移动相机方法上的谷歌地图空对象引用[关闭]

Posted 2023-05-06

【中文标题】移动相机方法上的谷歌地图空对象引用[关闭]

【英文标题】：Google Maps null object reference on move camera method [closed]

【发布时间】：2021-08-09 15:36:03

【问题描述】：

我正在尝试使用谷歌地图，即使用标记获取当前位置、搜索位置并根据搜索到的位置添加标记。我收到此错误

尝试在空对象引用上调用虚拟方法“void com.google.android.gms.maps.GoogleMap.moveCamera(com.google.android.gms.maps.CameraUpdate)”

我不明白为什么我会得到这个，我认为我实例化我的 GoogleMap 变量可能有问题，但我不知道如何解决这个问题。这是我的代码：

public class MapsActivity extends FragmentActivity implements OnMapReadyCallback 

private GoogleMap mMap;
Location mLocation;
Location sLocation;
FusedLocationProviderClient client;
private static final int Request_Code = 101;
EditText txtSrch;
ImageButton btnSrch;


protected void onCreate(Bundle savedInstanceState) 
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_maps);
    // Obtain the SupportMapFragment and get notified when the map is ready to be used.
    client = LocationServices.getFusedLocationProviderClient(this);
    getLastLocation();

btnSrch.setOnClickListener(new View.OnClickListener() 
        @Override
        public void onClick(View v) 
            geolocate();
        
    );

我做了这些方法：

private void geolocate()
       String search = txtSrch.getText().toString().trim();
       Geocoder geocoder = new Geocoder(MapsActivity.this);
       List<Address> list = new ArrayList<>();

   try
        list = geocoder.getFromLocationName(search, 1);


   
   catch (IOException e)
        e.printStackTrace();
   

   if(list.size() > 0)
       Address address = list.get(0);
       moveCamera(new LatLng(address.getLatitude(), address.getLongitude()), 6, "Searched Location");
   








private void moveCamera(LatLng latLng, float zoom, String title)
        mMap.moveCamera(CameraUpdateFactory.newLatLngZoom(latLng, zoom));
        MarkerOptions options = new MarkerOptions()
                .position(latLng)
                .title(title);
        mMap.addMarker(options);
   

private void getLastLocation() 
    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[]
                android.Manifest.permission.ACCESS_FINE_LOCATION, Request_Code);
        return;
    
    Task<Location> task = client.getLastLocation();
    task.addOnSuccessListener(new OnSuccessListener<Location>() 
        @Override
        public void onSuccess(Location location) 
            if(location != null)
                mLocation = location;
                Toast.makeText(getApplicationContext(),mLocation.getLatitude()+""+mLocation.getLongitude(), Toast.LENGTH_SHORT).show();
                double myLong = mLocation.getLongitude();
                double myLat = mLocation.getLatitude();
                SupportMapFragment supportMapFragment = (SupportMapFragment) getSupportFragmentManager().findFragmentById(R.id.map);
                supportMapFragment.getMapAsync(MapsActivity.this);
            
        
    );


@Override
public void onMapReady(GoogleMap googleMap) 
   LatLng latLng = new LatLng(mLocation.getLatitude(), mLocation.getLongitude());
   MarkerOptions markerOptions = new MarkerOptions().position(latLng).title("You Are Here");
   googleMap.animateCamera(CameraUpdateFactory.newLatLng(latLng));
   googleMap.animateCamera(CameraUpdateFactory.newLatLngZoom(latLng, 6));
   googleMap.addMarker(markerOptions);


@Override
public void onRequestPermissionsResult(int requestCode, @NonNull String[] permissions, @NonNull int[] grantResults) 
    switch (requestCode)
        case Request_Code:
            if(grantResults.length>0 && grantResults[0] == PackageManager.PERMISSION_GRANTED)
                getLastLocation();
            
            break;
    

老实说，我认为实例化 mMap 变量存在问题，我只是不知道该怎么办。任何帮助将不胜感激

【问题讨论】：

这能回答你的问题吗？ What is a NullPointerException, and how do I fix it?

I just don't know what to do about it 尝试使用时应确保它不为空

看起来你从未初始化过mMap

【参考方案1】：

是的。你是对的。需要启动你的 mMap。

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


//And before move camera, check mMap is not null

private void moveCamera(LatLng latLng, float zoom, String title)
if(mMap!=null)
        mMap.moveCamera(CameraUpdateFactory.newLatLngZoom(latLng, zoom));
        MarkerOptions options = new MarkerOptions()
                .position(latLng)
                .title(title);
        mMap.addMarker(options);