我正在尝试跟踪用户位置并根据他的移动在地图上绘制路径/路线（updatePolyline（），updateCamera（），updateMarker（）负责绘制路线）。程序编译，但关键的错误是当位置实际改变时不调用onLocationChanged（），因此，没有路径被绘制。
public class MapsActivity extends FragmentActivity implements OnMapReadyCallback, LocationListener {
private GoogleMap mMap; // Might be null if Google Play services APK is not available.
private PolylineOptions mPolylineOptions;
LocationManager locationManager;
private LatLng mLatLng;
double latitude, longitude;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_maps);
setUpMapIfNeeded();
// LocationManager lm = (LocationManager) getSystemService(Context.LOCATION_SERVICE);
this.locationManager = (LocationManager)getSystemService(Context.LOCATION_SERVICE);
Location location = locationManager.getLastKnownLocation(LocationManager.GPS_PROVIDER);
longitude = location.getLongitude();
latitude = location.getLatitude();
// if(location != null) {
//
// onLocationChanged(location);
// }
locationManager.requestLocationUpdates(LocationManager.GPS_PROVIDER, 2000, 10, this);
}
public void onLocationChanged(Location location) {
longitude = location.getLongitude();
latitude = location.getLatitude();
mLatLng = new LatLng(latitude, longitude);
runOnUiThread(new Runnable() {
@Override
public void run() {
updatePolyline();
updateCamera();
updateMarker();
}
});
}
@Override
public void onStatusChanged(String s, int i, Bundle bundle) {
}
@Override
public void onProviderEnabled(String s) {
}
@Override
public void onProviderDisabled(String s) {
}
@Override
public void onMapReady(GoogleMap map) {
mMap = map;
initializeMap();
}
private void updatePolyline() {
mMap.clear();
mMap.addPolyline(mPolylineOptions.add(mLatLng));
}
private void updateMarker() {
mMap.addMarker(new MarkerOptions().position(mLatLng));
}
private void updateCamera() {
mMap.animateCamera(CameraUpdateFactory.newLatLngZoom(mLatLng, 16));
}
private void initializeMap() {
mPolylineOptions = new PolylineOptions();
mPolylineOptions.color(Color.BLUE).width(10);
}
@Override
protected void onResume() {
super.onResume();
setUpMapIfNeeded();
}
private void setUpMapIfNeeded() {
if (mMap == null) {
mMap = ((SupportMapFragment) getSupportFragmentManager().findFragmentById(R.id.map)).getMap();
mMap.setMyLocationEnabled(true);
mMap.setOnMyLocationButtonClickListener(new GoogleMap.OnMyLocationButtonClickListener() {
@Override
public boolean onMyLocationButtonClick() {
LocationManager lm = null;
boolean gps_enabled = false, network_enabled = false;
if (lm == null)
lm = (LocationManager) getApplicationContext().getSystemService(Context.LOCATION_SERVICE);
try {
gps_enabled = lm.isProviderEnabled(LocationManager.GPS_PROVIDER);
} catch (Exception ex) {
}
try {
network_enabled = lm.isProviderEnabled(LocationManager.NETWORK_PROVIDER);
} catch (Exception ex) {
}
if (!gps_enabled && !network_enabled) {
AlertDialog.Builder dialog = new AlertDialog.Builder(MapsActivity.this);
dialog
.setTitle("No gps")
.setPositiveButton("Atšaukti", new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface paramDialogInterface, int paramInt) {
}
})
.setNegativeButton("Open settings", new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface paramDialogInterface, int paramInt) {
Intent myIntent = new Intent(Settings.ACTION_LOCATION_SOURCE_SETTINGS);
MapsActivity.this.startActivity(myIntent);
}
});
AlertDialog alert_dialog = dialog.create();
alert_dialog.show();
}
return false;
}
});
}
}
}