Question

我写了一个服务，提供GPS位置和位置更改我想比较位置信息与我的共享prefrence的值，并显示一个toast或alart对话但共享prefrence和tost dosnt工作因为上下文为null。这是我的代码和我的错误。请帮助我。谢谢

    public class Broadcastreceiver extends BroadcastReceiver {

    @Override
    public void onReceive(Context context, Intent intent) 
    {
        Intent service1=new Intent(context,GPSTracker.class);
        context.startService(service1);
        Log.i("service", "service"); 
    }

}

和

public class GPSTracker extends Service implements LocationListener 
        {
    SharedPreferences pref;
    @Override
    public void onCreate() 
    {
        pref=this.getSharedPreferences("mypref",0);
        super.onCreate();
    }

    @Override
    public void onStart(Intent intent, int startId) 
    {
        pref=this.getSharedPreferences("mypref",0);
        super.onStart(intent, startId);
    }
    private final Context mContext;

    // flag for GPS status
    boolean isGPSEnabled = false;

    // flag for network status
    boolean isNetworkEnabled = false;

    // flag for GPS status
    boolean canGetLocation = false;

    Location location; // location
    double latitude; // latitude
    double longitude; // longitude

    // The minimum distance to change Updates in meters
    private static final long MIN_DISTANCE_CHANGE_FOR_UPDATES = 10; // 10 meters

    // The minimum time between updates in milliseconds
    private static final long MIN_TIME_BW_UPDATES = 1000 * 60 * 1; // 1 minute

    // Declaring a Location Manager
    protected LocationManager locationManager;

    public GPSTracker(Context context) {
        this.mContext = context;
        getLocation();
    }

    public Location getLocation() 
    {
        try {
            locationManager = (LocationManager) mContext
                    .getSystemService(LOCATION_SERVICE);

            // getting GPS status
            isGPSEnabled = locationManager
                    .isProviderEnabled(LocationManager.GPS_PROVIDER);

            // getting network status
            isNetworkEnabled = locationManager
                    .isProviderEnabled(LocationManager.NETWORK_PROVIDER);

            if (!isGPSEnabled && !isNetworkEnabled) 
            {
                // no network provider is enabled
            } 
            else 
            {
                this.canGetLocation = true;
                if (isNetworkEnabled) 
                {
                    locationManager.requestLocationUpdates(
                            LocationManager.NETWORK_PROVIDER,
                            MIN_TIME_BW_UPDATES,
                            MIN_DISTANCE_CHANGE_FOR_UPDATES, this);
                    Log.d("Network", "Network");
                    if (locationManager != null) {
                        location = locationManager
                                .getLastKnownLocation(LocationManager.NETWORK_PROVIDER);
                        if (location != null) {
                            latitude = location.getLatitude();
                            longitude = location.getLongitude();
                        }
                    }
                }
                // if GPS Enabled get lat/long using GPS Services
                if (isGPSEnabled) 
                {
                    if (location == null) {
                        locationManager.requestLocationUpdates(
                                LocationManager.GPS_PROVIDER,
                                MIN_TIME_BW_UPDATES,
                                MIN_DISTANCE_CHANGE_FOR_UPDATES, this);
                        Log.d("GPS Enabled", "GPS Enabled");
                        if (locationManager != null) {
                            location = locationManager
                                    .getLastKnownLocation(LocationManager.GPS_PROVIDER);
                            if (location != null) {
                                latitude = location.getLatitude();
                                longitude = location.getLongitude();
                            }
                        }
                    }
                }
            }

        } catch (Exception e) {
            e.printStackTrace();
        }

        return location;
    }

    /**
     * Stop using GPS listener
     * Calling this function will stop using GPS in your app
     * */
    public void stopUsingGPS(){
        if(locationManager != null){
            locationManager.removeUpdates(GPSTracker.this);
        }       
    }

    /**
     * Function to get latitude
     * */
    public double getLatitude(){
        if(location != null){
            latitude = location.getLatitude();
        }

        // return latitude
        return latitude;
    }

    /**
     * Function to get longitude
     * */
    public double getLongitude(){
        if(location != null){
            longitude = location.getLongitude();
        }

        // return longitude
        return longitude;
    }

    /**
     * Function to check GPS/wifi enabled
     * @return boolean
     * */
    public boolean canGetLocation() {
        return this.canGetLocation;
    }

    /**
     * Function to show settings alert dialog
     * On pressing Settings button will lauch Settings Options
     * */
    public void showSettingsAlert(){
        AlertDialog.Builder alertDialog = new AlertDialog.Builder(mContext);

        // Setting Dialog Title
        alertDialog.setTitle("GPS is settings");

        // Setting Dialog Message
        alertDialog.setMessage("GPS is not enabled. Do you want to go to settings menu?");

        // On pressing Settings button
        alertDialog.setPositiveButton("Settings", new DialogInterface.OnClickListener() {
            public void onClick(DialogInterface dialog,int which) {
                Intent intent = new Intent(Settings.ACTION_LOCATION_SOURCE_SETTINGS);
                mContext.startActivity(intent);
            }
        });

        // on pressing cancel button
        alertDialog.setNegativeButton("Cancel", new DialogInterface.OnClickListener() {
            public void onClick(DialogInterface dialog, int which) {
            dialog.cancel();
            }
        });

        // Showing Alert Message
        alertDialog.show();
    }

    public void onLocationChanged(Location location)
    {
        Log.i("servise",Boolean.toString(pref.getBoolean("default", false)));
        if(pref.getBoolean("default", false)==true)
        {
            String defaultcity=pref.getString("defaultcity", null);
            double defaultlat=Double.parseDouble(pref.getString("defaultlat", null));
            double defaultlng=Double.parseDouble(pref.getString("defaultlng", null));
            Geocoder go=new Geocoder(GPSTracker.this);
            try 
            {
                List<Address> address=go.getFromLocation(latitude, latitude, 1);
                if(address.get(0).getAdminArea().equals(defaultcity))
                {

                }
                else
                {
                    if(latitude==defaultlat && longitude==defaultlng)
                    {

                    }
                    else
                    {
                        String s="Your current location has changed.It's better to change default place of praytimes application.";
                        Toast.makeText(this, s, Toast.LENGTH_LONG).show();
                        String TAG="locationchange";
                        Log.i(TAG,"Locationchanged");
                    }
                }
            } 
            catch (IOException e) 
            {
                e.printStackTrace();
            }
        }
    }

    public void onProviderDisabled(String provider) {
    }

    public void onProviderEnabled(String provider) {
    }

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

    @Override
    public IBinder onBind(Intent arg0) {
        return null;
    }

}

我的错误日志

Here is my error log

Answer 1

您的错误日志清楚地显示错误发生在GPSTracker方法中GPSTracker.onLocationChanged(...)的第214行。我们无法分辨出哪一行，但你可以，因此检查该行，查看该行上的对象引用，并解释为什么其中一行为空。

Answer 2

请尝试以下代码了解背景

context.getSystemService(LAYOUT_INFLATER_SERVICE)
getApplicationContext().getSharedPreferences(name, mode);

服务上下文为空

2 个答案: