位置服务关闭时应用程序崩溃。如何处理？

Question

我的应用在关闭位置服务时崩溃了。它给出了NullPointerException。我添加了粗略和精细位置的权限。现在我该如何处理？我想处理此异常并向用户提供“位置服务已关闭。请启用位置服务”的祝酒词。如果有人知道，请帮助。下面是我的代码。

package com.bddevs.ddbllocator;
import android.location.Location;
import android.location.LocationManager;
import android.os.Bundle;
import android.support.v7.app.ActionBarActivity;
import android.view.Menu;
import android.view.MenuItem;
import android.widget.Toast;

import com.google.android.gms.maps.CameraUpdateFactory;
import com.google.android.gms.maps.GoogleMap;
import com.google.android.gms.maps.SupportMapFragment;
import com.google.android.gms.maps.model.LatLng;
import com.google.android.gms.maps.model.MarkerOptions;

public class MainActivity extends ActionBarActivity {
private GoogleMap googleMap;;

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

}

private void setUpMapIfNeeded() {
    if (googleMap == null) {
        googleMap = ((SupportMapFragment) getSupportFragmentManager()
                .findFragmentById(R.id.map)).getMap();
        if (googleMap != null) {
            setUpMap();
        }
    }
}

private void setUpMap() {
    googleMap.setMyLocationEnabled(true);
    LocationManager locationmanager = (LocationManager) getSystemService(LOCATION_SERVICE);
    String provider = LocationManager.NETWORK_PROVIDER;

    Location myLocation = locationmanager.getLastKnownLocation(provider);
    googleMap.setMapType(GoogleMap.MAP_TYPE_TERRAIN);
    double latitude = myLocation.getLatitude();
    double longitude = myLocation.getLongitude();
    LatLng latlng = new LatLng(latitude, longitude);
    googleMap.moveCamera(CameraUpdateFactory.newLatLng(latlng));
    googleMap.animateCamera(CameraUpdateFactory.zoomTo(15));


}

@Override
public boolean onCreateOptionsMenu(Menu menu) {

    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.main, menu);
    return true;

}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    // Handle action bar item clicks here. The action bar will
    // automatically handle clicks on the Home/Up button, so long
    // as you specify a parent activity in AndroidManifest.xml.
    int id = item.getItemId();
    if (id == R.id.action_settings) {
        return true;
    }
    return super.onOptionsItemSelected(item);
}

}

如果可以，请帮忙。