FUNCIONA

public void onClick(View v) {
        switch (v.getId())
        {
            case R.id.btnJugar:
                Intent intent = new Intent(this, PuzzleActivity.class);
                intent.putExtra(NFILES, Integer.parseInt(spnNFiles.getSelectedItem().toString()));
                intent.putExtra(NCOLUMNES, Integer.parseInt(spnNColumnes.getSelectedItem().toString()));
                Bundle b = new Bundle();

                if(spnUsuaris.isSelected())
                {
                    Usuari jug = (Usuari) spnUsuaris.getSelectedItem();
                    intent.putExtra(USUARI, jug);
                    startActivity(intent);
                }
                else
                {
                    if(etNom.getText().toString().equals(""))
                    {
                        Toast toast = Toast.makeText(getApplicationContext(), "NO HAS INTRODUCIDO UN NOMBRE DE JUGADOR", Toast.LENGTH_LONG);
                        toast.show();
                    }
                    else {
                        Usuari jug = new Usuari(etNom.getText().toString());
                        b.putParcelable(USUARI,jug);
                        intent.putExtra(BUNDLE, b);
                        startActivity(intent);
                    }
                }
                break;
        }
    }