Not receiving location data from thread

问题:

I'm trying to send text messages containing the users location every so often using the timer. Initially, I ran into a nullpointerexception which was due to a simple mistake I made. Once this was fixed everything seemed to be running fine. However, it never gets my location, so, the text that keeps sending is saying "Could Not receive location".

What I am asking is why is it not getting my location? And what can I do to fix the problem?

There are no logcat errors and I am using two emulators to test this app (send text from one to the other). If you could provide any help or resolution it would be greatly appreciated! And if I'm overlooking something that may seem to be very simple please alert me that I am doing so. Thanks!

Here's the code:

    public class MessageService extends Service{
int counter = 0;
private Timer timer = new Timer();
public String textTime, phoneNumber;
public int updateInterval;
int lat, lng;
String coordinates, latitude, longitude;
LocationManager locationManager;

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

@Override
public int onStartCommand(Intent intent, int flags, int startId){
    //receives the intent extras from the calling intent
    textTime = intent.getStringExtra("textTime");
    phoneNumber = intent.getStringExtra("phone");

    phoneNumber = "5556";

    //the following if statement has to do with transferring the string textTime into a number that can be used
    if (textTime.equals("15 Minutes")) {
        updateInterval = (15 * (60000));
    }else if (textTime.equals("30 Minutes")) {
        updateInterval = (30 * (60000));
    }else if (textTime.equals("1 Hour")){
        updateInterval = (60 * (60000));
    }else {
        updateInterval = (15 * (60000));
    }

    locationManager = (LocationManager) this.getSystemService(Context.LOCATION_SERVICE);

    new Thread(){
        public void run(){
            Looper.prepare();
            // Define a listener that responds to location updates
            LocationListener locationListener = new LocationListener() {
                public void onLocationChanged(Location location) {
                  // Called when a new location is found by the network location provider.
                  //makeUseOfNewLocation(location);
                    lat = (int) (location.getLatitude() * 1E6);
                    lng = (int) (location.getLongitude() * 1E6);

                    latitude = Integer.toString(lat);
                    longitude = Integer.toString(lng);

                    coordinates = "Coordinates: " + latitude + ", " + longitude + ". Latitude: " + latitude + " Longitude: " + longitude + ". Respond 'END' to stop texts."; 
                }

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

                public void onProviderEnabled(String provider) {}

                public void onProviderDisabled(String provider) {}
              };

              Looper.loop();

              if (locationManager.isProviderEnabled(LocationManager.GPS_PROVIDER)){
                    locationManager.requestLocationUpdates(LocationManager.GPS_PROVIDER, 0, 0, locationListener);
              }else{
                    locationManager.requestLocationUpdates(LocationManager.NETWORK_PROVIDER, 0, 0, locationListener);
              }

        }
    }.start();


    //the following method should use a timer to send a sms message in a timed interval. It also should implement using a different thread
    doSomethingRepeatedly();

    return START_STICKY;

}

public void doSomethingRepeatedly(){
    timer.scheduleAtFixedRate(new TimerTask() {
        public void run() {
            //the following code should be what is done repeatedly
            //Log.d("MessageService", String.valueOf(++counter));

            sendSmsMessage();
        }
    }, 0, updateInterval);
}

//the following code handles sending the text message
public void sendSmsMessage(){
    SmsManager sms = SmsManager.getDefault();
    if (coordinates == null || coordinates.equals("")){
        coordinates = "Could Not Receive Location";
    }

    sms.sendTextMessage(phoneNumber, null, coordinates , null, null);

}

public void onDestroy() {
    super.onDestroy();

    if (timer != null) {
        timer.cancel();
    }
}




}//end of service

回答1:

Your LocationListener is probably being destroyed before onLocationChanged() can be called. Your Service should implement the LocationListener itself.

---

public class MessageService extends Service implements LocationListener {
    int counter = 0;
    private Timer timer = new Timer();
    public String textTime, phoneNumber;
    public int updateInterval;
    int lat, lng;
    String coordinates, latitude, longitude;
    LocationManager locationManager;

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

    @Override
    public int onStartCommand(Intent intent, int flags, int startId){
        //receives the intent extras from the calling intent
        textTime = intent.getStringExtra("textTime");
        phoneNumber = intent.getStringExtra("phone");

        phoneNumber = "5556";

        //the following if statement has to do with transferring the string textTime into a number that can be used
        if (textTime.equals("15 Minutes")) {
            updateInterval = (15 * (60000));
        }else if (textTime.equals("30 Minutes")) {
            updateInterval = (30 * (60000));
        }else if (textTime.equals("1 Hour")){
            updateInterval = (60 * (60000));
        }else {
            updateInterval = (15 * (60000));
        }

        locationManager = (LocationManager) this.getSystemService(Context.LOCATION_SERVICE);

        if (locationManager.isProviderEnabled(LocationManager.GPS_PROVIDER)){
            locationManager.requestLocationUpdates(LocationManager.GPS_PROVIDER, 0, 0, this);
        }else{
            locationManager.requestLocationUpdates(LocationManager.NETWORK_PROVIDER, 0, 0, this);
        }

        //the following method should use a timer to send a sms message in a timed interval. It also should implement using a different thread
        doSomethingRepeatedly();

        return START_STICKY;

    }

    public void doSomethingRepeatedly(){
        timer.scheduleAtFixedRate(new TimerTask() {
            public void run() {
                //the following code should be what is done repeatedly
                //Log.d("MessageService", String.valueOf(++counter));

                sendSmsMessage();
            }
        }, 0, updateInterval);
    }

    //the following code handles sending the text message
    public void sendSmsMessage(){
        SmsManager sms = SmsManager.getDefault();
        if (coordinates == null || coordinates.equals("")){
            coordinates = "Could Not Receive Location";
        }

        sms.sendTextMessage(phoneNumber, null, coordinates , null, null);

    }

    public void onDestroy() {
        super.onDestroy();

        if (timer != null) {
            timer.cancel();
        }
    }

    @Override
    public void onLocationChanged(Location location) {
        // Called when a new location is found by the network location provider.
        //makeUseOfNewLocation(location);
        lat = (int) (location.getLatitude() * 1E6);
        lng = (int) (location.getLongitude() * 1E6);

        latitude = Integer.toString(lat);
        longitude = Integer.toString(lng);

        coordinates = "Coordinates: " + latitude + ", " + longitude + ". Latitude: " + latitude + " Longitude: " + longitude + ". Respond 'END' to stop texts."; 
    }

    @Override
    public void onProviderDisabled(String provider) {}

    @Override
    public void onProviderEnabled(String provider) {}

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

回答2:

I can't quite understand your code, however if you are expecting one thread to update the coordinates field and then another thread to read the contents of coordinates, you need to make the coordinates field volatile.

Any values shared between threads need to be synchronized or somehow cross a memory barrier before they are visible.