当用户按下“后退”按钮或做出新的意图时，停止位置侦听器活动

package com.example.locationbeeper;

import android.location.Criteria;
import android.location.Location;
import android.location.LocationListener;
import android.location.LocationManager;
import android.media.AudioManager;
import android.media.ToneGenerator;
import android.os.Bundle;
import android.support.v4.app.FragmentActivity;



public class MainActivity extends FragmentActivity implements LocationListener {

    LocationManager locationManager;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        // set up location manager
        locationManager = (LocationManager) getSystemService(LOCATION_SERVICE);
        Criteria criteria = new Criteria();
        String bestProvider = locationManager.getBestProvider(criteria, true);
        Location location = locationManager.getLastKnownLocation(bestProvider);
        if (location != null) {
            onLocationChanged(location);
        }
        locationManager.requestLocationUpdates(bestProvider, 200, 5, this);  // time in miliseconds, distance in meters (Distance drains battry life) originally set to 20000 and 0
    }

    @Override
    public void onLocationChanged(Location location) {
        // beep when location changed
        final ToneGenerator tg = new ToneGenerator(AudioManager.STREAM_NOTIFICATION, 100);
        tg.startTone(ToneGenerator.TONE_PROP_BEEP);
    }

    @Override
    public void onSaveInstanceState(Bundle outState) {

    }

    @Override
    public void onProviderDisabled(String provider) {
        // TODO Auto-generated method stub
    }

    @Override
    public void onProviderEnabled(String provider) {
        // TODO Auto-generated method stub
    }

    @Override
    public void onStatusChanged(String provider, int status, Bundle extras) {
        // TODO Auto-generated method stub
    }

    @Override
    public void onPause(){
        super.onPause();
        
        locationManager = null;
    }


}