android getContentResolver（）订单问题

Question

tap 我试图在MyLocationListenerActivity中获取ContentResolver，以访问在此处实现为LogContentProvider的数据库。我已经在MainActivity中将MyLocationListenerActivity注册到locationManager。

public class MainActivity extends AppCompatActivity {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
    }

    public void trackingServiceButtonOnClick(View v) {
        startActivity(new Intent(MainActivity.this, 
    MyLocationListenerActivity.class));
    LocationManager locationManager = (LocationManager) getSystemService(Context.LOCATION_SERVICE);
    MyLocationListenerActivity myLocationListener = new MyLocationListenerActivity();

    try {
        locationManager.requestLocationUpdates(LocationManager.GPS_PROVIDER, 1, 1, myLocationListener);
    } catch (SecurityException e) {
        Log.d("debug", e.toString());
    }
    if (getContentResolver() != null) {
        Log.d("debug", "I can get content resolver");
    }
}

并且在MyLocationListenerActivity中，如果我想在onCreate（）中获取getContentResolver（），那很好，但是，如果我尝试在onLocationChanged中获取getContentResolver，则会出现错误“在空对象引用上获取contentResolver（）”，有人知道为什么吗这会发生吗？

public class MyLocationListenerActivity extends AppCompatActivity implements LocationListener {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_my_location_listener);
        // test() works fine here
        test();
    }

    public void test() {
        getContentResolver();
    }
    @Override
    public void onLocationChanged(Location location) {
        // error will happen here
        test();
    }
    @Override
    public void onStatusChanged(String provider, int status, Bundle extras) {
    }
    @Override
    public void onProviderEnabled(String provider) {
    }
    @Override
    public void onProviderDisabled(String provider) {
    }