
            _passwordText.setError(null);
        }

        return valid;
    }
}

the sign up activity

public class SignupActivity extends AppCompatActivity {
    private static final String TAG = "SignupActivity";


    EditText _nameText;
     EditText _emailText;
     EditText _passwordText;
    Button _signupButton;
    TextView _loginLink;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.acitivity_signup);
        //ButterKnife.bind(this);

        _signupButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                signup();
            }
        });

        _loginLink.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                // Finish the registration screen and return to the Login activity
                finish();
            }
        });
    }

    public void signup() {
        Log.d(TAG, "Signup");

        if (!validate()) {
            onSignupFailed();
            return;
        }

        _signupButton.setEnabled(false);

        final ProgressDialog progressDialog = new ProgressDialog(SignupActivity.this,
                R.style.AppTheme_Dark_Dialog);
        progressDialog.setIndeterminate(true);
        progressDialog.setMessage("Creating Account...");
        progressDialog.show();

        String name = _nameText.getText().toString();
        String email = _emailText.getText().toString();
        String password = _passwordText.getText().toString();

        // TODO: Implement your own signup logic here.

        new android.os.Handler().postDelayed(
                new Runnable() {
                    public void run() {
                        // On complete call either onSignupSuccess or onSignupFailed
                        // depending on success
                        onSignupSuccess();
                        // onSignupFailed();
                        progressDialog.dismiss();
                    }
                }, 3000);
    }


    public void onSignupSuccess() {
        _signupButton.setEnabled(true);
        setResult(RESULT_OK, null);
        finish();
    }

    public void onSignupFailed() {
        Toast.makeText(getBaseContext(), "Login failed", Toast.LENGTH_LONG).show();

        _signupButton.setEnabled(true);
    }

    public boolean validate() {
        boolean valid = true;

        String name = _nameText.getText().toString();
        String email = _emailText.getText().toString();
        String password = _passwordText.getText().toString();

        if (name.isEmpty() || name.length() < 3) {
            _nameText.setError("at least 3 characters");
            valid = false;
        } else {
            _nameText.setError(null);
        }

        if (email.isEmpty() || !android.util.Patterns.EMAIL_ADDRESS.matcher(email).matches()) {
            _emailText.setError("enter a valid email address");
            valid = false;
        } else {
            _emailText.setError(null);
        }

        if (password.isEmpty() || password.length() < 4 || password.length() > 10) {
            _passwordText.setError("between 4 and 10 alphanumeric characters");
            valid = false;
        } else {
            _passwordText.setError(null);
        }

        return valid;
    }
}

and the log is

FATAL EXCEPTION: main
                                                                                      Process: com.example.bhardwaj.logintrialtrans, PID: 21617
                                                                                      java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.bhardwaj.logintrialtrans/com.example.bhardwaj.logintrialtrans.LoginActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
                                                                                          at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2416)
                                                                                          at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476)
                                                                                          at android.app.ActivityThread.-wrap11(ActivityThread.java)
                                                                                          at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344)
                                                                                          at android.os.Handler.dispatchMessage(Handler.java:102)
                                                                                          at android.os.Looper.loop(Looper.java:148)
                                                                                          at android.app.ActivityThread.main(ActivityThread.java:5417)
                                                                                          at java.lang.reflect.Method.invoke(Native Method)
                                                                                          at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
                                                                                          at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
                                                                                       Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
                                                                                          at com.example.bhardwaj.logintrialtrans.LoginActivity.onCreate(LoginActivity.java:35)
                                                                                          at android.app.Activity.performCreate(Activity.java:6237)
                                                                                          at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1107)
                                                                                          at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2369)
                                                                                          at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476) 
                                                                                          at android.app.ActivityThread.-wrap11(ActivityThread.java) 
                                                                                          at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344) 
                                                                                          at android.os.Handler.dispatchMessage(Handler.java:102) 
                                                                                          at android.os.Looper.loop(Looper.java:148) 
                                                                                          at android.app.ActivityThread.main(ActivityThread.java:5417) 
                                                                                          at java.lang.reflect.Method.invoke(Native Method) 
                                                                                          at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726) 
                                                                                          at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)

Possible duplicate of [What is a Null Pointer Exception, and how do I fix it?](http://stackoverflow.com/questions/218384/what-is-a-null-pointer-exception-and-how-do-i-fix-it) — Selvin, Feb 02 '16 at 14:07

score 2 · Accepted Answer · answered Feb 02 '16 at 14:08

2

You haven't initialized your buttons in LoginActivity

Do this in onCreate of LoginActivity

 _signupLink = (Button) findViewById(R.id.signuplink); // use your id
 _loginButton = (Button) findViewById(R.id.loginbutton); // use your id

after calling setContentView()

Note: I guess you are using wrong xml in MainActivity and LoginActivity.

In MainAcitivity you have setContentView(R.layout.activity_login); and in LoginActivity you have setContentView(R.layout.activity_main);. Just saying based on the names of those xmls

answered Feb 02 '16 at 14:08

Rohit5k2

17,948
8
45
57

Thanks and sorry for the lame question – anupriya Feb 02 '16 at 14:32
@anupriya: Don't worry about it. Happens with most of us. – Rohit5k2 Feb 02 '16 at 14:34

score 0 · Answer 2 · answered Feb 02 '16 at 14:08

0

You need to use findViewById(R.id.YOUR_BUTTON_ID) to get a reference to the button before trying to set an onClickListener for it. Currently you're just creating a button object in your code but not linking it to a button in your layout.

answered Feb 02 '16 at 14:08

xiimoss

775
3
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Regarding Login and Sign Up Activity

2 Answers2