Android - GPS_PROVIDER

I'd like to know why I can not use GPS_PROVIDER . It works with NETWORK_PROVIDER , but I need GPS .

public class MainActivity extends AppCompatActivity {

private TextView textLati, textLong, textCidade, textEstado, textPais, textRua;

private LocationManager locationManager;

private Address endereco;
private final int REQUEST_LOCATION = 1;

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

    textLati =  (TextView) findViewById(R.id.txtLatitude);
    textLong  = (TextView) findViewById(R.id.txtLongitude);
    textCidade  = (TextView) findViewById(R.id.txtCidade);
    textEstado  = (TextView) findViewById(R.id.txtEstado);
    textPais  = (TextView) findViewById(R.id.txtPais);
    textRua  = (TextView) findViewById(R.id.txtRua);

    double latti = 0.0;
    double longi = 0.0;

    locationManager = (LocationManager) getSystemService(Context.LOCATION_SERVICE);
    if (ActivityCompat.checkSelfPermission(this, Manifest.permission.ACCESS_FINE_LOCATION) != PackageManager.PERMISSION_GRANTED
            && ActivityCompat.checkSelfPermission(this, Manifest.permission.ACCESS_COARSE_LOCATION)
            != PackageManager.PERMISSION_GRANTED) {
        ActivityCompat.requestPermissions(this, new String[]{Manifest.permission.ACCESS_FINE_LOCATION}, REQUEST_LOCATION);
    }else{
        Location location = locationManager.getLastKnownLocation(LocationManager.GPS_PROVIDER);
        if (location != null) {
             latti = location.getLatitude();
             longi   = location.getLongitude();

            textLati.setText("Latitude: "+latti);
            textLong.setText("Logitude: "+longi);
        }
    }
    try{
        endereco = buscaEndereco(latti, longi);

        textCidade.setText("Cidade: "+ endereco.getLocality());
        textEstado.setText("Estado: "+ endereco.getAdminArea());
        textPais.setText("Pais: "+ endereco.getCountryName());
        textRua.setText("" + endereco.getAddressLine(0));

    }catch (IOException e){
        e.printStackTrace();
    }

}



public Address buscaEndereco(double latitude, double longitude)throws IOException{
    Geocoder geocoder;
    Address address = null;
    List<Address> addresses;

    geocoder = new Geocoder(getApplicationContext());

    addresses = geocoder.getFromLocation(latitude, longitude, 1);

    if (addresses.size() > 0 ){
        address = addresses.get(0);
    }

    return address;
  }
}