java - 如何在onSensorChanged中使用GoogleMap.addMarker？

Question

调用 onSensorChanged 方法时如何旋转标记？我尝试了这段代码，但出现了 NullPointerException。我将 mMap 声明为全局变量并将其加载到 onMapReady 中。我想在我的 onSensorChanged 方法中使用它。我该如何解决这个问题？

我收到此错误:

java.lang.NullPointerException: Attempt to invoke virtual method 'com.google.android.gms.maps.model.Marker com.google.android.gms.maps.GoogleMap.addMarker(com.google.android.gms.maps.model.MarkerOptions)' on a null object reference

    @Override
    public void onMapReady(GoogleMap googleMap) {
        mMap = googleMap;
        mMap.getUiSettings().setZoomControlsEnabled(true);

        latLng_dest = getIntent().getExtras().getParcelable("latLng_dest");
        Log.d("LatLng_dest : ", latLng_dest.toString());

        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}, LOCATION_REQUEST);
            return;
        }
        mMap.setMyLocationEnabled(true);
        mMap.getUiSettings().setMyLocationButtonEnabled(false);
        // Call our direction function
        getDeviceLocation();

    }

    @Override
    public void onSensorChanged(SensorEvent event) {
        if (event.sensor == mRotationSensor) {
            if (event.values.length > 4) {
                float[] truncatedRotationVector = new float[4];
                System.arraycopy(event.values, 0, truncatedRotationVector, 0, 4);
                updateSensor(truncatedRotationVector);
            } else {
                updateSensor(event.values);
            }
        }

    }

    private void updateSensor(float[] vectors) {
        float[] rotationMatrix = new float[9];
        SensorManager.getRotationMatrixFromVector(rotationMatrix, vectors);
        int worldAxisX = SensorManager.AXIS_X;
        int worldAxisZ = SensorManager.AXIS_Z;
        float[] adjustedRotationMatrix = new float[9];
        SensorManager.remapCoordinateSystem(rotationMatrix, worldAxisX, worldAxisZ, adjustedRotationMatrix);
        float[] orientation = new float[3];
        SensorManager.getOrientation(adjustedRotationMatrix, orientation);
        azimuth = orientation[0]* FROM_RADS_TO_DEGS;
        float pitch = orientation[1] * FROM_RADS_TO_DEGS;
        float roll = orientation[2] * FROM_RADS_TO_DEGS;
        Log.d("", "updateSensor: Pitch "+pitch);
        Log.d("", "updateSensor: Roll "+roll);
        Log.d("", " "+mMap);
        markerOptions = new MarkerOptions().icon(bitmapDescriptorFromVector(MapsActivity.this, R.drawable.ic_navigation_black_24dp));
        ((TextView)findViewById(R.id.svtv2)).setText("Azimuth: "+azimuth+"\n"+"Pitch: "+pitch+"\n"+"Roll: "+roll);

        mMap.addMarker(markerOptions.rotation(azimuth));

    }

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_maps);
        setRequestedOrientation(ActivityInfo.SCREEN_ORIENTATION_PORTRAIT);
        mFusedLocationProviderClient = LocationServices.getFusedLocationProviderClient(this);
        // Obtain the SupportMapFragment and get notified when the map is ready to be used.
        initMap();
        //markerOptions = new MarkerOptions().icon(bitmapDescriptorFromVector(MapsActivity.this, R.drawable.ic_navigation_black_24dp));
        Button button = findViewById(R.id.but_dir);
        button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                textView = findViewById(R.id.svtv);
                textView.setText(instruction);
            }
        });


        /*new Timer().scheduleAtFixedRate(new TimerTask() {
            @Override
            public void run() {
            }
        },0,1);*/

        //Aquire a reference to the system Location Manager
        LocationManager locationManager = (LocationManager) this.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) {

            return;

        }


        final TextView live_inst = findViewById(R.id.svtv2);

        // Define a listener that responds to location updates
        LocationListener locationListener = new LocationListener() {

            @Override
            public void onLocationChanged(Location location) {
                // Called when a new location is found by the network location provider.
                //makeUseOfNewLocation(location);
                updateDeviceLocation(location);
            }

            @Override
            public void onStatusChanged(String provider, int status, Bundle extras) {
            }

            @Override
            public void onProviderEnabled(String provider) {
            }

            @Override
            public void onProviderDisabled(String provider) {
            }
        };
        // Register the listener with the Location Manager to receive location updates
        locationManager.requestLocationUpdates(LocationManager.GPS_PROVIDER, 1, 0, locationListener);

        try {
            mSensorManager = (SensorManager) getSystemService(MapsActivity.SENSOR_SERVICE);
            mRotationSensor = mSensorManager.getDefaultSensor(Sensor.TYPE_ROTATION_VECTOR);
            mSensorManager.registerListener(this, mRotationSensor, SENSOR_DELAY);
        } catch (Exception e) {
            Toast.makeText(this, "Hardware compatibility issue", Toast.LENGTH_LONG).show();
        }

    }

Answer 1

通常，onSenorChanged 会在您启动应用程序屏幕时立即触发。

通过这种方式，在传感器值更改后，您将尝试旋转 map 对象上的标记，该标记将为空，因为它是异步调用。

在调用“rotateMarker”方法之前进行空检查。

示例:

If (mMap != null) {
  // do rotate Map marker
}

注意:即使发生非常微小的变化，传感器值也会发生变化。只是为了增强性能，请使用 + 或 - 5 校准传感器值。

希望这些信息有帮助!