public void onBackPressed() {
        DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
        if (drawer.isDrawerOpen(GravityCompat.START)) {
            drawer.closeDrawer(GravityCompat.START);
        } else {
            super.onBackPressed();
        }
    }

public boolean onNavigationItemSelected(MenuItem item) {
    int id = item.getItemId();

    Fragment meuFragmento = null;
    boolean fragmentoSelec = false;

    if (id == R.id.nav_inicio) {
        meuFragmento = new bemVindoFragmento();
        fragmentoSelec = true;
    } else if (id == R.id.nav_consulta_lista) {
        meuFragmento = new consultarListaCursosFragmento();
        fragmentoSelec = true;
    }

    if (fragmentoSelec == true) {
        getSupportFragmentManager().beginTransaction().replace(R.id.content_principal, meuFragmento).commit();
    }

    DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
    drawer.closeDrawer(GravityCompat.START);

    return true;
}