Question

我正在开发一个应用，其中onLongClick将标记放到谷歌地图上。我的问题是在应用关闭时保存这些标记。

我使用了共享首选项来保存lat和lng的值，并在应用重新启动时加载这些值。但是，当我将这些值传递给方法来制作标记时，错误cat说我试图在空引用上调用方法。

非常感谢任何帮助。请在下面找到代码。

public class SecondMaps extends AppCompatActivity implements OnMapReadyCallback, GoogleMap.OnMapLongClickListener {

    private GoogleMap mMap;
    EditText addressEditText;
    String title;
    LatLng position1;

    SharedPreferences sharedPreferences;
    int locationCount;


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_second_maps);
        // Obtain the SupportMapFragment and get notified when the map is ready to be used.
        SupportMapFragment mapFragment = (SupportMapFragment) getSupportFragmentManager()
                .findFragmentById(R.id.map);
        mapFragment.getMapAsync(this);


        // Opening the sharedPreferences object
        sharedPreferences = getSharedPreferences("location", 0);

        // Getting number of locations already stored
        locationCount = sharedPreferences.getInt("locationCount", 0);


        // If locations are already saved
        if (locationCount != 0) {

            String lat = "";
            String lng = "";

            // Iterating through all the locations stored
            for (int i = 0; i < locationCount; i++) {

                // Getting the latitude of the i-th location
                lat = sharedPreferences.getString("lat" + i, "0");

                // Getting the longitude of the i-th location
                lng = sharedPreferences.getString("lng" + i, "0");


                Toast.makeText(this, lat + "," + lng, Toast.LENGTH_LONG).show();

                double lat3 = Double.valueOf(lat).doubleValue();
                double lng3 = Double.valueOf(lng).doubleValue();

                position1 = new LatLng(lat3, lng3);
                drawMarker(position1);
            }

        }

    }


    @Override
    public void onMapReady(GoogleMap googleMap) {
        mMap = googleMap;
        mMap.setOnMapLongClickListener(this);
        mMap.setMapType(GoogleMap.MAP_TYPE_HYBRID);
        if (ActivityCompat.checkSelfPermission(this, android.Manifest.permission.ACCESS_FINE_LOCATION) != PackageManager.PERMISSION_GRANTED && ActivityCompat.checkSelfPermission(this, android.Manifest.permission.ACCESS_COARSE_LOCATION) != PackageManager.PERMISSION_GRANTED) {
            return;
        }
        mMap.setMyLocationEnabled(true);
        mMap.setTrafficEnabled(true);
        mMap.getUiSettings().setZoomControlsEnabled(true);

        LocationManager locationManager = (LocationManager) getSystemService(Context.LOCATION_SERVICE);
        Criteria criteria = new Criteria();

        Location location = locationManager.getLastKnownLocation(locationManager.getBestProvider(criteria, false));
        if (location != null) {
            mMap.animateCamera(CameraUpdateFactory.newLatLngZoom(
                    new LatLng(location.getLatitude(), location.getLongitude()), 13));


            CameraPosition cameraPosition = new CameraPosition.Builder()
                    .target(new LatLng(location.getLatitude(), location.getLongitude()))      // Sets the center of the map to location user
                    .zoom(17)                   // Sets the zoom
                    .bearing(90)                // Sets the orientation of the camera to east
                            // Sets the tilt of the camera to 30 degrees
                    .build();                   // Creates a CameraPosition from the builder
            mMap.animateCamera(CameraUpdateFactory.newCameraPosition(cameraPosition));

        }
    }

    public void homeClick(MenuItem item) {
        startActivity(new Intent(this, Home.class));
    }

    public void mapClick(MenuItem item) {
        startActivity(new Intent(this, SecondMaps.class));
    }

    public void settingsClick(MenuItem item) {
        startActivity(new Intent(this, Settings.class));
    }

    @Override
    public void onMapLongClick(LatLng latLng) {

        addressEditText = (EditText) findViewById(R.id.editTextAddMarker);
        title = addressEditText.getText().toString();

        if (title.length() > 2) {
            MarkerOptions markerOpt1 = new MarkerOptions()
                    .title(title)
                    .anchor(0.5f, 0.5f);
            markerOpt1.position(latLng);
            mMap.addMarker(markerOpt1);
            Toast.makeText(this, "Reminder Added", Toast.LENGTH_LONG).show();

            addressEditText.setText("");

            locationCount++;

            /** Opening the editor object to write data to sharedPreferences */
            SharedPreferences.Editor editor = sharedPreferences.edit();

            // Storing the latitude for the i-th location
            editor.putString("lat" + Integer.toString((locationCount - 1)), Double.toString(latLng.latitude));

            // Storing the longitude for the i-th location
            editor.putString("lng" + Integer.toString((locationCount - 1)), Double.toString(latLng.longitude));

            // Storing the count of locations or marker count
            editor.putInt("locationCount", locationCount);


            /** Saving the values stored in the shared preferences */
            editor.commit();

        } else if (title.length() < 1) {
            Toast.makeText(this, "Enter Reminder", Toast.LENGTH_LONG).show();
        }
    }
    private void drawMarker(LatLng point){
        // Creating an instance of MarkerOptions
        MarkerOptions markerOptions = new MarkerOptions();

        // Setting latitude and longitude for the marker
        markerOptions.position(point);

        // Adding marker on the Google Map
        mMap.addMarker(markerOptions);
    }

    public void clearMarker(View view) {
        // Opening the editor object to delete data from sharedPreferences
        SharedPreferences.Editor editor = sharedPreferences.edit();

        // Clearing the editor
        editor.clear();

        // Committing the changes
        editor.commit();
    }
}

错误：

java.lang.RuntimeException: Unable to start activity ComponentInfo{conenterprize.remintherefv/conenterprize.remintherefv.SecondMaps}: 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

Answer 1

请勿尝试与onCreate或其他一些启动生命周期方法中的Google地图进行互动，因为地图在作为布局添加后不会立即就绪。

相反，请在onMapReady方法中绘制标记。

将谷歌地图标记保存到Android工作室的SharedPreferences中

1 个答案: