获取 NullPointerException：在空对象引用上的 GoogleMap.setMyLocationEnabled(boolean)

Question

我收到此错误

NullPointerException：尝试在空对象引用上调用虚拟方法 'void com.google.android.gms.maps.GoogleMap.setMyLocationEnabled(boolean)

并且应用程序由于此错误而崩溃。我想提一下，我在互联网上搜索并在这里寻找答案，但没有找到任何东西

这是我的代码：

public class MapsActivity extends FragmentActivity
        implements OnMapReadyCallback,
        GoogleMap.OnMapClickListener,
        GoogleMap.OnMapLongClickListener,
        GoogleMap.OnMarkerClickListener {

    private GoogleMap mMap;
    private GoogleMap googleMap;
    private ArrayList<LatLng> arrayPoints = null;
    PolylineOptions polylineOptions;
    private boolean checkClick = false;


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

        arrayPoints = new ArrayList<LatLng>();
        // 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);

        // display zoom map

        googleMap.setOnMapClickListener(this);
        googleMap.setOnMapLongClickListener(this);
        googleMap.setOnMarkerClickListener(this);

    }

    public GoogleMap getmMap() {
        return mMap;

    }


    /**
     * Manipulates the map once available.
     * This callback is triggered when the map is ready to be used.
     * This is where we can add markers or lines, add listeners or move the camera. In this case,
     * we just add a marker near Sydney, Australia.
     * If Google Play services is not installed on the device, the user will be prompted to install
     * it inside the SupportMapFragment. This method will only be triggered once the user has
     * installed Google Play services and returned to the app.
     */


    @Override
    public void onMapReady(final GoogleMap googleMap) {

        mMap = googleMap;
        googleMap.setMyLocationEnabled(true);

        mMap.setOnMapClickListener(new GoogleMap.OnMapClickListener() {
            @Override
            public void onMapClick(final LatLng latLng) {

                if (checkClick == false) {

                    LatLng currentLocation = null;
                    Marker marker = googleMap.addMarker(new MarkerOptions().position(currentLocation)
                            .icon(BitmapDescriptorFactory.fromResource(R.drawable.point)));

                }
            }
        });
    }

    @Override
    public void onMapLongClick(LatLng latLng) {

        googleMap.clear();
        arrayPoints.clear();
        checkClick = false;

    }

    @Override
    public boolean onMarkerClick(Marker marker) {
        // TODO Auto-generated method stub
        System.out.println("Marker lat long=" + marker.getPosition());
        System.out.println("First postion check" + arrayPoints.get(0));
        System.out
                .println("**********All arrayPoints***********" + arrayPoints);
        if (arrayPoints.get(0).equals(marker.getPosition())) {
            System.out.println("********First Point choose************");
            countPolygonPoints();
        }
        return false;
    }

    private void countPolygonPoints() {

        if (arrayPoints.size() >= 3) {
            checkClick = true;
            PolygonOptions polygonOptions = new PolygonOptions();
            polygonOptions.addAll(arrayPoints);
            polygonOptions.strokeColor(Color.BLUE);
            polygonOptions.strokeWidth(7);
            polygonOptions.fillColor(Color.CYAN);
            Polygon polygon = googleMap.addPolygon(polygonOptions);
        }
    }

    @Override
    public void onMapClick(LatLng latLng) {

    }
}

Answer 1

您的代码中有多个问题。

首先，您使用了两个GoogleMap 变量并且也没有正确初始化。你只需要一个。

private GoogleMap mMap;

其次，为了使用setMyLocationEnabled，您需要在运行时向用户请求位置权限：

if (ContextCompat.checkSelfPermission(this, android.Manifest.permission.ACCESS_FINE_LOCATION) ==
        PackageManager.PERMISSION_GRANTED &&
        ContextCompat.checkSelfPermission(this, android.Manifest.permission.ACCESS_COARSE_LOCATION) ==
                PackageManager.PERMISSION_GRANTED) {
    mMap.setMyLocationEnabled(true);
    mMap.getUiSettings().setMyLocationButtonEnabled(true);
}

然后您将currentLocation 设置为null 并将这个空变量传递给您的新标记。而是使用实际的latLng：

mMap.addMarker(new MarkerOptions().position(latLng));

最后，您实际上并没有将任何项目添加到您的arrayPoints ArrayList。我假设你想做这样的事情：

arrayPoints.add(marker.getPosition());

完整的工作代码如下。

import android.content.pm.PackageManager;
import android.graphics.Color;
import android.os.Bundle;

import androidx.core.content.ContextCompat;
import androidx.fragment.app.FragmentActivity;

import com.google.android.gms.maps.GoogleMap;
import com.google.android.gms.maps.OnMapReadyCallback;
import com.google.android.gms.maps.SupportMapFragment;
import com.google.android.gms.maps.model.LatLng;
import com.google.android.gms.maps.model.Marker;
import com.google.android.gms.maps.model.MarkerOptions;
import com.google.android.gms.maps.model.PolygonOptions;

import java.util.ArrayList;

public class MapsActivity extends FragmentActivity
        implements OnMapReadyCallback,
        GoogleMap.OnMapClickListener,
        GoogleMap.OnMapLongClickListener,
        GoogleMap.OnMarkerClickListener {

    private GoogleMap mMap;
    private ArrayList<LatLng> arrayPoints = null;
    private boolean checkClick = false;


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

        arrayPoints = new ArrayList<>();
        SupportMapFragment mapFragment = (SupportMapFragment) getSupportFragmentManager()
                .findFragmentById(R.id.map);
        mapFragment.getMapAsync(this);
    }

    @Override
    public void onMapReady(final GoogleMap googleMap) {
        mMap = googleMap;

        if (ContextCompat.checkSelfPermission(this, android.Manifest.permission.ACCESS_FINE_LOCATION) ==
                PackageManager.PERMISSION_GRANTED &&
                ContextCompat.checkSelfPermission(this, android.Manifest.permission.ACCESS_COARSE_LOCATION) ==
                        PackageManager.PERMISSION_GRANTED) {
            mMap.setMyLocationEnabled(true);
            mMap.getUiSettings().setMyLocationButtonEnabled(true);
        }

        mMap.setOnMapClickListener(this);
        mMap.setOnMapLongClickListener(this);
        mMap.setOnMarkerClickListener(this);

        mMap.setOnMapClickListener(new GoogleMap.OnMapClickListener() {
            @Override
            public void onMapClick(final LatLng latLng) {
                if (!checkClick) {
                    mMap.addMarker(new MarkerOptions().position(latLng));
                }
            }
        });
    }

    @Override
    public void onMapLongClick(LatLng latLng) {
        mMap.clear();
        arrayPoints.clear();
        checkClick = false;
    }

    @Override
    public boolean onMarkerClick(Marker marker) {
        arrayPoints.add(marker.getPosition());
        System.out.println("Marker lat long=" + marker.getPosition());
        System.out.println("First position check" + arrayPoints.get(0));
        System.out
                .println("**********All arrayPoints***********" + arrayPoints);
        if (arrayPoints.get(0).equals(marker.getPosition())) {
            System.out.println("********First Point choose************");
            countPolygonPoints();
        }
        return false;
    }

    private void countPolygonPoints() {
        if (arrayPoints.size() >= 3) {
            checkClick = true;
            PolygonOptions polygonOptions = new PolygonOptions();
            polygonOptions.addAll(arrayPoints);
            polygonOptions.strokeColor(Color.BLUE);
            polygonOptions.strokeWidth(7);
            polygonOptions.fillColor(Color.CYAN);
            mMap.addPolygon(polygonOptions);
        }
    }

    @Override
    public void onMapClick(LatLng latLng) {

    }
}

希望这会有所帮助！