java - 尝试对空对象引用调用虚拟方法 'double android.location.Location.getLatitude()'

Question

为什么我不知道，我犯了这个错误。程序之前运行过。但现在我犯了这个错误。谢谢你的帮助...

MenuActivity.java:

final Context context = this;
private LocationManager mLocationManager;
private String PROVİDER = LocationManager.GPS_PROVIDER;
private GoogleMap googleHarita;
Location mLocation;

public class MenuActivity extends FragmentActivity {
    final Context context = this;
    private static final int CAMERA_REQUEST = 1888;

    TextView e_kor, b_kor, acikAdres;
    Fragment harita;
    RadarView mRadarView = null;

    private LocationManager mLocationManager;
    private String PROVİDER = LocationManager.GPS_PROVIDER;
    private GoogleMap googleHarita=null;

    Location mLocation = null;
    TelephonyManager telemamanger;
    String getSimSerialNumber;



    @TargetApi(Build.VERSION_CODES.HONEYCOMB)
    @SuppressLint("NewApi")
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        // TODO Auto-generated method stub
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_menu);

        // telefon numarası nesnesi
        telemamanger = (TelephonyManager) getSystemService(TELEPHONY_SERVICE);
        e_kor = (TextView) findViewById(R.id.enlmkor);
        b_kor = (TextView) findViewById(R.id.bylmkor);
        acikAdres = (TextView) findViewById(R.id.acikAdres);

        // resim metodu
        mRadarView = (RadarView) findViewById(R.id.radarView);

        // radar çalıştırma metodları
        mRadarView.setShowCircles(true);
        mRadarView.startAnimation();

        // Konum-lokasyon kodları
        mLocationManager = (LocationManager) getSystemService(Context.LOCATION_SERVICE);
        final Location mLocation = mLocationManager
                .getLastKnownLocation(PROVİDER);

        if (googleHarita == null) {
            googleHarita = ((SupportMapFragment) getSupportFragmentManager()
                    .findFragmentById(R.id.haritafragment)).getMap();

            if (googleHarita != null) {
                LatLng koordinat = new LatLng(mLocation.getLatitude(),
                        mLocation.getLongitude());
                googleHarita.addMarker(new MarkerOptions().position(koordinat));
                googleHarita.moveCamera(CameraUpdateFactory.newLatLngZoom(
                        koordinat, 10));
            }
        }

        showLocation(mLocation);
        new GetAddressTask().execute(mLocation);

    }

    // Lokasyon işlemleri
    private void showLocation(Location location) {
        if (location == null) {
            Toast.makeText(getApplicationContext(), "Konum Bulunamadı",
                    Toast.LENGTH_SHORT).show();
        } else {
            e_kor.setText(location.getLatitude() + "");
            b_kor.setText(location.getLongitude() + "");
        }
    }   

    @Override
    protected void onPause() {
        super.onPause();
        mLocationManager.removeUpdates(listener);
    }

    @Override
    protected void onResume() {
        super.onResume();
        mLocationManager.requestLocationUpdates(PROVİDER, 0, 0, listener);
    }



    // Konum listener
    private LocationListener listener = new LocationListener() {
        @Override
        public void onLocationChanged(Location location) {
            showLocation(location);
        }

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

        @Override
        public void onProviderEnabled(String provider) {
        }

        @Override
        public void onProviderDisabled(String provider) {
        }
    };

public class GetAddressTask extends AsyncTask<Location, Void, String> {

    @Override
    protected String doInBackground(Location... locations) {
        Geocoder geocoder = new Geocoder(MenuActivity.this);
        Location location = locations[0];
        List<Address> addresses;
        String addrStr = null;
        try {
            addresses = (List<Address>) geocoder.getFromLocation(
                    location.getLatitude(), location.getLongitude(), 5);
            Address addr = addresses.get(0);
            addrStr = addr.getAddressLine(0) + ", " + addr.getAdminArea()
                    + ", " + addr.getCountryName();
        } catch (IOException e) {
            e.printStackTrace();
        }
        return addrStr;
    }

    @Override
    protected void onPostExecute(String result) {
        acikAdres.setText(result);
    }
}

我的日志猫:

11-10 02:20:50.508: E/AndroidRuntime(29376): FATAL EXCEPTION: main
11-10 02:20:50.508: E/AndroidRuntime(29376): Process: com.gpsacilbildirim, PID: 29376
11-10 02:20:50.508: E/AndroidRuntime(29376): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.gpsacilbildirim/com.gpsacilbildirim.MainActivity}: java.lang.RuntimeException: Unable to start activity ComponentInfo{com.gpsacilbildirim/com.gpsacilbildirim.MenuActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'double android.location.Location.getLatitude()' on a null object reference
11-10 02:20:50.508: E/AndroidRuntime(29376):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2658)
11-10 02:20:50.508: E/AndroidRuntime(29376):    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2723)
11-10 02:20:50.508: E/AndroidRuntime(29376):    at android.app.ActivityThread.access$900(ActivityThread.java:172)
11-10 02:20:50.508: E/AndroidRuntime(29376):    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1422)

Answer 1

您在 logcat 中看到的异常表明您的 Activity 的 onCreate 方法存在问题。

有趣的部分是: java.lang.NullPointerException:尝试在空对象引用上调用虚拟方法“double android.location.Location.getLatitude()”。它告诉您，您调用 getLatitude() 的任何对象都是 null。

查看方法的主体，只能在这一行上进行:LatLng koordinat = new LatLng(mLocation.getLatitude(), mLocation.getLongitude());。因此，您可以判断崩溃是由 mLocation 为 null 引起的。

您正在初始化mLocation，如下所示:mLocationManager.getLastKnownLocation(PROVICADER);。 documentation告诉您如果禁用提供程序，则可能会获得 null 返回值。

这应该回答“为什么”。现在您可以考虑为您的应用程序解决此问题的最佳方法。您可以尝试其他提供商吗？如果没有启用任何提供程序，您可以默认为通用位置吗？您是否想要显示一条错误消息，指示用户启用位置服务并提供重试的方法？