Material Design  Pantalla de login - parte 4

Codigo fuente

mLoginBtn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {

                SharedPreferences preference = getSharedPreferences("Reg",MODE_PRIVATE);
                String username = preference.getString("Username","");
                String password = preference.getString("Password","");


                if(mUsername.getText().toString().trim().length() == 0 && mPassword.getText().toString().trim().length() == 0 ){

                    Toast.makeText(MainActivity.this, "Los campos estan vacios.", Toast.LENGTH_SHORT).show();


                }else if(mUsername.getText().toString().trim().equals(username) && mPassword.getText().toString().trim().equals(password)){


                    Toast.makeText(MainActivity.this, "Bienvenido al sistema " + username, Toast.LENGTH_SHORT).show();
                    Intent intent = new Intent(MainActivity.this,PantallaPrincipal.class);
                    startActivity(intent);

                }



            }

        });