private AppSingleton(Context context) {
    mContext = context;
    mRequestQueue = getRequestQueue();
}

public static synchronized AppSingleton getInstance(Context context) {
    if (mAppSingletonInstance == null) {
        mAppSingletonInstance = new AppSingleton(context);
    }
    return mAppSingletonInstance;
}

public RequestQueue getRequestQueue() {
    if (mRequestQueue == null) {
        // getApplicationContext() is key, it keeps you from leaking the
        // Activity or BroadcastReceiver if someone passes one in.
        mRequestQueue = Volley.newRequestQueue(mContext.getApplicationContext());
    }
    return mRequestQueue;
}

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

private static final String TAG = "RegisterActivity";
private static final String URL_FOR_REGISTRATION = "http://192.168.0.110/android_login_example/register.php";
ProgressDialog progressDialog;

private EditText signupInputName, signupInputEmail, signupInputPassword, signupInputAge;
private Button btnSignUp;
private Button btnLinkLogin;
private RadioGroup genderRadioGroup;

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

    // Progress dialog
    progressDialog = new ProgressDialog(this);
    progressDialog.setCancelable(false);

    signupInputName = (EditText) findViewById(R.id.signup_input_name);
    signupInputEmail = (EditText) findViewById(R.id.signup_input_email);
    signupInputPassword = (EditText) findViewById(R.id.signup_input_password);
    signupInputAge = (EditText) findViewById(R.id.signup_input_age);

    btnSignUp = (Button) findViewById(R.id.btn_signup);
    btnLinkLogin = (Button) findViewById(R.id.btn_link_login);

    genderRadioGroup = (RadioGroup) findViewById(R.id.gender_radio_group);
    btnSignUp.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            submitForm();
        }
    });
    btnLinkLogin.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {

            Intent i = new Intent(getApplicationContext(),LoginActivity.class);
            startActivity(i);
        }
    });
}

private void submitForm() {

    int selectedId = genderRadioGroup.getCheckedRadioButtonId();
    String gender;
    if(selectedId == R.id.female_radio_btn)
        gender = "Female";
    else
        gender = "Male";

    registerUser(signupInputName.getText().toString(),
                 signupInputEmail.getText().toString(),
                 signupInputPassword.getText().toString(),
                 gender,
                 signupInputAge.getText().toString());
}

private void registerUser(final String name,  final String email, final String password,
                          final String gender, final String dob) {
    // Tag used to cancel the request
    String cancel_req_tag = "register";

    progressDialog.setMessage("Adding you ...");
    showDialog();

    StringRequest strReq = new StringRequest(Request.Method.POST,
            URL_FOR_REGISTRATION, 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) {
                    String user = jObj.getJSONObject("user").getString("name");
                    Toast.makeText(getApplicationContext(), "Hi " + user +", You are successfully Added!", Toast.LENGTH_SHORT).show();

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

                    String errorMsg = jObj.getString("error_msg");
                    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();
        }
    }) {
        @Override
        protected Map<String, String> getParams() {
            // Posting params to register url
            Map<String, String> params = new HashMap<String, String>();
            params.put("name", name);
            params.put("email", email);
            params.put("password", password);
            params.put("gender", gender);
            params.put("age", dob);
            return params;
        }
    };
    // Adding request to request queue
    AppSingleton.getInstance(getApplicationContext()).addToRequestQueue(strReq, cancel_req_tag);
}

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

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

private static final String TAG = "LoginActivity";
private static final String URL_FOR_LOGIN = "http://192.168.0.110/android_login_example/login.php";
ProgressDialog progressDialog;
private EditText loginInputEmail, loginInputPassword;
private Button btnlogin;
private Button btnLinkSignup;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_login);
    loginInputEmail = (EditText) findViewById(R.id.login_input_email);
    loginInputPassword = (EditText) findViewById(R.id.login_input_password);
    btnlogin = (Button) findViewById(R.id.btn_login);
    btnLinkSignup = (Button) findViewById(R.id.btn_link_signup);
    // Progress dialog
    progressDialog = new ProgressDialog(this);
    progressDialog.setCancelable(false);

    btnlogin.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            loginUser(loginInputEmail.getText().toString(), loginInputPassword.getText().toString());
        }
    });

    btnLinkSignup.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            Intent i = new Intent(getApplicationContext(), RegisterActivity.class);
            startActivity(i);
        }
    });
}

private void loginUser( final String email, final String password) {
    // Tag used to cancel the request
    String cancel_req_tag = "login";
    progressDialog.setMessage("Logging you in...");
    showDialog();
    StringRequest strReq = new StringRequest(Request.Method.POST,
            URL_FOR_LOGIN, 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) {
                    String user = jObj.getJSONObject("user").getString("name");
                    // Launch User activity
                    Intent intent = new Intent(
                            LoginActivity.this,
                            UserActivity.class);
                    intent.putExtra("username", user);
                    startActivity(intent);
                    finish();
                } else {

                    String errorMsg = jObj.getString("error_msg");
                    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, "Login Error: " + error.getMessage());
            Toast.makeText(getApplicationContext(),
                    error.getMessage(), Toast.LENGTH_LONG).show();
            hideDialog();
        }
    }) {

        @Override
        protected Map<String, String> getParams() {
            // Posting params to login url
            Map<String, String> params = new HashMap<String, String>();
            params.put("email", email);
            params.put("password", password);
            return params;
        }

    };
    // Adding request to request queue
    AppSingleton.getInstance(getApplicationContext()).addToRequestQueue(strReq,cancel_req_tag);
}

private void showDialog() {
    if (!progressDialog.isShowing())
        progressDialog.show();
}
private void hideDialog() {
    if (progressDialog.isShowing())
        progressDialog.dismiss();
}