Activity Android with login

MainActivity.java

package app;

import android.content.Context;
import android.content.Intent;
import android.content.SharedPreferences;
import android.os.Bundle;
import android.os.StrictMode;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;

import org.json.JSONException;

import app.Controller.User;
import app.Service.Permissions;
import app.Service.Support;
import app.View.TabActivity;

public class MainActivity extends AppCompatActivity {

    private TextView tvUsername, tvPassword;
    private EditText txtUsername, txtPassword;
    private TextView tv;

    @Override
    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        getSupportActionBar().setDisplayShowHomeEnabled(true);
        getSupportActionBar().setDisplayUseLogoEnabled(true);

        //Disabilita da StrictMode di android solo su sdk superiori a 9
        if (android.os.Build.VERSION.SDK_INT > 9) {
            StrictMode.ThreadPolicy policy = new StrictMode.ThreadPolicy.Builder().permitAll().build();
            StrictMode.setThreadPolicy(policy);
        }
        /* Istanza dei campi */
        tvUsername = (TextView) findViewById(R.id.usernametextview);
        txtUsername = (EditText) findViewById(R.id.usernameeditext);
        tvPassword = (TextView) findViewById(R.id.passwordtextview);
        txtPassword = (EditText) findViewById(R.id.passwordtext);
        final Button loginbutton = (Button) findViewById(R.id.buttonlogin);

        //Configuro la funzione Listener sul login button
        loginbutton.setOnClickListener(new View.OnClickListener() {
            public void onClick(View v) {

                // Code here executes on main thread after user presses button
                if (txtUsername.length() != 0 && txtPassword.length() != 0) {

                    if (Permissions.isOnline() == true) {
                        LoginFunction(txtUsername.getText().toString(), txtPassword.getText().toString(), true);
                    } else {
                        Support.Notification(MainActivity.this, "Errore", "Non stai navigando");
                    }
                }
            }
        });


        SharedPreferences sp1 = this.getSharedPreferences("Login", Context.MODE_PRIVATE);
        String userload = sp1.getString("Username", null);
        String pwdload = sp1.getString("Password", null);
        LoginFunction(userload, pwdload, false);

    }

    private void LoginFunction(String Username, String Password, Boolean ShowMessage) {
        User u = new User();
        Boolean ret = false;
        try {
            ret = u.Login(Username, Password);
            if (ret == true) {
                //Salvo le credenziali d'accesso in sharedPrefrences
                SharedPreferences sp = this.getSharedPreferences("Login", Context.MODE_PRIVATE);
                SharedPreferences.Editor Ed = sp.edit();
                Ed.putString("Username", txtUsername.getText().toString());
                Ed.putString("Password", txtPassword.getText().toString());
                Ed.commit();
                //Creo un oggetto Intent da inviare ad una activity
                Intent tabhome = new Intent(MainActivity.this, TabActivity.class);
                tabhome.putExtra("User", u);
                startActivity(tabhome);
            } else {
                if (ShowMessage == true) {
                    Support.Notification(MainActivity.this, "Errore", "Login non riuscito");
                }
            }
        } catch (JSONException e) {
            e.printStackTrace();
        }


    }


}