My app checks at a specific time whether a user is at a given location. I use the alarm manager to start a service that makes this call:
locationManager.requestLocationUpdates(bestProvider, 0, 0, listener);
And also checks:
locationManager.getLastKnownLocation(bestProvider);
But I'm having problems when running on a real device. For one thing, getLastKnownLocation is most likely the last place the GPS was on, which could be anywhere (i.e., it could be miles from the user's current location). So I'll just wait for requestLocationUpdates callbacks, and if they aren't there within two minutes, remove the listener and give up, right?
Wrong, because if the user's location is already stable (i.e., they've used GPS recently and haven't moved) then my listener will never be called because the location doesn't change. But the GPS will run until my listener is removed, draining the battery...
What is the right way to get the current location without mistaking an old location for the current location? I don't mind waiting a few minutes.
EDIT: It's possible that I'm wrong about the listener not being called, it may just take a little longer than I thought... Hard to say. I'd appreciate a definitive answer still.
The code may be something like that:
public class MyLocation {
Timer timer1;
LocationManager lm;
public boolean getLocation(Context context)
{
lm = (LocationManager) context.getSystemService(Context.LOCATION_SERVICE);
lm.requestLocationUpdates(LocationManager.GPS_PROVIDER, 0, 0, locationListenerGps);
timer1=new Timer();
timer1.schedule(new GetLastLocation(), 20000);
return true;
}
LocationListener locationListenerGps = new LocationListener() {
public void onLocationChanged(Location location) {
timer1.cancel();
lm.removeUpdates(this);
//use location as it is the latest value
}
public void onProviderDisabled(String provider) {}
public void onProviderEnabled(String provider) {}
public void onStatusChanged(String provider, int status, Bundle extras) {}
};
class GetLastLocation extends TimerTask {
#Override
public void run() {
lm.removeUpdates(locationListenerGps);
Location location=lm.getLastKnownLocation(LocationManager.NETWORK_PROVIDER);
//use location as we have not received the new value from listener
}
}
}
We start the listener and wait for update for some time (20 seconds in my example). If we receive update during this time we use it. If we don't receive an update during this time we use getLastKnownLocation value and stop the listener.
You can see my complete code here What is the simplest and most robust way to get the user's current location on Android?
EDIT (by asker): This is most of the answer, but my final solution uses a Handler instead of a Timer.
If the user's location is already stable, then getLastKnownLocation will return the current location. I'd call getLastKnownLocation first, look at the timestamp (compare Location.getElapsedRealTimeNanos() with SystemClock.elapsedRealTimeNanos()) then register a listener if the fix is too old.
Related
OLD QUESTION:
I'm trying to get my device's location coordinates and I've followed all the steps that I've found in multiple areas while researching. I've set up a LocationManager and used the requestLocationUpdates function that is tied to a LocationListener. However, the LocationListener does not respond. I've tried debugging as well as walking around outside in order for the onChangedLocation function to execute but nothing happens. In debugging the requestLocationUpdates function for my LocationManager is executed but the LocationListener is never executed.
locationManager = (LocationManager) getSystemService(LOCATION_SERVICE);
textView = (TextView) findViewById(R.id.textView);
textView2 = (TextView) findViewById(R.id.textView2);
locationListener = new myLocationListener();
textView.setText("Longitude", TextView.BufferType.NORMAL);
textView2.setText("Latitude", TextView.BufferType.NORMAL);
locationManager.requestLocationUpdates(LocationManager.GPS_PROVIDER, 3000, 0, locationListener);
requestLocationUpdates
Above is the use of the requestLocationUpdates function.
private class myLocationListener implements LocationListener {
#Override
public void onLocationChanged(Location location) {
//Log.e("Latitude: ", "" + location.getLatitude());
//Log.e("Longitude: ", "" + location.getLongitude());
if(location != null)
{
textView.setText(Double.toString(location.getLongitude()), TextView.BufferType.NORMAL);
textView2.setText(Double.toString(location.getLatitude()), TextView.BufferType.NORMAL);
}
else
{
textView.setText("No Location", TextView.BufferType.NORMAL);
textView2.setText("No Location", TextView.BufferType.NORMAL);
}
Toast.makeText(getApplicationContext(),"onLocationChanged Success",Toast.LENGTH_LONG).show();
}
#Override
public void onStatusChanged(String provider, int status, Bundle extras) {
}
#Override
public void onProviderEnabled(String provider) {
}
#Override
public void onProviderDisabled(String provider) {
Intent intent = new Intent(Settings.ACTION_LOCATION_SOURCE_SETTINGS);
startActivity(intent);
}
}
myLocationListener
This is myLocationListener that implements LocationListener. I've added a little bit of extra code for testing purposes. The toast would never pop up so it appears as though this code is never executed. If anyone could help me out with this I would really appreciate it.
Thank you!
NEW QUESTION:
After continuing on developing in this page while waiting for a response I noticed that it takes about a minute for the location services to actually begin working. So, now my question is: how do I overcome the obstacle of a user having to wait to use the app? I've seen apps that use location based content and it does not take that long. I know that there is the getLastKnownLocation function but what if a user travels 50 miles before opening the app again? Any help on this would be appreciated. Thank you!
Each device which makes location request for gps, has to wait until gps hardware become warm. The wait time changes by device and where you stay. If you are inside a building, this time could take 1 minute or more.
To avoid wait, you can use getLastKnownLocation method, if returns a cached location, check location's date via getTime method. Determine yourself, is it old location by your scenario ?
if it's too old location, you have to make location request and wait.
I have been trying to find the location obtained by GPS_Provider and Network_Provider for every 5 minutes and at the same time stamp for the two values obtained at any specific time.
I tried using the following location strategy given
LocationManager locationManager = (LocationManager) this.getSystemService(Context.LOCATION_SERVICE);
// 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);
}
public void onStatusChanged(String provider, int status, Bundle extras) {}
public void onProviderEnabled(String provider) {}
public void onProviderDisabled(String provider) {}
};
// Register the listener with the Location Manager to receive location updates
locationManager.requestLocationUpdates(LocationManager.NETWORK_PROVIDER, 300000, 0, locationListener)
locationManager.requestLocationUpdates(LocationManager.GPS_PROVIDER,300000, 0, locationListener)
But here the Location Manager will call the onLocationChanged() method of the listener if the time since last location update is greater than the notificationInterval.
This brings me some time stamp difference between values generated by GPS_Provider and Network_Provider after every 5 minutes.Is there any way such that I can find the location that GPS_Provider and Network_Provider generate at a same time stamp.
Example:
Now: GPS_Provider(lat,long) at 09:35:12 , Network_Provider(lat,long) at 09:35:14
I need: GPS_Provider(lat,long) at 09:35:12 , Network_Provider(lat,long) at 09:35:12
In short, no.
The location api doesn't work in a synchronous way, meaning you have no guarantee when exactly you'll get the update. the time frames which you supply state the maximum interval between updates.
Having said that, you could start the updates with lower interval (such as 50ms) and get a bunch of updates, sort them by the second of the timestamp and get the ones which have the same value.
Update
You can use the getLastKnownLocation method to get the last location known by the provider, check the docs here.
My app uses google map to show user's location in real time. Therefore I would like it to be updated with every data change on my Parse server.
I've looked all over the net and as I see it I have 3 options:
using syncAdapter - the problem is that everywhere it is written that it does not meant for real time data transfer (I don't really understand why), on other hand it must be more efficient than updating every 5 sec.
using asyncTask - the problem is that it probably consumes a lot of battery and data usage to run it every 5 sec.
using service - same problem as asyncTask.
As i'm very confused, please help me understand what is the appropriate way to implement my real time map.
Thank's all
The best way i know is to use LocationListener to update the location only if it has been changed. You can use the onLocationChanged() method to update the location.
public class LocationHelper {
private LocationManager locationManager;
private Location currentLocation;
public LocationHelper(Context context) {
locationManager = (LocationManager) context.getSystemService(Context.LOCATION_SERVICE);
locationManager.removeUpdates(locationListener);
locationManager.requestLocationUpdates(LocationManager.NETWORK_PROVIDER, 0, 0, locationListener);
}
public void setLocation(Location location) {
currentLocation = location;
}
private final LocationListener locationListener = new LocationListener() {
#Override
public void onLocationChanged(Location location) {
setLocation(location);//Only update location if it has changed.
}
#Override
public void onStatusChanged(String provider, int status, Bundle extras) {}
#Override
public void onProviderEnabled(String provider) {}
#Override
public void onProviderDisabled(String provider) {}
};
}
If the location hasn't been changed, you can just remember the last known location.
When I open my app and press a button I want it to request a single location solely from the GPS to get the most accurate location possible. I did the following:
LocationManager mlocManager = (LocationManager)GetActivity().getSystemService(Context.LOCATION_SERVICE);
if (mlocManager.isProviderEnabled(LocationManager.GPS_PROVIDER)) {
LocationListener mlocListener = new LocationManagerHelper(...);
Criteria criteria = new Criteria();
criteria.setAccuracy(Criteria.ACCURACY_FINE);//accuracy fine calls accuracy high
mlocManager.requestSingleUpdate(criteria,mlocListener,null);
}
When I open the GPS inside my house, go to the window and !only then! I press that button, I get a location far from me with the accuracy of 300-900! I thought that maybe a second request will improve it but even 4-5 requests remains on the same spot with the same low accuracy, also, the other requests are very fast as if it didn't really ask the GPS again for a location but took it from the cache of some sort.
If I open the GPS while I'm already near the window, the location is better and sometimes I get to accuracy of 20-30, the thing is, that even then, sometimes the accuracy is not that high so I was wondering how can I initialize the GPS/location so if I get a bad accuracy in the first try, at least it will give me a better one on the second try.
Thanks
It sounds like the LocationManager is using cached data like you suggest.
You could try using the requestLocationUpdates() method on LocationManager instead. If you just require the one location fix, then disable the locationUpdates by calling the removeUpdates() method
after first callback to LocationListener.
This approach will also allow you to wait for a location that has sufficient accuracy. The following code shows how to filter locations if the accuracy is too low for your needs.
LocationListener locationListener = new LocationListener() {
public void onLocationChanged(Location location) {
if (location.getAccuracy() > THRESHOLD) {
return;
}
//Act on location data here
//Then remove the updates once done
mlocManager.removeUpdates(mlocListener);
}
public void onProviderDisabled(String provider) {}
public void onProviderEnabled(String provider) {}
public void onStatusChanged(String provider, int status, Bundle extras) {}
};
i'm working on app, which must get latitude and longitude. in my case requestLocationUpdates (String provider, long minTime, float minDistance, LocationListener listener) is not in option. why? because i must get location just when user do something that location is needed (let's say he hits button). and i need location exactly on the time, when button is hit. in requestLocationUpdates, we can set minTime-if i set this let's say on 30000 the location at the "button hit time" won't be as good as i want. of the same reason minDistance is also not as good as i want. if i understant function requestLocationUpdates correct-when minTime and minDistance are set to 0, location is updating all the time. please correct me if i'm wrong. app is for company that i'm working at and that app will be used through the day and night. so if app will check for location updates all the time, battery would be often empty. that's why i need location just at the time, that button is hit. users are not having access to internet and gps. so i must use NETWORK_PROVIDER
I also have problems with getting location after reboot device. it doesnt work until i run google maps. users wont have avalible this either, so what function do google maps on android use to get location after reboot?
at the moment i use this code:
LocationManager mlocManager = (LocationManager)getSystemService(Context.LOCATION_SERVICE);
LocationListener mlocListener = new MyLocationListener();
mlocManager.requestLocationUpdates(LocationManager.NETWORK_PROVIDER, 0, 0, mlocListener);
mlocManager.removeUpdates(mlocListener);
public class MyLocationListener implements LocationListener{
#Override
public void onLocationChanged(Location loc){
latitude=loc.getLatitude();
longitude=loc.getLongitude();
Text = "My current location is: \n" + "Latitud = " + loc.getLatitude() + "\nLongitud = " + loc.getLongitude();
Toast.makeText( getApplicationContext(),Text,Toast.LENGTH_SHORT).show();
}
#Override
public void onProviderDisabled(String provider){}
#Override
public void onProviderEnabled(String provider){}
#Override
public void onStatusChanged(String provider, int status, Bundle extras){}
}
code is from here
but this code is not working right. if i press "get location button" the Toast is shown and location is correct. but then if i press button several times, it does nothing. -but after 5 minutes Toast is shown like hundred times... why is that?
You are immediately calling removeUpdates after the requestLocationUpdates. So, the listener is never registered. Call the removeUpdates in the onLocationChanged method.