Question

当我尝试运行我的代码时，我总是收到此错误：

java.lang.NullPointerException：尝试在空对象引用上调用虚拟方法'android.content.res.Resources android.content.Context.getResources（）'

我可以在我的模拟器中手动配置坐标，但仍然会出现同样的错误。

以下是获取位置坐标的代码。

LocationTracker.java

    public class LocationTracker extends MainActivity implements LocationListener {
    MainActivity activity;
    Context context;
    Location location;
    LocationManager lm;

    double lat,longi;


    boolean isGpsEnabled = false;
    boolean isNetworkEnabled = false;
    boolean canGetNetworkLocation = false;

    public LocationTracker (Context context) {
        this.context=context;
        getGPSLocation();
    }


    public Location getGPSLocation() {

        lm = (LocationManager) context.getSystemService(Context.LOCATION_SERVICE);
        isGpsEnabled = lm.isProviderEnabled(LocationManager.GPS_PROVIDER);


       if (isGpsEnabled) {

           /** Check for RUNTIME PERMISSION */
           if (ContextCompat.checkSelfPermission(context, Manifest.permission.ACCESS_FINE_LOCATION) == PackageManager.PERMISSION_GRANTED || ContextCompat.checkSelfPermission(context, Manifest.permission.ACCESS_COARSE_LOCATION) == PackageManager.PERMISSION_GRANTED) {

               if (location == null) {      //Request for NEW DATA coming from GPS
                   lm.requestLocationUpdates(LocationManager.GPS_PROVIDER,0,0,this);

                   if (lm != null) {    //Retrieve data from the earlier
                       location=lm.getLastKnownLocation(LocationManager.GPS_PROVIDER);

                       if (location != null) {
                            lat= location.getLatitude();
                            longi= location.getLongitude();
                       }
                   }
               }



           }else {
               ActivityCompat.requestPermissions(activity,new String[]{android.Manifest.permission.ACCESS_COARSE_LOCATION, Manifest.permission.ACCESS_FINE_LOCATION},123);
           }

       }else {

       }

    return location;
       }

    /** GET LATITUDE METHOD */
        public double getLatitude() {
            if (location != null) {
                lat=location.getLatitude();
            }

            return lat;
        }

    /** GET LONGITUDE METHOD */
        public double getLongitude () {
            if (location != null) {
                longi=location.getLongitude();
            }
            return longi;
        }

    @Override
    public void onLocationChanged(Location location) {
        lat= location.getLatitude();
        longi=location.getLongitude();
    }

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

    }

    @Override
    public void onProviderEnabled(String provider) {

    }

    @Override
    public void onProviderDisabled(String provider) {

    }
}

用于显示坐标的

和 MainActivity类。

public class MainActivity extends AppCompatActivity {
Context context;
DBHelper helper;
LocationTracker tracker;



TextView contactsTv,sendEmergencyTv;
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    helper=new DBHelper(getApplicationContext());


    /**
     * OnClick Listener in android
      */
    contactsTv=(TextView) findViewById(R.id.tv_createContacts);
    contactsTv.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            Intent intent= new Intent(MainActivity.this, ContactsActivity.class); //redirect to the COntacts dsadsadsa

            startActivity(intent);
        }
    });

sendEmergencyTv=(TextView)findViewById(R.id.tv_sendEmergency);
    sendEmergencyTv.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            tracker= new LocationTracker(MainActivity.this);
            double lat,longi;

            lat= tracker.getLatitude();
            longi= tracker.getLongitude();

            Toast.makeText(context,"Latitude: "+lat+ "Longitude: "+longi,Toast.LENGTH_LONG).show();
        }
    });
}

}

顺便说一下，我不确定在RequestPermission参数中的LocationTracker类中放置一个MainActivity实例。

Answer 1

下面：

ActivityCompat.requestPermissions(activity,
           new String[]{android.Manifest.permission.ACCESS_COARSE_LOCATION,
                       Manifest.permission.ACCESS_FINE_LOCATION},123);

由于activity为null，

行导致问题。

使用((Activity)context)代替activity。例如：

ActivityCompat.requestPermissions(((Activity)context),
           new String[]{android.Manifest.permission.ACCESS_COARSE_LOCATION,
                       Manifest.permission.ACCESS_FINE_LOCATION},123);

注意：

另外，因为LocationTracker是普通的java类，所以不需要在其中扩展Activity。

Answer 2

在第

行

ActivityCompat.requestPermissions(activity, new String[]{android.Manifest.permission.ACCESS_COARSE_LOCATION, Manifest.permission.ACCESS_FINE_LOCATION},123);

activity为空，因为它从未被赋值。

将LocationTracker构造函数更改为Activity而不是Context作为参数。

private Activity activity;

public LocationTracker (Activity activity) {
    this.activity = activity;
    getGPSLocation();
}

注意：请务必在该活动中实施onRequestPermissionsResult，以了解您是否已获得授权。

无法检索位置的经度纬度

2 个答案: