<Button
    android:id="@+id/bSignup"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:background="#FF0000"
    android:text="Sign Up"
    android:textColor="#FFFFFF"
    android:textSize="20sp"
    android:textStyle="bold" />

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

    final EditText etEmail = (EditText) findViewById(R.id.etEmail);
    final EditText etUsername = (EditText) findViewById(R.id.etUsername);
    final EditText etPassword = (EditText) findViewById(R.id.etPassword);
    final Button bSignup = (Button) findViewById(R.id.bSignup);

    bSignup.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            final String username = etUsername.getText().toString();
            final String email = etEmail.getText().toString();
            final String password = etPassword.getText().toString();

            Response.Listener<String> responseListener = new Response.Listener<String>(){

                @Override
                public void onResponse(String response) {
                    try {
                        JSONObject jsonResponse = new JSONObject(response);
                        boolean success = jsonResponse.getBoolean("success");

                        if (success){
                            Intent intent = new Intent(Signup.this, Signin.class);
                            Signup.this.startActivity(intent);
                        }else {
                            AlertDialog.Builder builder = new AlertDialog.Builder(Signup.this);
                            builder.setMessage("Sign up failed")
                                    .setNegativeButton("Retry", null)
                                    .create()
                                    .show();
                        }

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

            SignupRequest signupRequest = new SignupRequest(username, email, password, responseListener);
            RequestQueue queue = Volley.newRequestQueue(Signup.this);
            queue.add(signupRequest);
        }
    });
}